Lecture 8 Flashcards

1
Q

Spatial summation

A

When currents from nearly simultaneous graded potentials combine

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2
Q

Temporal summation

A

When two graded potential from one presynaptic neuron occur close in time

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3
Q

What is the overshoot

A

Region above 0mV

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4
Q

explain membrane potential changes during AP

A
  1. we start off at resting membrane potential (-70mV)
  2. graded potential arrives at axon hillock and membrane depolarizes to threshold (-55mV)
  3. voltage gated Na+ channels open at -55mV (Na rushes in) which causes permeability of Na+ to increase and massive depolarization
  4. now we’re in overshoot (+30mV), so voltage gated Na+ channels inactivate causing a decrease in Na+ permeability
  5. voltage gated k+ channels open (k moving out of cell) increasing k+ permeability and repolarizing back towards -70mV
  6. one ce we blow past -70mV at almost -90mV K+ channels will close and permeability to K+ will decrease
  7. membrane potential will go back to -70mV because potassium-sodium pump and k+ leak channels are still in effect
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5
Q

How can voltage gated Na+ channels act as a positive feedback loop once activated?

A
  1. depolarization triggers activation of Na+ channel
  2. Na+ enters the cell
  3. more depolarization
    It would end up getting to Ena (+60mV) and stay there
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6
Q

refractory period

A

limits how soon after an action potential another can be triggered

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7
Q

Na+ channels open and close _______ than the k+ channels

A

faster

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8
Q

absolute refractory period

A
  • most voltage gated Na+ channels are inactivated
  • no stimulus regardless of strength can trigger AP
  • excitatory = 0
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9
Q

relative refractory period

A
  • some voltage gated Na+ channels are recovered from inactivation and voltage gated k+ channels are still open
  • stronger stimulus is required to account for fewer available Na+ channels and hyperpolarizing k+ efflux
  • excitatory is recovering
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10
Q

what is key for propagation

A
  • high membrane resistance because we don’t want leak channels
  • low internal resistance because we want a large cell
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11
Q

myelin is a ________

A

insulator

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12
Q

loss of myelin

A
  • decrease membrane resistance
  • increase membrane capacitance
  • increased loss of current and voltage along axon
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13
Q

myelin is an insulator and enhances action potential propagation because:

A
  • it increases membrane resistance (Rm)
  • decreases membrane capacitance (Cm)
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14
Q

membrane capacitance is

A

a measure of how much charge should be separated across the membrane to produce a given voltage

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