Motor Control Flashcards
What are the structures involved in strategy of voluntary movements?
Association neocortex
Basal ganglion
What are the structures involved in tactics of voluntary movements?
Motor cortex
Cerebellum
What are the structures involved in execution of voluntary movements?
Brain stem
Spinal cord
What is the function of lateral pathways?
Control voluntary movements of distal muscles
Under direct cortical control
What is the functions of ventromedial pathways?
Control posture and locomotion
Under brain stem control
Where does the corticospinal tract originate?
2/3 in areas 4 + 6 of frontal motor cortex
Rest is somatosensory
Where does the corticospinal tract cross over?
Medulla/spinal cord junction
Where does corticospinal tract axons synapse to control muscles voluntarily?
Ventral horn motor neurones
Interneurones
Where does the rubrospinal tract start?
Red nucleus of the midbrain
Where does the rubrospinal tract receive input from?
Same cortical areas as the corticospinal tract
What happens when there is lesions to corticospinal and rubrospinal tracts?
Fine movements of arms and hands lost
Can’t move shoulders, elbows, wrist and fingers independently
What happens where there is a lesion to the corticospinal tract alone?
Same as CST + RST lesion
BUT after few months functions reappear
RST takes over
What is the role of the vestibulospinal tract?
Stabilises head and neck
What is the role of the tectospinal tract?
Ensures eyes remain stable as body moves
Where do pontine and medullary recticulospinal tracts originate?
Brain stem
What type of sensory information does the pontine and medullary reticulospinal tracts use?
Balance
Body position
Vision
What is the role of the pontine and medullary reticulospinal tracts?
Reflexly maintain balance and body position
Innervate trunk and antigravity muscles in limbs
What do voluntary movements require input from?
Motor cortex via lateral pathways
What is the role of primary motor cortex and pre-motor areas?
Plan and control precise voluntary movements
What do medial lower motor neurones control?
Axial and proximal limb muscles
What do lateral lower motor neurones do?
Innervate distal limb muscles
Where is the primary motor cortex located?
Precentral gyrus
What does the supplementary motor area innervate?
Distal motor units directly
What does the premotor area connect with?
Reticulospinal neurones innervating proximal motor units
What are the areas of cortex involved in planning and instructing voluntary movement?
Prefrontal cortex Area 6 (SMA, PMA) Area 4 Central sulcus S1 Posterior parietal cortex (Areas 5 + 7)
What does microstimulation in specific area of primary motor cortex induce?
Coordinated movements of hand and mouth
OR
Movements that bring hands into central space to inspect/manipulate objects
What type of inputs are required to form a mental image of body in space?
Somatosensory, propriceptive and visual inputs to the posterior parietal cortex
Where are decisions taken about which actions/movements to take and their likely outcome?
Prefrontal and parietal cortex
How are signals encoding desired actions converted into how to carry this out?
Axons from prefrontal and parietal cortex converge on area 6
When do PMA mirror neurones fire?
When self or others perform specific actions
Allows understanding of actions or intentions of others
How is postural instability corrected with a change in body position?
Rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurons
What happens before movements begin to stabilise position?
Brainstem reticular formation nuclei initiate feedforward anticipatory adjustments
What are the signs of UMN damage?
Flaccidity of contralateral muscles Increased muscle tone Hyperactive stretch reflex Clonus Loss of fine finger movements
What is the role of the basal ganglia motor loop?
Selects and initiates willed movements
Where does the major subcortical input to area 6 come from?
Ventral lateral nucleus in dorsal thalamus (VLo)
Where does input to the VLo come from?
Basal ganglia
What are the major components of basal ganglia?
Corpus striatum (caudate + putamen) = input zone Corticostriatal pathway
What do the medium spiny neurones in the putamen and caudate receive?
Excitatory (glutamatergic) cortical inputs on dendrites
When does the putamen fire?
Before limb/trunk movements
When does the caudate fire?
Before eye movements
What type of pathway connects the cortex to the putamen?
Excitatory pathway
What type of pathway connects the putamen to the globus pallidus?
Inhibitory
What type of pathway connects the globus pallidus to the VLo neurones?
Inhibitory
What type of pathway connects VLo back to the SMA?
Excitatory
What do globus pallidus neurones do at rest?
They are spontaneously active and inhibit VLo
What does cortical excitation do?
Excites putamen which inhibits the inhibitory globus pallidus = releases cells in VLo from inhibition so activity in VLo boosts SMA activity
What does the direct pathway through the basal ganglia act as?
Positive feedback loop
‘GO’ signal to SMA in cortex
Enhances initiation of movements by SMA
What is the role of the indirect pathway through the basal ganglia?
Antagonises the direct route
Striatum inhibits external GP which inhibits both internal GP and subthalamic nuclei
Cortex excites STN = excites GPi = inhibits thalamus
What is the purpose of the direct pathway through the basal ganglia?
Selects specific motor actions
What is the purpose of the indirect pathway through the basal ganglia?
Suppresses competing/inappropriate action
What is hypokinesia?
Slowness
Difficult to make voluntary movements
Increased muscle tone
Tremors of hand and jaw
What causes hypokinesia?
Degeneration of neurones in substantia nigra and their dopaminergic inputs to the striatum
What is the role of dopamine?
Enhances cortical inputs through the ‘direct’ pathway and suppress inputs through ‘indirect’ pathway
What happens to dopamine in Parkinsons?
Depleted which closes down activation of the focussed motor activities that funnel through the thalamus to the SMA
What does Huntington’s disease involve?
Hyperkinesia
Dementia
Personality disorders
What is characteristic chorea?
Spontaneous, uncontrolled, rapid flicks and major movements with no purpose
What causes characteristic chorea?
Profound loss of caudate, putamen and globus pallidus
How does lesions to the cerebellum affect movement?
Produces uncoordinated inaccurate movements
What areas make up a part of the huge cortico-ponto-cerebellar projection?
Layer 5
Areas 4 + 6
Somatosensory cortex
What is the role of the cerebellum in movement?
Instructs direction, timing and force of movement
