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Foundations in Medical Neuroscience > Action Potentials > Flashcards

Action Potentials Flashcards

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USMLE® Step 1 flashcards
1
Q

How long from start to finish is an action potential?

A

The process of an AP firing from start to finish is approximately 3ms with the peak at about 1ms!

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2
Q

what does resting membrane potential mean?

A

differences in concentration of ions – outside more positively charged

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3
Q

explain the features of resting membrane potential

A
  • Poised and ready to fire (measured as an electrical potential).
  • Electrical and chemical force at the same time:
    o Electrical force: opposites attract – outside more positive.
    o Chemical force: concentration gradient – unequal ion concentration.
  • Requires lots of energy (concentration gradient maintenance).
    o Na+/K+ exchanger
     3 Na+ out/2 K+ in
     Uses a lot of ATP
  • -70mV resting potential
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4
Q

what are the 2 forces during resting membrane potential?

A

electrical and chemical

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5
Q

electrical force at resting membrane potential

A

opposites attract – outside more positive.

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6
Q

chemical force at resting membrane potential

A

concentration gradient – unequal ion concentration.

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7
Q

how much energy does resting membrane potential require?

A

a lot!

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8
Q

what is the o Na+/K+ exchanger?

A

 3 Na+ out/2 K+ in
 Uses a lot of ATP

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9
Q

what is the figure for resting potential?

A
  • -70mV resting potential
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10
Q

Explain the process happening at resting membrane stage of AP if an excitatory NT is released

A

The NT attaches to the ligand-gated Na+ channel which opens the channel allowing Na+ to move down the concentration gradient.

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11
Q

explain what happens at the threshold stage of an AP

A

Intracellular becomes more positive

-55mV threshold met.

The threshold opens the voltage-gated Na+ channels in the axon hillock.

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12
Q

threshold figure

A

-55mV

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13
Q

what are A-?

A

big organic ions

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14
Q

what ions are more highly concentrated inside the neuron at rest?

A

K+
A-

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15
Q

what ions are more highly concentrated outside the neuron at rest?

A

Na+
Ca2+
Cl-

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16
Q

what happens at the peak of an AP?

A
  • voltage-gated Na+ channels close
  • Voltage-gated K+ channels open (K+ leaves neuron) (falling phase)
  • Voltage-gated K+ channels are also triggered by a change in the membrane potential but open with a 1ms delay allowing the electrical signal to generate and the AP to remain local (falling phase).
17
Q

why is there a delay before the K+ channels open?

A

open with a 1ms delay allowing the electrical signal to generate and the AP to remain local.

18
Q

what happens during the refractory period?

A
  • (after hyperpolarisation phase – neuron overcompensates)
  • -90mV before this
  • Can’t fire another AP (as below resting potential)
  • Na+/K+ exchanger gets to work to restore the resting state.
19
Q

figure of the refractory period

A

-90mV

20
Q

what happens in the falling phase?

A
  • Voltage-gated K+ channels open (K+ leaves neuron) (falling phase)
  • Voltage-gated K+ channels are also triggered by a change in the membrane potential but open with a 1ms delay allowing the electrical signal to generate and the AP to remain local.
21
Q

how does AP transfer from neuron to neuron?

A

Voltage-gated calcium channels allow the transfer of AP (turn electrical signal into chemical signal – NT)

  • Voltage-gated Ca2+ channels open
  • Ca2+ enters
  • NT move out of the presynaptic cell into the synapse and bind to the postsynaptic terminal.
22
Q

what is the all or nothing principle?

A

AP will either fire or it won’t (no varying strengths of AP.

23
Q

describe the action of inhibitory NT

A
  • Internal becomes more negative
  • Hyperpolarisation occurs (-85mV)
  • So much more Na+ is needed to reach the threshold

(ligand-gated Cl- channels are located on the dendrites).

24
Q

where are ligand-gated Cl- channels located?

A

on the dendrites

25
Q

clinical relevance of AP

A

many anaesthetics act by blocking voltage-gated Na+ channels and so block AP firing.

26
Q

explain the actions of glutamate

A
  • Increases potential an AP will fire (excitatory)
  • Causes depolarisation of neuronal cell membrane (internal becomes more positive)
  • Inhibited by alcohol
  • Umami flavour mimics glutamate actions as it contains high levels of sodium
27
Q

explain the actions of GABA

A
  • Decreases potential an AP will fire (inhibitory)
  • Causes hyperpolarisation of the neuronal cell membrane (internal becomes more negative)
  • Works with benzodiazepines
  • Potentiated by alcohol

Foundations in Medical Neuroscience (14 decks)

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