EX1; Excitable Cells; Potentials Flashcards Preview

AU14 Physiology > EX1; Excitable Cells; Potentials > Flashcards

Flashcards in EX1; Excitable Cells; Potentials Deck (52):
1

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

action potential

2

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

stimulus (light, temp, pain, etc.)

3

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

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

4

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

Na+ ions

5

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

electrical and concentration gradients

6

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

it moves closer to 0mV (depolarizes)

7

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

the membrane potential threshold

8

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

the prevailing membrane potential

9

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

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

10

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

an overshoot of 0mV, reaching 40mV

11

Upon the membrane potential overshoot, what voltage regulated channels open

K+; go from the inside to outside

12

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

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

13

Movement of K+ is driven by what

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

14

During the falling phase, what becomes of the Na channels

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

15

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)

afterpolarization

16

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

small

17

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

latent period

18

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

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

19

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

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

20

The end of the repolarization is close to what

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

21

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

subthreshold stimulus

22

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

threshold stimulus

23

This type of stimulus is greater than a threshold stimulus

suprathreshold stimulus

24

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

the immediate region of membrane

25

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

local responses

26

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

graded responses

27

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

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

28

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

all-or-none

29

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

absolute refractory period

30

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

relative refractory period

31

The refractory periods impose what

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

32

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

the rate of stimulus change; adaptation
referred to accommodation

33

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

adaptation = neuron
accommodation = ion channel

34

What are the four parameters of a stimulus

intensity (amplitude)
duration
rate of change
frequency

35

The stimulus strength-duration curve relates what

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

36

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

rheobase

37

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

utilization time

38

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

chronaxie

39

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

electrotonic currents

40

What is the potential change at the cathode

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

What is the potential change at the anode

hyperpolarizing potential change; anode attracts anions

42

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

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

43

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

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

44

What drives the AP in one direction

Na channel inactivation

45

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

Schwann cells

46

Where are Schwann cells not located

periodic nodes; nodes of Ranvier

47

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

myelin

48

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

True

49

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

saltatory conduction

50

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

multiple sclerosis

51

This contains many neurons

peripheral nerve

52

Velocity of an AP along the axon is dependent upon what

diameter; those with larger diameter have higher velocities