Motor unit and skeletal muscle contraction

Question 1

When is the only time a skeletal muscle will contract?

Answer 1

When it is stimulated by an electrical impulse by an electrical impulse from the CNS that exceeds the all or none threshold

Question 2

What are motor neurones?

Answer 2

Specialised cells that rapidly transmit nerve impulses to a group of muscle fibres

Question 3

Describe the features of a motor neurone

Answer 3

A cell body located in the brain or spinal cord with an extending axon that connects motor end plates to a group of muscle fibres

Question 4

What does the motor unit consist of?

Answer 4

The motor neurone and its corresponding muscle fibres

Question 5

What is resting potential?

Answer 5

The electrical difference between the inside of the axon (negative charge) and its surroundings (positive)

Question 6

How is resting potential affected by an activated nerve?

Answer 6

A sudden change in voltage as sodium ions diffuse into the axon which triggers a wave of action potential that travels from the cell body down the axon to the synapse

Question 7

What is action potential?

Answer 7

A positive electrical charge inside the nerve and muscle cells that conduct the nerve impulse down the neurone to the muscle fibre

Question 8

What does the electromechanical process of sending a nerve impulse to the muscle fibres rely on?

Answer 8

A nerve’s action potential to conduct the nerve impulse as a wave of electrical charge through the axon to the nerve plates

Question 9

What is a neurotransmitter?

Answer 9

A chemical produced and secreted by a neurone which transmits the nerve impulse across the synaptic cleft to the muscle fibre

Question 10

What chemical is produced by the neurotransmitter?

Answer 10

Acetylcholine

Question 11

What is the all or none law?

Answer 11

Complete or no muscular contraction depending on if the stimuli is above the threshold

Question 12

What is the neuromuscular junction?

Answer 12

Where the axon’s motor end plates meet the muscle fibre

Question 13

What is the synaptic cleft?

Answer 13

The small gap between the motor end plates and muscle fibre

Question 14

What is the function of acetylcholine?

Answer 14

It is secreted into the synaptic cleft to aid the creation of muscle action potential if the electrical charge is above a threshold

Question 15

Nerve impulse initiated in the (1) > impulse travels (2) by (3) to the synaptic cleft > (4) is secreted > muscle fibres contract if (5)

Answer 15

1 - motor neurone cell body 
2 - down the axon 
3 - action potential 
4 - acetylcholine 
5 - if the charge is above a threshold