Motor units

Question 1

What does a motor unit consist of

Answer 1

Motor neuron and number of muscle fibres

Question 2

What are motor neurons

Answer 2

Specialised cells which transmit nerve impulses to a group of muscle fibres

Question 3

Where does the electrical impulse travel

Answer 3

Down the extending axon which connect to motor end plates

Question 4

What is the name for where the axon motor end plates meet the muscle fibre

Answer 4

Neuromuscular junction

Question 5

What does action potential refer to

Answer 5

A positive electrical charge inside the motor unit

Question 6

What occurs when the motor unit receives a stimulus

Answer 6

Creates action potential that reaches or goes above threshold charge. All or none - all muscle fibres contract or none do

Question 7

What is the name for the gap between the motor end plate and muscle fibre

Answer 7

Synaptic cleft

Question 8

What is the name of the neurotransmitter that transmits the action potential across the synaptic cleft

Answer 8

Acetylcholine (Ach)

Question 9

How does the neurotransmitter Ach work

Answer 9

If enough is secreted and electrical charge is above threshold, muscle action potential is created which causes wave of contraction down the muscle fibre

Question 10

What is the all or none law

Answer 10

When stimulated all fibres within a motor unit will contract completely or none of them will

Question 11

What is an overview of the process involving motor units and contraction in 9 key stages

Answer 11

1. CNS sends electrical impulse to motor neuron
2. Neuron transmits nerve impulse
3. Movement of sodium ions into the axon causes depolarisation
4. Action potential conducts nerve impulse as a wave of electrical charge down the axon to motor end plates
5. Point where axon and motor end plates meet is neuromuscular junction
6. NT Ach carries action potential across synaptic cleft
7. If enough Ach is secreted and electrical charge is above threshold, muscle action potential is created
8. Creates a wave of contraction down the muscle fibre
9. Muscles contract with maximum force by all or none law