Neurons - Lecture 2 Action Potential

Question 1

The term used when the potential inside the cell moves closer to equilibrium potential of Na+ and away from the equilibrium potential of K+.
(If it becomes less negative)

Answer 1

DEPOLARISATION

Question 2

A brief fluctuation in membrane potential caused by a TRANSIENT opening of voltage-gated ion channels, which spreads like a wave, along axon.

Answer 2

ACTION POTENTIAL

Question 3

Action potential occurs after the membrane potential reaches certain voltage called the _______

Answer 3

THRESHOLD

Question 4

The threshold is about

Answer 4

• 55mV

Question 5

What are the 3 stages of action potential in neurons?

Answer 5

1. FAST DEPOLARISATION to about +30mV or overshoot after the membrane potential reaches threshold
2. REPOLARISATION
3. AFTER-HYPERPOLARISATION (AHP)

Question 6

The absolute refractory period

Answer 6

Stages 1 and 2

Question 7

Relative refractory period

Answer 7

Stage 3

Question 8

Why during the action potential the membrane potential (MP) transiently positive?

Answer 8

When MP reaches the threshold, there is a sudden activation (opening) of voltage -gated Na+ channels . At this moment there are more sodium than potassium by 20:1 therefore MP shifts towards the equilibrium potential of sodium.

Question 9

Why is the action potential of the membrane transiently positive?

Answer 9

Because, opening of voltage gated Na+ channels are only short lasting, as the channels quickly inactivate. Also, this is followed by a transient opening voltage gated K+ channels, leading to repolarisation and AHP shifts towards the equilibrium potential of potassium.

Question 10

True or false. When the voltage threshold is reached, sodium channels open and Na channels move into the dell along the concentration gradient.

Answer 10

False.. It should be .. Both the concentration gradient and electrical gradient.

Question 11

Influx potential of Na+ stops when

Answer 11

1. Inside potential is positive and attracts less Na+ ions less.
2. Na+ channels inactivate

Question 12

How can action potentials be generated?

Answer 12

Current follows the path of least resistance.

The two main paths are , outside from positive to negative and across the membrane only this can change the RMP.

Question 13

If current by an outside source flows through cell membrane from outside to inside ( the MP becomes more negative.

Answer 13

HYPERPOLARISATION

Question 14

If current flows from inside to outside if tve cell membrane (the MP becomes less negative )

Answer 14

DEPOLARISATION

Question 15

The term used to describe when the potential inside the cell moves closer to equilibrium potential of potassium and away from the equilibrium potential of sodium. ( if it becomes more potential )

Answer 15

HYPERPOLARISATION

Question 16

How ate APs generated physiologically in CNS in neurons?

Answer 16

In CNS neurons, APs are first generated in the axon initial or initial segment near the axon hillock which had the lowest threshold. Depolarisation to threshold is evoked by excitatory EPSPs which spreads mainly passively from dendrites.