10) Action Potentail

Question 1

Excitability and excitable tissue

Answer 1

The property of cells to respond rapidly to the action of stimulants

Nerve
Muscle
Glands

Question 2

Action potential definition and function

Answer 2

The rapid change in electrical potential that occurs between the inside and outside of then cell

Is called nerve impulse

The function is to carry information along nerve fibres
Cause contraction of muscle fibres
Stimulate secretion by glands

Question 3

Characteristics of action potential

Answer 3

Ap is generated when the membrane potentials rises above the threshold

The sign of the membrane changes during ap

All or nothing

Question 4

Experiment with Cole and Curtis

Answer 4

When the membrane is excited it drops 40 fold

The resistance of the cytoplasm and extracellular fluid doesn’t change

Permeability of membrane increases

Question 5

Hodgkin and Huxley

Answer 5

Investigation of the dependence of then membrane permeability to sodium and potassium ion on voltage and time

Development of mathematical model of the Ap

Question 6

Changes of conductivity during excitation

Answer 6

At the start the conductivity for sodium ions rises rapidly

A skirt growth for the conductivity or potassium ions takes place

Question 7

Changes of ion flux

Answer 7

The action potential is generated by sodium and potassium in opposite directions

Ap is generated due to the different development of these currents over time

Question 8

Initiation of action potential

Answer 8

The sodium ions enter the cell driven by the electrochemical gradient

The value of the membrane potential decreases becomes less negative

Question 9

Threshold potential

Answer 9

If the membrane potential reaches a specific critical value then voltage gated sodium channels open

The threshold is the membrane potential which opens the voltage gated channels

Question 10

Depolarisation phase

Answer 10

This is a process of positive feedback

This causes the voltage gated sodium ions channel to open. This causes more sodium ions to enter the cell and the inside of the cell becomes more positive and increases the membrane potential

Question 11

Operation of the sodium channels

Answer 11

M gate is the activation gate and it opens when the potential exceeds the threshold

h gate closes 1-3 seconds after the m is opened

Question 12

Peak of action potential

Answer 12

Is close to but lower than the equilibrium potential for the sodium ions

Question 13

Repolarisation

Answer 13

The sodium channel closes and then potassium channel opens. The membrane potential reverts back to the resting potential

Question 14

Hyper polarisation

Answer 14

The membrane potential reaches the rating potential by the potassium channel is slow to close

This causes more potassium to enter the cell and cause undershoot

Question 15

Refractory period

Answer 15

Absolute
This is when a new action potential can’t be gee rated whatever the strength of the stimulus

Relative
This is when it can be generated but the threshold is higher than usual

Question 16

Phases of action potential

Answer 16

Initiation of the action potential

Depolarisation

Peak

Repolarisation

Hyperpolarisation

Question 17

All or nothing

Answer 17

When the membrane depolarisation by the stimulus and it exceeds the threshold

Question 18

Function of the sodium potassium ion pump

Answer 18

The sodium potassium ion pump has no effect on the depolarisation and repolarisation phases

Cells can generate tens of thousands of action potentials with the pump

Question 19

Shape and amplitude of the action potential

Answer 19

The action potential generated is almost identical

The impulses propagating down the nerve fibre have identical shape and peak values

Question 20

Coding of stimulus strength and duration

Answer 20

A strong stimulus imitates the next impulse earlier during the refractory period than a weak stimulus

The burst lengths carries information about the duration of the stimulus