Functional Organization of Nervous Tissue

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Functional Organization of Nervous Tissue Dendrite Cell body Dendrite Axon To central Sensory nervous receptors (b) system Cell body To central nervous (a) (c) system ~~ Lt Axon 

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112 The Nervous System * Components - Brain, spinal cord, nerves, sensory receptors * Responsible for ~ Sensory perceptions, mental activities, stimulating muscle movements, secretions of many glands * Subdivisions — Central nervous system (CNS) - Peripheral nervous system (PNS) 

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Central Nervous System Central 0 9 system. * Consists of Spinal ‏الا‎ ‎Brain cord + Located in cranial vault of skull - Spinal cord + Located in vertebral 4 0 ۱ x canal ‏تسب‎ ۰ Brain and spinal Cranial Spinal cord nerves nerves ~ Continuous with each other at foramen magnum Peripheral nervous system 113 

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Peripheral Nervous System * Two subcategories ‏یله‎ - Sensory or afferent Dorsal root ganglion ‘Sensory neuron ser - Motor or efferent 1 ‏تا‎ ‎Divisions‏ کب ‎۵ Spinal ~ Somatic nervous spinal | nerve system ‎(a) Sensory receptor -/ core | 1 ie 4 Ventral root Skeletal ~ Autonomic Spinal nerve (©) 9f spinal nerve muscle nervous system ‎(ANS) ‎Spinal cord Autonomic ganglion 5 ye ۸ » Sympathetic ‎First motor neuron 8 ‘Second motor neuron Parasympath ‎Effector organ (e.g., smooth etic )2( ۵ Large intestine 3 6 2 + » Enteric ‎ ‎114 

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Nervous System _ Organization Response (output) Cardiac muscle, Skeletal smooth muscle, muscle and glands t Somatic Autonomic nervous ‏اس افر‎ system system ‏ب4‎ Motor division + conducts action potentials to the periphery 11-5 Stimulus (input) PNS Sensory division Sensory conducts action receptors, potentials nerves, ganglia, pain and plexuses 

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Cells of Nervous System * Neurons or nerve = ~ cells Neuron - Receive stimuli and cell body Presynaptic terminals transmit action Dendrites 2 1 Schwann yy, 1 potentials cell oie of Ree Ranier - Organization + Cell body or soma + Dendrites: Input + Axons: Output ٠ Neuroglia or glial ۳ 1 Nucleolus 29۲۲۷۶ ۱ Golgi apparatus cells Mitochonetion ‏ا‎ neurons 11-6 

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Types of Neurons Dendrite To central Reon Sensory receptors (b) systern Cell body To central nervous ¢ Functional classification © Ag) system ‏كد‎ ‎- Sensory or afferent: Action potentials toward cons” - Motor or efferent: Action potentials away from CNS - Interneurons or association neurons: Within CNS from one neuron to another * Structural classification ~ Multipolar, bipolar, unipolar ao 

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Neuroglia of CNS Foot processes Ependymal cells Astrocyte Capillary Ependymal cells _ * Astrocytes ~ Regulate extracellular brain fluid composition ~ Promote tight junctions to form blood-brain barrier + Ependymal Cells - Line brain ventricles and spinal cord central canal - Help form choroid plexuses that secrete CSF 118 

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19 Neuroglia of CNS es 6 Microglia! cell Myelin sheath * Microglia - Specialized macrophages * Oligodendrocytes - Form myelin sheaths if surround axon 

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Neuroglia of PNS * Schwann cells or neurolemmocytes ~ Wrap around portion of only one axon to form myelin sheath * Satellite cells ~ Surround neuron cell bodies in ganglia, provide support and nutrients 11-10 

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Myelinated and Unmyelinated Axons “Nucleus of Schwann cen ° Myelinated axons ~ Myelin protects Axon and insulates Myelin axons from one = another ‏ليسم‎ ~ Not continuous * Nodes of Ranvier ٠ Unmyelinated Axons axons Node of Ranvier 11-1 

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Electrical Signals * Cells produce electrical signals called action potentials ¢ Transfer of information from one part of body to another ¢ Electrical properties result from ionic concentration differences across plasma membrane and permeability of membrane 11-12 

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Sodium-Potassium Exchange mp Copy The Note Corgan ‏و‎ Feed ‏واه موه مس‎ Extracellular fluid ۱۰۰-0 Ke ۲ Nat 001 a bi site ‏سم سم‎ Cytoplasm @ ‏دعام‎ ‎3. Nat diffuse away from the carrier 1. Three Nat and ATP bind to the molecule, two K+ bind to the carrier carrier molecule. molecule, and the phosphate ‏عي‎ 5 is released. ee Cartier molecule om ‏بعر‎ resumes original shape Carrier molecule Breakdown of ‏ب‎ 9 changes shape Sp ate (releases (requires energy) ADP energy) OK 2. The ATP breaks down to ADP and 4. The carrier molecule resumes original phosphate and releases energy. shape, transporting K+ across the ‘The carrier molecule changes membrane, and K+ diffuse away from shape, and Na* are transported the carrier molecule, The carrier 11.13 across the membrane. molecule can again bind to Na* and ATP. 

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Membrane Permeability Extracellular fluid ‏اا‎ 2 Nat é @Na ‏ه هاه‎ 5 e ‏-هه‎ 0 © 1 ti Nongated Gated Na* Cl" channel Nongated channel (always K* channel (closed) open) ‘(always ۳ 0 Q Open} 0 oe 9 ® ° 2 Negatively 0 Cytoplasm 0 charged protein aa 

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Ion Channels * Nongated or leak channels ~ Always open and responsible for permeability - Specific for one type of ion although not absolute * Gated ion channels - Ligand-gated * Open or close in response to ligand binding to receptor as ACh - Voltage-gated * Open or close in response to small voltage changes 11-15 Acetylcholine 5۵۰ ۰ هه o— Nat Receptor site for. __," Closed Na* channel acetylcholine 22 » Open Nat ۳ channel Acetylcholine bound. to receptor sites Na+ diffuse through the open channel (b) 

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Resting Membrane Potential * Characteristics Number of charged molecules and ions inside and outside cell nearly equal Concentration of K+ higher inside than outside cell, Na* higher outside than inside At equilibrium there is very little movement of K+ or other ions across plasma membrane 11-16 K* diffuse out of the cell because 3 8 there is agreater | The resting concentration of || membrane K+ inside than 2 outside the ‏...امه‎ ۵ when the movement K+ move into the of K* out of cell because the | the cell is positively charged | equal to ions are attracted | their tothe negatively | movement charged proteins | intothecell. 7 ۰ and anions. Negatively charged proteins 

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Changes in Resting Membrane Datantial سا ‎Depolarization: movement‏ ‎(of RMP toward zeros‏ 3 Decrease in extracalul K" concentration 0 ion: mos = ‎further way from zero‏ انا ‎Time —>‏ ‎ ‎۳ ‎* K* concentration gradient alterations ‎¢ K* membrane permeability changes ~ Depolarization or hyperpolarization: Potential difference across membrane becomes smaller or less polar - Hyperpolarization: Potential difference becomes greater or more polar ۰ Na* membrane permeability changes ‎۳ 2 11-17 * Changes in Extracellular Ca?* concentrations 

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Local Potentials * Result from ~ Ligands binding to receptors ~ Changes in charge across membrane ‏كم‎ - Mechanical stimulation 1s - Temperature or changes Two equal stimuli - Spontaneous change in in short succession ili aia? permeability وا" ~ Magnitude varies from small to large depending on stimulus strength or frequency * Can summate or add onto each other 11:18 Successively stronger stimuli of short duration from 1-4 Time — (b) (mv) 8 (a) 

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Action Potentials * Series of permeability changes when a local potential causes depolarization of membrane ¢ Phases - Depolarization * More positive ~ Repolarization + More negative ¢ All-or-none principle - Camera flash system Depolarization Repolarization Threshold Local potential Afterpotential Time (ms) 11-19 +20 (mv) 

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Action Potential Gepgh ©The edn Hl Corpus be Perino rearedr epee or apy Nat Kr 9 diffuse: ‏ماه ماه‎ 2 2 im ‏اعت‎ mt ‏اج‎ ‎3 3 ۲ ‏نگ امه اگ امه نگ‎ Time Time Time Time Time kt 4 channel ‘channel ‏د‎ ‎opened. ‘opened ‏تا‎ ‎Kt Kr Nat channel Nar Nav ‘channet ‘channel 9 channel channel Kr ‘opened + opened channol ‏فو‎ closod. Inactivation gate closed Inactivation gate open ‘Activation Activation ‘Activation ‘Aetivation ‘gate closed ‘gate opened ‘gate opened gate closed 11-20 

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Refractory Period Sensitivity of area to further stimulation decreases for a time Parts - Absolute + Complete insensitivity exists to another stimulus + From beginning of action potential until near end of repolarization ~ Relative * A stronger-than- threshold stimulus can initiate another action potential 11-21 Threshold — Absolute! Relative ‏:بلك‎ Refractory period Time (ms) +204 (mv) 

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Action Potential Frequency * Number of potentials produced per unit of time to a stimulus * Threshold stimulus - Cause an action potential * Maximal stimulus * Submaximal stimulus ¢ Supramaximal stimulus 11-22 ‘Same frequency Maximal Supra- stimulus maximal stimulus Sub-‘Thresh- Sub- threshold old maximal stimulus stimulus stimulus Time (ms) —> (mv) 

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Action Potential << Capit 8h Neb ‏هدوت‎ ۳ arin quedo ely Outside of membrane becomes | Depolarization more negative as positive charges move away from it Inside of membrane becomes mor positive as positive charges move toward it ‏ب+ ببب‎ + + + ae refractory period 1 67+ ee prevents another aot ۷ action potential action potential —— > Action potential propagation 11-23 

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Saltatory Conduction Cet he Une Ht Or ne Poin pn pean ‏وش‎ 2 Node of Ranvier Schwan’ cell Internode ++ ++, ++ Direction of action potential propagation 11-24 سس 

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The Synapse ¢ Junction between Smooth muscle cells two cells Steetieal synapse * Site where action Positively charged ions ‏بت‎ * * 9 potentials in one Local current 577 cell cause action Plasma membrane 5 9 otentials in Gap junction: ۳ hi 11 Plasma membrane another ce ‏اد‎ * Types Connexons 1 Presynaptic - Postsynaptic 11-25 

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Chemical Synapses Components ~ Presynaptic terminal ~ Synaptic cleft - Postsynaptic membrane Neurotransmitters released by action potentials in presynaptic terminal — Synaptic vesicles - ~ Postsynaptic membrane Neurotransmitter removal 11-26 Action potential cat ۳ - Presynaptic terminal ‏نمی موم‎ 6 (GaP channel ‘Synaptic cleft Acetylcholine Acetylcholine bound to receptor site opens Postsynaptic —_ligand-gated Na* membrane ‘channel, 

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Neurotransmitter Remaval Copy ۳ ‏رورس‎ 5 0 7 ١ nm. ‏م۱‎ ‎0 © 11-27 (a) Acetylcholinesterase )0( 

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Summation Copy © The McGraw Hl Companes, re Pamesioncequed ‏ماه‎ dela |-(with temporal | summation) Axon hillock 11-28