Lecture 32 - Action Potentials

Question 1

Which of the following is not a GATED ion channel?

Answer 1

leak channels

Question 2

Which ion channels are responsible for the repolarization phase??

Answer 2

K+

Question 3

In the CNS, which cell type produces myelin??

Answer 3

Oligodendrocytes

Question 4

the cell membrane acts as a

Answer 4

selective filter

Question 5

describe the structure of the cell membrane

Answer 5

phospholipid bilayer stippled with transport channels and proteins

Question 6

what are the 3 types of gated ion channels

Answer 6

1. voltage-gated
2. ligand-gated
3. mechanically-gated

Question 7

what gate responds to a change in membrane potential. give an example.

Answer 7

voltage-gated
Na+/K+ channels

Question 8

what gate responds to the binding of a neurotransmitter. give an example.

Answer 8

ligand-gated
NMDA

Question 9

what gate responds to a physical change in the membrane. give an example.

Answer 9

mechanically-gated
mechano-receptors in skin

Question 10

T/F: leak channels are always open

Answer 10

TRUE

Question 11

cations

Answer 11

positive charge

Question 12

anion

Answer 12

negative charge

Question 13

____ is the main extracellular cation while ____ is the main anion

Answer 13

Na+; Cl-

Question 14

the main intracellular cation is ____

Answer 14

K+

Question 15

what two gradients are there

Answer 15

1. concentration
2. electrochemical

Question 16

the sodium-potassium ATPase pump transports what in and out of the cell

Answer 16

3 Na+ out
2 K+ in

Question 17

what is the function of the sodium-potassium ATPase pump

Answer 17

stabilize membrane potential

Question 18

what is the resting membrane potential? what is this value in neurons?

Answer 18

the electric potential difference across plasma membrane when non-excited
-70mV

Question 19

Describe electrochemical equilibrium

Answer 19

as potassium leaks out of the cell, the intracellular fluid becomes more negative and thus attracts the potassium back to the cell

*opposing forces acting on potassium crossing the plasma membrane

Question 20

The nerst equation signifies

Answer 20

the relationship of electrical and chemical forces acting on any ionic species across a semipermeable membrane

explains the electrochemical potential

Question 21

temporal summation

Answer 21

effect when impulses received at the same place on the neuron add up

Question 22

spatial summation

Answer 22

effect when simultaneous impulses received at different places on the neuron add up

Question 23

what is the threshold potential

Answer 23

value at which an action potential can be triggered

-50-55mV

Question 24

T/F: action potentials are short-lived and are considered all-or-none signals

Answer 24

TRUE

Question 25

Depolarize

Answer 25

getting closer to zero

Question 26

Repolarize

Answer 26

potassium in charge
bringing back to -70mV

Question 27

What are the 4 phases of action potentials

Answer 27

1. resting state
2. depolarization
3. repolarization
4. hyperpolarization

Question 28

Summarize the resting phase of action potentials

Answer 28

all gated Na+ and K+ channels are closed
resting membrane potential maintained

Question 29

Summarize the depolarization phase of action potentials

Answer 29

Na+ channels open
Na+ influx causes more depolarization
at the threshold of positive feedback causes a large spike (+30 mV)

Question 30

Summarize the repolarization phase of action potentials

Answer 30

Na+ channels inactivate, K+ channels open and go down their gradient
returns to resting potential

Question 31

Summarize the hyperpolarization phase of action potentials

Answer 31

some K+ channels remain open allowing efflux and membrane dips slightly below resting voltage

Question 32

What is the refractory period

Answer 32

period in which the cell is incapable of repeating an action potential

absolute - cannot generate
relative - possible, greater stimulus

Question 33

Pacemaker cells

Answer 33

noncontractile cells that spontaneously depolarize in heart

Question 34

3 parts of action potential in pacemaker

Answer 34

1. Pacemaker potential: K+ channels closed, Na+ open. the interior becomes more positive
2. Depolarization: Ca2+ channels open (-40mV) contributing to rise of potential
3. Repolarization: K+ channels open, allowing efflux, and becomes more negative

Question 35

summarize a contractile cardiac action potential

Answer 35

1. depolarization opens Na+ channels (rise AP from -90mV to +30mV)
2. depolarization by Na+ leads to opening of Ca2+ channels (at +30mV Na+ channels close)
3. after 200ms, Ca2+ channels close and K+ channels open. RMP achieved

Question 36

myelin sheaths ____ conduction velocity and _____ energy efficiency

Answer 36

increase; improve