15 - Motor control and the corticospinal tract

Question 1

How is skeletal muscle controlled?

Answer 1

• voluntary movements have an UMN and a LMN
• leaves the CNS (cerebral cortex), via the brainstem to the spinal cord

Question 2

Define voluntary movement.

Answer 2

• direct movement
• contraction of muscles
• pyramidal pathway

Question 3

Define involuntary movement.

Answer 3

• indirect movement
• balance and fluidity of movement
• unconscious and no delay
• extrapyramidal pathway

Question 4

Describe the extrapyramidal pathway.

Answer 4

• has both alpha and gamma fibres
• alpha fibres typically travel outwards from the CNS
• gamma fibres typically travel inwards to the CNS

Question 5

Describe the pyramidal pathway.

Answer 5

• alpha-alpha motor neurones
• decision leaves motor cortex via alpha neurone to the spinal cord, synapses with another alpha neurone to the target muscle

Question 6

What is the role of the basal ganglia in the corticospinal tract?

Answer 6

Initiate smooth movement

Question 7

What is the role of the thalamus in the CST?

Answer 7

• acts as the relay centre for movement feedback
• receives information from the BG, cerebellum and proprioception information

Question 8

What is the role of the extrapyramidal pathway in the CST?

Answer 8

• acts to support voluntary movement
• tells muscles not to move during actions

Question 9

What is the role of gamma neurones?

Answer 9

• PNS -> CNS
• monitor muscle spindle sensitivity aka the starting point for contraction
• known as the readiness potential

Question 10

Where is the pyramid located?

Answer 10

Anterior of the medulla, either side of the midline

Question 11

Describe the route of the UMN in the pyramidal pathway within the brain.

Answer 11

• two tracts, anterior and lateral
• axons leave from the PMC, SMC, pre-motor cortex and PSC
• travels through the corona radiata through the posterior limb of the IC
• travels to brainstem where 85% of fibres cross the medulla to form the LCST

Question 12

What is the role of the anterior CST?

Answer 12

Controls axial movements (muscles in the trunk) and posture

Question 13

What is the role of the LCST?

Answer 13

Controls voluntary movement of the contralateral limbs

Question 14

What are signs and symptoms of UMN lesions?

Answer 14

• spastic paralysis
• no significant muscle atrophy (LMN functioning and nourishing muscle)
• hyperreflexia and clonus (rigid twitching)
• hypertonia
• high gamma gain

Question 15

What is gamma gain?

Answer 15

Amplified reaction of gamma fibres, when not received information from the CNS (usually due to an UMN lesion)

Question 16

What is a common cause for an UMN lesion?

Answer 16

Stroke

Question 17

What is a common cause for a LMN lesion?

Answer 17

• trauma
• poliomyelitis

Question 18

What are signs and symptoms of LMN lesion?

Answer 18

• flaccid paralysis
• muscle atrophy (LMN nourishing muscle has died)
• fasciculations
• hyporeflexia (reflex arc is damaged)
• hypotonia (damaged gamma neurones)

Question 19

How does Babinski’s sign determine whether there is an UMN or LMN lesion?

Answer 19

• positive sign (extensor plantar response) = UMN
• negative sign (normal plantar response) = LMN