Motor Control Flashcards
what are the three levels in the motor control hierarchy?
> High: strategy (goal and movement strategy)
middle: tactics (sequence of muscles movements to achieve the goal)
low: execution (activation of motor neuron pools)
what do the ventral medial pathways of the spinal cord control?
posture and locomotion under brain stem control
1/3 of the corticospinal tract originate in what areas?
4 and 6 of the frontal motor cortex
where does the smaller rubrospinal tract start?
the red nucleus of the midbrain
what is the effect of a lesion on the corticospinal tract and the rubrospinal tract?
fine movements of arms and hands lost. cant move shoulders, elbows, wrist and fingers independently.
what is the effect of a lesion on the corticospinal tract alone?
there is loss of fine movements of the hands and arms but after a few months functions start to reappear as they have been taken over by the rubrospinal tract.
name the two lateral pathways controlling voluntary movement
> corticospinal tract
> rubrospinal tract
name the two ventromedial pathways controlling posture
> vestibulospinal tracts
> tectospinal tracts
what do the vestibulospinal tracts control?
head and neck stabalisation
what do the tectospinal tracts control?
eye stability as the body moves
what ventromedial pathways control the trunk and antigravity muscles?
the pontine and medullary reticulospinal tracts
what is the function of the pontine and medullary reticulospinal tracts?
they use sensory information about balance, body position and vision to reflexly maintain body position by innervating the trunk and limb muscles
how does the motor cortex directly activate spinal motor neurons?
by communicating via nuclei of ventromedial pathways
what do lateral tracts from the cortex control?
precise skilled voluntary movements
what is the primary motor cortex?
the precentral gyrus
what will weak stimulation of area 4 cause?
a weak twitch in specific contralateral muscles
what are the two somatotopically organised motor maps in area 6?
> premotor area
> supplementary motor area
how is a mental image of the body in space produced?
by somatosensory, proprioceptive and visual inputs to posterior parietal cortex (areas 5 and 7)
where are decisions made about action to take and their outcome?
the prefrontal and parietal cortex
what happens when axons from the prefrontal cortex and parietal cortex converge in area 6?
signals encoding what actions are desired are converted into how actions will be carried out
what does a change in body position initiate to correct postural instability?
a rapid compensatory feedback message from the brainstem vestibular nuclei to spinal cord motor neurons AND feedforward anticipatory adjustments by the reticular formation nuclei to stabilise posture
what does cortical damage cause?
immediate flaccidity of contralateral muscles (hypotonia). then after a few days spinal circuits regain function.
what does Babinski sign indicate?
incomplete upper control of spinal circuits
what makes up the corpus striatum?
two principle nuclei: caudate and putamen
what are the input zone for the basal ganglia?
caudate and putamen nuclei
what does the putamen fire before?
limb and trunk movements
what does the caudate fire before?
eye movements
what do medium spiny neurons in putamen and caudate receive?
excitatory cortical inputs on dendrites
what do medium spiny neurons integrate?
somatosensory, premotor and motor cortical inputs
what do the medium spiny neurons project inhibitory axons to?
> globus pallidus
> substantia nigra pars reticulata
what is the functional consequence of cortical activation of the putamen?
excitation
how does cortical activation of putamen boosts cortical excitation?
> at rest globus pallius neurons inhibit VL
cortical excitation excites putamen
putamen inhibits the inhibitory globus pallidus
this releases cells in VLo from inhibition so activity in VLo boosts SMA activity
what does the direct pathway of cortical input flow through the basal ganglia do?
selects specific motor actions
what does the indirect pathway of cortical input flow through the basal ganglia do?
suppresses competing/inappropriate action
how does the indirect pathway antagonise the direct pathway through the basal ganglia?
> striatum inhibits globus pallidus external which then inhibits the globus pallidus internal and the subthalmic nuclei
the cortex then excites the subthalmic nuclei which excites the GPI which inhibits the thalamus
what is hypokinesia?
> slowness and difficulty in making voluntary movements
increased muscle tone
tremors of the hand and jaw
what causes hypokinesia?
degeneration of neurons in the substrantia nigra and their dopaminergic (excitatory) inputs to the striatum
what does the depletion of dopamine cause?
closing down activation of focused motor activation that funnel through the thalamus to the SMA
what is the effect of dopamine on cortical inputs?
> enhancement through direct routes
> suppression through indirect routes
what is characteristic chorea?
spontaneous uncontrolled rapid flicks and major movements with no purpose seen in huntingtons
name a basal ganglia disorder
huntingtons
what causes huntingtons effects?
profound loss of caudate, putamen and globus pallidus: loss of inhibitory effects of the basal ganglia
what do lesions in the cerebellum produce?
uncoordinated inaccurate movements, ataxia
what parts of the bran are a large part of cortico-ponto-cerbellar projection?
> layer 5
areas 4
area 6
somatosensory cortex
through what does the cerebellum communicate tot he cortex?
via the ventrolateral thalamus
