Human Physiology Exam 1 Study Guide
Human Physiology Exam 1 Study Guide BIOL 3160
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This 32 page Study Guide was uploaded by MBattito on Friday January 29, 2016. The Study Guide belongs to BIOL 3160 at Clemson University taught by Dr. Tamara McNutt-Scott in Fall 2015. Since its upload, it has received 203 views. For similar materials see Human Physiology in Biological Sciences at Clemson University.
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Date Created: 01/29/16
Test 1 Study Guide: Chapter 1: Physiology: • Fundamentally represents the study of how living organisms work o Molecules à cells à tissue à organ à organ system o How organisms accomplish tasks essential for life • Function and integration o Body parts work together at various levels of organization and whole organism o No “part” works in isolation • Mechanisms and their effects o Sequence of events à parts of larger stories • Misconception: all is known History of Physiology: • Aristotle: o Speculated on function of human body o Good health associated with balance of humours § Humours: black bile, yellow bile, phlegm and blood • Erasistratus: “father of physiology” o Applied physical laws to study of human body o Studied cardiovascular and nervous systems o Performed dissections on live humans à noted increase in heart rate • William Harvey: o First to study biology quantitatively o One of the first to be able to accurately describe the parts of the body and systematic circulationà identified parts and their functions • Claude Bernard: “father of modern physiology” o Observed the milieu interieur o Found that animals possess control systems that could adjust to external and internal stimuli o Internal environment remains remarkably constant despite constantly changing external environment Father of American Physiology: Robley Dunglison • In the early 19 century in the US physiology was treated as an aspect of theory and practice of physics • 1824: Thomas Jefferson and the board members of the University of Virginia added Dunglison to the first faculty of the U of VA • Dunglison: o English physician o Professor of Anatomy, Physiology, Surgery, Materia Medica, Pharmacy and History of Medicine o Teaching was an explanation of “successive theories” o Published several books and articles § Human Physiology (1832) à landmark text Homeostasis and Feedback Control: • Homeostasis: maintenance of a relatively stable internal environment o Basically represented by the state of equilibrium of the body’s internal environment by dynamic processes of feedback and regulation o Reason for regulatory mechanisms o Is not an easy accomplishment § Every organ system is involved with the maintenance and necessitates integrated function o Major foundation for medical diagnostic procedures • Walter Cannon: coined the term homeostasis in his book, The Wisdom of the Body • How is the maintenance of homeostasis accomplished? Feedback mechanisms Feedback Mechanism: maintain homeostasis • Set point: normal range of measurements and values o Variable: factor or event being regulated • Control systems that promote homeostasis are characterized by 3 interdependent components: o Receptor: serve as sensors to determine what is out of balance § Uses afferent pathways (sensory pathways toward central nervous system) o Control/integrating center: uses efferent pathways (motor pathways away from central nervous system) o Effector: bring balance back • Why is it referred to as a “loop”? o “Loop” emphasizes feedback mechanism is a continuous cycle to maintain homeostasis • Is our internal environment absolutely constant? Are we always in a state of balance? o Our internal environment is not absolutely constant. We maintain a dynamic balance or consistency; that is overall our body is constant within a range but is not absolutely constant. Conditions stabilize around a set point; they must be in the range so physiological processes can run efficiently. Negative Feedback Mechanism: reverse direction control mechanism • Most common homeostatic control mechanism • Works because output of system causes a decrease or shuts off the original stimulus o Continuous, ongoing processes • All negative feedback mechanisms have the same goal: preventing sudden, severe changes in the body • Antagonistic effects: effectors have antagonistic actions, allowing for finer degree of control • Integration center does not always have to be in the central nervous system Positive Feedback mechanism: same direction control system • Enhance or exaggerate the response over the original stimulus, thus the output is increased • Usually control episodic or infrequent events that do not require continuous adjustments o Ex: blood clotting, breast feeding, parturition (child birth) • Limited occurrence because it proceeds with very little control Homeostatic imbalance: • Places an individual at higher risk of disease • Typically a result of certain pathological conditions and aging Homeostatic Regulation: • Regulatory mechanisms for homeostasis o Intrinsic: within organ o Extrinsic: “outside” organ § Nervous system: impacts homeostasis via nerves § Endocrine system: impacts homeostasis via hormones • Advantages: self regulatory and self initiated Disadvantages: automatic response sometimes does not help Cells: basic unit of structure and function • Simplest structural unit that complex, multicellular organisms can be divided into • Smallest unit of life • Retain functional characteristics of lfie Tissues: cells with similar functions • 4 Primary tissue types: o Connective o Muscle o Nervous o Epithelial Organ: 2+ primary tissues grouped into anatomical and functional units • Typically all 4 types of tissue presents • Activities and interactions of tissues determine physiology of organ Muscle Tissue: 3 types specialized for contraction 1.) Skeletal Muscle: generally attached to a bone via a tendon; the tongue is the exception o Skeletal muscle cells referred to as myofibers o Form in the 4 week of development as myoblasts § Myoblasts fuse together making skeletal muscle multinucleate o Arranged in bundles which vary in strength § Perform graded contractions controlled individuallyà allow us to change the degree of strength and finer degree of movement o Striated • Cardiac Muscle: Found in the wall of the heart o Cardiac muscle cells referred to as myocardial cells o Form a continuous sheet § Uninucleated § Referred to as branched § Striated as a result of the interactions between the contractile elements (actin and myosin) o Intercalated discs: couple cells mechanically and electrically • Smooth Muscle: Found in GI tract o Nonstriated, fusiform shape § Still has actin and myosin, just different interactions between them that do not form striations o Forms a sheet arranged circularly and or longitudinally o Performs peristalsis: wave-‐like contractionsà specifically in areas like the lumen What type of muscle is termed voluntary muscle? à Skeletal muscle; because it must be consciously initiated to move What type of muscle is termed involuntary? à Cardiac and smooth muscle; they are under the control of the autonomic nervous system – they do not have conscious control Nervous Tissue: • Consists of neurons and supporting cells o Neurons: highly specialized to generate and conduct nerve impulses à an electrical event § Constructed of a cell body (soma), dendrites and an axon • Can have multiple dendrites but only one axon • Each has structural attributes and functions § Cannot divide o Support Cells: Non-‐conducting cells that support, insulate and protect neurons § AKA neuroglial or glial cells § Main function is to make sure the neurons work as efficiently as possible § More abundant than neurons § Limited ability to divide Epithelial Tissue: cover body surfaces and line body cavities • Perform a variety of functions but primarily serves as a boundary • Classified according to number of layers and shape o Layers: § Simpler: 1 layer of cells § Stratified: multiple layers of cells o Shapes: § Squamous § Columnar § Cuboidal Epithelial tissue serving as a barrier • Site of regulation for substances entering/leaving body • To be effective it must be able to be sealed off à junctional complex o Junctional complex seals off epithelium at lumen allowing it to be a barrier § Composed of a tight junction, adhering junction and a desmosome § What allows us to regulate the entrance and exit of substances from the cell Glands: • Formed by epithelial tissue growing down into the connective tissue o Exocrine gland: forms from a cord or tubule § Has a duct and a secretory portion o Endocrine gland: forms from a cluster of cells § Has a secretory portion but no duct Exocrine Glands: • Components: o Duct o Secretory unit: § Acinus § Myoepithelial cells: surround acini • Classified by: o Number of ducts: § Simple (1 duct) § Branched (many ducts) o Type of secretory portion: § Tubular § Acinar/alveolar Connective Tissue • Characterized by: o Large amount of extracellular material in the spaces between connective tissue cells § Extracellular matrix is made up of fibers and ground substances; varies in composition arrangement between tissue types • Fibers: collagen fibers, elastic fibers and fibroblast • Ground substances: interstitial fluid, cell adhesion protein, glycocalyx o Comprised of varied cell types • Categorized into o Connective tissue proper: loose and dense connective tissue o Supportive connective tissue: bone and cartilage o Liquid connective tissue: blood Stem cells: • Tissues of an organ are comprised of differentiated cells o Highly specialized • Differentiation begins during embryonic development o Zygote/embro: one celled structure; fertilized egg § Contains totipotent stem cells à the least differentiated; can form any tissue type o Blastocyst-‐implantation § Pluripotent stem cellsà capable of forming unrelated cell types o Trilaminar embryo § Ectoderm, mesoderm and endoderm • Ives rise to 4 primary tissue types • Adult stem cells o Multipotent: form related cell types Hierarchical system to structural organization • Levels of cellular organization • Human body is a complex society of differentiated cells, which combine structurally an functionally to carry out life-‐sustaining processes • Cells basic units of the society and almost all exhibit fundamental activities common to all forms of life • One big community and if any one part starts having problems, everything else will be affected o Reliant and restricted by what is found below it Body Fluid Compartments: • Extracellular fluid: o Fluid in blood and spaces that surround cells § Found in plasma § Also found in interstitial, or tissue fluid à between the cells themselves • Intracellular fluid o Fluid within cells • Mainly comprised of water o Aqueous compartments o Properties of water have significant impact on functional characteristics • Compositions varied between compartments o Extracellular fluid considered to be more “homogenous” than intracellular fluid § Cells have specific functions so there is more variability in cell types; in extracellular fluid there is more exchange between them • What organ plays an important role in extracellular fluid composition/volume? o Kidneyà filters blood and eliminates water to impact and modify volume • Compartmentalization: ability to have barriers • Who serves as the “barriers”? o Epithelial tissue and plasma membrane • Properties of the barriers determine what moves between the compartments Chapter 6: Interactions Between Cells and the Extracellular Environment • Extracellular environment represents all constituents outside the cell Why is the extracellular matrix so important? • This is where cells obtain the nutrients they need and release their secretions (biproducts of their chemical processes) • They eliminate their wastes to be processed accordingly • Impact/interact with neighboring cells, different tissues and different organs Body Fluids: • Divided into compartments: o Extracellular: § Blood plasma and interstitial fluid § 33% of body fluids o Intracellular: § Within cells § 67% of body fluids • Fluids serve as communication link between cells, tissues and organs Extracellular Matrix • Complex network of proteins o Specific for any given tissue à not generic • Extracellular fluid interspersed within • Functions: o Scaffolding for cellular attachment o Transmits information to regulate activity, migration, growth and differentiation • Composed of fibrous proteins and ground substances o Ground substances: analogous to a hydrated gel and location of interstitial fluid § Comprised of glycoproteins and proteoglycans • Highly functional, complex organization of molecules chemically linked to extracellular protein fibers and glycoproteins of glycocalyx • Integrins: adhesion molecule between cells and extracellular matrix o Physically joins extracellular and intracellular compartments o Serve to relay signals or integrate them à communication element • Block integrin: block functions of integrins o Example: found in snake venom; binding site on platelets which slows blood clotting Transport across the plasma membrane • Plasma membrane: o Serves as a “barrier” to movement – extracellular and intracellular compartments o Selectively permeable à dynamic; ability to change permeability • Membrane transport processes o Passive transport: does not require energy § Ex. Diffusion: flow along a concentration gradient from high to low o Active transport: require energy o Carrier-‐mediated transport: requires a carrier protein Diffusion and Osmosis • Molecules of a solution are in constant motion • Solvent: what the particle is dissolved in • Solute: the particle being dissolved • Osmosis: diffusion of water to reach equilibrium between concentration gradients o Mass net movement of water from high water concentration to low; however still some small movement from low to high • Mean diffusion time: time to reach equilibrium o Increases with distanceà distance kept within 100micrometers for effective exchange § Beyond 100 micrometers our bodies cannot effectively transport material fast enough Diffusion through a plasma membrane • Nonpolar molecules: o Oxygen gas o Steroids • Small polar covalent molecules without charge o Carbon dioxide o Ethanol o Urea • Ability of these molecules to cross easily allows for efficient cellular respiration o Our environment is always oxygen rich so it can freely flow into cells and carbon dioxide can easily exit Membrane channels • Used for charge inorganic ions such as sodium and potassium • Can be open or gated • Gated channels have the ability to open or close o Allows a degree of regulation o Regulated by particular physiological stimuli • For large, polar molecules, carrier proteins are needed in the plasma membrane for movement Rate of Diffusion: speed of diffusion per unit time • J=PA (C -‐C ) 0 i o J represents the net flow o (C -‐0) i represents the concentration gradient o A represents the surface area o P represents the membrane permeability coefficient • Factors effecting rate of diffusion: o Magnitude of concentration gradient o Diffusing substance’s permeability to plasma membrane o Temperature à rate increases as temperature does o Surface area availability § Ex. Microvilli increase surface area to assure there is enough space for diffusion to be run efficiently o Distance • Magnitude of concentration gradient is the driving force for diffusion, but will not move if plasma membrane is not permeable to that molecule Osmosis • Net diffusion of water o Follows a concentration gradient • Requirements: o Concentration difference of solute between sides of membrane o Membrane selectively impermeable to solute § Non-‐penetrating solute à cannot move across membrane § Osmotically active: creates osmotic pressure (“pull” of water via a solute) o Essentially, solute cannot cross the membrane, so equilibrium must be reached by movement of water instead of solute to alter the solute concentration • Aquaporins: open water channels o Facilitate movement of water o Present in some cell types or can be inserted in response to regulatory molecules Osmotic Pressure • Represents the pressure that must be applied to a solution to prevent the net flow of water • Indicates how strongly a solution draws water • Water drawn more rapidly with greater solute concentration Molarity vs. Molality • Molarity: ratio of solute to volume of solution o Ratio of solute to solvent not completely specified o Amount of water changes due to the molecular weight of substances • Molality: ratio of solute to solvent o Better measurement of concentration when discussing osmosis o Compares compartments (solute and solvent) better Osmolality: • Osmotic pressure depends on the ratio of solute to solvent, not chemical characteristics of solute o Therefore osmolality is more appropriate (Osm) § Total molality of a solution • Electrolytes will ionize in water and therefore alter the concentrations • Blood plasma and other biological fluids have a complex osmolality due to the presence of organize molecules and electrolytes o Cell activity leads to constant change Tonicity: • Describes effect of solution on osmotic movement of water, thus cell shape and volume o Solute load (normal osmolality)=300mOsm • Solutions describes by how they change cell volume (and thus shape) by causing water movement • Take into account both solute concentration and solute permeability for each solute crossing the plasma membrane • Examples: using a 300mOsm cell placed in the following solutions: o 400mOsm solution: water will flow out because it is in a hypertonic solution à cell will shrink o 300mOsm solution: there will be no net movement because it is in an isotonic solution à cell size remains the same o 200mOsm: water will flow into the cell because it is in a hypotonic solutionà cell will swell When a cell comes in contact with a solution, hypertonic or hypotonic, the initial concentration of solutes determines the degree of change • If a cell were placed in a solution containing 100mOsm impermeant solutes, how would its final volume compare to its initial volume? o The final volume would be tripled Homeostasis of Plasma Concentration • Variety of mechanisms exist to keep blood plasma osmolality maintained within very narrow limits • Osmoreceptors: serve as sensor and integrating center • Ex. Dehydration: blood volume decreases and plasma osmolality increases o Osmoreceptors found in the hypothalamus o Signal posterior pituitary to secrete ADH o Efferent pathway leads the ADH to the kidneys o Signals to increase water intake o Negative feedback mechanism Carrier-‐Mediated Transport • Cellular metabolism relies on the cell’s ability to uptake molecules it needs from the EC fluid • Many of these molecules cannot be attained by simple diffusionà require protein carriers • Carrier proteins display the characteristics of saturation o When at capacity, it cannot move anything further • If carriers can transport more than on molecule type, then they will compete for transport o Specificity, saturation, competition Facilitated Diffusion • Cell stimulated, passive transport • Carriers are inserted into plasma membrane to meet the cell’s needs • Carriers are not static à can change them to adapt o Can transport molecules in both ways from the plasma membrane to regulate intake Active Transport: Primary • Energy required for carrier function • Typically, molecules/ions moved against their concentration gradient (from low to high concentration) o Binding of molecule to be transported to “recognition site” o Binding stimulates ATP hydrolysis o Phosphorylation causes carrier protein to undergo conformational change o Hinge-‐like motion of carrier protein releases transported molecule to other side • Often referred to as pumps Ex. Sodium-‐Potassium Pump: • Binds 3 sodium ions out of the cell and 2 potassium ions in • Created steep ion gradient • Functions: o Provides energy for coupled transport of other molecules o Used to generate electrochemical events (impulses) in nervous and muscle tissue à action potentials o Sodium movement important for osmotic reasons § Stops, observe increase in sodium, causes osmotic influx of water (damage cell) Active Transport: Secondary • Driven indirectly by passive ion gradients created by operation of primary active pump • Can move molecules such as glucose using the sodium gradient • What happens if the Sodium-‐Potassium pump is poisoned? o The cell will no longer be able to move sodium and potassium and anything associated with or utilizing the pump will also stop Movement of solutes across a typical plasma membrane involving membrane proteins • Many of these membrane proteins can be modulated by various signals o Results in controlled rise or fall of specific solute fluxes across plasma membrane • Specialized cells may contain additional transporters and channels Transport across epithelial membranes • Epithelial cells line the body’s surface as well as cavities of hollow organs o Molecules entering the body must pass through an epithelial cell layer Junctional complex • Presence and number dependent on location • Composed of: o Tight junction: physically joins; seals/binds o Adhering junction: “glues” together; proteins on both sides that have an element allowing them to stick together à attach to the cytoskeleton of the cell and support the apical surface o Desmosome: “velcroes” together • All components not only seal off epithelial membrane but also provide some of its characteristics Bulk transport: • Movement of molecules too large to be transported through plasma membrane • Endocytosis: brings molecules into the cell o Phagocytosis: form a vacuole to bring in à “cell eating” o Pinocytosis: vacuum in liquid molecules à “cell drinking” o Receptor mediated: uses carriers to bring in molecules • Exocytosis: release molecules from cells à secretion Membrane Potential: difference, or potential difference in charge across the membrane • Separation of oppositely charged ions that has the potential to do work if they come together • Results from: o Action of Na-‐K pump: creates a concentration gradient § Potassium has open leakage channels because it is much bigger than sodiumà potassium leaks out creating an unequal distribution at the plasma membrane o Permeability of plasma membrane: leakage channels produce an unequal distribution of charges across the plasma membrane; however, if you add up the charges it is equal o Presence of impermeant molecules: fixed anions draw cations into cell Equilibrium Potentials: • Many inorganic ions maintained at specific concentrations within intracellular and extracellular fluid o Contributes to membrane potential o Impact of each ion depends on its § Concentration gradient § Membrane permeability o Potassium § Plasma membrane is more permeable to this ion à Major role in membrane potential • Consider a membrane only permeable to potassium, what would be the membrane potential? o This would cause the intracellular potassium concentration to increase to a point; then potassium ions would begin to leave the cell by net diffusionà reaching a state of equilibrium o Potassium equilliubium potential = -‐90mV § For a value more negative, it would draw more K+ into the cell § For a value less negative, it would diffuse out of the cell o Sodium equilibrium potential would be 66mV • Useful to know because they tell us what happens to the membrane potentials when the plasma membrane becomes highly permeable to one particular ion Nernst Equation: • Allows us to determine the electrical potential necessary to balance a given ion concentration gradient across a plasma membrane so no net flux of the ion occurs • Diffusion gradients of an ion depend on concentration differences • Equilibrium potential depends on ratio of ion concentration on both sides of plasma membrane • Nernst equation permits calculation of theoretical equilibrium potential for specific ion if we know its concentration • It differs between ion species o Magnitude and direction o Cation value is negative § The concentration inside is greater than the concentration outside • What happens when more than one ion channel is open? o GHK equation (Vm) o Vm=membrane potential of the cell plasma membrane • Nernst Equation: ▯▯ ▯▯ E x log ▯ ▯ ▯ E xequilibrium potential in mV for ion x Z=valence of the ion (+1 for Na+ or K+) X oconcentration of the ion outside of the cell X=ioncentration of the ion inside the cell Goldman-‐Hodgkin-‐Katz (GHK) equation: ▯▯ ▯ ▯ ▯ ▯▯ ▯▯ ▯ ▯ ▯▯▯▯▯ ]▯ V m61 log ▯ ▯ ▯ ▯ ▯ ▯▯ ▯▯ ▯▯ ▯ [▯▯▯] ▯ ▯ ▯ ▯ ▯.▯▯ ▯▯▯ ▯(▯.▯▯)(▯) V m61 log = -‐68mV ▯ ▯▯▯ ▯ ▯.▯▯ ▯▯ ▯(▯.▯▯)(▯▯▯) • Takes into account each ions permeability coefficientà Nernst equation does not • Note the chloride ion concentration inside and outside are reversed because it is negatively charged à therefore movement has opposite effect on membrane Resting Membrane Potential (RMP) • Membrane potential of a cell at “rest” or a cell in an inactive state • Depends on: o Ratio of concentrations (X /X)o oi each ion on both sides of the plasma membrane o Specific permeability of membrane to each ion • Most important “players”: o Potassium ion (K+), sodium ion (Na+) and chloride ion (Cl-‐) o Individual contribution dependent on concentration differences across the plasma membrane and permeabilities § Any change in an ions extraceullular concentration will change the RMP but only to the extent the membrane is permeable § Change in the cell membranes permeability for any given ion will change its RMP • Cellular range: -‐65mV to -‐85mV Question: Would lowering a neuron’s intracellular potassium concentration by 1mM have the same effect on RMP as raising the extracellular potassium concentration by 1mM? à No; changing the extracellular [K] has a greater effect on the equilibrium potential and thus the resting membrane potential. This is because the ratio of external to internal [K] is changed more when extracellular levels go from 5 to 6 (20% increase) than when intracellular levels are lowered from 150 to 149mM (0.7%). This can be confirmed by the Nernst equation Role of Sodium-‐Potassium Pumps (Na-‐K pumps): • Runs continuously to maintain ion concentration • RMP is less than the equilibrium à causes some K+ to leak out and therefore is not in equilibrium with respect to [Na+] or [K+] • The concentrations are still maintained constant, though, because of the constant expenditure of energy in active transport by the Na-‐K pumps • The pump acts to counter the K+ leaks and maintain the membrane potential • Electronegative effect: it pumps 3Na+ out of the cell and 2 K+ into the cellà causes unequal transport of charge o Adds about 3mV to the membrane potential (very minimal effect on RMP) Cell signaling: • Refers to how cells communicate with each other (intercellular communication) o Many release regulatory molecules into extracellular environment o General categories: § Paracrine: local mechanismà regulates a nearby target cell § Synaptic: functional connectionà the means by which neurons regulate their target cell • Synaptic gaps between two cells contain chemical regulators (neurotransmitters) to release signal § Endocrine: long distance mechanism à regulate target cells via hormones • Gap Junctions: provide direct communication between cells by fusing plasma membranes together and permitting diffusion from one cell’s cytoplasm to the next o As long as the gap junctions are open, things will be moving through them Regulatory Molecules: • Exert fine control over the physiology of our tissues and organs • Target cells: only present on the target organs o Must display a target receptor protein for signaling/regulatory molecule Signal transduction pathways • Mechanism for lipid-‐soluble messengers o Receptors will not be on the membrane because it can get through it o Receptors will be in the cytosol or nucleus • Mechanism for water soluble messengers o If a molecule is polar or too large to penetrate through the plasma membrane, the receptor must be located on the membrane and a second messenger system is utilized o The molecule does not enter the cell, so its actions are produced by the second messengers o Key second messenger: cyclic adenosine monophosphate (cAMP) o Receptors can be an enzymeà binding activates the enzyme G-‐protein: • Three-‐protein subunits that shuttle between receptors and different membrane effector proteins o Includes specific enzymes and ion channels o Protein subunits: alpha, beta and gamma • The G-‐protein activates an effector protein to initiate a cellular response o Requires GTP for energy Mechanism for lipid-‐soluble messengers o Receptors will not be on the membrane because it can get through it o Receptors will be in the cytosol or nucleus Cessation of activity in signal transduction • Important because chronic overstimulation can be detrimental to cell • Key event is stopping receptor activation • Can be stopped by: o Decreasing the concentration of the first messenger o Chemically altering the receptorà lowers the affinity for first messenger o Phosphorylating the receptor à prevents G-‐protein from binding o Endocytose the receptor-‐ligand complex à removes the receptor from the plasma membrane Chapter 7: The Nervous System – Neurons and Synapses The nervous system is responsible for the coordination of cell function in the human body • “Control” systems: o Nervous system: for quick acting responses o Endocrine system: for slow-‐acting, long-‐term responses • Need multiple systems because we need to make corrections at different paces o Quick corrections necessary in the moment are not always good in the long termà thus aided by the endocrine system • Nervous system: o Trillions of cells distributed in a network o Communicate via electrical and chemical signals § Chemical signaling is more dominant o Maintains homeostasis by: § Coordinating functions of internal organs allowing to work as a whole § Mediating sensation: ability to perceive those sensors § Controlling voluntary movement § Encoding complexity of brain: ability to process and respond to changes in our internal and external environment Structural organization of the nervous system • Central nervous system: o The brain and spinal cord o Utilizes efferent pathways via somatic and autonomic motor nerves § Sympathetic § Parasympathetic § Enteric • Peripheral nervous system: o Cranial nerves (arising from the brain) and spinal nerves (arising from the spine) o Utilizes efferent pathways via somatic, visceral and special sensory nerves • Composed of neurons and glial cells o Neurons: basic structural and functional unit of the nervous system § Enables perception of sensory stimuli, learning, memory and the control of muscles and glands o Glial cells: aid the function of neurons § About 5 times more abundant than neurons § Can divide mitotically à why brain tumors are usually composed of glial cells rather than neurons Neurons • Vary in size and shape • Principle regions o Cell body/soma: serves as integration center o Dendrites: receptive area § Have many on one neuron o Axon: transmission area – sends info out § Each neuron only has one • Axonal transport: o Energy dependent o Two different components for removing different materials § Fast component: transports membranous vesicles • Important for synaptic transmission • Travels 400mm/day § Slow component: transports microfilaments and microtubules • Proteins important for synaptic function • Travels 2-‐8mm/day o Anterograde and retrograde: represent direction of flow § Anterograde: moves from soma à axon • Uses secretory vesicles and kinesin protein § Retrograde: moves from axon à soma • Uses dynein proteins and recycled membrane vesicle • Can also move harmful things in as well o Ex. brings in rabies virus, herpes, Lou Gehrig’s disease, etc. Classification of neurons • Structural classification: based on the number of processes that extend from the cell body o Pseudounipolar: one large axon with many dendritic branches § Sensory neurons o Bipolar: one dendrite and one axon at either end of the soma § Typically found in the retina of the eye o Multipolar: one axon and multiple dendrites § Motor neurons § Most common type of neurons • Functional classification: based on the direction in which they conduct impulses o Efferent/motor neurons: signals from central nervous system to peripheral nervous system § Somatic motor neurons: responsible for reflex and voluntary control of skeletal muscle § Autonomic motor neurons: innervate the involuntary effectors (smooth muscle, cardiac muscle, glands) o Afferent/sensory neurons: signals from peripheral nervous system to central nervous system o Association/interneurons: communicate between sensory and motor neurons § Typically multipolar § Found in central nervous system • Nerve: bundle of axons located in the peripheral nervous system • Tract: bundle of axons located in the central nervous system Supporting cells: • 4 types of glial cells of the central nervous system: o Astrocytes: help to regulate the external environment of neurons in the central nervous system o Microglia: migrate through the central nervous system and phagocytize foreign and degenerated material § Unique because they derive from cells that were produced in the embryonic yolk sac and migrated into the developing neural tube o Ependymal cells: epithelial cells that line the ventricles of the brain and the central canal of the spinal cord o Oligodendrocytes: form the myelin sheath around axons of the cen
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