Somatic motor system

Question 1

Purpose of somatic motor pathways?

Answer 1

• Controls contractions of skeletal muscle.

- Always involve at least 2 motor neurones - upper and lower.

Question 2

Describe the upper motor neurone?

Answer 2

• Cell body lies in a CNS centre.
• Synapses with lower.
• Innervates a single motor unit.

Question 3

Describe the lower motor neurone?

Answer 3

• Cell body lies in a nucleus of the brain stem.

- Triggers a contraction in innervated muscle.

Question 4

Name the 3 major pathways (descending tracts)?

Answer 4

• Corticobulbar tract.
• Lateral coricospinal tract.
• Anterior corticospinal tract.

Question 5

Functions of the coritobulbar tracts?

Answer 5

-Provide conscious control over skeletal muscles that move the eye, jaw, face and muscles of neck and pharynx.

Question 6

Describe and draw the cortico - bulbar pathways?

Answer 6

• Upper motor neurone = arise from cell bodies in primary motor cortex, axons pass through internal capsule, descend to brain stem.
• Synapse with lower motor neurone of cranial nerves.

Question 7

Describe and draw the lateral cortico - spinal tract?

Answer 7

• Upper motor nerone arise from cell bodies in PMC, pre central gyrus of frontal, axons pass through internal capsule, descend through brain stem to medulla, axons cross over to other side at the pyramids, descend in opposite side of spinal cord.
• Synapses with lower motor neurone and exits through interveterbral formina.

Question 8

Describe and draw the anterior cortico - spinal tract?

Answer 8

• Upper MN arises from cell bodies in PMC, pre central gyrus, axons pass through capsule, descend through brain stem to medulla, axons stay on same side descending through spinal cord. At spinal segment, crosses over to other side.
• Synapses with lower MN at anterior horn, exits through intervertrbral foramina, nerve innervates muscle via a neuromuscular junction.

Question 9

Describe the neuromuscular junction?

Answer 9

Pre - synaptic axon terminal.
Neurotransmitter (acetylcholine).
Synaptic cleft.
Postsynaptic membrnae.

Question 10

Describe the process of action potential crossing synapse?

Answer 10

• Action potential arrives, depolarizes synaptic knob.
• Calcium ions enter knob, trigger release of ACh.
• ACh binds to receptors, depolarizes postsynaptic membrane.
• AChE breaks ACh into acetate and choline.

Question 11

What is the difference between lateral and anterior corticospinal pathways?

Answer 11

• Lateral = As descend, visible along medulla, Axons CROSS to opposite sides of spinal cord.
• Anterior = Spinal segment axon crosses over to opposite side of spinal cord before synapsing.

Question 12

Describe reflexes?

Answer 12

• Automatic responses coordinated within spinal cord.
• Protective = removing body from noxious stimuli.
• Postural = body position as move.

Question 13

Describe the control of body movement?

Answer 13

• Receptors sense change in joint movements, muscle tension and length.
• Golgi organs respond to muscle tension.
• Contraction.