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
what type of glial cells make myelin in the PNS
Schwann cells
26
what is electronic spread
passive process (doesn't require proteins) spread of depolarization, happens in all membranes and decays with distance
27
why doesn't an action potential decay with distance
they are regenerated at each node
28
what is an orthodromic action potential
it moves down axon away from cell body towards terminus
29
what is an antidromic action potential
moves up an axon towards cell body
30
what 3 things govern the passive spread of charge
shape of cell, resistance to ion flow across membrane and in cytoplasm, and capacitance of membrane
31
what 2 things determine the conduction velocity
axonal diameter (larger = faster) and if it is myelinated or not
32
what is the actual current/conductance that develops
the sum of all individual openings and closings of ion channels
33
what is a Na+ channel made up of
1 large alpha subunit and 1 or more beta subunit that is specific to type of Na+ channel
34
what is the large alpha subunit of the Na+ channel made of
4 transmembrane domains (forms ion conduction pore) - each domain has 6 membrane spanning regions
35
what does the 4th membrane spanning helix in each domain of Na+ do
contains voltage sensors for the channel
36
what is the absolute refractory period
no action potential of any type may be generated - no matter how large the stimulus intensity (excitability = 0)
37
what is the relative refractory period
smaller than normal height action potential may be generated in response to a larger than normal stimulus (excitability = increases)
38
what is excitability
likelihood that a neuron will fire an action potential at its normal threshold (lower excitability - the greater the stimulus intensity must be)
39
what is the Hodgkin cycle
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
when would a Ca2+ channels open
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