Lecture 26- Membrane Potential

Question 1

Voltage

Answer 1

Measure of the amount of difference in electrical charge between two points called the potential difference

Question 2

Current

Answer 2

Flow of electrical charge from point to point

Dependent on voltage and resistance

Question 3

Types of ion channels

Answer 3

Leakage (non gated) channels - always open

Chemically gated (ligand-gated) channels- open when correct chemical binds to channel

Mechanically-gated channels- open when membrane receptor is physically bent or stretched

Voltage gated channels- open in response to a change in membrane potential

Question 4

When ion channels are open…

Answer 4

Ions diffuse through channels to other side along their electrochemical gradients

Question 5

When ions channels close…

Answer 5

Ion pumps use ATP to put the ions back where they were before the channels open

Question 6

Resting membrane potential

Answer 6

Difference in electrical charge across cell membrane (approx. -70mV)

This point the cell is polarized

Only exists across the membrane

Question 7

What causes resting membrane potential?

Answer 7

Differences in the ion concentration of intracellular and extracellular fluids

Differential membrane permeability tot nose ions because of different channels and pumps

Question 8

Resting membrane potential sodium and potassium

Answer 8

Inside of cell has lower concentration of sodium ions and higher potassium ions

More leakage channels for potassium than sodium, easier for potassium to leak out than for sodium to leak in

Because of potassium leaking out along membrane, more cations on outside and more anions on inside

ATP pumps move sodium to outside and potassium to inside , leakage moves some potassium back to outside, ends up slightly more positive than outside

Question 9

Changing membrane potential

Answer 9

Neurons use changes in membrane potential as communication signals and can be brought on by changes in membrane permeability to any ion/ ion concentrations on the two sides of the membrane.

Question 10

What can changes in membrane potential produce?

Answer 10

Grade potentials (short distance)

Action potentials (long distance)

Question 11

Depolarization

Answer 11

Inside of membrane becomes less negative

Increase probability of nerve impulse

Question 12

Hyperpolarization

Answer 12

Inside of membrane becomes more negatively charged

Decrease probability of nerve impulses

Question 13

Graded potentials

Answer 13

Short lived changes in membrane potentials
Can be depolarized or hyperpolarized

“Graded” because the magnitude of stimulus corresponds to magnitude of response

Question 14

Receptor potentials

Answer 14

Graded potentials occurring on receptors of sensory neurons

Question 15

postsynaptic potentials

Answer 15

Graded potentials occurring in response to neurotransmitter released from another neuron

Question 16

Action potentials

Answer 16

all-or-none phenomena: they either happen completely, in the case of a threshold stimulus, or not at all, in the event of a subthreshold stimulus.

Higher-stimulus intensity is from the increased frequency of action potentials

One size

Question 17

Resting state

Answer 17

All voltage-gated Na+ and K+ channels are closed.
The axon plasma membrane is at resting membrane potential:
small buildup of negative charges along inside surface of membrane and an equal buildup of positive charges along outside surface of membrane.

Question 18

Depolarizing phase

Answer 18

When membrane potential of axon reaches threshold, the Na+ channel activation gates open.
As Na+ ions move through these channels into the neuron, a buildup of positive charges forms along inside surface of membrane and the membrane becomes depolarized.

Question 19

Repolarizing phase

Answer 19

Na+ channel inactivation gates close and K+ channels open.

The membrane starts to become repolarized as some K+ ions leave the neuron and a few negative charges begin to build up along the inside surface of the membrane.

Question 20

Repolarization continues to hyperpolarization

Answer 20

K+ outflow continues.
As more K+ ions leave the neuron, more negative charges build up along inside surface of membrane.
Na+ channel activation gates close and inactivation gates open. Return to resting state when K+ gates close.