Nerve impulses

Question 1

Explain stages of action potential including repolarisation, hyperpolarisation and resting potential

Answer 1

R-potential difference +30mV so Na+ channels closed but K+ channels open so K+ diffuse out of neurone down K+ gradient as membrane is more permeable to K+ but loss of + charge means inside of neurone more -

H-K+ channels too slow to close so too many K+ diffuse out (leaky) potential difference more - than resting potential Na+ channels still closed membrane requires greater increase to reach threshold potential but cell membrane can’t be excited again until resting state reached again=refractory period.

RP-Na/K pump returns membrane to -70mV until another stimulus

Question 2

If ion channels can’t open during refractory period, what does this mean?

Answer 2

• action potentials uni-directional
• action potentials discrete and don’t overlap
• limit on frequency of nerve impulses being transmitted

Question 3

Explain the all or nothing principle

Answer 3

threshold potential not reached=action potential not fired

action potentials always +30mV where larger stimulus results in higher frequency of action potentials

Question 4

What factors affect transmission of impulse?

Answer 4

Myelination-action potentials/depolarisation only occurs in nodes of ranvier so neurone’s cytoplasm conducts enough electrical charge to depolarise next node so impulse can jump by ‘saltatory conduction’ increasing speed of conduction.

Increase diameter of axon-less resistance to flow of ions in cytoplasm

Higher body temperature-rate of diffusion of ions faster BUT past 40 degrees=proteins denatured so speed decreases