Exam 2 Lecture - Membrane Potential

Question 1

What is the resting membrane potential (RMP)?

Answer 1

-65 mV

Question 2

What does the RMP represent?

Answer 2

reflects the uneven distribution of ions across the plasma membrane by the electrochemical gradients

Question 3

What are the electrochemical gradients created by?

Answer 3

• the sodium/potassium pump
• K and Cl: non-gated or leak channels
• Na: a few nongated or some other channels for Na
• intracellular anions that are too large to exit the cell

Question 4

What is sensory receptor signal transduction?

Answer 4

conversion of the sensory stimulus

Question 5

What does the sensory stimulus open?

Answer 5

• Mechano-gated Na channels
• Heat-gated Na channels
• Cold-gated Na channels

Question 6

What does opening stimulus specific Na channels lead to?

Answer 6

depolarizing of the receptor membrane

Question 7

What is a potential produced by sensory transduction?

Answer 7

a depolarizing event resulting from inward current flow

Question 8

What is depolarizing potential of receptor membrane referred to as?

Answer 8

receptor potential

Question 9

What does receptor potential lead to?

Answer 9

action potential

Question 10

When is an action potential created?

Answer 10

When the receptor potential goes over the threshold potential

Question 11

What is the threshold potential?

Answer 11

(-55mV)

Question 12

What does the generation of action potential require?

Answer 12

• Voltage gated Na channels

- Voltage gated K channels

Question 13

What is depolarization?

Answer 13

the decrease in the potential difference across the plasma membrane, going more positive, approaching 0mV

Question 14

What is overshoot?

Answer 14

When the difference goes over 0mV

Question 15

What is repolarization?

Answer 15

the return of membrane potential to its normal RMP

Question 16

What is hyperpolarization?

Answer 16

the increase in the potential difference across the membrane, going more negative, away from the RMP

Question 17

Explain the importance of the threshold membrane potential.

Answer 17

an action potential will only be generated if the receptor potential goes over -55 mV

Question 18

When will Na cross the membrane?

Answer 18

only at the activated state (-55 mV), not during resting or inactivated

Question 19

When do the voltage gated channels open?

Answer 19

Once the receptor potential reaches threshold

Question 20

What direction does Na flow when its voltage gated channel is open?

Answer 20

in

Question 21

What direction does K flow when its voltage gated channel is open?

Answer 21

out

Question 22

What ion channel is involved with generating depolarization?

Answer 22

opening stimulus of specific Na channels lead to depolarization

Question 23

What ion channels are involved with generating overshoot and repolarization?

Answer 23

Voltage gated Na and K channels

Question 24

What ion channels are involved with generating hyperpolarization?

Answer 24

K tries to reach equilibrium potential of -80 mV but cannot because the channel closes before it can do so

Question 25

What is the absolute refractory period?

Answer 25

period during which voltage-gated Na channels are in an inactivated state and action potential cannot be generated

Question 26

What is the relative refractory period?

Answer 26

a stronger than normal stimulus is needed to elicit action potentials (need more stimulus to bring hyperpolarized region up to threshold)

Question 27

How do local anesthetics and tetrodotoxin block sensory signals from reaching their destinations?

Answer 27

tetrodotoxin prevents the generation of action potentials by blocking voltage gated Na channels

Question 28

How does hyperkalemia affect resting membrane potential?

Answer 28

makes it easier to generate an action potential

resting potential is more positive

Question 29

How does hypokalemia affect resting membrane potential?

Answer 29

makes it more difficult to generate an action potential’

resting potential is more negative

Question 30

How is the action potential spread in a nonmyelinated axon?

Answer 30

the action potential triggers a local depolarizing electrical current that spreads along the axon, activating adjacent voltage-gated Na and K channels and generates an AP

Question 31

What is the propagation of a non-myelinated action potential considered?

Answer 31

nondecremental

Question 32

How does the action potential spread in a myelinated axon?

Answer 32

The action potential generates local currents that are strong enough to generate a new action potential
the voltage gated channels are at the node of ranvier
the myelination increases the conduction speed between each node

Question 33

What does the propagation of a myelinated axon involve?

Answer 33

the generation of a new AP at each node of Ranvier resulting in saltatory conduction (ap jumps from node to node)

Question 34

What two factors influence the conduction velocity of action potentials?

Answer 34

Size of axons and myelination (the larger the axon, the longer the internode, the faster the conduction speed)

Question 35

Why does demyelination affect the conduction of action potentials?

Answer 35

loss of myelin decreases the signal transmission efficiency and action potentials cannot reach the node of Ranvier which is where the Na and K channels are located at