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This 12 page Study Guide was uploaded by Daniela escontrela on Saturday January 31, 2015. The Study Guide belongs to BIL360 at University of Miami taught by Dr. McDonald in Fall. Since its upload, it has received 148 views. For similar materials see Comparative Physiology in Biology at University of Miami.
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Date Created: 01/31/15
Lecture 7 Neurons Nerve cells neuron Soma cell body dendrites collect information from the world axon long projection that comes off the soma axon terminal where nerve impulse ends synapse space Change in electrical potential of some AP potential travels down axon NT released at terminal because of change in electrical potential NT binds to receptors on post synaptic cell Glial cells support neurons physically and metabolically myelin sheath Schwann cells PNS Oligodendrytes CNS Astrocytes link up capillaries to neurons win the CNS liaison between blood and neuron Microglial cells immune support for neurons Number of glial cells indicative of evolutionary complexity Electrical current movement of charge Potential difference separation of positive and negative charge Potential difference does work when charges allowed to flow as current Cell membrane separates charges positive outside and negative inside creates voltage difference Measure membrane potential using voltmeter When recording microelectrode in cytoplasm voltmeter records resting membrane potential 65mV Without resistance Cell membrane would see no voltage difference cell membrane impedes movement of charges Cell s passive response to current depends on passive electrical properties of membrane Resistance ability of charged molecule to cross cell membrane inc channelsdec resistance Capacitance thicker cell membranelower capacitance because lower impact Passive electrical properties of the cell delay changes in membrane voltage The higher the resistance or capacitance the higher the time constant the longer it takes voltage to change Time constant time it takes the voltage change to reach 63 of its final volume Passive electrical properties of the cell limit the spread of graded potentials Voltage change decreases exponentially w distance electrotonic conduction Steepness of this decrease is describe but the membrane length constant Increasing membrane resistance Rm increases length constant current trapped in membrane so can travel further Increasing internal resistance decreases length constant Membrane resistance membrane capacitance resting membrane potential time constant length constant passive electrical properties Resting membrane potentials depend on selective permeability to ions Electrical equilibrium concentration diffusion force equal but opposite to electrical force Nernst equation gives equilibrium potential when charge would stop moving Goldman equation takes permeability and concentrations into account More permeating ions have more effect Action potentials Result from voltage dependent changes in membrane permeabilities to ions because the ion channels that produce AP are voltage gated Resting membrane potential potassium leak channel always open high permeability to potassium and drives cell toward equilibrium potential Voltage gated Na and K channels closed Rising phase voltage gated sodium channels open sodium into cell depolarization towards equilibrium potential for sodium Falling Phase voltage gated Na channels close voltage gated K channels open potassium leaves repolarization cells inside becomes more negative Undershoot hyperpolarization because voltage gated K channels slow to close The changes in membrane permeability that cause AP can be visualized as the actions of individual ion channels Na Channels open quick but become inactivated quick K channels longer to open but stay open a long time AP at one location on an axon can initiate an AP at a neighboring location Propagation of AP dependent on local currents Subject to time and length constant Voltage gated sodium channel opens sodium spreads both ways inside the axon membrane further the sodium spreads the more slight depolarization more Na channels open Local current supported by capacitive current positive charge inside repels positive charge outside attracts negative charge change in membrane potential bigger Absolute refractory period when Na channels inactivated nothing wakes them up by time activated again AP has moved on Relative refractory period K channels still open to get AP need much bigger stimulus Increase axon diameterdecrease in internal resistanceincrease conduction velocityincrease electrotonic conductionloca currents can go further down the axon Myelinated axon Has gaps called nodes of Ranvier AP occur here This causes increase in membrane resistanceincrease in length constant Time constant stays same because capacitance decreases but resistance increases Increasing temperature increases the conduction velocity Lecture 8 Synapses Electrical synapses transmits signals through gap junctions instantaneously electrical current from one cell flows directly into next cell changing its membrane potential current in BOTH directions fast responses Chemical synapses transmits signals with help of NT presynaptic electrical signal transduced to chemical signal release NT slower transmission can amplify current flow excitatory or inhibitory one way presynaptic postsynaptic plasticity important for learning onotropic ligand gated channels fast responses direct increases in permeability Metabotropic g protein coupled receptors slow response Synaptic potential what happens in post synaptic cell when NT binds to it Graded change Variable in amplitude and spread decrementally Excitatory synaptic potential towards voltage threshold depolarizes Inhibitory synaptic potential away from voltage threshold hyperpolarizes Temporal summation sum NT released at different times Spatial summation cell adds together stimulus from 2 different neurons Neuronal integration take into account temporal and spatial Neuromuscularjunction Large synaptic response release of NT causes muscle fiber to contract 1 2 3 4 Uquot 10 AP travels down axon of presynaptic cell Causes depolarization in axon terminal Depolarization stimulated opening of voltage gated calcium channels in presynaptic cell Calcium flows into cell down its electrochemical gradient calcium necessary for movement of vesicles containing NT to move from cytoplasm to cell membrane NT released NT is acetylcholine into the synapse NT binds to receptor on postsynaptic cell Ach receptors ligand gated channel ligand is NT acetylcholine Ach non selective cation channelNa rushes in and K trickles out causes depolarization Depolarization activates other voltage gated Na channels AP occurs in muscularjunction Acetylcholine left in synapse broken down by enzyme acetylcholinesterase and taken back to presynaptic cell this enzyme important in regulating response leaving NT in synapse longerbigger response Postsynaptic potentials result from permeability changes that are NT dependent and voltage independent Neuromuscular vs Neuronal EPSPs 1 2 Glutamate is the most common NT in the CNS rather than acetylcholine Ach Neuronal EPSPs are much smaller in size compared to neuromuscular Because for neuromuscularjunctions the EPSPs result in AP relay synapses In the CNS need summation to reach voltage threshold and have AP integrating synapses thousands of synapses synapsing onto single cell in CNS Acetylcholine synthesized and stored in presynaptic cell Availability of choline limiting factor in rate of Ach release Acetylcholine broken down by acetylcolynesterase into choline and acetate Choline goes back to presynaptic cell choline also supplied by blood Two kinds of NTS 1 Small nucleotide NTs I Amino acid NTs used in most CNS synapses fast EPSPs glutamate fast IPSPs GABA and glycine I Biogenic amines in few neurons have widely projected endings receptors for these NTs have slow metabotropic actions 2 Neuroactive peptides I Peptides present in a few CNS neuron Neurons characterized by type of NT it releases most neurons release a majority of one type of NT postsynaptic cell receives many NT from many presynaptic cells NT can mediate different effects by activating different receptors Serotonin reuptake and SSRI action When release serotonin into synapse can be I Broken down by monoaminoxidase I Taken back up by serotonin transporters to presynaptic cell f suffering from depression have low levels of serotonin in synapse Two antidepressants 1 MAOI monoaminoxidase inhibitor targets monoaminoxidase so serotonin is not broken down 2 SSRI selective serotonin reuptake inhibitors target serotonin transporters so serotonin is not taken back up by presynaptic cell 5HT1a receptor impedes action of antidepressants Synaptic plasticity synapses change properties with time and activity Presynaptically NT released at different rates Postsynaptically sensitivity to NT can differ Facilitation response increases over time Antifacilitation response decreases over time Habituation decrease in intensity of reflex response Antifacilitation I In the Aplysia due to decrease in release of NT from presynaptic cell Sensitization prolonged enhancement of a reflex response to a stimulus facilitation I Neuron involved in head shock synapses onto sensory neuron I When shock organism in head the neuron involved will release serotonin I Serotonin will bind to serotonin receptors G coupled on sensory neuron inc cAMP I cAMP causes increase in cyclic dependent protein kinase which causes phosphorylation of existing proteins inactivate K channels and stimulate Ca channels inactivation of K channels broadens AP depolarization prolonged I more calcium channels activated bc they are voltage gated more Camore NT released Lecture 10 Sensory Processes Sensory cell transforms stimulus energy into electrical energy Activated by stimuli other than synaptic activity Clustered in sense organs Classification by sensory modality receptor type mechanism of transduction location of stimulus energy relative to body Group receptors by stimuli they receive Mechanoreception and touch Stretch activated channels Insects hair plate or bristle sensillium I Opening of ion channel involved is very fast I If move hair platesbristle will pinch the top of a mechanoreceptor causes stretch in the cell membrane of that receptor Stretch opens non selective cation channels and causes mechanoreceptor to have a reversal potential I Receptor potential of sensory receptors results from inward flow of current mostly Na I Channels involved non voltage dependent stretch dependent nonselective in permeability causes reversal potential Pacinian Corpuscle mammalian mechanoreceptor I Encapsulated nerve ending in deep layers of skin I These mechanoreceptors respond to deformation of outer quotonion skin I If squeeze for prolonged time would see AP at onset of pressure and when squeeze removed only acts when pressure changes desensitizes very quickly Receptor adaptation decrease with time in response of a receptor to a steadily maintained stimulus Phasic receptors rapidly adapting generate short burst of AP at onset of stimulus but adapt rapidly and completely Tonic receptors slowly adapting discharge of train of AP throughout the duration of the stimulus Vestibular organs Vestibular receptors detect gravity and acceleration to maintain balance Statocyst common vestibular organ for equilibrium reception invertebrates I Statolith small hard particle that sits on hair cells movement of particle against hair cells stimulates or inhibits depending on direction of motion Vertebrate vestibular organs are part of the sensory system called the acoustico lateralis system sensory cells are hair cells bending of stereocilia transduced into a receptor potential I Hair cells lack axon but synaptically excite axons of sensory neurons Stereocilia microvillia kinocilium large cilia Stereocilia towards kinocilium depolarizationnerve impulse Stereocilia away from kinociliumhyperpolarizationno nerve impulse Stereocilia joined together by filamentous tip links displacement of stereocilia in positive direction stretches tip linksopens cation channelsdepolarizing of cell Human vestibular organ in inner ear Three semicircular canals detect angular acceleration at right angles to each other and fluid filled when moveaccelerate fluid rotates and movement of fluid against hair cell will move stereocilia in one direction or another causing depolarization or hyperpolarization Two Otolith organs sacculus and utriculus detect linear movement and acceleration hair cell moving against hard Otolith 0 Sound Reception Auditory receptors are hair cells lose their kinocilium during development Three parts of the ear external middle and inner 1 2 Sound pressure wave vibrates the tympanic membrane Vibration transmitted to oval window by three middle ear ossicles malleus incus and stapes These three small bones concentrate vibrations into small oval window which allows for the amplification of sound into the inner ear middle air ossicles help in efficient transfer of sound energy from air to liquid of inner ear Sound waves pushing in at oval window set up traveling pressure waves in the fluid filled cochlea Produce minute movements of the basilar membrane bears the auditory hair cells depending on frequency of sound basilar membrane will vibrate in different regions 0 Basilar membrane is narrow and rigid at the base ofthe cochlea and more flexible atapex 0 Low frequency sound vibration of whole membrane with peak at apex 0 High frequency sound whole membrane doesn t vibrate and peak at base With live cochlea found a more pronounced responseamplified response membrane vibrated at particular frequencies but vibration was amplified cochlear amplifier 0 Basilar membrane moves up pushes on outer hair cells which hit the tectorial membrane which causes a response The outer hair cells are smushed against the tectorial membrane but when they get pushed up they contract and shorten pulling up the basilar membrane creating an even more pronounced response 0 Inner hair cells on basilar membrane help transmit response to brain auditory input to brain Chemoreception For terrestrial organisms the distinction between taste and olfaction is very clear Taste is mediated by specialized chemoreceptive organs placed bear the mouth and the stimuli are in liquid form Taste in insects taste receptors called sensillabetween 24 chemoreceptor cells and a single mechanoreceptor sensilla found in the tarsus and labellum Taste in vertebrates taste receptor cells grouped together in taste buds in mammals the taste buds are confined to small swellings called papillae I Taste buds have receptor cells supporting cells and basal cells High sensitivity to sweet taste at tip of tongue and sensitivity to other tastes increases as go back on tongue I Salty and sour Ionotropic receptors I Sweet umami and bitter mediated by metabotropic receptors Olfaction in insects Olfactory receptors respond to airborne odorants at low concentrations Localized in variety of sensilla and are concentrated in the antenna Pheromone detection Olfaction in vertebrates Main olfactory system and most have vomeronasal system receptor cells respond specifically to one or only a few pheromones with high selectivity Main olfactory system each olfactory receptor cell is a bipolar neuron with a cell body in the olfactory epithelium I One long dendrite with olfactory cilia extending into mucus layer I Unmyelinated axon that synapses with cells in olfactory bulb I Dendrites of olfactory cells have cAMP gated channels that are activated by oderants ligand increases cAMP which opens channels from inside I Odorant binds to olfactory receptor on cell membrane on neuron G protein activated this activates adenylyl cyclase which increases cAMP The increased cAMP turns on cation channels so Na and Ca can enter the celldepolarization Ca binds to Ca activated Cl channel so Cl leaves further depolarization AP Lecture 11 Photoreception Photoreceptors contain photopigments molecules that absorb and transduce light into an electrical signal Ciliary photoreceptors modified cilia contain the photopigment Rhabdometric photoreceptors collections of microvilli contain the photopigment Photoreceptors are in the eyes so can determine where light is coming from Four types of eyes Retinal eye photopigment behind photoreceptors determine direction of light no image formation Eyecup pigment allows directionality of light if opening small enough can work like pinhole camera and create an image Camera eye lens and cornea to concentrate light Compound thousands of camera eyes The vertebrate eye Cornea an lens focus an inverted image of the visual field on the retina ris diaphragm constricts the opening of the pupil to limit light entry and enhance resolution Retina has the photoreceptors Rods more sensitive used in dim light on periphery of retina Cones used in brighter light for color and high acuity vision center of eye Light Transduction 1 Light activates photopigment rhodopsin I Light absorbing molecule conjugate of retinalvitamin A and opsinprotein I From bent form resting form to straight form activated leads to conformational changes in the whole molecule I Rhodopsin is a G coupled receptor 2 Activated rhodopsin decreases cGMP in the photoreceptor cytoplasm I Rhodopsin stimulates transducin I Transducin stimulates cGMP enzyme breaks down cGMP to 5 GMP I The decrease in cytoplasmic concentrations of cGMP acts as a intracellular messenger to convey a change from the disc membrane to the outer surface membrane 3 Decrease in cGMP causes cGMP gated Na channels to closehyperpolarization Dark cGMP gated channels open and a continuous movement of Na into the cells through the channels and out of the cell via NaK ATPase dark current high metabolism resting membrane potential closer to Na equilibrium potential because of high permeability to it Visual sensory processing Photoreceptors respond to light vertebrate visual system responds to contrast Fovea central highacuity region intervening cell layers and blood vessels displaced Blindspot created by the optic nerve coming off the inner side of the retina Ganglion cells Their axons form the optic nerve Respond to stimulation over a large visual area I The receptive field of a sensory neuron is the area of the retina from which the impulse activity of that neuron can be influenced by light one ganglion receives info from many photoreceptors On center stimulated when photoreceptors in center of RF stimulated by light Off center on periphery of RF and stimulated by light on periphery Synaptic connections of the retina straight through pathways Project radially through the retina at right angled to its surface Photoreceptors to bipolar cells to ganglion cells Give rise to the properties of the center of a ganglion s RF How light in center of RF affects ganglion cells Cone in center of RF light hits cone hyperpolarizes cone wi synapse onto on or off center bipolar cells On center stimulated by light in center off center inhibited by light in center On center bipolar ce synapses onto on center ganglion cell I Light hits center of RF stimulates cone cone hyperpolarizes on center bipolar ce depolarizes on center ganglion cell depolarizes cause AP Off center bipolar ce synapses onto off center ganglion cell I Light hits center of RF cone hyperpolarizes off center bipolar ce hyperpolarizes off center ganglion cell hyperpolarizes no AP Photoreceptors ALWAYS hyperpolarize in response to light Lateral pathways Extend along retinal sheet via horizontal cells and amacrine cells Give rise to the properties of the antagonistic surround of ganglion s RF How light in surround of ganglion cell s RF works its way back to ganglion cell Horizontal ces move signal to center of RF where ganglion cell is On center ganglion ces inhibited by light in surround of RF I Light hits photoreceptors in surround photoreceptor hyperpolarizes I Cone synapses onto horizontal cell and causes it to hyperpolarize I Horizontal ce moves signal to other cone in center of RF which depolarizes I Depolarization causes hyperpolarization in on center bipolar cell and the hyperpolarization in on center ganglion cell Off center ganglion cells I Light hits photoreceptors in surround photoreceptor hyperpolarizes I Cone synapses onto horizontal cell and causes it to hyperpolarize I Horizontal ce moves signal to other cone in center of RF which depolarizes I Depolarization causes depolarization in off center bipolar cell and off center ganglion cell AP Central visual projections The major visual projection of mammals is the geniculostriate system The optic nerve synapses onto the lateral geniculate nucleus Neurons from the lateral geniculate nucleus project to the primary visual cortex Two major types of neurons in the visual cortex simple and complex both have preferred axis of orientation Simple matters where the stimulatory bar is in the receptive field Complex doesn t matter where stimulatory bas is in RF as long as parallel to axis Photoreceptors in insects called retinular cells 8 in circle have different forms of rhodopsin detect UV light Lecture 12 Endocrine and Neuroendocrine Physiology Paracrines affect other cells and autocrines affects itself local chemical messengers Three categories I Neurdomodulators released in conjunction with NT regulate activity of post synaptic cell I Cytokines immune function I Epicosanoids inflammation Pheromones and kairomones external chemical messengers Pheromones between members of the same species Kairomones between members of same species not for communication Hormones long distance communication within animal Released by nonneuronal endocrine cells or by neuroendocrine cells Regulatory influences on function of other tissuesorgans Bind to receptor molecules expressed by target cells Travel in blood long distance Slow widespread responses This type of cell communication older than neural transmission Three types of hormones 1 Steroid hormones made from cholesterol lipid soluble bind to intracellular receptor affect gene expression 2 Peptide and protein hormones ie Insulin short or long strain of aa water soluble extracellular receptors modulate existing proteins 3 Amine hormones single aa converted to hormone characteristics of peptide and lipid hormones Endocrine glands Make up group of cells that secrete hormone directly to circulatory system and modulate body processes Ductless richly vascularized discrete and diffuse glands Two classes of endocrine cells 1 Epithelial nonneural endocrine secrete hormone in to blood cell in response to other hormones 2 Neuroendocrine synapses onto blood stream release chemical into blood release hormone in response to neural stimulus electrical stimulus to chemical stimulus Difference between endocrine and neuron cells Neuron cell to cell directly pinpoint precise short time Endocrine one cell affects multiple cells through blood Pituitary gland Below the hypothalamus consists of neurohypophysis posterior and adenohypophosis anterior Posterior pituitary Outgrowth of brain Three parts median eminence floor of hypolthalamus pars nervosa and infundibular stalk Two peptide hormones ADH and oxytocin released into blood by pars nervosa Synthesized by two neurosecretory cells within the hypothalamus the paraventricular nuclei and the supraoptic nuclei I Axons from their cell bodies run through the infundibular stalk to the pars nervosa Anterior pituitary Three parts pars distalis pars intermedia and pars tuberalis Nonneuronal endocrine cells Secretion of anterior pituitary hormones controlled by hypothalamic neurohormones 1 Neurosecretory cells in hypothalamus secrete hormone into bloodstream capillaries of median eminence 2 Go down blood and travel to portal vessels second blood stream located in anterior pituitary 3 Stimulate or inhibit release of anterior pituitary hormones 2 capillary beds one in median eminence and other in anterior pituitary Linked by portal vessels Anterior pituitary hormones exert their effects on nonendocrine tissues or on other endocrine glands Hormonal modulation Feedback hormone affects its own secretion of hormone positive or negative Synergism producing an enhanced response Permissiveness the presence of one hormone is required for the other to exert and effect Antagonism one hormone opposes the action of another When the secretions of one endocrine gland act on another in sequence axis Hypothalamic pituitary adrenal HPA axis mammalian stress response Hormonal and neuronal modulation control HPA axis Responses to stress 1 Primary response rapid release of stress hormones into the circulation 2 Secondary response biochemical and physiological changes mediated by the stress hormones 3 Tertiary response whole animalpopulations level changes associated with stress Insulin favors the storage of all 3 major classes of nutrients hypoglycemic effect Glucagon increases production of glucose into the blood stimulates glycogenolysis and gluconeogenesis hyperglycemic effect
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