Motor Control II Flashcards
how is the overall movement direction encoded?
Each neurone has a preferred direction but responses of all neurons are combined to produce a population vector
what adjustments are made before movements begin?
anticipatory feedforward adjustments
what initiates feedforward anticipatory adjustments to stabilize posture?
brainstem reticular formation nuclei (controlled by the cortex)
what does cortical damage cause?
causes immediate flaccidity of contralateral muscles. Lift limb and release-drops passively
what is the babinski sign?
(normal adult, plantar flexion)
baby and cortical damage, extension – both indicate incomplete upper control of spinal circuits
describe Spasticity
increased muscle tone, hyperactive stretch reflex – due to removal of cortical suppressive influences
where does Major subcortical input to area 6 come from?
ventral lateral nucleus(VLo) in dorsal thalamus
what does the Basal ganglia motor loop do?
selects and initiates willed movements
describe the Basal ganglia motor loop
cycles via - cortex through basal ganglia and thalamus(VLo) - back to SMA in cortex
what is the input zone of the basal ganglia?
Corpus striatum - includes 2 principal nuclei the caudate and the putamen
what is the corticostriatal pathway?
multiple parallel pathways with different functions
when do the caudate and the putamen fire?
putamen fires before limb/trunk movements
caudate fires before eye movements
both are predictive of movements
what is glutamatergic?
excitatory axons
what is gabaergic?
axons are inhibitory
where do putamen and caudate project?
globus pallidus and to substantia nigra pars reticulata
what type of neurones go from Cortex to putamen?
excitatory
what type of neurones go from Putamen to Globus pallidus ?
inhibitory
what type of neurones go from Globus pallidus to VLo neurones?
inhibitory
what type of neurones go from VLo to SMA?
excitatory
so what is the functional consequence of cortical activation of putamen?
excitation
Why does cortical activation of putamen boost cortical excitation?
At rest globus pallidus neurones are spontaneously active and inhibit VL
So 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
describe the Cortical input flow by direct pathway
acts as a positive feedback loop, a “GO” signal to the SMA in cortex
it enhances the initiation of movements by the SMA
input from cortex releases Globus pallidus inhibition
describe the Cortical input flow by indirect pathway
antagonizes the direct route
Striatum inhibits GPe (globus pallidus external) which then inhibits both GPi (GPinternal) and STN (subthalamic nuclei)
Cortex excites STN; this excites Gpi; which inhibits thalamus
what is the role of the direct and indirect pathways?
Direct pathway selects specific motor actions
indirect pathway suppresses competing/inappropriate action
what is Parkinson’s disease?
type of hypokinesia
slowness, difficult to make voluntary movements, increased muscle tone (rigidity), tremors of hand and jaw.
what causes Parkinson’s disease?
caused by degeneration of neurones in substrantia nigra (SN) and their dopaminergic (excitatory) inputs to the striatum
describe Huntington’s disease
involves hyperkinesia with dementia and personality disorders
spontaneous, uncontrolled, rapid flicks and major movements with no purpose
what causes Huntington’s disease?
profound loss of caudate, putamen and globus pallidus
so loss of the ongoing inhibitory effects of the basal ganglia
what do lesions to cerebellum produce?
uncoordinated inaccurate movements
eg ataxia : fail to touch nose with eyes shut
what makes up the huge cortico-ponto-cerebellar projection?
Layer 5, areas 4 & 6, somatosensory cortex
what is the cortico-ponto-cerebellar projection?
connects cortex, pontine nuclei and cerebellum
what connects the cerebellum back to cortex?
via ventrolateral thalamus
what is the role of the cerebellum?
instructs direction, timing and force
describe the feedback motor loop through lateral cerebellum
through pons, cerebellum, thalamus and back to cortex
