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The Nervous System: Neural Tissue

The Nervous System: Neural Tissue. Coordination of activities: Nervous System. Nervous System: Swift, brief, temporary Functions: (motor & sensory) Provide sensation Integrate info Coordinate voluntary & involuntary activities Regulate & control systems. Nervous System Overview.

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The Nervous System: Neural Tissue

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  1. The Nervous System:Neural Tissue

  2. Coordination of activities:Nervous System • Nervous System: • Swift, brief, temporary • Functions: (motor & sensory) • Provide sensation • Integrate info • Coordinate voluntary & involuntary activities • Regulate & control systems

  3. Nervous System Overview • 2 Anatomical Divisions • Central Nervous System (CNS) • Brain and spinal cord • Peripheral Nervous System (PNS) • Somatic Nervous System (SNS) • Autonomic Nervous System (ANS) • Sympathetic N. S.- “flight or fight” • Parasympathetic N. S.- “rest & repose” • http://itc.gsw.edu/faculty/gfisk/anim/index.html • 2 Functional Divisions (based on function) • Afferent: Sensory (muscles/ glands CNS) • Efferent: Motor (CNS muscles/ glands

  4. Cellular Organization in Neural Tissue • Neurons: (=Nerve cells) • Soma (cell body) • Dendrites • Axon & Nodes of Ranvier/ Internodes • Synaptic terminals (knobs) • Neuroglia= Glial Cells • Protects neurons • Provides support • Phagocytes

  5. Neuron Diagram

  6. Neuron Functional Classifications • Sensory Neurons= Afferent fibers • TO CNS from ext & int environment • Cell bodies in peripheral ganglia • neurons • from sensory receptors spinal cord • Types: • Somatic Sensory Neurons: ext environment • Exteroceptors: sight, smell, hear, touch • Proprioceptors: position joints & muscles • Visceral Sensory Neurons= Interoceptors: internal envmt like visceral systems & taste, deep pressure, pain

  7. Neuron Functional Classification • Motor Neurons: Efferent fibers • From CNS to effectors (muscles/ glands) • Stimulates or modifies activity of peripheral tissues, organs, organ systems • Types: • Somatic Motor Neurons: • Voluntary skeletal muscle • Spinal cord neuromuscular junction • Visceral Motor Neurons (of ANS) • Involuntary peripheral effectors • Spinal Cord (preganglionic fibers) peripheral ganglion (PNS cell bodies) postganglionic fibers effectors

  8. Neuron Functional Classification • Interneurons= Association Neurons • b/w sensory & motor neurons • Located entirely in brain & spinal cord • Function: • Analysis of sensory inputs • Coordination of motor outputs • Classified as excitatory or inhibitory

  9. Nervous System:Functional Classification Organization

  10. Neuron Communication • Synapse • Space between synaptic knob & next cell • Neurons communicate with: • Other neurons • Other Cells: • Neuromuscular Junction • Neuroglandular Junction • Neurotransmitters • Chemical messenger at synapse

  11. Resting Membrane Potential • Intracellular Fluids: High in [K+] • Extracellular Fluids: High in [Na+] • Na+/K+ exchange pump • Pump 2K+ in and 3 Na+ out • Resting potential: -70mV • Ion Channels: • Passive channels: always open & “leaky” • Active or Gated Channels: • Chemically regulated: neurotransmitter • Voltage regulated: voltage changes • Mechanically regulated: physical stim (Merkel’s discs)

  12. Neuron Electrical Signal: Action Potential • Action Potential: • Electrical signal • Stimulated by neurotransmitter, voltage change, or physical stimulus • Rules to occur: • Depolarization to threshold (-60 to -55mV) • Occurs in axons & muscle fibers (down T-tubules) • All action potentials generated are identical (gun) • All-or-None Response (toll booth)

  13. Action Potential Generation: Steps • Activate voltage-gated Na+ channelsdepolarization • Increase membrane potential: Na+ in • Inactivate Voltage-gated Na+ channels: • +30mV close & can’t be opened • Activate Voltage-Gated K+ channels repolarization • Decrease membrane potential (-70mV): K+ out • Return to resting membrane potential: -70mV • Voltage-gated Na+ channels closed, can open. • Voltage-gated K+ channels closing with delay of 1msec  hyperpolarization (below -70mV) • After 1msec normal resting potential (-70mV) • Action Potential travels to next portion of membrane

  14. Action Potential: Steps & Graph

  15. Refractory Periods of Action Potentials • Absolute refractory period: Repolarization • Membrane CAN’T respond to stim • From opening voltage-gated Na+ channels end of action potential • Action potential: one direction away from soma. • Relative refractory period: Hyperpolarization • Only LARGER stimulus can initiate axn potential • From when voltage-gated Na+ channels are restored to normal (closed but able to open) state, but voltage-gated K+ channels still open.

  16. Refractory Period & Axn Pot Movement

  17. Action Potential Conduction Velocity • Myelin sheath • Continuous conduction: segment by segment • Unmyelinated axons • Saltatory Conduction: leap from node to node • Myelinated axons: ions can’t pass lipid nodes • http://www.blackwellpublishing.com/matthews/actionp.html • Axon Diameter • Type A: Largest, myelinated fastest (300mph) • sk. mm. motor neurons, balance & L.T. • Type B: Smaller, myelinated medium (40mph) • Type C: Smallest, unmyelinated slowest (2mph) • Both B & C carry pain, temp, to smooth mm & glands

  18. Continuous v. Saltatory Conduction

  19. Cocaine Effects on Dopamine

  20. Other Factors on Rate of A.P. • Hormones can promote facilitation or inhibition • Presynaptic inhibition: inhibits Ca2+ channels decr postsynaptic stim (i.e. GABA) • Presynaptic Facilitation: keep Ca2+ channels open • [Na+, K+, Ca2+] (dehydration or kidney dz), pH (basic  convulsions, acidic inhibition), temp changes

  21. Other Neurotransmitters: Excite & Inhibit

  22. ATP needed for: Synthesis, release, & recycling NT Movement of materials Recovery from a.p.: [ion]- Na+/ K+ pump ATP Production: Aerobic glycolysis (no glucose stores) Need uninterrupted blood supply for O2 & glucose Stroke: less than 1-2 hrs few weeks to recover longer permanent ATP Needs & Production

  23. Drug Effects: Interferes w/ NT synthesis Alter rate of NT release Prevent NT inactivation Prevent NT binding to receptors Caffeine lowers threshold at axon hillock more sensitive to stim (facilitation) “jumpy” Nicotine bind to receptor sites on postsynaptic membrane & stimulate it no enzymes to remove it Examples Botulinus toxin: blocks release Ach at presynaptic membrane paralysis Black Widow spiders venom : cause massive release of Ach cramps/ spasms Anticholinesterase drugs: block breakdown Ach by AchE extreme contract (ex: nerve gases, pst controls) Atropine: prevent Ach binding to postsynaptic neuron paralysis (curare plant extract) Ach Drugs & Synaptic Function

  24. Drug Effects on Ach Synapses

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