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Neurophysiology NEUROTRANSMISSION

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Title: Chapter 12 Subject: Nervous Tissue Author: maria Last modified by: Murray, Kim L Created Date: 3/15/2006 4:31:41 AM Document presentation format – PowerPoint PPT presentation

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Title: Neurophysiology NEUROTRANSMISSION


1
Chapter 12
  • Neurophysiology NEUROTRANSMISSION

2
Chemical Synapse Vocabulary
  • Presynaptic neuron
  • Postsynaptic neuron
  • Synapse means of communication between each
    neuron and the next cell space
  • Excitatory neurotransmitters chemicals that
    cause nerve impulses (e.g. ACh, glutamate)
  • Inhibitory neurotransmitters chemicals that
    inhibit nerve impulses (e.g.gama aminobutyric
    acid GABA)

3
Steps of Synaptic Transmission
  • Step 1 Action potential arrives at the axon
    terminal
  • Step 2 Release of neurotransmitter from a
    vesicle
  • Step 3 Neurotransmitter binds to receptor site
    on ion channel on postsynaptic neuron
  • Step 4 Ions cross the membrane through open
    channels
  • Step 5 The influx of ions causes action
    potential in postsynaptic neuron (details are
    coming up - ?)
  • Step 6 Removal of neurotransmitter
  • www.mind.ilstu.edu/flash/synapse_1.swf

4
Major Neurotransmitters in the Body
  • Acetylcholine regulates muscles and memory
    mostly excitatory
  • Dopamine produces feelings of pleasure mostly
    inhibitory
  • GABA major inhibitory neurotransmitter in the
    brain
  • Glutamate - major excitatory neurotransmitter in
    the brain
  • Seratonin involved in many functions including
    mood, appetite, and sensory perception
    inhibitory in pain pathways
  • Norephinephrine regulates normal brain
    processes and is a part of the fight-or-flight
    response usually excitatory

5
Resting Membrane Potential (RMP)
The outside of the cell is more positive (Na)
than the inside (K)
  • Electrical charge gradient associated with the
    cell membrane typically -70 millivolts

6
Protein Channels
  • Ion protein channels are chemically, mechanically
    or voltage regulated
  • Ion channels open in response to the particular
    stimulus and allow ions to flow in or out the
    cell
  • Flow of ions changes the membrane
    potential/voltage
  • Sudden change in membrane potential that
    accompanies activity action potential (nerve
    impulse)

7
A Special Ion Channel Na/K ATPase
  • When a neuron is at rest, there is a slow leakage
    of Na into the cell K out of the cell (along
    concentration gradient)
  • Na/K ATPase pumps 3 Na out and 2 K in per ATP
    hydrolysis thus prevents reaching equilibrium
    of Na K ions

8
Steps of Action Potential
  • Step 1 Resting
  • Step 2 Depolarization
  • Step 3 Repolarization
  • Step 4 Return to normal permeability

9
  • Step 1 Resting (-70 mV)
  • Step 2 Depolarization
  • Neurotransmitters bind to their receptors on a
    postsynaptic neuron, chemically gated Na
    channels open, Na flows in, and local potential
    reaches a threshold limit (-55mV)
  • Then, voltage-gated Na channels open and Na
    ions rush into the cell
  • Membrane potential reaches 30 mV

10
  • Step 3 Repolarization
  • Na channels close when the inside of the axon
    becomes sufficiently positive (30 mV)
  • Voltage-regulated K channels open K flows out

11
  • Step 4 Return to resting potential
  • Ion movements drive the membrane potential back
    toward resting membrane potential value
  • Na/K ATPase continues pumping ions, adjusting
    levels back to resting equilibrium levels
  • Hyperpolarization - briefly the exterior of the
    membrane is more negative than resting potential
    voltage level
  • Refractory period - the time during which a nerve
    cell cannot generate another action potential
    despite stimulation

12
And Another Look
  • www.blackwellpublishing.com/matthews/channel.html
  • www.blackwellpublishing.com/matthews/actionp.html

13
  • Closer Look at Action Potential
  • http//itc.gsw.edu/faculty/gfisk/anim/actionpotent
    ial.swf
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