Membrane potential

Question 1

What are the 2 types of membrane potentials?

Answer 1

Resting and Action potentials

Question 2

Resting membrane potential

Answer 2

Both voltage gated Na+ and K+ channels are closed
Ranges from -40 ~ -90 mv

Question 3

Why is the voltage always negative?

Answer 3

Because more positive charge is moving out of the cell than going in

Question 4

What part of the body has -40 mV?

Answer 4

heart

Question 5

What part of the body has -90 mV?

Answer 5

Neurons and muscles

Question 6

What are the major determinants of RMP?

Answer 6

1. Na+, K+ ATPase pump
2. Ions moving towards a dynamic equilibrium
3. Differential permeability of the membrane

Question 7

Resting membrane potential depends on what?

Answer 7

The equilibrium of K+

Question 8

Equilibrium Potential

Answer 8

When the uneven K+ charge (more inside) produces a voltage across the membrane

Question 9

Resting membrane is more permeable to ______ than to ______

Answer 9

1. K+
2. Na+ ions

Question 10

Why is resting membrane more permeable to K+ than to Na+

Answer 10

There are more K+ leak channels –> K+ reach equilibrium and equilibrium potential easier

Question 11

What does the equilibrium potential for the more permeant K+ determine?

Answer 11

RMP than the EP of Na in more neurons

Question 12

What does disturbance in Na and K levels lead to?

Answer 12

Disturbances in the membrane potential (nerves and muscles)

Question 13

Nernst Equation

Answer 13

Ex= RT / zF In [Xoutside] / [Xinside]

Ex= -60 mV / z log [Xinside] / [Xoutside]

Question 14

Action Potential

Answer 14

A regenerative electrical signal that begins at the axons initial segment resulting from competing EPSP and IPSP and spreading down the length of the axon without decreasing magnitude

Question 15

What happens if the cell doesn’t reach threshold potential?

Answer 15

Action potential won’t occur

Question 16

Depolarization

Answer 16

Cells will bring in + charge –> in the plasma membrane it’s +, attracting + ions from ECF –> when the cell goes from -70 to -50 the voltage- gated sodium channels will open –> if enough channels are open then the threshold is surpassed -> action potential initiated

Question 17

Repolarization

Answer 17

The membrane potential goes toward the resting potential
Na+ channels self-inactivated, K+ channels are open
Membrane potential move temporarily below its resting level to a hyperpolarized state

Question 18

Postsynaptic potential

Answer 18

RMP in muscles and neurons changed by synaptic signals from presynaptic cells

Question 19

Synaptic Signals

Answer 19

Electrical, mechanical and chemical

Question 20

What will synaptic signals change?

Answer 20

The permeability of the membrane sodium

Question 21

For post synaptic potential to generate an action potential, what does it have to do?

Answer 21

It has to reach a threshold potential

Question 22

Why is the action potential essential?

Answer 22

To transmit information between neurons

Question 23

EPSP

Answer 23

Excitatory postsynaptic potential
It’s “excitatory” because such a synaptic transmission increases the chances for an AP at the initial segment of the postsynaptic cell’s axon

Question 24

How is a membrane depolarized?

Answer 24

When an presynaptic signal changes the postsynaptic membrane potential to a more positive value
Na+ channels open, this allows Na+ ions to diffuse into the neurons moving the membrane potential towards the more positive sodium equilibrium potential

Question 25

When is a membrane hyperpolarized?

Answer 25

When an EPSP changes the postsynaptic membrane potential to a more negative value

Question 26

IPSP

Answer 26

Inhibitory Postsynaptic potential
It’s “inhibitory” because usch a synaptic transmission decreases the chances for an AP at the initial segment of the postsynaptic cell’s axon

Question 27

______ drives the membrane potential toward the threshold for an action potential

Answer 27

EPSP

Question 28

_____ drives the membrane potential away from the threshold for an action potential

Answer 28

IPSP

Question 29

EPSP and IPSP characteristics

Answer 29

Transient
Magnitude of PSP is small and decreases with distance from the originating synapse
Greatest at the synapse

Question 30

Why are PSP’s transient?

Answer 30

The chemical transmitted is quickly removed from the synapse

Question 31

Hyperpolization

Answer 31

Due to the flow of K+ ions out through the voltage gated K+ channels, in addition to the flow out through K+ leak channels, and the membrane potential is closer to the K+ equilibrium potential

Question 32

AP time

Answer 32

Takes about 2-3 msec in neurons, longer in muscle cells

Question 33

AP path

Answer 33

Generated in the axon’s initial segment –> moves down the unmyelinated axon as positive charges passively migrate to the immediately adjacent membrane to trigger an action potential there

Question 34

AP characteristics

Answer 34

All or none
Always the same size
Either not triggered at all or triggered completely

Question 35

Speed of AP

Answer 35

Varies and is affected by internal diameter and myelination state of the axon
Small: unmyelinated, slow (0.5 m/s)
Large: heavily myelinated, fast (> 90 m/sec)

Question 36

Where can AP and ion exchange occur?

Answer 36

Only in the nodes of Ranvier and jumps from one node to the next (Saltatory conduction)

Question 37

What does an AP cause?

Answer 37

At the neuromuscular junction, it causes a muscle fiber to twitch (contract)

Question 38

Local Anesthetics (lidocaine)

Answer 38

Blocks voltage gated Na channels –>
Prevents permeability –>
Prevents AP –>
Somatosensory info not transmitted

Question 39

Clinical Significance: Local Anesthetics

Answer 39

Tetrodoxin
Lidocaine