Motor Control Flashcards
What are the different pathways in which the brain is connected to the spinal cord for motor innervation?
Ventral pathways - corticospinal tract & rubrospinal tract
Ventromedial pathways - tectospinal tract, vestibulospinal tract & pontine and medullary reticulospinal tract
What would be lost if there was a lesion of the corticospinal tract and the rubrospinal tract?
Loss of fine movements of arms, hands
Can move shoulders, elbows, and fingers independently
What would be lost if there was lesion of the corticospinal tract but not the rubrospinal tract?
Loss of fine movements and moving limbs independently
However these functions would re appear after a few months as the Rubrospinal tract would take over
How do you refine voluntary movements ?
Motorneurones from the motor cortex both excite and inhibit agonist and antagonist muscles monosynaptically
Where does the corticospinal tract originate?
2/3rd area 4 & 6
1/3rd is somatosensory
Where does the rubrospinal tract originate?
Red nucleus of midbrain
Where does the pontine and medullary reticulospinal tract originate?
The brainstem
What ventromedial pathway is responsible for ensuring eyes remian stable when the body moves?
Tectospinal tract
What ventromedial pathway is responsible for stabalising the head?
The vestibulospinal tract
What ventromedial patwhay is responsible for maintaining balance and body position?
Pontomedullary reticulospinal tract
Where does axons from the corticospinal tract synapse?
Dorsal horn
What areas are responsible for planing and controlling precise movements?
Primary cortex (area 4) Pre motor cortex (area 6)
What is area 6 sub divided into?
Pre motor area
Supplementary motor area
Regarding area 6, what ‘sub area’ innervates distal motor neurones directly? And which one innervates proximal motor units?
Proximal = pre motor area Distal = supplementary area
What area is responsible for proprioception?
Posterior parietal cortex ( area 5 and 7)
If we only think about movements but done carry them out what part of our brain is active?
Area 6
Area 4 is the area for doing it by activating neurones of the CST and RST
What does it mean by there is a feedforward mechanism that controls movement?
Before there is a change in body position, brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustments to stabilise posture
What are the clinical signs of upper motor neurone syndrome?
Initial hypotonia - spinal shock
Immediate flaccidity of contralateral muscles
Days later spinal circuits regain function as spared connections and new connections sprout Babski’s sign - plantar flexion Hypertonic - spasticity , clonus Hyperreactive reflexes Loss of fine finger movements
What is the main function of the basal ganglia?
Initiation of voluntary movements
What are the names of the basal ganglia?
Corpus striatum - putamen and globus pallidus
Caudate
Substantia nigra
Where does motor subcortical input to area 6 come from?
Ventral lateral nucleus in dorsal thalamus
Where does basal ganglia recieve information from?
Pre frontal, frontal and parietal cortex’s
Which pathway through he spinal cord does the basal ganglia follow before it sends information to the VLo?
corticospinal tract
What basal ganglia are excitatory and inhibitory?
Putamen and caudate = excitatory
Globus pallidus and substantia nigra = inhibitory
What is the difference in the direct and indirect pathway of the basal ganglia?
Direct pathway - positive feedback loop to initiate the ‘go’ signal
Indirect pathway - antagonises the direct loop
Name 2 basal ganglia disorders.
Huntington’s
Parkinson’s
What is Parkinson’s caused by?
Degeneration of neurones in substantia nigra and their dopaminergic (excitatory) inputs to the striatum
What is the clinical presentation of Parkinson’s?
Hypokinesia - slowness, difficulty to make voluntary movements
Increased muscle tone
Tremor of hands and jaw
What is the clinical presentation of Huntington’s disease?
Hyperkinesia with dementia and personality disorders
Spontaneous uncontrolled rapid flicks and major movements
What pathways are affected in Parkinson’s and Huntington’s?
Both the direct and indirect pathways are affect in Parkinson’s and Huntington’s
What does lesions to the cerebellum produce?
Uncontrolled inaccurate movements
Ataxia - unable to touch nose with eyes shut
Similar to alcohol which suppresses cerebellar circuits.
The signals for fine tuning of muscular contraction from the thalamus are travelled to the cortex via what?
Ventrolateral thalamus (VLo)
What is the main function of the cerebellum?
Direction, timing and force - fine tuning of muscular contraction
what is the corpus striatum and their function?
included 2 principle basal ganglia:
- caudate and the putamen
they are the input zones of the basal ganglia
through which pathway does the corpus striatum receive inputs?
corticostriatal pathway
the corpus striatum is predictive of movements.
what specifically do they do that makes them predictors of movements?
the putamen the fires limb/trunk movements
the caudate fires before eye movements
describe the motor loop regarding basal ganglia?
cortex to putamen = excitatory
putamen to globus pallidus = inhibitory
globus pallidus - Vlo = inhibitory
Vlo - SMA = excitatory
where does information received from the basal to the Vlo send it to?
the supplementary motor area in the cortex
why does inhibition of the globus pallidus cause excitation of the Vlo to SMA?
at rest globus pallidus neurones are spontaneously active and inhibit Vlo
inhibition of globus pallidus therefore releases the Vlo from inhibition = excitation from Vlo - SMA
Where does the pyramidal tract decussate?
Lower level part of the medulla at the decussation of the pyramids
Where does the pyramidal tract originate?
Frontal lobe, pre central gyrus, area 4
If there is damage to the pyramidal tract what would be lost?
Motor function
If there is an UMN lesion, why does this cause increased reflexes?
A knee jerk is a monosynaptic reflex mediated at the level of the spinal cord by the LMN.
UMN are tonically inhibitory to the LMN. Therefore when these UMN are damaged there is no inhibition of the LMN so the reflexes become increased
