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MCBM Part 2 > Talbot - The Action Potential > Flashcards

Talbot - The Action Potential Flashcards

1
Q

what is a resting potential and what is it for a typical cell

A

a potential maintained across a membrane of excitable cells = -60/-70mV

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2
Q

what is hyperpolarization

A

membrane potential is more negative than the rest - due to an influx of anions or efflux cations

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3
Q

what is depolarization

A

membrane potential is less negative or positive than the rest - due to influx of cations or efflux of anions

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4
Q

what is the threshold potential

A

level of depolarization that triggers an action potential

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5
Q

what is a graded potential

A

variable strength signals that travel short distances and lose strength as they travel - may initiate an action potential

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6
Q

what are the 2 membrane domains in the neuron

A

somatodendritic domain and axonal domain

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7
Q

where is the somatodendritic domain located

A

membrane of cell body/soma and dendrites (all cells everywhere)

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8
Q

where is the axonal domain located

A

starts at axon hillock and includes axon and nerve terminals (only neuron cells)

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9
Q

what are the 2 types of openings located on the somatodendritic domain

A

ligand-gated channels and GPCR (G-protein coupled receptors)

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10
Q

how do ligand-gated channels work

A

they directly link incoming signals to opening of channel

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11
Q

how do GPCR (G-protein coupled receptors) work

A

they indirectly link the receptor to ion channel - activation of G-protein = open channel

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12
Q

what type of response do ligand-gated channels and GPCR have to changes in membrane potential

A

can only respond passively to changes in membrane potential = graded potentials

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13
Q

what is the amplitude of the voltage deflection across the membrane proportional to

A

the amplitude of the stimulus pulse (current) - assuming constant resistance (V=IR)

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14
Q

what type of channels are located on the axon

A

Voltage-gated Na and K channels

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15
Q

what type of channels are located at the nerve termini

A

Voltage-gated Na, K, and Ca channels

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16
Q

what type of response does the axonal domain have

A

all or nothing response

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17
Q

what happens if the magnitude of the graded potential reaches and goes above threshold

A

an action potential is developed - maximum all or none voltage

18
Q

what happens if the depolarizing stimulus is less than threshold

A

no action potential is generated

19
Q

does the depolarizing stimulus intensity change the type of response given

A

no - same as long as it is above threshold

20
Q

what is the path of an action potential

A

from resting state - depolarization phase - repolarization phase - hyperpolarizing phase

21
Q

what is happening to the ion channels in the resting phase

A

all voltage-gated Na+ and K+ channels are closed (K+ have some leaking) - permeability to K+ is greater than Na+

22
Q

what is happening to the ion channels in the depolarizing phase (rising phase)

A

Na+ channels open/activate and Na+ goes into the cell (K+ are slower to open) becomes more positive and approaches the equilibrium potential of Na (ENa) - Na+ permeability is higher than K+

23
Q

what is happening to the ion channels in the repolarizing phase (falling phase)

A

the Na+ channels become inactive (NOT closed) and K+ channels are open - K+ leaving the cell making the cell more negative and membrane potential move towards the equilibrium potential K+ (Ek)

24
Q

what is happening to the ion channels in the hyperpolarizing phase

A

K+ channels slowly close and Na+ are still inactive and start to close (K+ stay open longer than Na+ allowing membrane potential to fall below resting)

25
Q

what type of glial cells make myelin in the PNS

A

Schwann cells

26
Q

what is electronic spread

A

passive process (doesn’t require proteins) spread of depolarization, happens in all membranes and decays with distance

27
Q

why doesn’t an action potential decay with distance

A

they are regenerated at each node

28
Q

what is an orthodromic action potential

A

it moves down axon away from cell body towards terminus

29
Q

what is an antidromic action potential

A

moves up an axon towards cell body

30
Q

what 3 things govern the passive spread of charge

A

shape of cell, resistance to ion flow across membrane and in cytoplasm, and capacitance of membrane

31
Q

what 2 things determine the conduction velocity

A

axonal diameter (larger = faster) and if it is myelinated or not

32
Q

what is the actual current/conductance that develops

A

the sum of all individual openings and closings of ion channels

33
Q

what is a Na+ channel made up of

A

1 large alpha subunit and 1 or more beta subunit that is specific to type of Na+ channel

34
Q

what is the large alpha subunit of the Na+ channel made of

A

4 transmembrane domains (forms ion conduction pore) - each domain has 6 membrane spanning regions

35
Q

what does the 4th membrane spanning helix in each domain of Na+ do

A

contains voltage sensors for the channel

36
Q

what is the absolute refractory period

A

no action potential of any type may be generated - no matter how large the stimulus intensity (excitability = 0)

37
Q

what is the relative refractory period

A

smaller than normal height action potential may be generated in response to a larger than normal stimulus (excitability = increases)

38
Q

what is excitability

A

likelihood that a neuron will fire an action potential at its normal threshold (lower excitability - the greater the stimulus intensity must be)

39
Q

what is the Hodgkin cycle

A

positive feedback in voltage-gated Na+ channels: as Na+ channels are opened the membrane is further depolarized (inducing more Na+ channels to open) and the cycle continues - need an outside mechanism to stop cycle

40
Q

when would a Ca2+ channels open

A

located in the nerve terminus - opens in response to depolarization and Ca2+ flows into the cell acting as a “second” messenger to trigger the release of vesicles containing neurotransmitters

MCBM Part 2 (15 decks)

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