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 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 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 Amy Warenda Czura, Ph.D.1SCCC BIO130 Chapter 12 Handout2. 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. Excititory 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. Excititory 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 Amy Warenda Czura, Ph.D.2SCCC BIO130 Chapter 12 HandoutAmy Warenda Czura, Ph.D.3SCCC BIO130 Chapter 12 Handout/ soma/somaAmy Warenda Czura, Ph.D.4SCCC BIO130 Chapter 12 HandoutSchwann CellStructural Classification of NeuronsAmy Warenda Czura, Ph.D.5SCCC BIO130 Chapter 12 HandoutThe Generation of anAction Potential-55 mV1. 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 triggered2. Activation of sodium channels and rapid depolarization:- at threshold (-55mV), voltage-regulated sodium channels on the excitable membrane open- Na+ flows into the cell depolarizing it- the transmembrane potential rapidly changes from -55mV to +30mV3. 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 it4. 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 -70mVAmy Warenda Czura, Ph.D.6SCCC BIO130 Chapter 12 HandoutCholinergic Synapse (Acetylcholine as neurotransmitter)terminalAmy Warenda Czura, Ph.D.7SCCC BIO130 Chapter 12 HandoutNeurotransmitter