Lecture 7: Generation of Action Potentials Flashcards

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1
Q

3 phases of AP

A
  1. depolarization
  2. repolarization
  3. after-hyperpolarization
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2
Q

absolute refractory period

A
  • period where cell is incapable of generating a new AP

- caused by inactivation of VG Na+ channels

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3
Q

Relative refractory period

A
  • more difficult to generate a new AP
  • occurs at after-hyperpolarization until resting membrane potential is reestablished
  • only bigger stimulus/GP will generate a new AP
  • K+ efflux and inactivation of Na+ channels causes RRP
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4
Q

How is AP generated?

A

Voltage gated channels are controlled by membrane potential, and changes in MP will open or close them
-2 channels in the axon hillock : Na+ and K+

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5
Q

Depolarization

A

Occurs when Vm reaches threshold potential and Na+ channels open first, Na+ entering the cell causes depolarization

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6
Q

Repolarization

A

K+ channels open more slowly than Na+ channels, so when Na+ close K+ remain open
-K+ leaving causes repolarization

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7
Q

After-hyperpolarization

A
  • occurs when voltage-gated K+ channels close

- represents time needed for extra K+ near outside membrane to disperse

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8
Q

Ion movement during AP

A
  • only a few ions move in or out of the cell during AP
  • approx. 1 of every 100,000 K+ ions move to change Em from +30 to -70
  • any noticeable change in movement is restored by Na+/K+ ATPase
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9
Q

What re-establishes resting Vm?

A

by the Na+/K+ ATPase, but not during AP
-the duration of the after-hyperpolarization represents the time required for extra K+ near outside membrane to diffuse away

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10
Q

VG Na+ channel has two gates

A

has activation gate that is voltage dependent, and an inactivation gate that is time dependent
-act. gate opens due to depolar and inact closes after a certain period of time, then repolar. closes the act. gate and time opens the inact., returning the channel to rest position

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11
Q

Why don’t we see AP in dendrites and cell bodies?

A

density of VG Na+ channels must be high for positive feedback mechanism to function, which they are at axon, but not elsewhere

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12
Q

What does “excitability” mean?

A

-ability to generate a new AP when stimulated
-the easier it is to generate an AP, the more excitable the membrane is
The more excitable, the lower the threshold stimulus needed to generate an AP

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13
Q

definition of threshold stimulus and threshold MP***

A
  • the min stimulus that needs to be applied on the neuron

- min MP needed to be reached to open the critical number of Na+VG channels to start the positive feedback loop

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14
Q

Signal Coding def

A

how info about duration and strength of stimulus is passed on to postsynaptic axon

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15
Q

signal coding and frequency of AP

A

AP frequency codes the strength of stimuli, therefore AP frequency also increases with stronger stimuli (how frequent they are=how strong stim is)
-duration of a series of AP codes for duration of the stimulus (how many there are=duration)

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16
Q

Suprathreshold stimulus…

A

can trigger an AP during the relative refractory period

17
Q

Why is the movement of relatively few ions across the membrane sufficient to change the membrane potential?

A

the ions cause a LOCAL change in potential that quickly conducts through the cytosol