Electric potential of cells

Question 1

What is the resting membrane potential of a cell?

Answer 1

-70 mV

Question 2

What does the Goldman-Hodgkin-Katz (GHK) equation describe?

Answer 2

The diffusion potential when a membrane is permeable to several ions.

Question 3

What is the GHK equation?

Answer 3

Add pic

Question 4

The impact of each ion on membrane potential is ______ proportional to the membrane permeability for that ion.

Answer 4

Directly

Question 5

Why is the Na/K ATPase considered to be electrogenic?

Answer 5

Each ATP hydrolyzed pumps 3 Na out of the cell and 2 K in. i.e. an additional + charge on the outside creating an internally negative membrane potential.

Question 6

What ion is the primary contributor to resting membrane potential and how?

Answer 6

K+ due to passive diffusional efflux of K+ due to higher permeability and electric potential

Question 7

What effect does adding + charge external cell have on the polarization?

Answer 7

None! The overall charge and electrostatic forces are so strong, the cell would not thus be considered hyperpolarized. Adding a neutral solution containing K+ to reduce the concentration gradient (and thus reduce efflux of K+).

Question 8

What are receptor or generator potentials?

Answer 8

Small depolarizations originated by specialized structures in response to specific stimuli (e.g. heat, pressure, etc.)

Question 9

What happens during voltage-gated sodium leak channels?

Answer 9

Na channels open and sodium floods into the cell. This brings K+ even further from its equilibrium potential, increasing the K+ driving force and creating an outward current though the leak K+ channels that tends to repolarize the cell.

Question 10

What happens when the K+ driving force is increased due to sodium influx?

Answer 10

Na+ inward current exceeds K+, the cell is more depolarized activating additional Na channels to open…this is how you reach threshold!

Question 11

What happens when threshold is reached?

Answer 11

A ton of sodium channels open (gNa), this drives towards ENa, and the driving potential for sodium (INa) decreases.

Question 12

When sodium channels inactivate after threshold, there is a delay in…

Answer 12

Voltage-gated K+ channel is activated. This increase in K permeability moves K+ out, generating an outward K current (k), ultimately repolarizing the membrane.

Question 13

As it approaches Ek, the cell is momentarily _______.

Answer 13

Hyperpolarized

Question 14

The ________ of the action potential in any part of the axon acts as an electrical stimulus for the initiation of the action potential.

Answer 14

leading edge

Question 15

_______ spreads beyond the local depolarization to initiate APs/depolarizations in other cells.

Answer 15

Current

Question 16

Do large or small diameter axons conduct faster?

Answer 16

Large diameter

Question 17

Each muscle fiber is controlled by a branch from _____ motor neuron(s).

Answer 17

One!!

Question 18

What is a motor unit?

Answer 18

A motor neuron together with all of the individual muscle fibers it contacts.

Question 19

A single muscle is composed of _____ motor units. How does this affect force of contraction?

Answer 19

Muscle fibers from different motor units. A more forceful contraction will activate more motor units of a single muscle.

Question 20

When a motor neuron is activated, it generates and propagates an action potential, ___ the muscle fibers in that motor unit contract.

Answer 20

ALL

Question 21

What happens when the action potential reaches the terminal of the muscle fiber axon?

Answer 21

Depolarization causes voltage-gated Ca2+ channels and Ca2+ enters the cytosol.

Question 22

What does the influx of calcium in the cytosol do?

Answer 22

Cytosolic calcium promotes the fusion of vesicles containing acetylcholine (ACh) with the neuronal plasma membrane. Ach release in the cleft binds its receptor at the motor-end plate.

Question 23

What happens when ACh binds at the motor-end plate?

Answer 23

Na and K-permeable channels open resulting in a larger Na influx than K influx…inward current depolarizes the motor end-plate producing local currents that bring the adjacent muscle PM to threshold and the signal is propagated.

Question 24

ntraction called?What is a single muscle co

Answer 24

Twitch

Question 25

End-plate potential/depolarization reaches into the interior of the muscle via numerous ______ in the form of transverse _________.

Answer 25

Surface invaginations, t-tubules.

Question 26

What is Ek?

Answer 26

-96 mV

Question 27

Which way do K+ leak?

Answer 27

Out of the cell (desire to reach Ek of -96).

Question 28

If the Na/K pump stopped working, what would happen?

Answer 28

The cell would slowly depolarize to reach the ENa (+66mV).

Question 29

As membrane potential approaches ENa, what happens?

Answer 29

Voltage-gated sodium channels close and voltage-gated potassium channels open (“delayed channels”). They close upon repolarization and only leak channels are open -> resting membrane potential achieved.

Question 30

Conductance is ______ proportional to the number of open channels.

Answer 30

Directly