Trans - Neuronal Excitability II

Question 1

transient shift of membrane potential in a localized cell area

Answer 1

local potential

Question 2

characteristics of local potential

Answer 2

1. localized
2. graded
3. decrementally transmitted
4. may be summated
5. very rapid

Question 3

[T/F] local potential is faster than AP

Answer 3

T

Question 4

types of local potential

Answer 4

1. synaptic - IPSP or EPSP
2. generator potential - sensory organs
3. electronic potential - associated with AP

Question 5

potential that occurs in sensory organs

Answer 5

generator potential

Question 6

local potential that occurs along the axon as the action potential travels along it

Answer 6

electronic potential

Question 7

time required for a membrane potential to change after a stimulus is applied

Answer 7

time constant

Question 8

high resistance - ______ time constant

Answer 8

greater

Question 9

high capacitance - _______ time constant

Answer 9

greater

Question 10

ability to store charges of opposite signs on two opposing surfaces

Answer 10

capacitance

Question 11

less leakage of ions across the membrane means that local potential will _________

Answer 11

travel farther from the source

Question 12

distance at which the initial transmembrane volume change has fallen to 37% of its peak value

Answer 12

space constant

Question 13

relationship of space constant to transmembrane resistance

Answer 13

directly related

Question 14

relationship of space constant and internal axoplasmic resistance

Answer 14

inversely related

Question 15

the larger the space constant, the ______ along the membrane a voltage change is observed after a stimulus is applied

Answer 15

farther

Question 16

transmembrane resistance

Answer 16

how well a membrane blocks ions from leaving

Question 17

the higher the transmembrane resistance, the _____ the space constant

Answer 17

higher

Question 18

internal axoplasmic resistance

Answer 18

resistance to ion flow within the axon

Question 19

how does internal axoplasmic resistance affect space constant

Answer 19

when the resistance is high, ions cannot mvove away from the source quickly –> lesser space constant

Question 20

action potential - define

Answer 20

fleeting, self-renewing wave of depolarization (positive wave) that propagates without decrement along the entire length of the nerve axon at high speed

Question 21

orthodromic conduction

Answer 21

conduction in one direction ( in axon away from soma)

Question 22

antidromic conduction

Answer 22

conduction from axon toward soma

Question 23

conformations of Na gate, and components

Answer 23

1. resting - activation gate closed, inactivation gate open
2. open - activation gate open, inactivation gate open
3. inactive - activation gate open, inactivation gate closed

Question 24

effect of reaching threshold potential

Answer 24

opening of Na and K gates, action potential starts

Question 25

spike potential

Answer 25

rapid rise and fall of membrane potential due to fast sodium gates

Question 26

absolute refractory period - define

Answer 26

no new AP is produced no matter how strong the stimuli

Question 27

absolute refractory period - mechanism

Answer 27

all Na gates are already open, no new change in Na gradient can be created

Question 28

relative refractory period - define

Answer 28

stronger than normal stimulus can cause AP

Question 29

relative refractory period - mechanism

Answer 29

some Na channels are closed again - may be reopened to generate new AP

Question 30

prevents AP from reversing direction

Answer 30

relative refractory period

Question 31

supranormal refractory period - define

Answer 31

easier to reach threshold and create AP because the electrical charge inside the membrane is nearer the threshold

Question 32

supranormal refractory period - mechanism

Answer 32

continued efflux of K due to slow K channels - causes membrane potential to be relatively more negative

Question 33

subnormal period

Answer 33

overshooting of membrane repolarization due to slow K gates

Question 34

subnormal period is corrected by:

Answer 34

Na-K pump

Question 35

AP has constant ____ and _______

Answer 35

amplitude and form

Question 36

an increase in the axon diameter will (1)_______ the space constant, (2)_______ the time constant, and (3)_______ the conduction speed

Answer 36

1. increase 2. decrease 3. increase

Question 37

myelinated axon conduction velocity

Answer 37

3-120 m/sec

Question 38

unmyelinated axon conduction velocity

Answer 38

0.5-2 m/sec

Question 39

presence of myelin leads to (1)_______ in effective resistance of axonal membrane. why?

Answer 39

1. increase, because ions must flow through myelin before reaching ECF

Question 40

presence of myelin leads to (1)________ in effective capacitance. why?

Answer 40

1. decrease, because of the greater distance between ECF and ICF

Question 41

saltatory conduction

Answer 41

electrical signal jumping from one node of ranvier to the next