Mortor Units

Question 1

What structures does a motor unit consist of?

Answer 1

-motor neurone

• muscle fibre

Question 2

Describe how a nerve impulse travels from a motor unit to a muscle fibre?

Answer 2

1. motor neurone receives a nerve impulse from the CNS and sends it down the axon
2. a positive charge (known as the action potential) transmits the impulse down the axon
3. the nerve impulse then reaches the neuromuscular junction
4. the nerve impulse then has to cross the synaptic cleft ( which is a gap between the axon and muscle fibre)
5. so then a neurotransmitter is then secreted into the synaptic cleft so that the nerve impulse can cross into the muscle fibre
6. so then if the nerve impulse is above the set threshold then all muscle fibres will contract

if the nerve impulse is below the set threshold then no muscle fibre will contract.

Question 3

What is the all or none law?

Answer 3

if a nerve impulse is above a set threshold then all muscle fibres will contract