EX1; Excitable Cells; Potentials

Question 1

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

Answer 1

action potential

Question 2

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

Answer 2

stimulus (light, temp, pain, etc.)

Question 3

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

Answer 3

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

Question 4

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

Answer 4

Na+ ions

Question 5

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

Answer 5

electrical and concentration gradients

Question 6

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

Answer 6

it moves closer to 0mV (depolarizes)

Question 7

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

Answer 7

the membrane potential threshold

Question 8

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

Answer 8

the prevailing membrane potential

Question 9

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

Answer 9

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

Question 10

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

Answer 10

an overshoot of 0mV, reaching 40mV

Question 11

Upon the membrane potential overshoot, what voltage regulated channels open

Answer 11

K+; go from the inside to outside

Question 12

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

Answer 12

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

Question 13

Movement of K+ is driven by what

Answer 13

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

Question 14

During the falling phase, what becomes of the Na channels

Answer 14

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

Question 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)

Answer 15

afterpolarization

Question 16

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

Answer 16

small

Question 17

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

Answer 17

latent period

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

The end of the repolarization is close to what

Answer 20

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

Question 21

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

Answer 21

subthreshold stimulus

Question 22

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

Answer 22

threshold stimulus

Question 23

This type of stimulus is greater than a threshold stimulus

Answer 23

suprathreshold stimulus

Question 24

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

Answer 24

the immediate region of membrane

Question 25

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

Answer 25

local responses

Question 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

Answer 26

graded responses

Question 27

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

Answer 27

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

Question 28

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

Answer 28

all-or-none

Question 29

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

Answer 29

absolute refractory period

Question 30

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

Answer 30

relative refractory period

Question 31

The refractory periods impose what

Answer 31

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

Question 32

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

Answer 32

the rate of stimulus change; adaptation | referred to accommodation

Question 33

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

Answer 33

``` adaptation = neuron accommodation = ion channel ```

Question 34

What are the four parameters of a stimulus

Answer 34

intensity (amplitude) duration rate of change frequency

Question 35

The stimulus strength-duration curve relates what

Answer 35

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

Question 36

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

Answer 36

rheobase

Question 37

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

Answer 37

utilization time

Question 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

Answer 38

chronaxie

Question 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

Answer 39

electrotonic currents

Question 40

What is the potential change at the cathode

Answer 40

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

Question 41

What is the potential change at the anode

Answer 41

hyperpolarizing potential change; anode attracts anions

Question 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

Answer 42

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

Question 43

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

Answer 43

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

Question 44

What drives the AP in one direction

Answer 44

Na channel inactivation

Question 45

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

Answer 45

Schwann cells

Question 46

Where are Schwann cells not located

Answer 46

periodic nodes; nodes of Ranvier

Question 47

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

Answer 47

myelin

Question 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

Answer 48

True

Question 49

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

Answer 49

saltatory conduction

Question 50

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

Answer 50

multiple sclerosis

Question 51

This contains many neurons

Answer 51

peripheral nerve

Question 52

Velocity of an AP along the axon is dependent upon what

Answer 52

diameter; those with larger diameter have higher velocities