Membrane and Action Potential

Question 1

what is the action potential?

Answer 1

a rapid, all or none change in the membrane potential followed by a return to the resting membrane potential

Question 2

what type of channels are the basis for action potentials?

Answer 2

voltage dependent ion channels

Question 3

how is an action potential propagated?

Answer 3

with the same shape and size along the entire length of an axon

Question 4

where are action potentials initiated?

Answer 4

at the initial segment of the axon

Question 5

what is the action potential the basis for?

Answer 5

the signal carrying ability of nerve cells

Question 6

the patterns of conducted action potentials encode what?

Answer 6

the information conveyed by the nerve cells

Question 7

what are the nodes of ranvier?

Answer 7

they help propagate the action potential from the cell body to the axon terminal

Question 8

what is the purpose of the nernst equation?

Answer 8

it allows the electrical potential across the membrane at equilibrium to be predicted exactly and how sodium is kept outside and potassium ions kept inside

Question 9

what is the Goldman equation?

Answer 9

determined voltage concentration to keep cells on their respectful side of the cell, intracellular ions vs extracellular ions

Question 10

at the peak of the membrane potential, what ion runs the show and name corresponding voltage?

Answer 10

sodium at +58

Question 11

at hyperpolarization, which ion runs the show?

Answer 11

potassium at -90, but other ions play a factor in returning the membrane back to resting potential

Question 12

how many gates do sodium channels have?

Answer 12

2, M gate (middle) and H gate (cytosolic side)

Question 13

relate the M gate and H gate to the various states of the membrane potential

Answer 13

Resting state, sodium channels are closed, end gates closed and H gates are opened. During depolarization, M gate opens up to allow sodium influx. For repolarization, H gate closed first to prevent sodium influx. In the undershoot, both are closed. During resting state, H gate opened and M gate closed, easier to open when depolarization happens again.

Question 14

what is the effect of ischemia on the membrane potential?

Answer 14

In ischemic tissue, rate of recovery is longer because cells stay in the depolarized state. They were going through a systolic process, MI, happens recovery is halted and so less sodium channels participating in the next depolarization state and so erratic passages from atrium to ventricle, translated on the ECG.

Question 15

resistance is much higher in an axon with a smaller diameter, T/F?

Answer 15

T

Question 16

You need to change the membrane potential of neurons to carry information (like action potentials). Instead of pumping ions out of equilibrium and opening and closing ion-selective channels (which is difficult to understand) why don’t neurons just use ATP to pump positive ions in to depolarize and out to repolarize during an action potential?

pumps using ATP can not select between positive and negative ions

pumps using ATP are not fast enough to change the membrane potential in 1-2 milliseconds which is the time course of a typical action potential.

there would not be enough ATP available

pumps using ATP can not move significant amounts of ions

Answer 16

pumps using ATP are not fast enough to change the membrane potential in 1-2 milliseconds which is the time course of a typical action potential.

Question 17

one of the most potent poisons known, specifically blocks the Na+ channel

Answer 17

Tetrodotoxin (TTX)

Question 18

how does tetrodotoxin (TTX) work?

Answer 18

TTX binds to the extracellular side of the sodium channel

Question 19

this poison blocks K+ channels

Answer 19

Tetraethylammonium (TEA+)

Question 20

how does Tetraethylammonium (TEA+) work?

Answer 20

TEA+ enters the K+ channel from the cytoplasmic side and blocks the channel because TEA is unable to pass through it.

Question 21

what species of animals contain tetrodotoxin (TTX)?

Answer 21

puffer fish, also known as blowfish

Question 22

You decide to take your chances and have some of that amazing puffer fish you’ve heard so much about. Unfortunately, your sushi chef got his license from a questionable online university and he leaves in too much tetrodotoxin (TTX). The sensory neurons in your lips stop firing action potentials and your lips go numb because:

the TTX blocks potassium channels, hyperpolarizing the membrane

the TTX blocks sodium channels, preventing the membrane from hyperpolarizing

the TTX blocks sodium channels, preventing the membrane from depolarizing.

the TTX opens sodium channels, depolarizing the membrane

Answer 22

the TTX blocks sodium channels, preventing the membrane from depolarizing.

Question 23

what is the relationship between synaptobrevin and botulinum toxin?

Answer 23

Synaptobrevin can be eliminated or degraded by botulinum toxin, then the muscle cannot be contracted; very popular for wrinkling free treatment of the face like botox

Question 24

Eating home-canned vegetables or smoked fish is associated with the transmission of botulism. Clostridium botulinum synthesizes its neurotoxin, which is a specific protease affecting the presynaptic protein called synaptobrevin. An individual suffering from botulism with this specific protease would ________?

Be unable to open voltage-gated Ca2+ channels along the presynaptic membrane following an action potential

Have a massive discharge of synaptic vesicles even with low extracellular Ca2+

Be unable to utilize ATP for endocytosis

Result in diminished or absent end-plate potentials on the skeletal muscle membrane.

Answer 24

Result in diminished or absent end-plate potentials on the skeletal muscle membrane.

Question 25

how is the velocity of conduction determined?

Answer 25

by the electrical properties of the axon.

Question 26

a large diameter axon has faster or slower conduction velocity?

Answer 26

faster

Question 27

Since it takes much longer to generate an action potential at each node than it does for the action potential to be conducted between nodes, the action potential appears to jump from node to node, what is this called?

Answer 27

saltatory conduction

Question 28

what are receptor potentials?

Answer 28

changes in membrane potential that result from transduction of a sensory stimulus.

Question 29

what is receptor adaptation?

Answer 29

a mechanism for signaling the temporal features of a stimulus

Question 30

what defines the modality of the sensory pathway?

Answer 30

The specific type of energy that stimulates a response in the receptor cell

Question 31

what encodes stimulus intensity, frequency, and duration?

Answer 31

Timing, duration, and patterns of action potentials

Question 32

how is the action potential generated?

Answer 32

by the rapid opening and subsequent voltage inactivation of voltage-dependent Na+ channels and the delayed opening and closing of voltage-dependent K+ channels.

Question 33

what are ion channels?

Answer 33

integral membrane proteins that have ion-selective pores.

Question 34

what are the two states of an ion channel? how does this work for a voltage dependent channel?

Answer 34

high conductance (open) and zero conductance (closed). The channel oscillates randomly between the open and closed states.

For a voltage-dependent channel, the fraction of time that the channel spends in the open state is a function of the transmembrane potential difference.

Question 35

The action potential is propagated rather than merely being conducted, T/F, explain

Answer 35

The action potential is propagated rather than merely being conducted; it is regenerated as it moves along the axon. In this way an action potential remains the same size and shape as it is conducted.

Question 36

what are the major factors determining the absolute and relative refractory periods that limit the maximum firing rate of action potentials.

Answer 36

Voltage inactivation of Na+ channels and membrane hyperpolarization due to slow closure of K+ channels