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AU14 Physiology > EX1; Excitable Cells; Potentials > Flashcards

EX1; Excitable Cells; Potentials Flashcards

1
Q

This is a large transient change in membrane potential (neurons and muscle cells)

A

action potential

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2
Q

This change in the environment causes a change in the membrane potential of a resting cells in the depolarizing direction

A

stimulus (light, temp, pain, etc.)

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3
Q

What is the sequence of events after a stimulus leading to an action potential

A

stimulus –> depolarized membrane (dendrites of a neuron) –> depolarized cell body –> AP develops at initial segments then propagates along the axon

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4
Q

The first step to develop an action potential is to increase membrane permeability to what

A

Na+ ions

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5
Q

The Na ions enter through voltage regulated Na channels, driven by what

A

electrical and concentration gradients

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6
Q

Upon Na+ ions entering the cell, what happens to the membrane potential

A

it moves closer to 0mV (depolarizes)

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7
Q

If depolarization is sufficiently large, this point will be reached which causes additional Na channels to open

A

the membrane potential threshold

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8
Q

Voltage-regulated channels are in the open or closed state determined by what

A

the prevailing membrane potential

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9
Q

As more Na+ enters the cells, it is a positive feed back cycle termed the rising phase; what does this mean

A

the opening of voltage gated Na channels
increases membrane Na permeability
increasing flow of Na into cell
decreasing the membrane potential (depolarization)
which opens the voltage gates Na channels

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10
Q

The membrane potential is very rapidly moves toward 0mc resulting in what

A

an overshoot of 0mV, reaching 40mV

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11
Q

Upon the membrane potential overshoot, what voltage regulated channels open

A

K+; go from the inside to outside

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12
Q

Upon K+ leaving the cell, the membrane potential abruptly reverses direction and returns to what

A

resting value and K+ ions diffuse out, carrying their + charge with them; referred to falling out phase

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13
Q

Movement of K+ is driven by what

A

concentration gradient and initially by electrical gradient as long as potential is positive

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14
Q

During the falling phase, what becomes of the Na channels

A

the Na channels close due to the membrane becoming more negative; “Na inactivating”

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15
Q

This is a phase of hyperpolarization; the rapid depolarization and repolarization, complete in ~1ms but overall talks >10ms (shoot past -70mV to ~100mV, then back to -70mV)

A

afterpolarization

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16
Q

The movement of a small/large number of ions results in a large change in membrane potential

A

small

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17
Q

This is a very brief period between applying a stimulus and the beginning of depolarization during rising phase of an AP

A

latent period

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18
Q

The latent period precedes the “foot” of AP, which is what

A

the portion of the rising phase before threshold is reached; channel opening

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19
Q

Why does the peak of the action potential stop at approximately 40mV

A

the peak of AP(40) approaches the E (equilibrium voltage) of Na (58)
Na is free to cross the membrane (during rising phase) until its ionic gradient is in equilibrium with membrane potential; the concentration and electrical gradient nearly balance each other at peak of AP

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20
Q

The end of the repolarization is close to what

A

the equilibrium voltage of K+; K+ freely crosses membrane during falling phase until its ionic gradient is in equilibrium with membrane potential, the concentration and electrical gradient nearly balance each other at the end of AP

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21
Q

This type of stimulus is insufficient to take a membrane to threshold

A

subthreshold stimulus

22
Q

This type of stimulus is just sufficient to take membrane to threshold

A

threshold stimulus

23
Q

This type of stimulus is greater than a threshold stimulus

A

suprathreshold stimulus

24
Q

Events (potential changes) resulting from a sub threshold stimulus are confine to what

A

the immediate region of membrane

25
Q

These are small depolarization or hyper polarization which do not move along the membrane

A

local responses

26
Q

This response is proportional to the stimulus strength; can be relatively weak and elicit changes in membrane potential that are subthreshold and not propagated

A

graded responses

27
Q

A threshold stimulus cause and action potential to occur and once it passes the threshold level, what occurs

A

it continues to completion and propagates along the entire length of an axon

28
Q

Once an AP crosses the threshold level, and continues to completion this is termed what

A

all-or-none

29
Q

This is a brief period when a second threshold stimulus or even a supra threshold stimulus cannot elicit a second AP

A

absolute refractory period

30
Q

For this longer period after an AP, a suprathreshold stimulus can elicit another AP but a threshold stimulus still cannot

A

relative refractory period

31
Q

The refractory periods impose what

A

an upper limit on the frequency at while cells can fire APs

32
Q

The transition from the closed to open state of the ion channels is dependent upon what; whether the stimulus be instant or slow

A

the rate of stimulus change; adaptation

referred to accommodation

33
Q

Adaptation is a property of what and accommodation is a property of what

A 
adaptation = neuron
accommodation = ion channel
34
Q

What are the four parameters of a stimulus

A

intensity (amplitude)
duration
rate of change
frequency

35
Q

The stimulus strength-duration curve relates what

A

strength (intenisty) of an instantaneous stimulus to the duration of the same stimulus that is required to elicit a response (AP)

36
Q

This is the magnitude of the least intense stimulus that can elicit a response

A

rheobase

37
Q

This is the duration required to elicit a response by a stimulus with a rheobase magnitude

A

utilization time

38
Q

This is the duration required to elicit response for a stimulus that has a magnitude that is twice the rheobase magnitude; can be used to compare excitability of different cells

A

chronaxie

39
Q

These are currents that occur at the immediate site of the stimulating electrodes, they do not propagate (passive currents), will give rise to AP if sufficient magnitude

A

electrotonic currents

40
Q

What is the potential change at the cathode

A

depolarizing; cathode causes cations (CCC) to move toward it, in both ECF and inside cell, that + ions inside cell are trapped and results in depolarization

41
Q

What is the potential change at the anode

A

hyperpolarizing potential change; anode attracts anions

42
Q

The stimulus that occurs at the site of the cathode which results in a depolarizing potential change at the site, causing local currents, this in turn cues what

A

depolarization of adjacent regions, this, if sufficient, will trigger an AP

43
Q

One AP does not move along the axon, rather, what occurs

A

every site along an axon undergoes a change in membrane potential (unless myelinated)

44
Q

What drives the AP in one direction

A

Na channel inactivation

45
Q

These cells surround axons, wrapping an extensive layer of plasma membrane around the axon

A

Schwann cells

46
Q

Where are Schwann cells not located

A

periodic nodes; nodes of Ranvier

47
Q

The layer of the Schwann cell is what; an excellent electrical insulator

A

myelin

48
Q

True or False
Local currents inside axon spread much further in the presence of myelin, allowing the AP to be only generated at the nodes

A

True

49
Q

What is the term when an AP skips along the axon; increasing the velocity of AP

A

saltatory conduction

50
Q

What is the breakdown of myelin, resulting in gross motor abnormalities

A

multiple sclerosis

51
Q

This contains many neurons

A

peripheral nerve

52
Q

Velocity of an AP along the axon is dependent upon what

A

diameter; those with larger diameter have higher velocities

AU14 Physiology (24 decks)

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