Nerve Impulse

Question 1

How are nerve impulse generated

Answer 1

Changes in concentrations of ions inside and outside nerve cell causing a potential difference (PD), called action potential

Trasmite an electrical signal between nerve cells

Question 2

How are action potentials reached

Answer 2

If threshold potential not reached, nothing happens

A new action potential cannot be generated in same section of membrane for about 5milliseconds. Makes sur impulse travels in 1 direction along nerve fibres

Question 3

What is depolarisation

Answer 3

Refers to sudden change in membrane potential from relatively negative to positive internal charge

Question 4

Process of depolarisation

Answer 4

During it:

• Voltage gated sodium ion channels open due to an electrical stimulus
• As Na+ rushes back into cell, the Na+ diffuse into cell raising the charge from neg to pov

If threshold potential not reached, nothing happens

Question 5

Process of repolarisation

Answer 5

Once cell depolarised, voltage gated sodium ion channels close

Repol is when:

• Raised positive charge inside cell causes potassium channels to open. K+ ions move down their electrochemical gradient, diffusing out of cell
• As K+ diffuses out of cell, membrane potential falls and starts to approach resting potential

K+ gates close

Question 6

Recovery

Answer 6

Resting potential equilibrium restored

K+ moves back into cell through non-voltage gated channels

Repol typically overshoots resting membrane potential, making membrane potential more negative. Known as hyper polarisation

Question 7

Saltatory Condution

Answer 7

Only region of myelinated nerve fibre that can depolarise at node of Ranvier where there is no myelin. Means nerve impulse can travel much longer distance

Can also travel faster than without myelin and impulse ‘jumps’ from one node to next