Chapter 12 Nervous Tissue Lecture Outline

Neural tissue 1. Neurons 2. Neuroglia Nervous system 1. Central Nervous System (CNS) brain, spinal cord 2. Peripheral Nervous System (PNS) Nerves Cranial nerves Spinal nerves A. Sensory / Afferent division 1. Somatic afferent 2. Visceral afferent B. Motor / Efferent division 1. Somatic Nervous System (SNS) 2. Autonomic Nervous System (ANS) A. Sympathetic B. Parasympathetic Histology Neurons Function Nerve impulses Characteristics 1. Longevity 2. Amitotic 3. High metabolic rate Structure Soma / Perikaryon Nucleus Nucleolus Nissl bodies Neurofilaments Neurofibrils Neurotubules Cell processes 1. Dendrites Dendritic spines 2. Axon Axon hillock Axolemma Axon collaterals Synaptic terminal or knob Vesicles Neurotransmitter Myelin sheath Oligodendrocytes Schwann cell / Neurilemma cell Axoplasmic transport Neurotubules Kinesins Anterograde transport Retrograde transport Synapse Presynaptic cell

Axon terminal Synaptic knob Synaptic terminal Neurotransmitters Post synaptic cell Structural classification 1. Anaxonic neurons 2. Bipolar neurons 3. Unipolar neurons 4. Multipolar neurons Functional classification 1. Sensory / Afferent neurons Ganglia A. Somatic sensory neurons B. Visceral sensory neurons 2. Motor / Efferent neurons A. Somatic motor neurons B. Visceral / Autonomic neurons 3. Interneurons / Association neurons Neuroglia cells CNS 1. Ependymal cells Central canal, Ventricles Cerebrospinal fluid (CSF) 2. Astrocytes A. Blood brain barrier B. Framework C. Repair D. Development E. Control environment 3. Oligodendrocytes Myelin Nodes (of Ranvier) White matter 4. Microglia Phagocytic PNS 1. Satellite cells Regulation 2. Schwann cells / Neurilemma cell Myelin Neurilemma Nodes (of Ranvier) Neurophysiology Transmembrane potential Cations outside Proteins (negative) inside Voltage Current Resistance Ohm’s law: current = voltage ÷ resistance Resting transmembrane potential = -70mV Membrane channels 1. Passive / Leak channels

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2. Active channels A. Chemically regulated / Ligand-gated B. Voltage regulated Axolemma & Sacolemma C. Mechanically regulated Electrochemical gradient Sodium-Potassium pump 3 Na+ out 2 K+ in Equilibrium potential K+ = -90mV Na+ = +66mV Graded potential Depolarization Hyperpolarization Repolarization Action potential Excitable membrane Threshold = -55mV “all or none” Generation of an action potential 1. Depolarization to threshold 2. Activation of Na+ channels Rapid depolarization 3. Inactivation of Na+ channels Activation of K+ channels 4. Return to normal permeability Absolute refractory period Relative refractory period Speed of propagation 1. Myelination A. Continuous propagation Unmyelinated B. Saltatory propagation Myelinated 2. Axon diameter A. Type A fibers Saltatory B. Type B fibers Saltatory C. Type C fibers Continuous Multiple sclerosis Synapses 1. Electrical synapse Gap junctions 2. Chemical synapse Synaptic cleft Neurotransmitter 1. Excitatory neurotransmitter Depolarization 2. Inhibitory neurotransmitter Hyperpolarization Action at a Cholinergic synapse 1. Action potential depolarizes synaptic knob 2. Ca2+ cause release of Ach 3. Na+ channels open on post synaptic cell

4. Ach broken down by AchE Action of neurotransmitters 1. Direct effect Receptor = ion channel 2. Indirect effect: via 2nd messengers Receptor = G protein Adenylate cyclase ATP → cAMP Ion channels or Enzyme Post synaptic potentials 1. Excitatory Post Synaptic Potential (EPSP) Depolarization 2. Inhibitory Post Synaptic Potential (IPSP) Hyperpolarization Summation 1. Temporal summation 2. Spatial summation Facilitated Post synaptic potentiation Neuromodulators Neurotransitters 1. Acetylcholine (Ach) Cholinergic synapse 2. Norepinephrine (NE) Adrenergic synapse 3. Dopamine Cocaine Parkinson’s disease 4. Serotonin Antidepressants / Antianxiety meds 5. GABA Alcohol Disruption of neural function: 1. pH 2. Ion concentrations 3. Temperature 4. Nutrients Glucose 5. Oxygen Aerobic respiration

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The Generation of anAction Potential

-55 mV

1. Depolarization to threshold:- a graded potential depolarizes local membrane and flows toward the axon- if threshold is met (-55mV) at the hillock, an action potential will be triggered

2. Activation of sodium channels and rapid depolarization:- at threshold (-55mV), voltage-regulated sodium channels on the excitable axolemma membrane open- Na+ flows into the cell depolarizing it- the transmembrane potential rapidly changes from -55mV to +30mV

3. Inactivation of sodium channels and activation of potassium channels:- at +30mV Na+ channels close and K+

channels open- K+ flows out of the cell repolarizing it

4. Return to normal permeability:- at -70mV K+ channels begin to close- the cell hyperpolarizes to -90mV until all channels finish closing- leak channels restore the resting membrane potential to -70mV

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Cholinergic Synapse (Acetylcholine as neurotransmitter)

terminal

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Neurotransmitter Mechanism of Action

1. Direct effect on membrane potential

2. Indirect effect on membrane potential

- open or close ion channels upon binding to the post synaptic cell- provides a rapid response- e.g. ACh (Cholinergic synapse)

- binds a receptor that activates a G protein in the post synapic cell- active G protein activates a second messenger (cAMP, cGMP, diacylglyceride, Ca++)- the second messenger opens ion channels or activates enzymes- provides slower but longer lasting effects- e.g. Norepinephrine (Adrenergic synapse)

Example of indirect action:1. Neurotransmitter binds receptor2. Receptor activates G protein3. G protein activates adenylate cyclase4. Adenylate cyclase converts ATP into cyclic AMP5. cAMP opens ion channels

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