ch 12 nervous tissue.txt

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ch 12 nervous tissue.txt
2010-12-11 16:16:47


nervous tissue
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  1. Sensory function
    sense changes in internal and external environment thru SENSORY receptors
  2. Integrative function
    Analyze SENSORY information, stores some aspects and makes decisions regarding behaviors
  3. Motor function
    respond to stimuli by initiating action
  4. CNS
    central nervous system: consists of brain and spinal cord
  5. PNS
    peripheral nervous system: consists of cranial & spinal nerves, contain
  6. Somatic Nervous System
    • voluntary
    • Involves:
    • neurons from sensory receptors to the CNS
    • Motor neurons to the skeletal muscle tissue
  7. Autonomic Nervous System
    • involuntary
    • Involves:
    • neurons from visceral organs to the CNS
    • motor neurons to the smooth & cardiac muscle
    • -sympathetic division: fight or flight
    • -parasympathetic division: rest & digest (essential for life)
  8. Resting Membrane Potential
    • -70mV - cell is polarized (more positive extracellular)
    • involves more Na outside of cell and more K inside cell
    • NEGATIVE ions INSIDE cell membrane..and POSITIVE ions OUTSIDE cell membrane
  9. What happens during an action potential?
    Voltage-gated Na and K channels open in sequence
  10. Depolarization
    • results from a chemical or mechanical stimulus
    • Voltage-gated Na channels open and Na rushes into the cell
    • -55mV (cell is more positive due to influx of Na)
    • Positive feedback process
  11. Repolarization
    • K+ channels open
    • -70mV (K releases from cell decreasing its positive charge)
    • K channels opening is slower than Na influx
    • Na flow influx starts once K channels finally open
  12. Hyperpolarization
    • Too much K+ is released from cell
    • -90mV (need to put more K into the cell to go back to -70mV resting potential)
  13. Refractory Period
    involves when a neuron cannot operate another action potential
  14. Absolute Refractory Period
    when even a strong stimulus cannot begin another action potential
  15. chemical vs electrical synapses
    • Electrical: tissue --> nerve, can also synchronize groups of neurons
    • Chemical: nerve --> nerve. Info transfer from presynaptic neuron to a postsynaptic neuron
  16. Does strength of the stimulus relate to the speed of the nerve impulse?
    No, the speed of the impulse is the SAME no matter what strength of stimulus
  17. Chemical Synapses characteristics
    • One-way info transfer
    • Action potential reaches end bulb and voltage-gated Ca+2 channels open
    • Ca+2 flows inward triggering release of neurotransmitter
    • Neurotransmitters cross synaptic cleft and bind to receptors (the more neurotransmitters released the greater change in potential of postsynaptic cleft)
  18. Result of Ca in BAD neurons
    vasorestriction - LACK of blood supply to the area
  19. Effects of Neurotransmitters
    • Excitatory
    • Inhibitory
    • Both effects present in PNS and CNS
    • Same neurons can be both excitatory and inhibitory
  20. Excitatory effect on neurotransmitter
    • occurs during depolarization, this postsynaptic potential is called EPSP
    • results from opening of Na channels
    • Postsynaptic cell MORE likely to reach threshold
  21. Inhibitory effect on neurotransmitter
    • results from opening of Cl- or K+ channels
    • Causes postsynaptic cell to become more Hyperpolarized
    • postsynaptic cell LESS likely to reach threshold
  22. Summation
    the release of neurotransmitters at the same time
  23. Agonist
    enhances neurotransmitter effects
  24. Antagonist
    blocks action of neurotransmitters, decreasing their effect
  25. 3 responses
    • 1. Small ESPS occurs: potential reaches -56mV ONLY
    • 2. impulse is generated: threshold reaches, membrane potential is AT LEAST -56mV
    • 3. ISPS occurs: membrane is HYPERPOLARIZED, potential drops BELOW -70mV
  26. Neural circuits
    • network of neurons may contain thousands or millions of neurons
    • These circuits are involved in many activities, including:
    • breathing
    • short-term memory
    • waking up
  27. Regeneration and Repair of Neurons
    • PNS can repair damaged dendrites or axons, BUT mostly scar tissue forms instead
    • CNS has NO possible form of repair, due to: lack of neurolemma and growth stimulating factors
    • due to rapid formation of scar tissue