BIL 360: Chapter Outlines for Exam 2
BIL 360: Chapter Outlines for Exam 2 BIL 360
Popular in Comparative physiology
Popular in Biology
This 57 page Bundle was uploaded by Caitlyn Traenkle on Tuesday September 29, 2015. The Bundle belongs to BIL 360 at University of Miami taught by in Fall 2015. Since its upload, it has received 13 views. For similar materials see Comparative physiology in Biology at University of Miami.
Reviews for BIL 360: Chapter Outlines for Exam 2
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 09/29/15
Ch 10 Thermal Relations 10072014 Thermoregulation maintenance of relatively constant tissue temp Endotherms animal s tissues warmed by its metabolic production of heat Most are thermoregulators Homeotherms thermoregulate by physiological means Ectothems thermal conditions outside body determines body temp Poikilotherms have variable body temps 0 Can thermoregulate via behavior Heterotherms difference in thermal relations from one time to another or one body region to another within a single individual Temporal heterothermy different thermal relations at different times 0 Ex hibernating species Regional heterothermy different thermal relations from one region of body to another Temp important bc Environment temp ambient temp is a principle determinant of animal s metabolic rate and thus rate the animal must acquire food Temp of animal s tissues plays principal role in determining functional properties of tissues and tissue constituents Temp often plays biggest role in determining geographical ranges of species Temperature and Heat Temperature measure of the speedintensity of incessant random molecular motions Heat energy that a substance possesses by virtue of the random motions of its atomicmolecular constituents o Depends on of atoms and molecules and their speed 0 Larger object has higher heat than small object of same temp Direction of heat transfer heat moves by conductionconvection from region of high temp to region of low temp 0 Transfer of heat raises temp of object receiving heat lower temp of object losing heat Thermal equilibrium when temp same heat doesn t move in net fashion Heat Transfer bw Animals and Their Environments Heattransfer mechanisms conduction convection evaporation thermal radiation 0 Each can gainlose heat simultaneously 0 Sum total of heat gainsloses equal for temp of animal to be constant Conduction and Convection convection is intrinsically faster Conduction heat diffusion transfer of heat thru material that is macroscopically motionless solids 0 Heat moves strictly by atomicmolecular interactions atomsmolecules on one side agitated and increase agitation of atoms farther in substance by interatomic collisions Convection transfer of heat thru material by means of macroscopic motion of the substance uid ow required Evaporation the change of water from liquid to gas carries much heat away 0 Evaporation body of water from respiratory passages or skin of animal takes heat away from animal s body bc water absorbs substantial amount of heat when its state changes from liquid to gas Latent heat of vaporization amount of heat required to vaporize water Thermal radiation permits widely spaced objects to exchange heat at the speed of light All objects emit electromagnetic radiation objects are original sources of radiation Emitted radiation travels at speed of light until striking solid surface where it s absorbed 0 Ex big ears on rabbits cool them down bc emit more radiation Electromagnetic radiation emitted over range of wavelengths depends on surface temp of object o Shorter wavelength higher surface temp 0 Not all wavelengths of radiation visible infrared Radiant energy when it hits an object can be absorbed re ected or passes thru 0 Depends on surface properties of object Radiant exchanges in biosphere that don t involve the sun Organismsobjects identical in their emittance and absorptive properties surface temp Ts major determinant of radiative heat exchange without including sun 0 Energy passes in net fashion from warmer to cooler object 0 Net rate of heat transfer bw 2 objects is proportional o Direction of net heat transfer from high Ts to low Ts The night sky as a radiant object sun absent Radiant temperature of the sky atmosphere emits radiation as function of it s temp 0 Air temp at ground lower higher than radiant temp of night sky 0 Loses heat to atmosphere 0 Ex frosts Solar radiation 0 Emits radiation at wavelengths shorter than 34micrometers Solar radiant energy at of near visible wavelengths 0 Dark surfaces absorb more solar radiation Poikilothermy Ectothermy o Poikilothermy most common type of thermal relation in animals 0 Poikilothermy emphasizes the variability of body temp o Aquatic poik animals have body temp essentially the same as the o Terrestrial poik not necessarily same temp as air bc of thermalradiation heat transfer or evaporation still poik bc body temp determined by equilibration with the sum total of thermal conditions in their environment Ectothermy emphasizes that outside conditions determine the body temp Poikilotherms often exert behavioral control over their body temps 0 Natural envir Typically vary from place to place in thermal conditions poik can behaviorally choose where they position themselves and thus control body temp o Behavioral thermoregulation poik behaviorally maintains a relatively constant body temp 0 Simple stay in area with preferred temp o Bask in sun until body temp in preferred range 0 Shuttle bw sun and shade Poikilotherms must be able to function over a range of body temps 0 Limitation of behavioral thermoregulation l dependent on thermal opportunities 0 Cloudy day will have colder body temp 0 Must be thermal generalist capable of functioning at variety of different body temps Euythermal can function over wide range of body temps o Stenothermal comparatively narrow ranges of body temp they can function with Poikilothems respond physiologically to their environments in all 3 major time frames 0 Acute responses responses that individual animals exhibit promptly after their body temps are altered Chronic responses acclimation or acclimitazation changes individual animals undergo whem they live in altered thermal envir for a prolonged period of time Evolutionary changes ways that physiology of poiks may be modi ed by changes in the frequencies of genes when populations live in different envir over many generations Acute responses Metabolic rate is an approximately exponential function of body temp Usual pattern of poik is that the resting MR increase approximately exponentially with animals body temp o bc of required activation energy as temp of cell increases a molecules in cell become more agitated have higher energy levels 0 rxns speed up approx exponentially as cell temp rises 0 depends on enzymes bc MR enzyme catalyzed way to describe an exp relation bw MR and temp is to specify the multiplicative factor by which the rate increase when body temp increases by standardized increment of 10C temperature coefficient 010 Rt Rt10 o Rt rate at any body temp Chronic responses Acclimation often blunts metabolic responses to temp o Acclimation when animal chronically living at different temp range their resting MR acclimates to that temp Compensation after physiological rate has been raisedlowered by abrupt change in body temp any subsequent longterm tendency for the rate to return towards original 0 Compensation is partial if rate returns only partially to orig level o If sh allowed to acclimate to each temp before their MR measured their MR is less affected by changes of body temp than if they re shifted rapidly from 1 temp to another acclimation blunts response to changes in temp Mechanisms of metabolic acclimation 0 Cells modify their amounts of key ratelimiting enzymes Krebs cycle and etransport chain Acclimation to cold temp greater amounts of enzymes synthesized Increased enzymes tends to speed metabolic rxns Acclimation to warm temp initially speeds MR then MR slows as acclimation occurs 0 Cells orchestrate their own biochemistry via enzymes Acclimatization animal adjusts to gradual change in environment 0 Acclimation occurs in short period of time Consequence of acclimation and acclimatization physiology of individual often depends signi cantly on its recent individual history Evolutionary changes Species are often specialized to live at their respective body temps Related poik species often spend much of their time at different body temps Some physiological differences among species living as dif body temps so dramatic that there s no doubt about the existence of evolved adaptive specializations 0 Some species can only live a temps that would kill other animals 0 Problems with studying evolutionary adaptation to temp 0 Cannot be bred in captivity individuals collected from nature worry that difference may exist bw sets of animals of different species not bc they differ genetically 0 Species from thermally different environments often unable to live successfully at single temp cannot just compare in single lab experiment Lizard species with different preferred body temps Advantage of thermoregulation tissues and cells can improve their performance by becoming thermally specialized ls true lizard species with high preferred body temps should have tissues specialized to function at high temps while species with low preferred temp should exhibit tissue specialization at lower temps 0 Some processes take place optimally in certain sets of related species when body temps at preferred levels but there are exceonns Thermoregulation and tissue thermal specialization have often evolved in tandem Fish and invertebrates of polar seas Hypothesis species of shinverts in polar seas maintain higher resting and avg MR in cold waters than related tempzone or tropical species could maintain in same waters 0 True for certain groups of polar poiks Evidence for evolutionary specialization in polar poiks 0 At nearfreezing tissue temps protein synthesis more rapid in livers of polar species than those in temperatezone species 0 Skeletal muscles of polar sh able to generate more mechanical power at polar temps than muscle of temperate zone sh Polar muscles richer in mitochondria Temp and heat matter to animals bc they affect the rates of processes and the functional states of molecules 0 Temp and heat important for animal tissues bc o Temps of tissues affect rates of tissue processes 0 Temps of tissues affect molecular conformations and thus the functional states of molecules Conformation of protein depends on temp bc stabilized by weak noncovalent bonds 0 Functional properties of a proteins depend on its conformation 0 Functional properties of protein vary with temp 0 Animals living in dif temp regimes often have evolved different molecular forms of proteins forms that are differentially suited to function in divergent temp regimes 0 Ex crystalline protein in eye lenses of cow and tropical fish at freezing temp became opaque from denaturation while lens of polar sh did not bc protein has different form 0 Enzymesubstrate af nity of enzyme important functional property bc it determines how readily molecule able to form an enzyme substrates complex 0 Af nity changes with temp 0 Too low af nitiy enzyme incapable of forming complexes with substrate 0 Too high af nity enzyme so prone to forming complexes becomes uncontrollable bc functional prop of enzymes depend on temp any enzyme can be highly functional as certain tissue temp while only marginally functional at other temps 0 so species with dif body temps evolved dif molecular forms of enzymes 0 ex 6 different forms of LDH all 6 species have about the same enzymesubstrate affinity when they re at their respective body temps particular enzymes typically specialized to function best within certain temp ranges proteins thus require certain temps to function optimally o tissues may change amount of enzyme it synthesizes occurs during acclimationacclimatization but it cannot change the type of enzyme Implications for global warming 0 How much tissue temp must change for the change to have signi cant consequences not very much 0 Worry that temps will change too quickly for evolution to keep up 0 Sensitive animals temp specialized will most likely die off More on enzyme adaptation to temp Catalytic rate constant k measures number of substrate molecules that an enzyme is capable of converting to product per unit of time Usual pattern enzyme homologs from cold water species exhibit higher k values than warm water species 0 Enzyme homologs of species in cold water have greater intrinsic ability to speed rxns helps offset rxnslowing effects of low temps Generalizations o Homologous enzymes often differ in only relatively few amino acid positions helps explain how species can readily evolve adaptively different enzyme homologs 0 Altered amino acid positions located outside the substrate binding site so site is constant or nearconstant explains why all homologs catalyze same rxn Myosin isoforms exemplify that protein isoforms sometimes change during acclimation and acclimatization Muscle contractile function depends on variety of proteins Individual of particular species capable of synthesizing multiple molecular forms of each protein provides basis for wide range of phenotypic plasticity o lsoforms various molecular forms of particular protein 0 Possible bc multiple genes in gene family coding for the protein present in 1 individual 0 Change in isoforms key in acclimation synthesize isoforms in altered proportions and switch out old isoform for new ones Lipids and homeoviscous adaptation 0 Function prop of lipids depend on prevailing temps 0 Functional prop of lipids uidity of phospholipids in cell membranes and intracellular membranes o Membrane uidity measure of how readily the phospholipid molecules in membrane move 0 Fluidity increases at temp increases 0 All species have about the same membrane uidity when living at their respective normal body temps Homeoviscous adaptation maintenance of relatively constant membrane uidity regardless of tissue temp 0 Possible bc chem composition of membrane phospholipids differ among species 0 Tissue with membranes built of particular phospholipids will have correct membrane uidity only if its temp correct Chemical bases for homeoviscour adaptation modi cation of number of double bonds in fatty acid tails of membrane phos 0 Double bonds create bends in tails bends interfere with close packing o Fluidity increases as number of double bonds increases unsaturation 0 Polar species more unsaturated lipids to remain uid at cold temps Individuals able to alter membrane phos that they synthesize o Phos composition in membrane restructured during acclimationacclimatization that produce homeoviscous adap on 0 Can be chronic or acute change Poikilotherms threatened with freezing they may survive by preventing freezing or by tolerating it If poik exposed to temps colder than those necessary to freeze water they face threat of freezing Animal body uids have lower freezing points than water bc of their solute conc The freezing process in solutions and tissues Supercooling when aqueous solu progressively cooled commonly remain unfrozen even when temp fall below freezing points unstable can spontaneously freeze at any moment Supercooling point temp of supercooled solu where it spontaneously freezes in short period of time 0 Exposure to ice induces freezing in supercooled solu Freezing point temp above which solu cannot freeze and below which it deterministically freezes in presence of ice 0 Depends on conc of dissolved entities Melting point lowest temp that melting occurs 0 Usually equal to freezing point Intracellular freezing freezing win cells usually kills cells Extracellular freezing ice formation in body uids Formation of ice starts here some animals tolerant Freezing pt of unfrozen uid lowered by incr in solute conc 0 At xed temp formation of ice in extracellular uid a self limiting process water freezes only until freezing pt of unfrozen liquid becomes low enough to equal prevailing temp lntraextracellular uids have similar osmotic pressures in unfrozen animal water has little tendency to enterleave cells by osmosis o Disrupted by freezing of extracellular unfrozen extracellular osmotically more conc than intracellular osmotic loss of water 0 Selflimiting bc stops after intracellular osmotic pressure risen to equal extracellular osmotic pressure 0 By concentrating intracellular uids lowers intracell freezing pt loss of water from cells prevents intracellular freezing The adaptive responses of animals to freezing conditions 0 Most poik behaviorally avoid freezing conditions Mechanisms of poiks exposed to freezing 0 Production of antifreeze compounds 0 Supercooling o Tolerance of freezing Freezeintolerant die if they freeze antifreeze and supercooling prevent freezing o Freezingtolerant ability to survive extensive freezing of extracellular body water response to freezing by freezing Production of antifreeze compounds Antifreeze compounds dissolved substances added to body uids speci cally to lower freezing point of body uids 0 2 types of antifreezes o Colligative antifreezes affect freezing pt by increasing total conc of solutes in body uids 0 Noncolligative antifreeze certain proteins and glycoproteins bind to nascent ice crystals suppressing growth of ice by preventing water molecules from freely joining 0 Thermal hysteresis freezing pts substantially lower than their MP 0 Antifreeze synthesizes principally in marine teleost sh and insects Supercooling 0 Animals modify their probabilities of spontaneous freezing during supercooling Alter qualityquantity of icenucleating agents acts as foci for initiation of freezing 0 Lack of icenucleating agents supercooling pt far below freezing pt Tolerance of freezing OO For freezingtolerant animals extracellular freezing safe and helps prevent intracellular freezing Undergo physiological change in winter that limit the degree of supercooling in extracellular uids 0 Synthesize icenucleating agents add to extracellular uid 0 Expose to envir ice have body surface that permits external ice to induce freezing of extracellular uid Depends on addition of certain organic solutes to all body uids 0 ncr solute in extracellular limits amount of extracellular ice formation before conc of unfrozen extracellular uids rise high enough to prevent further freezing o ncr solute in intracellular limits amount of water lost from cells for them to come to osmotic equilibrium with freeze concentrated extracellular uids Homeothermy in Mammals an Birds Homeothermy regulation of body temp by physiological means 0 Gives birdsmammals more independence Mammals and birds independently evolved their forms of homeothermy 0 Avg body temp doesn t vary much with climate Deepbody temp not absolutely const daily cycles higher during active phases or when under heat stress Able to specialize cellular functions but has high energy cost 0 Increase food requirements Thermoregulation requires neurons that sense body temp and control centers in brain that process thermoregulation sensory info and orchestrate mechanisms to stabilize body temp Metabolic rate rises in cold and hot envir bc of the costs of homeothermy Resting MR varies with ambient temp Thermonuetral zone TNZ range of ambient temp where resting MR independent of ambient temp and constant 0 Lowercritical temp lowest ambient temp in TNZ o Uppercritical temp highest temp in TNZ 0 Critical temps depend on species and affected by acclimationacclimatization Basal metabolic rate BMR MR when resting and fasting in TNZ Resting MR increases as ambient temp goes outside TNZ increases MR to maintain constant body temp The shape of the metabolismtemp curve depends on fundamental heatexchange principles 0 Dry heat transfer heat transfer that doesn t involve evaporation of water convection conduction radiation 0 At temps withinbelow TNZ evaporation minor 0 Linear heattransfer equation 0 M CTb Ta 0 M metabolic rate 0 TbTa difference in ambient and body temp driving force for dry heat transfer 0 C thermal conductance measure of how readily heat can move by dry heat transfer from body to envir 0 High C low resistance to dry heat loss low C high resistance 0 Insulation l Resistance to dry heat loss 1C o M 1lTbTa TNZ insulation is modulated to keep the rate of heat loss constant 0 M remains constant at all ambient temps in TNZ 0 Modulation of insulation with constant metabolic heat production principal means by which mammalbird thermoregulates in TNZ Ambient temp lowered in TNZ TbTa increases animal responds by increasing l 0 Increase in resistance to heat loss counterbalances the increase in driving force for heat loss TbTa 0 So animals actual rate of heat loss remains constant Allows M to be constant 0 Width of TNZ varies among species depends on extent they can modulate their insulation 0 Small species have narrower TNZ Temperatures below thermoneutrality 0 Principal means of thermoregulation at ambient temp below thermoneutrality is modulation of its rate of metabolic heat production 0 Below TNZ increases MR o Lowercritical temp represents the Ta below which its insulator adjustments become inadequate o maximized at lowercritical temp Value of at ambient temp below TNZ constant Tb and C all constant below TNZ Only 2 variables M and Ta linear equation Slope is C Xint Tb Temperatures above thermoneutrality 2 process to respond to ambient temp above thermoneutrality 0 active evaporative cooling incr rate of evaporation o hyperthermia allow body temp to rise to unusually high levels 0 both incr MR 0 active evaporation required work 0 hyperthermia tissues accelerate metabolism when warmed doesn t always incr MR 0 As Ta rises driving force for dry heat loss TbTa decr animal faces greater challenge to get rid of basal metabolic heat production 0 Ta in TNZ responds by decr resistance to dry heat loss insulation 0 At uppercritical temp insulation reach minimum cannot offset decrease in TbTa Active evaporation and hyperthermia promote heat loss so animal not overheated by their metabolic heat production 0 When TagtTb dry heat transfer carries envir heat into body 0 Active evap must assume all burden of removing heat Homeothermy is metabolically expensive 0 To quantify compare MR of vert homeotherms and poik at similar tissue temps 0 Compare BMR of mammalsbirds with resting MR of likesized poik OOO o If both at rest and fasting and measure MR get BMR of mammal and standard metabolic rate SMR of reptile MR of mammal 410x higher than reptile At cold ambient temps MR mammalsbirds rise MR of poik falls 0 Gives even greater difference Insulation is modulated by adjustments of the pelage or plumage blood ow and posture Mechanisms of mammalbird to thermoregulate physiologically o Vary insulation by erectioncompression of hairfeathers Pilomotor response mammals Ptilomoto response birds Decr Ta win TNZ hairfeathers erect pelageplumage uffed out traps layer of motionless air incr resistance to heat transfer 0 Vasomotor responses alter rate of blood ow to skin and super cial body parts Cold temp constrict blood ow 0 Postural responses alter amount of body surface area directly exposed to ambient condition Low temp animal curls up 0 Small animals have higher SV ratio and don t have as thick pelage or plumage Heat production is increases below thermoneutrality Thermogenic mechanisms specialized to generate heat Shivering contractionrelaxation of muscle in high frequency rhythms mediated by motor neurons of somatic nervous system 0 Uses ATP and liberates heat Nonshivering thermogenesis NST when move to cold temp rates shiver and then slowly stop after some time 0 Brown adipose tissue BAT brown fat specialized adipose tissue that differs greatly in structure and function from white fat 0 Occurs in discrete masses 0 Receive rich supply of blood vessels 0 Great numbers of large mitochondria Sympathetic nervous system releases norepinephrine in BAT o BAT increases rate of oxidation stored in lipids high rate of heat production 0 Prominent in 3 types of mammals o Coldacclimated or winteracclimatized adults 0 Hibernators o Newborns Regional heterothermy in cold environments allowing some tissues to cool can have advantages 0 Regional heterothermy allowing some parts of body to be dif temp Appendages have high surface area lose a lot of heat 0 Limit loss of heat in appendages by allowing them to cool 0 Curtail circulation to them to cool Countercurrent heat exchange permits selective restriction of heat ow to appendages Countercurrent heat exchange depends on transfer of heat bw 2 closely juxtaposed uid streams owing in opposite directions 0 Encourages heat transfer from arterial blood to venous blood venous blood carries heat back to body core 0 Shortcircuits the ow of heat into the appendage 0 Can be deactivated by control of set of veins in use 0 Rete mirabile arrangement where main arteries and veins in limb split up to form many ne vessels that intermingle Mammals and birds in hot environments their rst line of defense are often not evaporation Con of evaporation its carries water away Nonevaporative defenses o Behavioral defenses burrowing underground 0 Insulator defenses thick fur 0 Body temp cycling of body temp and profound hyperthermia Cycling of body temp Body temp cycles up and down permits some of heat that enters body at hot part of day to be temporarily stored in body and later voided Ex camels Hyperthermia Rise in body temp entails heat storage aids in water conservation Keeping a cool brain 0 Brain kept cooler than other parts of body can tolerate less temp permits animal to take enhanced advantage of bene ts of body temp cycling and hyperthermia o mechanism countercurrent heat exchange in arterial blood supplying brain 0 arteries divide into plexus of small vessels carotoid rete mirabile in sinus that s immersed in lake of venous blood Active evaporative cooling is the ultimate line of defense against overheating lf heat accumulating in excess levels active evap cooling used to reestablish balance bw heat gainloss Sweating uid secreted by way of ducts of sweat glands thru epidermis of skin onto skin surface incr evap Panting incr in rate of breathing in response to heat stress 0 Evap cooling from water evap from warm moist membranes lining respiratory tract into air breathed inout o Resonant freq in thorax vibrates less muscular work needed 0 Advantage forcibly drives air saturated with water vapor away 0 Con induce respiratory alkalosis an elevation of pH of body uids caused by excessive removal of C02 0 Gular uttering rapidly vibrating gular area birds 0 driven by exing of hyoid apparatus and promotes evap by incr ow of air over moist vascular oral membranes The Physiology of Control Neurons and Endocrine Cells Compared Integration a process that produces coherency and results in a harmonious function 0 Cellular integration processes within cells 0 Wholeanimal integration selective combination and processing of sensory endocrine and CNS info in ways that promote harmonious functioning of the whole organism Carried out by nerve and endocrine cells control systems Control system system that sets the level of a particular variable temp blood pressure that s being controlled 0 Info from sensors determine signals its sends to effectors that modify the controlled variable 0 Usually operate on negative feedback principles and are stabilized Neurons transmit electrical signals to target cells Neuron a cell that s specially adapted to generate an electrical signal via an action potential brief selfpropagating impulse that travels from place to place in the cell Synapses cellcell contact point where neuron receives input from other neurons or sensory cells 0 Allows for transmission of info bw neurons thru conversion of a signal from electrical to chemical to electrical Dendrites branching processes where synaptic input occurs Presynaptic cell cell who s synapse receives the signal Neurotransmitter chemical substance released into synaptic cleft space bw cells 0 Exert speci c physiological effects on postsynaptic cell by binding to neurotransmitter receptors 0 Result in new electrical impulse in target neuron 0 Can have excitatory or inhibitory effect Cell body soma part of neuron where signal integration and impulse generation occur has nucleus Axon long conduction component of a neuron propagate action potential along its length 0 Axon arises from axon hillock leads to axon initial segment site of AP initiation o Axons from 1 neuron sometimes collect into bundles tracts CNS nerves in peripheral nervous system Presynaptic terminals where axon ends places where neuronal output occurs 0 Form synapses with other neurons or other types of cells muscle bers 0 lnnervate cells neurons that form synaptic endings on a cell Nervous system extended networks of neurons in animal s body along with supporting cells 0 Central nervous system CNS brain and spinal cord 0 Peripheral nervous system PNS all other parts o Afferent neurons neurons that relay sensory signals to integrative centers of the CNS 0 Efferent neurons neurons that relay control signals instructions from CNS to target cells that are under nervous control muscle or secretory cells 0 lnterneurons neurons that are entirely within the CNS Neural control has 2 features fast and addressed discrete lines of communication Endocrine cells broadcast hormones Endocrine system produces signals that are broadly distributed throughout animals body unlike nervous system whose signals are precisely targeted 0 Release hormones into blood or extracellular uid 0 Hormones carried throughout body 0 For hormone to elicit response cell must have receptor proteins for that hormone Target cells cells that response to hormone Endocrine control has 2 features slow and broadcast 0 Slow bc takes time to initiate travel be absorbed may act for extended period of time o Broadcast bc all cells in body exposed to it commonly affects the whole tissues and often multiple tissues Nervous systems and endocrine systems tend to control different processes Nervous system controls n rapid movements of discrete muscles endocrine system controls more widespread prolonged activities metabolic changes 0 Most tissues under duel control 0 Ex skeletal muscle each motor neuron innervates a separate set of muscle bers controls contraction hormone insulin controls metabolic activity by facilitating muscle s uptake of glucose from blood incr rate of glycogen synthesis 0 Can exert control over each other interaction bw systems occurs in both directions The Cellular Organization of Neural Tissue Nervous system composed mostly of neural tissue neurons and glial cells connective tissue cells of circulatory system 0 Cell theory organisms composed of cells cells are structural and functional units of organization all cells come from preexisting cell as a result of cell division Reticular theory nervous systems composed of complex continuous meshworks of cells and processes in protoplasmic continuity with each other ie cells ran together wo boundaries Neuron doctrine neurons are anatomically distinct and are the structural functional and developmental units of organization of nervous systems Neurons are structurally adapted to transmit action potentials Neuronal soma similar to nonneural cells has all the organelles o Neurons very active in protein synthesis so have extensive welldeveloped rough ER 0 Nissl substance aggregates of rough ER in neuron soma Neurons classi ed by of processes emanating from the soma o Unipolar 1 process bipolar 2 mutipoar 3 or more Dendrite receptive element of neuron that conveys info to soma 0 Short branched vary in diameter Axon output element carries info away from soma to other cells 0 Single long constant diameter few branches 0 Larger axons surrounded by myelin sheath multiple wrappings of insulation glial cell membranes that incr speed of impulse transmission lnsulates the axon incr velocity of impulse propagation Not all axons myelinated Glial cells support neurons physically and metabolically Glial cells nerve glue surround the neurons 0 Function bind neurons together and maintain form and structural organization of nervous system 0 Different glial cells have different functions 0 Vertebrates have 2 kinds of ensheathing glial cells envelope axons of neurons Schwann cells PNS and oligodendrocytes CNS Astrocytes line outside surfaces of capillaries in vert CNS act as metabolic intermediates bw capillaries and neurons Take up neurotransmitters and supply metabolic substrates to neurons Regulate extracellular ion conc nervous sym development Microglial cells mediate immune responses in neural Ussue The Ionic Basis of Membrane Potentials Ions atoms that have a net charge bc they have unequal numbers of protons and electrons 0 Electric current I net movement of charges 0 Voltage V potential difference separation of positive and negative charges 0 Electrical activity of nerve cells a property of the cell membrane transmembrane potentials o In cells aqueous solutions electrical charges are ions 0 Voltage results from local imbalances of ion charges 0 Charge neutrality of bulk solutions so only portion of cell that determines electrical properties is its outer cell membrane Cell membranes have passive electrical properties Resistance and capac ance Passive responses cell s electrical properties don t change 0 Action potentials are active responses properties change Passive electrical properties determines cell s passive response 0 Resistance R limits ion current ow across membrane 0 Capacitance C ability to store electrical charge 0 R and C depend on membrane surface area measured per unit of area 0 If C doesn t change R may or may not change 0 Cell s passive electrical properties conditions where R doesn t change 0 Passive electrical properties govern how voltages change over space and time along axons Do not explain generation of APs R generates change 0 Study squid axons bc large can cut out ligate ends penetrate with microelectrode measures V o Resting membrane potential Vm potential dif across axon membrane insidenegative o Membrane resistance Rm needed to maintain Vm otherwise ions would diffuse freely Use second microelectrode to generate pulse of current I depending on current direction it causes 0 Depolarization membrane potential V becomes less negative toward 0 o Hyperpolarization V becomes more negative away from 0 Ohm s law current I should change membrane potential V proportionally to resistance R 0 AV IR 0 AV change in potential graded potential 0 l current amps o R resistance ohms Passive electrical properties retard membrane voltage changes 0 Delay in polarizing membrane occurs bc membrane behaves electrically like a resistor and a capacitor in parallel Lipid biayer behaves like a capacitor 0 Bilayer blocks exchange of ions insulative properties enable oppositely charged ions to accumulate along inner and outer surfaces of membrane 0 Ion channels behave like resistors 0 Allow ions to ow across membrane at rate governed by structure of channels and potential difference bw inside and outside of membrane 0 Current rst redistributed charges on membrane capacitance then ows thru membrane resistance l redistribution of charges slows change in V by factor that increases if R or C increased Passive electrical properties limit the spread of graded potentials Passive spread V change will decrease exponentially with distance from source producing it 0 Reason as current ows inside axon some leaks out thru ion channeb Resting membrane potentials depend on selective permeability to ions Nernst equation Cell s membrane permeable to different kinds of ion established and maintains insidenegative voltage 0 Selectively permeable ion channels that are speci c to certain ions A controlled condition bc ion channels openclose 0 Ex cell contains K and nonpermeating charged ions A 0 Cell in bath of 2 nonpermeating ion Na and A o Membrane only permeable to K o K tends to diffuse out of cell down it s conc gradient Charge neutrality maintained in bulk solution so A would follow K across membrane but A nonpermeable A accumulates at inner surface K accumulates on outer surface Develops net charge separation at the membrane Net negative charge on inner surface and net positive charge outside moves K ions back into cell by forces of charge attraction and repulsion Eventually reaches electrochemical equilibrium no net movement of ions concentration diffusion equals opposing electrical force Only possible if there s an electrical force across mem Nernst equation relation bw conc difference of a permeating ion across membrane and the V at equilibrium 0 000000 E RTzFnCoutCin E membrane potential electromotive force mV R gas const T absolute temp z charge for the ion valence of the ion C ion conc on either side of mem Larger conc diff larger membrane potential E Incr C difference increases conc gradient of ion increases E to oppose it Simpli ed by including constant values and particular temp Ex For K at 18degrees n E 58 ogCoutCin n Cout 10mM Cin 100mM n Equilibrium potential for potassium Ek 58mV o Membrane potential at which K ions at electrochemical equilibrium There s an equilibrium potential for each ion on concentration differences result from active ion transport and from passive diffusion o All cells maintain higher conc of K and lower conc of Na and CI in intracellular uids 0 Concentration ratios of ions in all cells similar 0 Difference in ion conc bw intra and extracellular uids result from active transport of some ions and passive distribution of other ions 0 Pumps active ion transport requires input of energy from hydrolysis of ATP maintains nonequilibrium levels of ions 0 NaKATPase pump actively transports Na out K in Counteracts leakage channels 0 Permeating ions have different conc without pumps bc cells have large conc of nonpermeation anions permeating ions Cl must be distributed unequally Conc distribution of living cells neither Na nor K at equil passive diffusion produces net movement of both Na in K out Membrane potentials depend on the permeabilities to and concentration gradients of several ion species The Goldman equation 0 Resting membrane potential largely determine by K conc bc membrane more permeable to K than to other ions 0 But membrane permeable somewhat to other ions 0 Contribution of each ion weighted by its ability to permeate the membrane more permeating more effect Goldman equation Vm produced by the contributions of several permeating ion species K Na Cl 0 Vm RTF PkKoPnaNaoPclCli PkKiPnaNaiPclClo P relative permeability for that ion io insideoutside cell can simplify further ignore Cl If more permeable to Na l membrane potential E approaches Ena equilibrium potential for Na 0 More permeable to K E approaches Ek Electrogenic pumps also have small direct effect on Vm lonic hypothesis conc of ions insideoutside a cell maintained in steady state by a mix of active transport processes ATPase pumps and passive transport processes diffusion 0 Further asserts that ion conc and permeability determine resting membrane potential Vm Goldman eq 0 2 kinds of active iontransport mechanisms 0 Electroneural pumps transport equal quantities of charge in and out change ion conc wo generating electrical current 0 Electrogenic pumps transport unequal quantities of charge in and out generating electrical current 0000 ions The Action Potential Excitable cells neurons muscle cells ability to generate electrical signals Action potentials are voltagedependent allor nothing electrical signals APs result from voltagedependent changes in membrane permeabilities to ions bc ion channels are voltagegated opening depends on Vm Action potential AP momentary reversal of membrane potential Vm from 65mV insidenegative to 40mV insidepositive lasting 1msec o Triggered by depolarization of mem reaches the voltage threshold goes above suprathreshold AP has rising phase peaks above OmV falling phase rapid repolarization short undershoot below Vm hyperpolarization then back to Vm of 65mV Voltagedependent properties of APs o 3 inward owing current pulses hyperpolarize mem proportional to current strength hyperpolarization can induce APs bc it doesn t change permeabilities o 2 outward currents depolarize mem no signi cant change in membrane resistance Allornothing depolarization below threshold elicits no impulse all suprathreshold depolarizations produce complete impulses similar in amplitude and duration produce identical AP Absolute refractory period immediately following an AP another AP cannot be generated for at least 1msec 0 Relative refractory period harder to generate AP for a few msec longer Suprathreshold depolarizing current elicits train of discrete APs propagates along axon without decrease in amplitude and at a constant velocity depends on axon diameter APs are allor nothing electrical signals in excitable cells that propagate rapidly and without degradation over long distances Action potentials result from changes in membrane permeabilities to AP results from intense localized increases in permeabilities to speci c ions 0 Increases are voltage and time dependent Permeabilities and ion channels At Vm of 65mV membrane most permeable to K ions Leakage channels normally open not voltagegated allow K to diffuse following electrochemical gradient 0 remain open during AP but voltagegate channels swamp their effects Rising phase depolarization and polarity reversal o Depolarizes past threshold 0 Voltagegated Na channels open increases Pna 0 Higher Na conc outside Na rushes in toward Ena 0 Makes membrane momentarily insidepositive 0 Falling phase 2 changes in mem permeability o Voltagegated Na channels inactivated decreases Pna 0 After delay voltagegated K channels open incr Pk K ow out drive membrane toward Ek Undershoot afterhyperpolarization o Membrane remains permeable to K caused by slower opening of K channels The Hodgkin cycle explains the rising phase of the action potential 0 Critical feature of AP generation Pna that produces depolarization depends on depolarization Hodgkin cycle describes the effects of depolarizing an excitable membrane in which Pna is voltagedependent 3 processes in positive feedback loop 0 Initial depolarization opening of voltagegated Na channels incr Pna o Increases Na ow 0 Permeability to Na further depolarizes membrane 0 Positive feedback loop begins and ends with Na channel inactivated Molecular structure of the voltagedependent ion channels reveals their functional properties Voltagegated Na channel proteins change tertiary structure in response to membrane depolarization o 3 conformations closed open inactivated major alpha protein forms the channel itself 0 is a single polypeptide chain has 4 domains 0 each domain consists of amino acid sequences similar to other 3 sequence homology 0 each domain has 6 membranespanning segments 0 domains surround aqueous channel pore thru which Na ions can diffuse in response to depolarization particular structural regions of channel protein impart particular functional properties 0 channel s voltagesensor segments thought to move outward in response to depolarization leads to overall conformation change in channel from closed to open 0 P loop lines pore of ion channel helps mediate ion selectivity Cytoplasmic loop mediated inactivation of Na channel acts like a ball on string that can block the open channel from cytoplasmic side 0 Other voltagegated channels similar in overall structure and have homology in aa sequence 0 Voltagegated channel superfamily of membrane proteins homology suggests that ion channels evolutionarily related 0 Na and Ca2 channels most similar in structure The Propagation of Action Potentials Single axons can be at least 1m long Electrotonic voltage change on membrane amplitude decreases exponentially with distance passive spread 0 There must be a mechanism to amplifyrefresh the electrical signal APs can propagate bc AP at one location can initiate an AP at a neighboring locations with that same allornothing amplitude as the original AP repeat process down axon Local circuits of current propagate an action potential 0 AP at one locus on axon depolarizes adjacent locus by setting up local circuits of current ow 0 Complete local circuit composed of series of ionic and capacitive currents broken into 4 components 0 At locus of AP ionic current begins with in ow of Na thru open channel into cytosol o lons ow in intracellular uid carrying current to more distant parts of membrane 0 Ion movements change distribution of charges on membrane capac ance Cations accumulate along interior displace charges repels equivalent number of cations from exterior Ions not crossing o Extracellular ionic current complete local circuit as cations move toward locus of the AP and anions move away 0 AP propagates to adjacent portion of axon bc capacitive depolarization produced by local current lowers the membrane potential to threshold 0 Then Hodgkin cycle takes over Membrane refractory periods prevent bidirectional propagation Axon can conduct impulses equally will in either direction but normally impulses start at one end of axon and travel in 1 direction 0 As impulse propagated localized currents depolarize membrane behind it in refractory period 0 3 aspects of ionic mechanism of APs produce absolute and relative refractory periods following impulse o 1 Inactivation of Na channels persists until Vm returns to negative resting state 1msec prevents channels from entering Hodgkin cycle until AP far enough away to minimize local depolarization o 2 Increased Pk doesn t decrease to resting levels until after repolarization lingering Pk incr hyperpolarizes membrane toward Ek region away from its voltage threshold 0 3 Increased Pk renders membrane refractory bc it represents a decreased membrane resistance decr R local currents cause smaller V change more current needed to depolarize to threshold refractory periods outlast backward spread of local currents prevents reverse propagation of APs The conduction velocity of an action potential depends on axon diameter myelination and temperature 0 2 conduction parameters 0 Spatial parameter farther local currents spread along axon farther than can directly depolarize membrane to threshold sooner an AP will result increase speed of local currents incr mem length increase conduction velocity of AP Large diameter and myelination incr spatial spread of local currents 0 Temporal parameter less time for membrane to reach threshold faster conduction velocity Diameter myelination temp Axon diameter and conduction velocity 0 Larger diameter axons l increased AP velocity 0 Larger diameter axons have longer length constants thus more distance spread of local currents Length constant depends on resistance across membrane Rm and axoplasmic resistance Ri to current ow along axon length Mem surface area incr proportionally with incr axon diameter Myelination increases conduction velocity Myelinated axon wrapped with layers of glial membrane Myelin multiwrapped insulating layer Nodes of Ranvier gaps bw myelin lnternodes insulated part of axon bw the nodes most of axon On myelinated axons APs occur only at the nodes thus exhibit salutatory conduction APs jump saltate from node to node without active propagation in internode Myelin incr R of myelinated axon local currents cant leak out thru high membrane R of adjacent internode instead ow farther to next node 0 Myelin incr spatial spread of local currents l incr AP velocity Myelin also decreases membrane C incr velocity by increasing axon length constant without increasing the time constant Myelinated axons permit vertebrates to have neural coordinating and control systems with smalldiameter axons that conduct rapidly 0 With reduction in axon diameters more axons can be incorporated into nervous system Temperature Gating of voltage dependent ion channels thus time course of membrane depolarization to threshold tempdependent o lncr temp l increase AP velocity 0 Homeothermy and myelination allowed further axon miniaturization and higher conduction velocities Synapse specialized site of contact of a neuron with another neuron or effector Locus where the presynaptic neuron in uences the function of another cell postsynaptic neuron or effector Neurons separated by synaptic cleft Synapse can work chemically or electrically Can excite or inhibit postsynaptic cell Synaptic potential can result from permeability incr or decr Synaptic action can be fast or slow Can act immediately and directly on membrane potential of postsynaptic cell 0 Or can have indirect longer lasting effects Ionotropic synaptic action fast produces direct changes in ion permeability and thus membrane potential Metabotropic synaptic action sow produces chemical signal transduction changes in postsynaptic ce Synaptic Transmission ls Usually Chemical but Can Be Electrical 0 2 kinds of synapses electrical and chemical 0 both rapidly change membrane potential of post ce Electrical synapses transmit signal instantaneously Electrical synapse eectrica currents from one cell ow directly into next cell changing its membrane potential 0 Fast found in nervous system Also advantageous for groups of neurons that re synchronously 0 Current ow in either direction often not polarized Gap junction specialized ocus where protein channels bridge the gap bw 2 cells directly connecting their cytoplasm 0 Provide low R path for current ow coupling cells 0 Electrical coupling hyper or depolarizes of one cell produces weaker corresponding change in other cell Decr bc gap junction has some R Larger gap junction l lower R stronger coupling 0 Electrical synapses act on shortlatency synaptic relays presynaptic action potential triggers postsynaptic action potential 0 Weaker coupling or high threshold of pre cell may produce only subthreshold depolarization in post cell 0 Most are birdirectional transmit V changes in both directions 0 Electrical synapse bc giant axon and giant motor neuron of cray sh is rectifying current ow in only 1 direction Gap junctions narrow space bw pre and post cells 0 Connexons array of channel structure that bridge the narrow gap separating membranes form channels that connect cytoplasm of the 2 cells nnexons innexin proteins that form gap junctions in invert protostomes Chemical synapses can modify and amplify signals Chemical synapses have discontinuity bw cells synaptic cleft a barrier to direct electrical communication 0 Presynaptic electrical signal transduced into a chemical signal release of neurotransmitters from presynaptic terminals neurotransmitters diffuse to postsynaptic membrane bind to receptors specialized to generate electrical or chemical change in response to binding Synaptic vesicles stores neurotransmitters at axon terminal of pre neuron 0 Active zones tufts of electrondense material on cytoplasmic side of presynaptic membrane where synaptic vesicles release neurotransmitters o Postsynaptic densities dense aggregate at post membrane where accumulation of neurotransmitters and scaffolding proteins organize receptors and other proteins at synapse Presynaptic neuron release neurotransmitters in response to AP 0 Neurotransmitter synthesized in pre neuron stored in vesicles 0 Released by Ca2 dependent exocytosis o Neurotransmitter bind to receptor in post membrane 0 When binds post membrane usually produces change in post membrane potential Neurotransmitter receptors work in 2 ways 0 lonotropic receptors fast changes in membrane potential by directly increasing permeability to ions acts as receptors and ion channels 0 Metabotropic receptors slow long lasting modulatory effects trigger signaling cascade of second messengers in post cell Chemical synapse advantages 0 Can amplify current ow Presynaptic AP causes release of few or many vesicles each contains thousands of transmitters depending on of active zones and size of presynaptic terminal amt transmitter released can open many channels and amplify postsynaptic current 0 Can be excitatory or inhibitory Electrical usually excitatory o Are oneway Presynaptic neuron excitedinhibits post cell Most electrical 2 way 0 Much more modi able in their properties Use makes stronger plasticity Synaptic Potentials Control Neuronal Excitability Function of synaptic transmission control excitability of postsynaptic cell Neurotransmitters diffuse across synapse generates synaptic potential transitory graded change in Vm in post cell Synaptic potential that depolarizes membrane excitatory o Excitation incr in probability that cell will generate impulse AP or is already generating AP causes incr in impulse freq one that hyperpolarizes membrane inhibitory 0 Inhibition decr in prob of impulse generation or decr in impulse freq Excitatory and inhibitory effects of multiple synapses are summed to control postsynaptic AP Synapses onto a spinal motor neuron exemplify function of fast synaptic potentials Excitatory postsynaptic potentials EPSP produce synaptic potentials that are graded depolarizations in motor neuron 0 Each has brief rising phase and exponential decay ESPSs combined in 2 ways 0 Temporal summation nerve A stimulated repeatedly and rapidly those EPSPs combined 0 Spatial summation simultaneously occurring EPSPs produced by different nerves combined Inhibitory postsynaptic potentials IPSP synaptic potentials brie y hyperpolarize motorneuron membrane drive membrane potential away from threshold opp of EPSP effects 0 Also produce temporal and spatial summation effects Balance of EPSPs and lPSPs determine whether motor neuron generates impulses Synapses excite or inhibit a neuron by depolarization or hyperpolarization at the site of impulse initiation Neuronal integration output of neuron temporal sequence of APs a complex function of synaptic input output input Function of spatial temporal summation and spatial relationships of excitatory and inhibitory synapses o axosomatic synapse synapse on soma short distance from axon initial segment amplitude of post potentials decr small amount in their passive spread o axodendritic synapse synapse on dendrite long dist from axon hillock potential at dendrite tip much smaller than initial amplitude bc of its spread synapse closer to axon hillock have more effect on output of post cell Fast Chemical Synaptic Actions Are Exempli ed by the Vertebrate Neuromuscular Junction mechanisms of action of fast chemical synapses consider synapses onto motor neurons in the CNS by study of peripheral synapses Vertebrate skeletal neuromuscularjunction model for chemical synaptic transmission 0 Each muscle ber innervated by 1 motor neuron junction functions as a relay synapse each AP in motor neuron evokes a large EPSP in muscle ber reaches threshold elicits AP in muscle ber Chemical synapses work by releasing and responding to neurotransmitters o 1 AP depolarizes axon preterminal of motor neuron o for neuromuscularjunction neurotransmitter is acetylcholine ACh 2 opens Ca2 channels 3 Ca2 entry triggers vesicle fusion to release ACh into synaptic cleft 4 ACh diffuses rapidly across cleft and binds to ACh receptors at postmembrane 5 At neuromuscularjunction ACh receptors ligandgated channels opened by binding opening allows ion ow produces EPSP spreads decrementally 6 EPSP large enough to depolarize muscle ber membrane to threshold and initiate AP 0 7 Muscle ber AP propagates to end of ber depolarizes entire membrane initiating contraction 8 Action of transmitter terminated by enzymatic degradation or by reuptake o ACh destroyed by acetylcholinesterase in cleft extracellular matrix 0 9 Choline transporter retrieves choline into presynaptic terminal for ACh resynthesizes Postsynaptic potentials result from permeability changes that are neurotransmitter dependent and voltageindependent P changes depend on neurotransmitter not voltage Controlled by ligandgated channels open by binding of neurotransmitter not from depolarization An EPSP results from a simultaneous increase in the postsynaptic membrane s permeability to Na and K ACh receptor opens becomes permeable to Na and K During EPSP Pna and Pk increase simultaneously to generate AP Synaptic current ion ows thru open channels produces depolarization that is the rising phase of EPSP 0 Large driving force for Na entry toward Ena o Vm close to Ek driving force for K entry smaller Both Na and K contribute to synaptic current drive membrane toward potential near 0 o Reversal potential of the Eepsp current value near 0 that s bw Ena and Ek value of Vm beyond which an EPSP would reverse its polarity EPSPs bw neurons resemble neuromuscular EPSPs but are smaller Similar o waveform fast rise exponential return lasting 1020msec o Ionic mechanisms Neurotransmitter binds to incr P of Na and K ions 0 Both have reversal potentials near 0 2 major differences 0 CNS of verts neurotransmitter mediating fast EPSP is glutamate instead of ACh o EPSP in CNS much smaller bc neuromuscularjunction large many active zones so many vesicles and more transmitters Different bc neuromuscularjunction is a relay synapse CNS synapses are integrating Fast lPSPs can result from an increase in permeability to chloride Waveform of fast lPSP resembles EPSP by hyperpolarizing not depolarizing Fast lPSPs result from incr in Pcl mediated by GABA or glycine neurotransmitters Common mechanism for GABAmediated synaptic inhibition 0 AP in presynaptic GABA neuron causes vesicle fusion and GABA release 0 GABA diffuses to postmembrane bind to receptors open to allow Cl ion thru 0 Mammalian neurons Cl pumped out hyperpolarizing cell toward Ecl o lncr Pcl inhibitory bc locks membrane potential at value more hyperpolarized than threshold V Fast chemical synapses neurotransmitters bind receptors and incr P to ions leads to postsynaptic potential 0 Excitatory or inhibitory depends on ion species that go thru open channels Presynaptic Neurons Release Neurotransmitter Molecules in Quantal Packets Neurotransmitters synthesized and stored in presynaptic terminal and released by presynaptic impulses ACh synthesized and stored in presynaptic terminal ACh synthesized from choline and acetyl coenzyme A in cytoplasm of presynaptic terminal 0 Catalyzed by choline acetyltransferase ACh then taken into vesicles by vesicular transport molecule Choline availability the limiting factor for rate of ACh synthesis ACh in axon terminal stored in various compartments 0 Some vesicles docked at release site rapid release 0 Others anchored to cytoskeleton in interior terminal storage Neurotransmitter release requires voltagedependent Ca2 in ux Neurotransmitter release requires presynaptic depolarization and Ca2ions Depolarization stimulus for neutrans release 0 More release incr depolarization Release of ACh into synaptic cleft depends on in ux of Ca2 ions into presynaptic terminal 0 All neutrans release Ca2 dependent Depolarization of premembrane opens Ca2 channels Ca2 enters and triggers neutrans release 0 Intracellular conc of Ca2 lower than extracellular driving force to enter incr Ca2 conc neat the channel Neurotransmitter release is quantal and vesicular ACh released in packets quanta equal to contents of 1 vesicle Without stimulation spontaneous low freq release of quanta miniature EPSPs mEPSPs Depolarization of terminal by presynaptic AP incr probability of release of each of the many vesicles Synaptic vesicles are cycled at nerve terminals in distant steps Vesicular release hypothesis quantal release of neurotransmitter corresponds to vesicular exocytosis o Fusing exocytosis vesicles should be seen in electron micrographs and vesicular membranes must be recycles Process of recycling vesicular membranes 0 Synaptic vesicles mobilized or targeted to move to release sites where they dock and primed until Ca2 ions trigger fusion of vesicular and presynaptic membranes 0 2 modes of fusion and retrieval of vesicular membranes 0 classical exocytosis vesicular membrane merges with terminal membrane and new vesicle later retrieved by endocytosis pinching off from terminal mem aided by proteins clathrin and dyamin slower higher rates of release 0 kissandrun fusion docked vesicle opens fusion pore to release transmitter into cleft without completely becoming integrated into terminal membrane vesicle then reinternalised without pinching off faster lower rates of release Several proteins play roles in vesicular release and recycling 0 Proteins of exocytosis release of neurotransmitters similar to those of exocytosis release in other cells 0 Basic mechanism conserved in eukaryotic cells Vesicular mobilizationtargeting move from storage to active zone 0 Synapsin attached to vesicles to actin cytoskeleton in mobilization attachment released when synapsin phosphorylated permits vesicle to migrate to active zone 0 Vesicle may attach reversible to terminal membrane followed by docking irreversible 0 Docking interaction of SNAREs Vesicular vSNAREs intertwine with terminalmembrane tSNAREs to hold docked vesicle to active zone 0 vesicleassociated membrane protein VAMP a major vSNARE connects with tSNARE syntaxin and SNAP docked vesicles primed by proteins Munc18 complexin o depolarization Ca2 entry Ca2 bind to vesicle protein synaptotagmin triggers formation of a fusion pore may lead to complete exocytotic fusion of docked vesicle and pre membrane rab3 may inhibit excessive fusion and release 0 cytoplasmic proteins disassemble SNARE complexes after fusion 0 protein dynamin promotes pinchingoff of vesicles thru ATP dependent mechanism 0 o vesicular endocytosis associated with clathrin protein Neurotransmitters Are of 2 General Kinds Smallmolecule neurotransmitters mostly amines and amino acids Neuropeptides chains of aa Cholinergic synapses neurotransmitter is ACh best known bc part of neuromuscular junction Noradrenergic adrenergic synapses neurotransmitter is norepinephrine next best known bc are peripheral synapses in sympathetic nervous system Neurons have one or more characteristic neurotransmitters Neurons metabolically specialized to synthesize and release particular neurotransmitter or combo Cotransmitters multiple neurotransmitters released by single neuron Single neutrans can produce variety of postsynaptic effects 0 Postsynaptic neuron receives synapses from many kinds of presynaptic neurons each has dif neurtrans An agent is identi ed as a neurotransmitter if it meets several criteria 0 Neurtrans present in presynaptic terminal with synthetic machinery Nuertrans released upon presynaptic stimulation amt sufficient to exert postsynaptic action When neurotrans added to extracellular uid should mimic effect of presynaptic stimulation induce change in P Mechanism for removal of neurotrans should exist enzymatic or reuptake Effects of drugs on transmission at synapse may help identify its neurotrans and receptors Vertebrate neurotransmitters have several general modes of action 0 Most synapses in CNS use aa neurotrans 0 Most fast EPSPSs result from glutamate 0 Fast lPSPs from GABA or glycine o Biogenic amines ACh norepinephrine dopamine serotonin found in relatively few neurons but these neurons have widely projecting endings that release transmitter over broader areas volume transmission 0 These receptors have slow actions that modulate neuronal activities Peptides present in substantial numbers of CNS neurons 0 Neuroactive peptide may be coreleased with 1 small molecule neurtrans Multiple Receptors Many neurotrans mediate different postsynaptic action at different postsynaptic cells 0 Ex ACh excites skeletal muscle via EPSPs but inhibits vert heat muscle via lPSPs 0 Effects involve different P change in dif postcells 0 Different postreceptors mediate different effects one ligand gates channel one a Gproteincouple receptor 0 Most neurotrans affect more than one kind of receptor Termination of neurotransmitter action enzymes and reuptake o Neurotrans active for short time must be cleared from cleft for normal synaptic function 0 Temporal and spatial effects of neurotrans action limited in 2 ways 0 Enzymatic destruction and reuptake active transport to retrieve neurotrans or its products 0 Ex ACh enzymatically digested by AChE in cleft product of break down are choline and actetate choline transported back into preterminal by transporter Termination and reuptake can be combined norepinephrine o Vesicle recycling endocytotic pinching of organelles neurotrans actively transported back against conc gradient Peptide neurotransmitters differ from smallmolecule neurotransmitters in synthesis release and termination Small neurotrans synthesized in axon terminals 0 Peptide neurotrans synthesized in soma transported down axon for release Synthesized on ribosomes of rough ER Propeptide peptide neurotrans synthesized as part of larger precursor polypeptide o Propeptide packed into large densecore vesicles transported down axon cleaved enzymatically into pieces Exocytosis of large densecored vesicles not at active zones requires higher AP allows more Ca2 build up Peptide neurotrans not retrieved once released digested by extracellular peptidases Neurotransmitter systems have been conserved in evolution Postsynaptic Receptors for Fast lonotropic Actions Ligand Gated Channels lonotropic receptors produce effects directly fast also ligand gated ion channel Metabotropic receptors produce effects indirectly receptor initiates cascade of messenger molecules slower longer lasting effects ACh receptors are ligandgated channels that function as lonotropic receptors 0 Ex nicotinic ACh receptor produces EPSPs at vert neuromuscular juncUon 0 Alpha subunit binds to ACh Undergoes conformation change to form ion channel permeable to Na and K Many but not all ligandgated channel receptors have evolved from a common ancestor ligandgated channel superfamiliy lonotropic glutamate receptors unrelated Postsynaptic Receptors for Slow Metabotropic Actions G ProteinCouple Receptors G proteincouple receptors GPRCs initiate signal transduction cascades GPRCs activate other membrane proteins G proteins Metabotropic receptors act via second messengers Act to incr conc of intracellular second messenger intracellular signaling molecule carries signal to interior of cells 0 Ex cyclic AMP CAMP Norepinephrine acts on GPRC activated by binding of neurotrans activates membrane protein G protein 0 Process of GPCR signaling cascade o 1 Neurotrans binds to GPCR bumps into G protein 0 2 Activates a G protein G protein has 3 subunits n inactive alpha subunit binds GDP n activated G protein encounters activated receptor exchanges GDP for GTP O 3 alpha subunit dissociates from beta and gamma 4 alpha subunit activated enzyme adenylyl cyclase catalyzes conversion of ATP to cAMP cAMP activates a protein kinase 0 5 cAMPdependent protein kinase can phosphorylate membrane proteins indirectly gate as open or close 0 6 Also can phos cytoplasmic and nuclear proteins that regulate gene expression 0 7 Neurotrans binding has widespread longlasting effects on postsynaptic cells Other mechanisms of Gprotein mediated activity 0 Can activate ion channel directly without second messenger Demonstrates 3 features of synaptic function 0 Particular neurotran can mediate different effects by activating dif kinds of receptors 0 G proteins can act on channels directly without 2nCI mess 0 Channels can be gated by signals other than voltage or direct neurotrans binding GPCRs mediate permeability decrease synaptic potentials and presynaptic inhibition Presynaptic inhibition PSI speci c inhibitory interaction where 1 axon terminal ends on another axon terminal causes decrease in amt of neurotrans that 2nCI terminal releases per AP 0 Sensitivity ability to distinguish among stimuli of different intensity Speci city ability to distinguish among stimuli of different types Sensory receptor cell cell specialized to transform energy of a stimulus into an electrical signal Vary in sensitivity 0 Speci c to certain stimulus Stimulus form of external energy external to cell to which a sensory receptor cell can respond Organization of Sensory System Sensory receptors clustered together in sense organs structure specialized for reception of particular kinds of stimuli Sensory systems sense organs and all of their associated central processing areas Sensory transduction process of sensory receptor converting stimulus energy to electrical signal receptor potential 0 May or may not lead to AP in CNS Receptors want to incr surface area to incr receptor number and sensitivity 0 lncr via cilia and microvilli Sensory receptor cells can be classi ed in 4 different ways Sensory modality subjective to nature of stimulus vision hearing touch smell taste 0 Also balance temp electrical and magnetic elds UV 0 Form of stimulus energy excited sensory receptors at receptor surface photoreceptors electromagnetic receptors auditory mechanical vestibular for balance chemical smell and taste Mechanism of transport 0 lonotropic transduction stimulus received and transduced into electrical signal lonotropic receptors ligandgated channels same molecule binds neurotransmitter and acts as ion channel Mechanical hearing thermoreception electrorecption some taste 0 Metabotropic transduction receptor acts like a neurotransmitter or hormone activated GPCR Metabotropic GPCPs binding of neurotransmitter activates G protein leads to metabolic cascade that openschanneb Vision vert olfaction some taste 0 Location source of stimulus energy relative to the body 0 Exteroreceptors sensory cells that respond to stimuli outside body 0 lnteroreceptors respond to internal stimuli pH osmotic conc of blood Sensory receptor cells transduce and encode sensory information Sensory receptors have 2 functional roles o Transduce convert stimulus energy to electrical signal receptor potential Receptor potential depolarization of sensory cell can trigger AP that propagates to CNS if reaches threshold o Encode sensory cell encodes info about a stimulus carries stimulus info via trains of APs to CNS Only info that CNS receives known Principle of labeled lines sensory modality or quality of sensation associated with stimulus depends only on which receptor cells are stimulated rather than how they are stimulated 0 Even tho receptors speci c to a stimulus any form of stimulus can excite if enough of it poking eye 0 Axons of dif receptors separated and project to speci c regions of CNS 0 ln CNS axon arrangement maps onto location of receptors Mechanoreception and Touch Mechanreceptors cells specialized to respond to dif types of mechanical stimuli o Mediate sense of touch pressure equilibrium hearing types of osmotic stimulation lnsect bristle sensilla exemplify mechanoreceptor responses Sensillum mini sense organ on sensory bristles or hairs o Mechanosensory or chemosensory o Mechanosensory bristles hollow have sensory neuron endings 0 Tip of mechanoreceptor cell s dendrite at base of bristle shaft 0 When bristle move deforms membrane at distal tip of dendrite opens stretchactivated channels 0 In ow of cations produces receptor potential primary electrical response of sensory receptor cell to stimulation o If receptor potential suprathreshold depolarizes sensory neuron generates APs propagate to CNS 0 Magnitude of stimulus encoded by sensory cell Stronger bristle de ection l higher freq of APs 0 Cell identity informs CNS that stimulus is mechanical de ection of particular bristle on body Touch receptors in skin of mammals have specialized endings Dorsal root ganglion DRG sensory neuron that send their distal processes into skin and their central axons into dorsal of sensory part of spinal cord 0 Forms 4 kinds of specialized endings with epithelial cells 0 Merkel disc just below skin epidermis tactile sensing of form and texture and light touch Respond indirectly to indentation of skin 0 Meissner corpuscles formed from 26 sensory neuron endings associated with Schwann cells and collagen o Ruffini endings and Pacinian corpuscles deeper in skin sensitive to pressure Sensory adaptation freq of APs in response to constant stimulus deceases over time o 2 basic types of responses tonic slowly adapting decr in freq over time n merkel disc ruffini endings phasic rapidly adapting signal changes in touch or pressure a meissner corpulus burst of APs at rst then ceases during maintained stimulus n pacinian corpuccles usually give just 1 AP impulse at onset or offset of prolonged stimulus o CNS sensory cortex receives info about location of touch intensity and duration Proprioceptors monitor internal mechanical stimuli Proprioceptors interoceptive mechanoreceptors that monitor movement position mechanical stress and tension in body 0 Associated with musculoskeletal system inof about muscle contraction position movement of body 0 Also in skin and vision Vestibular Organs and Hearing 0 Most animals have mechanaoreceptor organs for orientation to gravity and for sound detection Statocyst organs allows jelly sh to orient with respect to gravity 0 Has grains of sand or CaCO3 dense material sinks within statocyst stimulates receptors by bending cilia Insects hear with tympanal organs 0 Sound radiating pressure disturbance waves of compressed air or water propagate away from vibrating sound source o Auditory organs specialized to detect waves sometimes measure freq Tympanal organ ear drum thin and exible moves in response to sound waves 0 Mechanosensory cells attached to tympanum stimulated by its movement 0 Can be in different locations on insect body Auditory organs thus have evolved repeatedly in dif insect groups at dif location of body How sound stimulates tymapnal organs of noctuid moth o Paired thoracic tympanal organs have only 2 neurons that respond to sound 0 Freq sensitivity equal to bat echolocation 0 Sound intensity coded by impulse freq in each receptor and by highthreshold of 2nCI neuron Shorter response latency incr intensity 0 Directional info sound from left response in left ear greater Vertebrate hair cells are used in hearing and vestibular sense Hair cells for vertebrates sensory mechanoreceptor cells for acousticlateralis system vestibular organs for balance and detection of acceleration lateral line that detects water ow and other stimuli 0 An epithelial cell with apical tufts of microvilli hair bundles Bending of stereocilia single microvilli transduced into receptor potential 0 When pushed stereocilia pivot at base produces shearing force in hair bundle becomes receptor potential opens ion channeb Hair cells don t have axons so don t generate APs release neurotransmitters that conduct APs Directionally sensitive displacement toward tallest stereocilum depolarizes cell incr amt of neurotransmitters released incr freq of APs 0 Displacement to shortest hyperpolarized decr neurotransmitters decr freq of APs Vertebrate vestibular organs sense acceleration and gravity Vestibular organs subserve sensory functions of acceleration and balance in vertebrates o Paired vestibular organs adjacent to auditory organs in inner ear and use similar hair cells 0 Eardrum separates external ear from middle ear air lled contains bones that transmit sound vibration from ear drum to inner ear vestibular organs and cochlea Semicircular canals detects angular acceleration of head and body 0 each vestibular organ has 3 on different geometric planes 0 lled with uid push against hair cells crista ampullaris during acceleration o de ects bundle of hair openclose mechanoreceptive channeb 0 hair cells depolarized on one side hyperpolarized on other info sent to CNS 0 2 otolith organs detect linear movement and acceleration 0 hair cells oriented horizontally and vertically 0 covered by gelatinous mass otolithic membrane 0 crystals of CaCO3 on top when head move crystals lag behind cause membrane to slide against hair bundle o de ected hair bundle creates membrane potential Sound stimuli create movements in the vertebrate cochlea that excite auditory hair cells Mammalian ear receives and ampli es sound pressure waves 0 3 parts of ear 0 external ear distal to ear drum 0 air lled middle ear 0 liquid lled inner ear includes cochlea sound waves vibrate eardrum tympanic membrane transmitted to oval window of inner ear by middle ear ossicles function of middle ear ossicles transfer sound energy from air to liquid of inner ear 0 energy transfer poor bw liquids cannot be compressed pressure in inner ear must be augmented o ossicles increase pressure by applying forces from large area eardrum to smaller area oval window Cochlea coiled tube with uid lled chambers o Basilar membrane separates cochlea into upper and lower chamber As oval window moves creates uid movement in cochlea Movement vibrates basilar membrane stimulates auditory hair cells Varies in width and thickness along length sound waves of dif freq vibrate membrane maximally at different points a Location indicates freq 0 When basilar membrane moves stimulates hair cells in region of cochlea organ of Corti Stereocilia of hair cells push against tectorial membrane and are displaced generate receptor potential 0 Inner hair cells primary source of auditory input to brain Auditory hair cells make synaptic contact with afferent neurons of auditory cochlear nerve 0 Outer hair cells respond to sound and responsible amplify it Hair length changes length in response to changes in membrane potential ampli es local movement of basilar membrane Ampli ed sound acting on inner hair cells 0 Organization of hair cells on basilar membrane of cochlea allow speci c hair cells to respond to speci c sound freq Coding for highlow freq spatially mapped Spatial coding of freq info maintained in auditory pathways leading to auditory cortex The localization of sound determined by analysis of auditory signals in CNS 0 Single ear can t provide directional info auditory localization requires comparison of the 2 ears 0 Sound time difference any sound not straight ahead or behind arrives at 2 ears at dif time 0 Sound source to left reaches left ear rst 0 Dif in time of arrival increases with incr offset 0 Sound intensity difference sound louder in ear that more directly faces the source 0 Sound doesn t go around corners well far ear thus in a sound shadow blocked by head Owl very good at localizing sound horizontally and vertically 0 Right ear more upward left ear more downward lncr intensity dif bw ears Horiz sound source coded by time dif Vert axis coded by intensity dif o Neurons in owl midbrain represent a map each neuron space speci c responding to sound only from particular direction Sound sources mapped in 2D Chemoreception and Taste Chemoreception sensory response to a chemical stimulus 0 Taste gustatory sense Receptors in mouth stimuli in liquid form 0 Olfaction sense of smell Receptors on antennae of insects and nose in verts Stimuli airborne lnsect taste is localized at chemoreceptive sensilla Taste receptors located on sensilla bristles have dendrites of 24 chemoreceptor cells and 1 mechanoreceptor o Shaft has hole at tip water and taste molecules enter 0 Taste sensilla found in numerous locations on insect body 0 Each chemoreceptor sensitive to particular chemical stimulus 0 Sugar cell salt cell water cell bitterdeterrent cell Taste in mammals mediated by receptor cells in taste buds Taste receptors are epithelial synapse with neuron carry signal to taste centers in brain 0 Taste cells grouped into taste buds on tongue and back of mouth 0 Papillae clusters of taste buds Mechanisms of taste transduction differ for dif tastes o lonotropic transduction salt and sour Salt taste receptor has channels permeable to Na Na conc in mouth incr membrane potential depolarizes Sour adicity mediated by channel H modulates permeability of channels to more numerous cations o Metabotropic transduction sweet bitter umami savory All sensed by metabotropic GPCRs taste molecule binds Use similar G proteins Olfaction Olfaction in insects Sensilla on antennae detect chemical at a distance similar to taste sensilla in structure 0 Entire shaft perforated with many tiny holes lead to tiny channels tubules penetrating exoskeleton 0 Receptor send thin dendritic processes into shaft bathed in uid sensillar lymph Odorant molecules enter pores travel down tubules dissolve in sensillar lymph bind to olfactory receptor OR on dendrite membrane 0 Some OR neurons odor generalist cells detect wide variety of odors other OR neurons odor specialist responsive to pheromones smell used for communication 0 use for sex attractant or deterrent ovipositiondeterrent trail marking alarm colonyrecognition Mammalian olfactory epithelium contains odor generalist receptor cells Olfactory epithelium main system s olfactory receptive surface lines part of nasal cavity 0 OR cell is a bipolar neuron in cell body of olfactory epithelium Dendrite extends from cell body to mucusy epithelial surface end in dendritic knob projects into mucus cilia project from knob cilia are sites of transduction o Odorant molecule dissolves in mucus interacts with binding proteins interact with receptor of cilia OR cell axons extend to olfactory bulb in forebrain synapse with secondorder olfactory bulb OR initiates Gprotein mediated signal cascade produces intracellular cAMP that diffuses in cytoplasm and opened cyclic nucleotidegates channels 0 Each OR expresses gene for only 1 kind of GPCR but many odorants can bind to 1 kind of OR o Dif odorants stimulate dif population of receptors combine signal 0 Broader binding affinity of olfactory GPCR allow system to responds to more odors OR cells send axons to olfactory bulbs in CNS each axon end within a globular cluster glomerulus 0 Receptor types kept segregated among dif glomeri The vomeronasal organ of mammals detects pheromones Vomeronasal organ 2nCI olfactory system located below main olfactory epithelium on each side of nose 0 Specialized for detecting particular odors pheromones 0 When unusual odor detected pheromone pumps air into lumen so air wafts over vomeronasal receptors Photoreception Visual systems carry out photoreception and processing of visual signals photoreceptors sensory receptors sensitive to light 0 ex rhodopsin a GPRC Photoreceptor cells and eyes of different groups have evolved similarities and differences Photoreception response of sensory cell to light Eye lightresponsive sense organ contain photoreceptors mediating light responses 0 Differ in complexity o 2 types evolved separately camera eye lens forms an inverted image on array of photoreceptors at back of eye a simple snail a complex humans octopi compound eye many facets ommatidia each with own lens together produce a mosaic image tiles of individual ommatidial responses I clam y Rhodopsin consists of retinal conjugated to opsin a GPCR Photopigment pigment that absorbs light consists of protein containing associated nonpeptide organic molecule chromophore 0 Absorption of photon by chromophore produces chemical rxn triggers transduction cascade Chromophore of animal photoreceptors retinal bound to integrate membrane protein opsin to produce lightsensitive pigment rhodopsin Light causes retinal to undergo photochemical rxn cistrans followed by conformation change in opsin produced activated rhodopsin o Rhodopsin activates G protein signal transduction cascade The Vertebrate eye focuses light onto retinal rods and cones Camera eye cornea and lens focus an inverted image of visual eld on retina 0 Light refracted bent at surfaces where materials differ in dens y Retina photoreceptor rods and cones containing layer at back of eye inverted 0 Also contains network of neurons Horizontal cells bipolar cells amacrine cells ganglion cells Perform the rst stages of visual integration Fovea area of high visual acuity intervening cell layers and blood vessels displaced to side contains tightly packed cones lack rods in this area 0 Blind spot at optic disc where ganglion axons exit retina o Consequence of inverted retina Rods and cones of the retina transduce light into a hyperpolarizing receptor potential Photoreceptor outer segments contain many attened lamellae of membranes 0 2 photoreceptors in retina o rods sensitive to low light lamellae form internalized attened discs not connected to extracellular space need intracellular messenger o cones color acuity bright light lamella continuous with extracellular space Transduction of light into electrical signal in rod and cone photoreceptors o 1 Light activates rhodopsin o 2 Activated rhodopsin stimulates G protein to activate a phosphodiesterase enzyme 0 3 Enzyme decrease conc of cyclic GMP in photoreceptor cytoplasm o 4 Decr in cGMP closes cyclic nucleotidegated ion channels Na in ux decreases photoreceptor hyperpolarizes o In dark 00 High conc of cGMP in rod Binds to channel opens Na ow inward hyperpolarization Resting Na permeability of rodcon higher than in normal neuron membrane potential less negative Vm 30mV more depolarized causes Dark current constant in ow of Na must be constantly counteracted by actively pumping out o In light 0 O O 0 Low conc cGMP bc rxns at disc membrane result in degradation of cGMP Light stimulated rhodopsin activates G protein transducin G protein stimulates cGMP phosphodiesterases PDE PDE activation decr cytoplasmic conc of cGMP channels close 2nCI messenger mediated response to light in rod outer segment decr Na in ux hyperpolarization changes in Vm close Ca2 channels low Ca2 conc l decr glutamate release I dehyperpolarizes bipolar cells Visual Sensory processing Photoreceptors respond to light visual system respond to pattern contrasts or changes in light level and color 0 Conversion of sensitivity to light to contrast occurs in retina and partially in brain Retinal neurons respond to contrast Retina have rodcone photoreceptors and 4 kinds of integrating neurons 0 Bipolar cells receive input from photoreceptors 0 Horizontal cells create connections in outer plexiform layer 0 Amacrine cells create connections in inner plexiform layer 0 Ganglion cells produce output of the retina Receptive eld area of retina that reports to a single ganglion o Receptive elds divided in 2 areas center and surround o Oncenter cell incr rate of impulse when center of receptive eld illuminated Suppressed when surround stimulated Max stimulation when all center stimulated and none of surround o Offcenter cell opposite inhabited by light in center excited by light in surround o 2 retinal pathways 0 straightthrough pathways produce center of ganglion receptive eld photoreceptors l bipolar cells l ganglion o lateral pathways produce surround of ganglion receptive eld extend along retinal sheet via horizontal and amacrine light stimulus hyperpolarizes offcenter bipolar cell synapases to offcenter ganglion hyperpolarizes light in oncenter hyperpolarizes cones to depolarize bipolar cell synapses onto oncenter ganglion and depolarizes it 0 light in surround opposes light in center The vertebrate brain integrates visual information thru parallel pathways Color vision accomplished by populations of photoreceptors that contain different photopigments Ability to see color depends on differential sensitivities of photopigments of different wavelengths of light 0 Spectral sensitivities to dif types of cones broad and overlapping perception of color base on ration of excitation of different cones comparison of outputs from small number of receptor types Receptors dispersed across retina in mosaic pattern Outputs of receptors combined and compared to produce sensation of color Monochromats no color vision Dichromat 2 cone types dogs Trichromat 3 cone types humans 0 Purple only nonspectral color we perceive Tetrachromat 4 cone types birds 0 Have cone sensitive to UV light 0 Many insects also can see UV light Mantis shrimp 16 dif photoreceptor types and 12 specialized for color vision 0 Introduction to Endocrine Principles 2 control systems in animal bodies nervous system fast addressed direct endocrine system slower and longerlasting broadcast Neurotransmitters in chemical synapse travel across synaptic cleft 0 after stimulated with AP moving along axon affect postsynaptic cell Hormone endocrine signals 0 carried thru bloodstream reaches whole body widespread response as long as the cell has the correct receptor 0 response takes longer and can last longer Hormone A chemical substance produced and released by nonneural endocrine cells or by neurons 0 Exerts regulatory in uences on the function of other distant cells reached via the blood 0 Effective at low concentrations Epithelial nonneural endocrine cell releases hormone Nonhormone chemical messengers o Paracrine and autocrine substances affect nearby cells 0 Classi ed separately bc not in circulatory system 0 C02 in blood Hormones bind to receptors expressed by target cells Hormone only interacts with target cells express receptors that speci cally bind to hormone Widespread effects bc many different cells have the receptors Sensitivity of target cell to hormone depends on number of functional receptors the target cell expresses for that hormone 0 Changes with up and downregulation of receptors 0 Also depends on hormone conc in blood Concentrations of hormones in blood vary Hormone rates of synthesis and secretion must be controlled to be regulators Higher rate secreted l higher conc l greater effect on target cells Hormones eventually degrade bio halflife 0 So conc depends on balance of secretion and degradation Peripheral activation some hormones converted to more active form after secretion Most hormones fall into 3 chemical classes Steroid hormones synthesized from cholesterol 0 Secreted by gonads adrenal cortex skin placenta o Lipidsoluble can pass thru cell membrane Peptide hormones chains of aas 0 Include insulin growth hormone o Vary in size 0 Soluble in aqueous solutions Amine hormones modi ed aas o Melatonin secreted from pineal gland derived from typtophan o Synthesize in thyroid glad rich in iodine 0 Some soluble in water other in lipids Water or lipid soluble can be transported in blood bound to water soluble carrier proteins 0 Provide reservoir of bound hormones that can be drawn upon o Extend their halflives Hormones exert effects by producing biochemical changes in target cells Hormones bind to speci c receptors Lipidsoluble hormones bind to intracellular receptors 0 Receptors in cytoplasm or nucleus 0 Bind to receptor forms hormonereceptor complex acts as transcription factor that interacts with target cell DNA to alter gene expression 0 Turn protein synthesis onoff 0 Can bind to membrane exert nongenomic effects Watersoluble hormones receptor in cell membrane external binding sites 0 Mediate hormone actions by altering membrane permeability or by activation intracellular 2nCI messenger system Synthesis Storage and Release of Hormones Peptide hormones are synthesized at ribosomes stored in vesicles secreted on demand Insulin produced as a preprohormone preproinsulin 0 Nucleotide sequence translated to determine aa sequence of preprohormone synthesized at ribosomes o Preproinsulin has 4 regions 0 C segement cleaved becomes insulin 0 P segment cleaved becomes proinsulin Proinsulin travel to Golgi put in secretry vesicles C fragments retained in secretory vesciles secreted with mature insulin 0 Secreted by Ca2 dependent exocytosis 0 Negative feedback with blood glucose conc Steroid hormones synthesized on demand prior to secretion released into blood by diffusion Synthesized from cholesterol from fat in diet o Steroidogenic steroidproducing endocrine cells and liver cells also synthesize cholesterol bc not watersoluble circulate in blood bound to lipoprotein carrier complexes 0 lowdensity lipoprotein LDL transport cholesterol to cells 0 high density lipoprotein HDL carry cholesterol away from cells to liver verts produced by endocrine cells of gonads adrenal cortex skin placenta dif steroidogenic cells have dif sets of enzymes produce dif end product synthesis convert cholesterol to pregnenlone travel from mitochondria to smooth ER steroids not stockpiled in vesicles when cell stimulated made from precursors stored in lipid droplets and immediately secreted Types of endocrine glands and cells Secretory cells may be organized into discrete organs 0 Endocrine glands Discrete endocrine cells grouped together Diffuse cells scattered among nonendocrine tissue Intermediate bw the 2 Endocrine cells and glands may be 0 Epithelial nonneural Stimulated by hormonal input Produce hormones o neurosecretory functions more like a neurons Produce neurohormones Signaled by neurons Often release neurohormones at neurohemal organ contained in axon terminals site for neurohormonal release Control of Endocrine Secretion The Vertebrate Pituitary o Pituitary gland below hypothalamus 2 parts 0 Anterior pituitary and posterior pituitary The posterior pituitary illustrates neural control of neurosecretory cells Hypothalamic neurosecretory cells extend axons thru median eminence forms part of oor of hypothalamus along infundibular stalk into pars nervoas axons terminate at capillaries 2 peptide hormones released in pars nervosa o vasopressin ADH limits production of urine and stimulates constriction of arterioles o oxytocin cause contractions of uterus during birth ejection of milk 0 2 clusters of cell bodies in hypothalamus o paraventricular nuclein and supraoptic nuclei 0 sites of production of the 2 peptides 0 release hormone by exocytosis neural control of neurosecretory cells 0 neurosecretory cells produce and secrete 2 peptide hormones integrate synaptic input from host of neurons The anterior pituitary illustrates neurosecretory control of endocrine cells Nonneural endocrine tissue Divided into pars distalis pars intermedia pars tuberalis All hormones produced are peptides proteins or glycoproteins o Produces hormones GH prolactin MSH TSH ACTH LH FSH Neurosecretory cells of hypothalamus secrete releasing hormones and inhibitory hormones carried thru portal system to anterior pituitary o Neurosecretory neurons extend into arterial in ow travel thru hypothelamohypophysial portal vessels 0 Stimulate endocrine neurons to make their hormone 0 Interface bw brain and endocrine system not part of brain but under its control Hormones and neural input modulate endocrine control pathways Hormones know general function and location Hypothalamus secretes peptides corticotropinreleasing hormone CRH Stimulates secretion of ACTH Posterior pituitary peptides vasopressinantidiuretic hormone ADH Regulate water reabsorption at kidney vasoconstriction Anterior pituitary secretes peptides adrenocorticotropic hormone ACTH Stimulates glucocorticoid secretion by adrenal cortex 0 Supports adrenal cortical tissue tropic action Adrenal cortex secrete steroids glucocorticoids cortisol corticosterone Pa rt of stress response Affects metabolism of many tissues to increase blood glucose and cause protein and fat catabolism Adrenal medulla epinephrine norepinephrine Pa rt of stress response Reinforce sympathetic nervous system 0 In uence cardiovascular function and organic metabolism of many Ussues Islets of Langerhans pancreas peptides Insulin promotes uptake and storage of nutrients by most cells Glucagon maintains blood levels of nutrients after a meal and during stress Mammalian Stress Response Autonomic nervous system and HPA axis coordinate stress response 0 Stress l sympathetic nervous system ght or ight system releases epinephrine and norepinephrine from sympathetic nerve terminals and adrenal medulla l incr heart raterespiration rates blood pressure l incr blood ow incr air ow constricts blood ow suppress digestive functions epinephrine stimulates release of glucose to release extra energy from stores inhibit insulin secretion mac glucose hypothalamic neurosecretory cells release CRH o CRH acts as a nuerohormone to stimulate ACTH secretion HPA axis Epinephrine also stimulates secretion of ACTH o CRH acts a neurotransmitter in brain stimulates sympathetic ght or ight system anterior pituitary secretes ACTH ACTH stimulates secretion of glucocorticoids by adrenal cortex 0 Reinforce actions of sympathetic nervous system 0 Metabolic effects facilitate release of usable sources of energy to blood Stimulate catabolism of protein in musclebone Stimulate liver to produce glucose gluconeogenesis lnhibit secretion of insulin Stimulate catabolism of fats fatty acids used as energy source Metabolic actions of glucocorticoids coordinate with norepinephrineepinephrine to ensure glues availability 0 Feedback negatively on CRH and ACTH cells of HPA axis Modulates stress response Decr ACTH l decr glucocorticoids l blood conc returns to normal
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'