Neurones

Question 1

Explain how a resting potential is maintained.

Answer 1

1. polarised membrane, outside positive charge and inside negative charge because of different amounts of ions
2. Na+/K+ ATPase channels, transporting 3Na+ outside of the cell and 2K+ inside the axon.
3. membrane is permeable to sodium and potassium ions through channels in the membrane
4. resting potential is around -70mV

Question 2

Describe and explain an action potential.

Answer 2

1. a stimulus excites a membrane, making voltage gated Na+ channels open and Na+ move down the gradient into the axon
2. membrane is depolarised, threshold value has been surpassed and more Na+ move into the axon.
3. at a potential difference of around +30mV, voltage gated Na+ channels close and voltage gated K+ channels open, membrane is repolarised.
4. the K+ channels are too slow to close so go beyond the resting potential, hyperpolaristion of the membrane, refractory period
5. resting potential is reached again, -70mV.

Question 3

What is the purpose of a refractory period?

Answer 3

A refractory period acts as a time delay between one action potential and the next, making sure they don’t overlap. Also making sure that there is a limit to the frequency at which nerve impulses can be transmitted and that action potentials are undirectional.

Question 4

Describe the all or nothing principle.

Answer 4

Once a threshold value has been reached, an action potential will always be the same size. The frequency of the action potential tells the brain the strength of the stimulus.

Question 5

Describe the effect of myelination on a response.

Answer 5

A myelin sheath is an electrical insulator made up of schwann cells and broken up by nodes of ranvier, where Na+ channels are concentrated. This allows saltatory conduction, which is a really quick response as action potentials can jump between nodes of ranvier.

Question 6

How does axon diameter impact the speed of conduction?

Answer 6

Bigger diameters conduct a signal much more quickly because there’s less resistance to the flow of ions through the cytoplasm, depolarisation can occur quicker.

Question 7

How does temperature impact the speed of conduction?

Answer 7

Speed of conduction increases when temperature increases because ions have more kinetic energy to diffuse faster.