Motor Control 2 Flashcards
What is the significance of a neurone having its greatest discharge in one direction of movement?
It means the responses of all neurones are combined to produce a population vector
Movement direction is encoded by the integrated activity of all the neurones
Where does body position feedback information travel from? and to?
Travels from brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability
What is responsible for feedforward anticipatory adjustments to stabilize posture?
Brainstem reticular formation nuclei (controlled by the cortex)
What is the result of cortical damage on contralateral muscles?
•cortical damage causes immediate flaccidity of contralateral muscles. Lift limb and release, drops passively
Hypotonia is a feature of spinal shock, what happens several days later?
•days later spinal circuits regain function - spared connections strengthen and new connections sprout. A consistent pattern of motor signs emerges
What is the babinski sign and what is it a sign of?
•Babinski sign – normal adult, plantar flexion – baby and cortical damage, extension – both indicate incomplete upper control of spinal circuits
What are features of spasticity?
Increased muscle tone
Hyperactive stratch reflex
Clonus
What causes spasticity?
Loss of cortical suppressive influences
What is the loop that occurs within tha basal ganglia when selecting willed movements?
Subcortical information to the pre-motor area largely comes from the ventral lateral nucleus of the dorsal thalamus.
Input into this is called the VLo and is formed by the basal ganglia
The basal ganglia are targets of the pre-frontal cortex, the frontal cortex and the motor cortex.
Define corpus striatum
Corpus striatum (striped body) - includes two principal nuclei the caudate and the putamen
They are the input zone of the basal ganglia
The internal capsule is also included in the corpus striatum
What is the name given to the pathways associated with the corpus striatum?
•corticostriatal pathway - multiple parallel pathways with different functions
How does the caudate nucleus and the putamen communicate with the cortex?
•medium spiny neurones in putamen and caudate receive excitatory (glutamatergic) cortical inputs on dendrites
The caudate and the putamen have large dendritic trees, what type of information do these dendritic trees integrate?
•somatosensory, premotor and motor cortical inputs
Which nucleus is responsible for firing before limb/trunk movement?
Putamen
Which nucleus is responsible for firing before eye moevements?
Caudate
What are the excitatory components of the motor loop?
Cortex to putamen
VLo to SMA
What are the inhibatory components of the motor circuit?
Putamen to globus pallidus
Globus pallidus to VLo
What is the effect of cortical excitation on SMA activity?
- excites putamen which
- inhibits the inhibitory Globus pallidus which therefore
- releases cells in VLo from inhibition so
- activity in VLo boosts SMA activity
Positive FEEDBACK loop
Explain B at rest
Globus pallidus neurones are spontaneoously active and inhibit the ventral lateral nucleus of the dorsal thalamus
Explain what happens when A is transiently excited?
Striatum causes inhibition of the globus palidus inhibition - therefore the the VL is disinhibited and excited D - the upper motor neurones in the SMA
Describe what happens during the indirect pathway of the motor loop
- 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 difference in function between the direct and the indirect pathways of the motor loop?
Direct pathway - selects specific motor actions
Indirect pathway - suppresses competing / inappropriate action
Name a disease associated with a basal ganglion disorder
Parkinsons
What are the features of parkinsons?
Hypokinesia - slowness, difficulty to make voluntary movements
What is the cause of parkinsons?
•caused by degeneration of neurones in substrantia nigra (SN) and their dopaminergic (excitatory) inputs to the striatum
What is the effect of dopamine on the direct and indirect pathway?
Direct - enhances cortical inputs
Indirect - Suppress inputs
What is the effect of depletion of dopamine?
•Reduces the number of focussed motor activities that funnel through thalamus to SMA
What are the features of hungtingtons disease?
Hyperkinesia
Dementia
Personality disorders
Characteristic chorea - Uncontrolled rapid flicks and major movement with no purpose
What is the cause of Hungtingtons disease?
•Profound loss of caudate, putamen and globus pallidus
Loss of ongoing inhibatory effects of the basal ganglia
Where do 50 % of CNS neurones come from?
Cerebellum
What is the result of a lesion to the cerebellum?
Produce uncoordinated and innacurate movements - ataxia
What parts of the brain are included in the cortico - ponto - cerebellar projection?
Layer 5, areas 4 & 6, somatosensory cortex
What does the cortico - ponto cerebellar projection connect?
Cortex, pontine nuclei and cerebellum
How does the cerebellum project back to the cortex?
Through the ventrolateral thalamus
What does the cerebellum instruct?
Direction, timing and force
Also involved in motor learning
Describe the feedback loop involving the cerebellum
pons, cerebellum, thalamus and back to cortex
