chapter 11 - nervous system; part 4

Question 1

what is a graded potential?

Answer 1

a small change in the resting membrane potential that is confined to a small area of the plasma membrane; graded potentials can summate, or add together

Question 2

what could an increase in membrane potential to NA+ cause?

Answer 2

it can cause graded depolarization, and an increase in membrane permeability to k+ or cl- can result in graded hyperpolarization

Question 3

when is the term graded potential used?

Answer 3

it is used because a stronger stimulus produces a greater potential change than a weaker stimulus

Question 4

why does a graded potential decrease?

Answer 4

it decreases in magnitude as the distance from the stimulation increases

Question 5

what is an action potential?

Answer 5

it is a larger change in the resting membrane potential that spreads over the entire surface of the cell

Question 6

what is a threshold?

Answer 6

it is the membrane potential at which a graded potential depolarizes the plasma membrane sufficiently to produce an action potential

Question 7

what happens when an action potential occurs?

Answer 7

it occurs in an all-or-none fashion; if action potentials occur, they are of the same magnitude, no matter how strong the stimulus

Question 8

depolarization

Answer 8

occurs as the inside of the membrane becomes more positive because NA 1 diffuse into the cell through voltage-gated ion channels

Question 9

repolarization

Answer 9

a return of the membrane potential toward the resting state; it occurs because voltage-gated NA+ channels close and Na+ diffusion into the cell slows to resting levels and because voltage-gated K+ channels continue to open and K+ diffuse out of the cell

Question 10

what is the after potential?

Answer 10

it is a brief period of hyperpolarization following repolarization

Question 11

absolute refractory period

Answer 11

it is the time during an action potential when a second stimulus, no matter how strong, cannot initiate another action potential

Question 12

relative refractory period

Answer 12

follows the absolute refractory period and is the time during which a stronger-than-threshold stimulus can evoke another action potential

Question 13

subthreshold

Answer 13

it is a stimulus that produces only a graded potential

Question 14

what does a threshold stimulus cause?

Answer 14

it causes a graded potential that reaches threshold and results in a single action potential

Question 15

submaximal stimulus

Answer 15

it is a greater than a threshold stimulus and weaker than a maximal stimulus; the action potential frequency increases as the strength of the submaximal stimulus increases

Question 16

maximal/supramaximal stimulus

Answer 16

this stimulus produces a maximum frequency of action potentials

Question 17

what can an action potential generate?

Answer 17

it can generate local currents, which stimulate voltage-gated NA+ channels in adjacent regions of the plasma membrane to open, producing a new action potential

Question 18

propagation in an unmyelinated axon

Answer 18

action potentials are generated immediately adjacent to previous action potentials

Question 19

propagation in a myelinated axon

Answer 19

action potentials are generated at successive nodes of ranvier

Question 20

what are electrical synapses?

Answer 20

they are gap junctions in which tubular proteins called connexons allow local currents to move between cells; at an electrical synapses, an action potential in one cell generates a local current that causes an action potential in an adjacent cell