The Motor Unit

Question 1

What is the 1st phase of the motor unit?

Answer 1

The nerve impulse is initiated in the motor neurone cell body

Question 2

What is the 2nd phase in the motor unit?

Answer 2

Nerve impulse is conducted down the axon of the motor neurone by a nerve action potential to the synaptic cleft

Question 3

What is the 3rd phase of the motor unit?

Answer 3

A neurotransmitter called acetylcholine (Ach) is secreted into the synaptic cleft to conduct the impulse across the gap

Question 4

What is the 4th phase of the motor unit?

Answer 4

If the electrical charge is above a threshold,the muscle fibres will contract - this happens in an all or none fashion

Question 5

What is the all or none law?

Answer 5

When a motor unit receives a stimulus it creates an action potential, the action potential will reach a threshold charge and all the muscle fibres will contract at once. If the action potential doesn’t reach the threshold none of the fibres will contract.

Question 6

What is action potential?

Answer 6

A positive electrical charge inside the nerve+muscle cells that conducts the nerve impulse down the neuron and into the muscle fibres

Question 7

What is the function/purpose of the motor unit?

Answer 7

To carry nerve impulses from the brain+spinal cord to the muscle fibres - initiating muscle contraction