15 - Motor control and the corticospinal tract Flashcards
How is skeletal muscle controlled?
- voluntary movements have an UMN and a LMN
- leaves the CNS (cerebral cortex), via the brainstem to the spinal cord
Define voluntary movement.
- direct movement
- contraction of muscles
- pyramidal pathway
Define involuntary movement.
- indirect movement
- balance and fluidity of movement
- unconscious and no delay
- extrapyramidal pathway
Describe the extrapyramidal pathway.
- has both alpha and gamma fibres
- alpha fibres typically travel outwards from the CNS
- gamma fibres typically travel inwards to the CNS
Describe the pyramidal pathway.
- alpha-alpha motor neurones
- decision leaves motor cortex via alpha neurone to the spinal cord, synapses with another alpha neurone to the target muscle
What is the role of the basal ganglia in the corticospinal tract?
Initiate smooth movement
What is the role of the thalamus in the CST?
- acts as the relay centre for movement feedback
- receives information from the BG, cerebellum and proprioception information
What is the role of the extrapyramidal pathway in the CST?
- acts to support voluntary movement
- tells muscles not to move during actions
What is the role of gamma neurones?
- PNS -> CNS
- monitor muscle spindle sensitivity aka the starting point for contraction
- known as the readiness potential
Where is the pyramid located?
Anterior of the medulla, either side of the midline
Describe the route of the UMN in the pyramidal pathway within the brain.
- 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
What is the role of the anterior CST?
Controls axial movements (muscles in the trunk) and posture
What is the role of the LCST?
Controls voluntary movement of the contralateral limbs
What are signs and symptoms of UMN lesions?
- spastic paralysis
- no significant muscle atrophy (LMN functioning and nourishing muscle)
- hyperreflexia and clonus (rigid twitching)
- hypertonia
- high gamma gain
What is gamma gain?
Amplified reaction of gamma fibres, when not received information from the CNS (usually due to an UMN lesion)