Motor System

Question 1

Where is the voluntary neurons to the muscles of the neck, trunk and limbs have their somas located in?

Answer 1

The ventral horn of the spinal cord

Question 2

What is a motor unit?

Answer 2

One voluntary motor neuron and all the muscle cells it innervates.

Fingers have small motor unit

Trunk has larger motor unit

Question 3

What is a lower motor neuron?

Answer 3

A motor neuron that directly innervates muscles
Soma in the CNS
Axon in the PNS

Question 4

What is the voluntary motor neuron that innervates skeletal muscle cells that are capable of producing movement are called?

Answer 4

Alpha motor neurons

-Are multipolar neurons

Question 5

What happens at the neuromuscular junction?

Answer 5

A synapse between the motor neuron axon terminal and muscle cell.

-The neurotransmitter is acetylcholine.

Question 6

The neurotransmitter is always?

Answer 6

An excitatory synapse

Question 7

Where does muscle relaxation come from?

Answer 7

preventing an AP in the innervating lower motor neuron.

ie: inhibiting the innervating the lower motor neuron, not from an inhibitory synapse in the muscle
Relax= inhibit lower motor neuron

Question 8

What is released to cause an AP which causes a contraction of the muscle?

Answer 8

ACh (acetylcholine)

Question 9

Small amounts of ACh are released from the axon terminal even at rest. The ACh acts as a what for muscles cells?

Answer 9

Myotrophic factor

-Creates small end plate potentials on muscle membrane

Question 10

What does an end plate potential do?

Answer 10

Stimulates genes for protein production

Question 11

What is one hallmark of an injury to the lower motor neuron?

Answer 11

Rapid and pronounced atrophy

• From lack of contraction = disuse atrophy
• Partly from loss of myotrophic properties of ACh = neurogenic atrophy