Neurophysiology

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Neurophysiology
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Regions of the Brain and Spinal Cord

• White matter dense collections of myelinated
  fibers
• Gray matter mostly soma and unmyelinated fibers

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Neuron Classification

• Structural
• Multipolar three or more processes (99)
• Bipolar two processes (axon and dendrite) (eye
  and olfactory)
• Unipolar single, short process ganglia in PNS
  as sensory

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Resting Membrane Potential (Vr)

• potential difference (70 mV) across the
  membrane of a resting neuron
• generated by different concentrations of Na,
  K, Cl?, and protein anions (A?)
• Ionic differences are the consequence of
• Differential permeability of the neurilemma to
  Na and K
• Operation of the sodium-potassium pump

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InterActive Physiology Nervous System I
Membrane Potential
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Resting Membrane Potential
Figure 11.7
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Resting Membrane Potential (Vr)
Figure 11.8
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Changes in Membrane Potential

• Depolarization the inside of the membrane
  becomes less negative
• Repolarization the membrane returns to its
  resting membrane potential
• Hyperpolarization the inside of the membrane
  becomes more negative than the resting potential

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Graded Potentials

• Short-lived, local changes in membrane potential
• Decrease in intensity with distance
• Magnitude varies directly with the strength of
  the stimulus
• Sufficiently strong graded potentials can
  initiate action potentials

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Action Potentials (APs)

• brief reversal of membrane potential with a total
  amplitude of 100 mV
• only generated by muscle cells and neurons
• Do not decrease in strength over distance
• principal means of neural communication
• action potential in the axon of a neuron is a
  nerve impulse

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Absolute Refractory Period

• The absolute refractory period
• Prevents the neuron from generating an action
  potential
• Ensures that each action potential is separate
• Enforces one-way transmission of nerve impulses

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Saltatory Conduction

• only at the nodes of Ranvier
• Voltage-gated Na channels are concentrated at
  these nodes
• Action potentials jump from one node to the next
• Much faster than conduction along unmyelinated
  axons

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Saltatory Conduction
Figure 11.16