Nerve Impulse Conduction

Question 1

Describe resting potential

Answer 1

~ Occurs in axon membrane
- Charge difference generated with Na and K ions using energy from ATP —> 3 Na+ ions pumped out, 2 K+ ions pumped in by sodium/potassium pump
- K+ ions diffuse out of open K channel, created negative charge inside membrane of ~ -70mV
- Neurone membrane is polarised
- Voltage-gated channels are closed

Question 2

Describe action potential

Answer 2

Depolarisation
1- Stimulus energy triggers voltage-gated sodium channels to open
2- Influx of Na ions via diffusion, increases charge from -70 to -55mV, triggers more Na channels to open
3- Membrane is depolarised as there is no longer a charge difference
Repolarisation
1- when ~ +40mV is reached , Na channels close and voltage gates K channels open
2- K ions can leave —> overshoot as too many leave = hyperpolarisation as the membrane reaches below -70mV
3- Na/K pumps reactivate and axon returns to resting potential

Question 3

Define nerve impulse

Answer 3

Self-propagating wave of electrical activity which travels along the axon membrane

Question 4

What is saltatory conduction and how does it affect transmission?

Answer 4

• Ionic exchanges at nodes of Ranvier —> sodium ions diffuse across the neurons from one node to another; appears to ‘jump’
• Speeds up transmission, up to 120ms^-1