Skeletal Muscle Contraction

Question 1

Definition of motor neuron

Answer 1

A nerve cell which conducts a nerve impulse to a group of muscle fibres

Question 2

Definition of motor unit

Answer 2

A motor neuron and the muscle fibres stimulated by its axon

Question 3

Definition of action potential

Answer 3

Positive electrical charge inside the nerve and muscle cells which conducts the nerve impulse down the neuron and into its muscle fibre

Question 4

Definition of neurotransmitter

Answer 4

A chemical (acetylcholine) produced and secreted by a neuron which transmits the nerve impulse across the synaptic cleft to the muscle fibre

Question 5

Definition of all-or-none law

Answer 5

Depending on whether the stimulus is above a threshold, all muscle fibres will give a complete contraction or none at all

Question 6

What is the role of a motor unit?

Answer 6

1. Never impulse initiated from the motor neuron cell body
2. Nerve impulse is conducted down the axon of the motor neuron by a nerve action potential to the synaptic cleft
3. Neurotransmitter acetylcholine is secreted into the synaptic cleft to conduct the nerve impulse across the gap
4. If the electrical charge is above a threshold, the muscle fibre will contract
5. This happens in an ‘all-or-none’ fashion