motor control 1 Flashcards
what are the 3 levels of motor control hierarchy?
high
middle
low
what are the structures associated with high motor control?
association neocortex
basal ganglia
what are the structures associated with middle motor control?
motor cortex
cerebellum
what are the structures associated with low motor control?
brainstem
spinal cord
what do the lateral pathways of the spinal cord control?
voluntary movements of distal muscles - under direct cortical control
what do ventromedial pathways control?
posture and locomotion - under brain stem control
where does the corticospinal tract decussate?
medulla/spinal cord junction
how do CST axons control muscles?
they synapse on ventral horn motor neurones and interneurons
where does 2/3ds of the CST originate?
areas 4 and 6 of the frontal motor cortex - rest is somatosensory
where does the rubrospinal tract originate?
red nucleus of the midbrain
what happens if there are lesions in the CST and RST?
fine movements of the arms and hands lost.
unable to move shoulders, elbows, wrist and fingers independently
what happens if there is a lesion in the CST but not the RST?
fine movements initially lost but after a few months functions reapper because the RST takes over
what does the vestibulospinal tract do?
stabilizes head and neck
what does the tetospinal tract do?
ensures eyes remain stable as body moves
where do the pontine and medullary reticulospinal tracts originate?
brainstem
what sensory information do the pontine and medullary Reticulospinal tracts use?
balance
body position
vision
what is the function of the pontine and medullary reticulospinal tracts?
reflexly maintain balance and body position
innervate trunk and antigravity muscles in limbs
what does the motor cortex do when complex movement is required?
directly activates spinal motoneurones and frees them from reflex control by communicating via nuclei of ventromedial pathways
where do the medial tracts of white matter originate?
brainstem
where do the lateral tracts of white matter develop?
cortex
where in the brain is the primary motor cortex?
precentral gyrus
what does the cerebral cortex need to know in order to plan movement?
where the body is in space
where it wants to go
needs to select a plan to get there
what is the function of the supplementary motor area?
innervates distal motor units directly
what is the function of the premotor area?
connects reticulospinal neurones innervating proximal motor units
why is area 6 of the brain sometimes described as a “junction”?
it is where signals encoding what actions are desired are converted into how the actions will be carried out
what happens with regard to blood flow to the brain during practised voluntary finger movements?
blood flow increases in the following areas: somatosensory posterior parietal prefrontal cortex areas 6 and 4
if you were to “think” about making a movement, which area would be active?
area 6 but not area 4- area 4 is for “doing it”
what are the decision making neurones in command centres?
neurones in the premotor area
when are neurones in area 6 fired?
during movement
when movement is imagined
when you see others making a specific movement
how is the direction of movement decided?
neurone discharge is greatest in a preferred direction
each neurone has a preferred direction but responses of all neurons are combined to produce a population vector
overall movement direction is encoded by the integrated activity of all neurones
what does a change in body position initiate in regard to feedback?
messages from brainstem vestiblar nuclei to spinal cord motor neurones to correct postural instability
what must happen before movements to change body position start?
brainstem reticular formation nuclei (controlled by the cortex) initiate feed forward anticipatory adjustments to stabilize posture
what does cortical damage cause?
immediate flaccidity of contralateral muscle
what causes initial hypotonia?
spinal circuits being derived of cortical input
how do spinal circuits manage to regain their function in spinal shock?
days later, spared connections strengthen and new connection sprout - consistent pattern of motor signs emerges
what does the babinski sign indicate?
incomplete upper control of spinal circuits
what results in spasticity?
removal of cortical suppressive influences
where does the major subcortical input to area 6 of the brain come from?
ventral lateral nucleus in dorsal thalamus
what is the basal ganglia motor loop?
information cycles from the cortex through the thalamus and basal ganglia, then back to the SMA in cortex
what are the major components of basal ganglia?
corpus striatum
what is the input zone of the basal ganglia?
caudate
putamen
where does the corpus striatum receive input from?
all over the cortex; the corticostriatal pathway is made up of multiple parallel pathways with different functions
where are medium spiny neurones located?
putamen and caudate
what kind of signals do medium spiny neurones receive on their dendrites?
excitatory cortical inputs
what kind of inputs do medium spiny neurones integrate?
somatosensory
premotor
motor cortical
where do the axons of medium spiny neurones project to?
globus pallidus
substantia nigra
pars reticula
when do the neurones of the putamen fire?
before limb/trunk movements
when do the neurones of the caudate fire?
before eye movements
what is the functional consequence of cortical activation of the putamen?
excitation
how does cortical activation of the putamen result in an excitatory signal being sent to the SMA?
putamen sends inhib signal to globus pallidus
globus pallidus sends inhib signal to VLo
VLo then sends excitatory signal to the SMA
what do globus pallidus neurones do at rest?
inhibit the VL signal
what is the effect of inhibiting the globus pallidus?
releases cells in VLo from inhibition so activity in VLo boosts SMA activity
how does the indirect basal ganglia loop work?
antagonizes the direct route:
striatum inhibits globus pallidus externa which then inhibits the GPi and the subthalamic nuclei
what effect does exciting the subthalamic nuclei have
excites GPi which inhibits thalamus
what is the function of the indirect pathway
suppresses competing/inappropriate action to the movement initiated by the direct pathway
what is hypokinesia and what is it a sign of?
slowness
difficulty making voluntary movements
increased muscle tone (rigidity)
tremors of hand and jaw
what is the pathology of parkinsons disease?
degeneration of neurones in the substantia nigra and their dopaminergic (excitatory) inputs to the striatum
what is the effect of dopamine in the basal ganglia pathway?
can enhance cortical inputs through the direct pathway and suppress inputs through the indirect pathway?
what is the effect of depletion of dopamine?
closes down activation of the focussed motor activities that funnel through the thalamus to the SMA
what is huntingtons disease caused by?
profound loss of caudate, putamen and globus pallidus - therefore loss of the ongoing inhibitory effects of the basal ganglia
what percentage of CNS neurones does the cerebellum contain?
50 percent
what do lesions of the cerebellum produce?
uncoordinated, inaccurate movements
what parts of movement does the cerebellum instruct?
direction
timing
force
how is the cerebellum linked back to the cortex?
ventrolateral thalamus
how does the motor loop for voluntary movement undergo refinement?
via involvement of a feedback loop through the pons, cerebellum, thalamus and then back to the cortex
