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NERVOUS SYSTEM

NERVOUS SYSTEM. NERVOUS TISSUE. Nervous System - General. Control System Regulator of Homeostasis Electrical Impulses Rapid & Transient Effects. Nervous System - Functions. Sensory - Monitors Internal & External Environments Integrative Analyzes Sensory Information Stores

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NERVOUS SYSTEM

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  1. NERVOUS SYSTEM NERVOUS TISSUE

  2. Nervous System - General • Control System • Regulator of Homeostasis • Electrical Impulses • Rapid & Transient Effects

  3. Nervous System - Functions • Sensory - Monitors Internal & External Environments • Integrative • Analyzes Sensory Information • Stores • Makes Decisions Regarding Appropriate Responses • Motor – Controls muscles & glands; responds to sensory information

  4. Nervous System Divisions • Central Nervous System (CNS) • Brain, Spinal Cord • Dorsal Body Cavity • Integration & Command Center • Peripheral Nervous System (PNS) • All Neural Tissue outside CNS • Nerves (Cranial & Spinal) • Carries Info. Between CNS & Rest of Body • Sensory & motor

  5. Peripheral Nervous System • Sensory • Afferent • Conveys sensory information to CNS • Motor • Efferent • Conveys motor commands to muscles & glands

  6. PNS Motor Divisions • Somatic Nervous System (SNS) • Voluntary Control of Skeletal Muscles • Autonomic Nervous System (ANS) • Involuntary Control of Smooth Muscle, Cardiac Muscle & Glands • Sympathetic Division • Parasympathetic Division

  7. Cells of Nervous System • Neurons • Basic Unit of Nervous System • Most Specialized Cell in Body • Conduct Impulses • Neuroglia (“Nerve Glue”) • Support, Framework (fill spaces) & Phagocytes • Most Numerous • Can Divide & Multiply

  8. Neurons - Structure • Cell Body (Soma) • Nucleus & Various Organelles • Nissl Bodies (Rough ER) • Neurofibrils (Cytoskeletal) • Dendrites • Numerous, Short, Branched Processes • Receive Impulse from other Neurons or Receptors • Carry Impulse Towards Cell Body (Afferent)

  9. Fig. 8.3

  10. Neurons – Structure continued • Axon • Long, Usually Singular Process • Many Mitochondria, Neurofibrils • Carries Impulse Away from Cell Body (Efferent) • Carries Impulse Towards: • ANOTHER NEURON • MUSCLE FIBER • GLAND CELL

  11. Neurons – Axon continued • Axon Hillock (Joins Cell Body & Axon) • Collaterals (Axon Branches) • Axon/Synaptic Terminals • Numerous, Fine Processes at end of Axon & Axon Collaterals • Some with Synaptic Knobs

  12. Neurons – Axon continued • Myelination • Most Axons • Enclosed in Schwann Cells (Neurolemmocyte) • Myelin Sheath – Multilayered, Inner, Fatty • Neurolemma – Outer Schwann Cell Membrane & Cytoplasm

  13. Fig. 8.6

  14. Neurons – Axon Myelination continued • Insulates & Increases Speed of Conduction • Nodes of Ranvier • Occur Along Axon Between Schwann Cells • No Myelin

  15. Neurons – Functional Classification • Sensory • Afferent • Connect Receptors & CNS • Motor • Efferent • Carry Commands from CNS to Effectors • Interneurons (Association) • CNS • Integrate Sensory & Motor • Most Numerous

  16. Neurons – Structural Classification • Unipolar • One Process (Dendrites & Axon Fused) • Sensory • Bipolar • Two Processes: One Dendrite, One Axon • Rare (Special Senses) • Multipolar • Several Dendrites, One Axon • Common • Motor & Interneurons

  17. Neurons - Terminology • Gray Matter – Unmyelinated Fibers & Cell Bodies • White Matter – Myelinated Axons • Nerve – Bundle of Fibers (Axons) in PNS • Tract – Bundle of Fibers in CNS • Ganglia – Clusters of Neuron Cell Bodies in PNS • Nuclei – Clusters of Neuron Cell Bodies in CNS

  18. Neuroglia • CNS • Astrocytes • Large, Star-shaped • Link Neurons & Blood Vessels; Help form Blood-brain Barrier • Oligodendrocytes • Form Myelin Sheath • Microglia • Derived from WBCs, Phagocytes

  19. Fig. 8.5abc

  20. Neuroglia continued • Ependymal Cells • Epithelium • Line Ventricles & Central Canal • Produce & Help Circulate CSF • PNS • Schwann Cells (Neurolemmocytes) • Form Myelin Sheath • Satellite Cells • Support, Cushion Ganglia

  21. Nerve Impulse Transmission • Two mechanisms involved • Transmission along a neuron • An electrical process • Transmission between neurons • A chemical process • Occurs at synapse

  22. Neuron Physiology • Transmission Requirements: • Resting Membrane Potential (Cell Membrane is Polarized) • Ion Channels in Cell Membrane (Allow Ions to Cross When Open) • Delivery of Threshold Stimulus

  23. Conduction Along Neuron • Resting Membrane Potential (+/Na+ outside, -/K+ inside • Appropriate Threshold Stimulus Opens Na+ Channels • Na+ Diffuses into Neuron, Results in Depolarization • Depolarization wave spreads from dendrite to axon

  24. Fig. 8.11

  25. Conduction Along Neuron continued • Na+ Channels Close, K+ Channels Open & K+ Diffuses Out of Neuron • Results In Repolarization • Action Potential = Depolarization + Repolarization (dendrite to axon) • Repolarization Required before another Action Potential • Sodium-Potassium Pump moves Na+ out & K+ in (Requires Energy)

  26. Conduction continued • All-or-None Principle • Neurons respond to stimuli by generating an impulse (action potential), or don’t respond at all • Refractory Period • Neurons must repolarize their cell membranes before they respond to subsequent stimuli

  27. Types of Conduction • Continuous • Typical of Unmyelinated Neurons (Slower) • Steps as Previously Described • Saltatory • Occurs along Myelinated Neurons • No Current where Myelin occurs • Action Potential Leaps from Node of Ranvier to Node • Faster!

  28. Fig. 8.12

  29. Synaptic Transmission • Arriving Action Potential Depolarizes Synaptic Knob • Ca++ Enters Cytoplasm of Presynaptic Neuron • Exocytosis of Synaptic Vesicles, Releasing Neurotransmitter • Neurotransmitter Diffuses across Synaptic Cleft & Binds to Receptors on Postsynaptic Membrane • Na+ Channels Open, Postsynaptic Membrane Depolarizes

  30. Fig. 8.13

  31. Neurotransmitters • Excitatory – Cause Depolarization/Na+ ions channels open (Dopamine) • Inhibitory – Raise the Threshold/ K+ or Cl- ion channels open (Serotonin & GABA) • Removed by Specific Enzymes

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