Motor Control II Flashcards
true or false:
commands to perform precise movements are encoded in the integrated activity of large populations of neurones in M1
true
how is posture instability corrected?
A change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones
In addition before movements begin, brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustments to stabilize postur
what is initial hypotonia?
“spinal shock” - spinal circuits are deprived of cortical input
what is the babinski sign?
- adult, plantar flexion – baby or cortical damage – extension : both indicate incomplete upper control of spinal circuits
what does increased muscle tone, hyperactive stretch reflex, clonus oscillatory contract/relax muscles in response to stretch cause?
removal of cortical suppressive (inhibitory) influences
where does the Major subcortical input to area 6 come from?
ventral lateral nucleus in dorsal thalamus (Vlo)
where does Input to VLo comes from
basal ganglia
what are te Major components of basal ganglia
Corpus striatum (striped body) - includes two principal nuclei the caudate and the putamen
where does Corpus striatum receives inputs from ?
all over cortex –
corticostriatal pathway - multiple parallel pathways with different functions
medium spiny neurones in putamen and caudate receive excitatory (glutamatergic) cortical inputs on?
dentrites
each cortical axon contacts ….. of spiny neurones so integrating the influence of …. of cortical cells
1000s
are the axons inhibitory or excitatory?
inhibitory (GABAergic)
where do the axons project to?
globus pallidus and to substantia nigra pars reticulata
does the putamen fire before limb/trunk movements or after?
before
does the caudate fire after eye movements or before?
before
what type of pathway is cortex to putamen?
excitatory pathway
what type of pathway is putamen to globus pallidus?
inhibitory
what type of pathway is globus pallidus to VLo neurones?
inhibitory
what type of pathway is VLo back to SMA?
excitatory
functional consequence of cortical activation of putamen is
excitation
what happens to globus pallidus at rest?
neurones are spontaneously active and inhibit VLo
function of Cortical excitation
excites putamen which
inhibits the inhibitory Globus pallidus which therefore
releases cells in VLo from inhibition so
activity in VLo boosts SMA activity
This acts as a positive feedback loop focussing or funnelling activation of widespread cortical areas back onto cortical SMA
what does the gating operation of the basal ganglia depend on?
a type of disinhibitory arrangement
what does the direct pathway act as? and what is its function?
positive feedback loop, a “GO” signal to the SMA in cortex
it enhances the initiation of movements by the SMA
what is the indirect pathway?
antagonizes the direct route
Striatum inhibits GPe (globus pallidus external) which then inhibits both GPi (GP internal) and STN (subthalamic nuclei)
Cortex excites STN; this excites Gpi; which inhibits thalamus
Direct pathway selects specific motor actions
Indirect pathway suppresses competing/inappropriate action
what is the direct pathway via?
caudate/putamen
what is the indirect pathway via?
subthalmic nucleus
what is are examples of basal ganglia disorders?
parkinsons disease
huntington’s disease
what is hypokinesia?
slowness, difficult to make voluntary movements, increased muscle tone (rigidity), tremors of hand and jaw.
how is hypokinesia caused?
degeneration of neurones in substrantia nigra (SN) and their dopaminergic (excitatory) inputs to the striatum
true or false:
dopamine can enhance cortical inputs through the “direct” pathway and suppress inputs through “indirect” pathway
true
what does the depletion of dopamine cause?
closes down activation of the focussed motor activities that funnel through thalamus to SMA
what is characteristic chorea?
spontaneous, uncontrolled, rapid flicks and major movements with no purpose
what is the cause of characteristic chorea?
profound loss of caudate, putamen and globus pallidus
so loss of the ongoing inhibitory effects of the basal ganglia
how much of the total CNS neurones come from the cerebellum?
50%
what do lesions to the cerebellum cause?
produce uncoordinated inaccurate movements : ataxia : fail to touch nose with eyes shut : similar to alcohol which depresses cerebellar circuits
what are parts of the cortico-ponto-cerebellar projection?
Layer 5, areas 4 & 6, somatosensory cortex
what is the cortico-ponto-cerebellar projection
connects cortex, pontine nuclei and cerebellum - 20 mill axons, 20x more that CST
