Motor Control 2 Flashcards
How are lots of neurones involved in deciding a direction
As Each one has a preferred direction and will fire greater for a movement in that direction than any other
Whats happens to the discharging neurones when you have a preferred direction
Neurones preferring that direction will fire more and others less resulting in a population vector.
What controls the overall movement direction
Population vector encoded by the integrated activity of all the neurones.
How does feedback occurs when you need to correct postural instability
Via vestibulo-spinal system
(brainstem vestibular nuclei to spinal cord motor neurones)
To correct postural instability
How do you stabilise posture before movement occurs
Reticular formation via Reticulospinal tracts make feedforward anticipatory adjustment to stabilise posture before you make a move
What is the symptoms of upper motor neurone syndrome/damage to descending motor pathway
Spinal shock - spinal cord deprived of cortical input
Babinskis sign
Spasticity
Loss of fine finger movements
The symptoms of an upper motor lesion depends on what
Injury site
What is the affect of cortical damage
Immediate flaccidity of contralateral muscle - have no drive
What occurs after spinal shock in upper motor lesion that leads to the return of reflexes
Days later spinal circuits regain function - spared connections strengthen and new connections sprout.
A consistent pattern of motor signs emerges
What is seen in spasticity
Increased muscle tone
hyperactive stretch reflex
Clonus oscillatory contract/relax muscles in reponse to stretch
Why does spasticity occur in upper motor lessons
Due to removal of cortical suppressive influences
What does Babinskis sign indicate
Incomplete upper control of spinal circuits
What is the overall pathway of the motor loop
Communication occurs from motor cortex to the basal ganglia then to ventral lateral nucleus in dorsal thalamus (VLo) then back to the supplementary areas in the cortex area 6
What part of the cortex targets the basal ganglia motor loop
Frontal (motor cortex4+6)
Prefrontal
Parietal (sensory cortex)
What is the overall function of the cortical activation of basal ganglia
Part of a motor loop with the function of a Positive Feedback Loop which focusses widespread cortical activation onto the Supplementary Motor Area
What two pathway does information from the motor cortex reach the spinal cord
Lateral pathway (red nucleus)
Ventromedial pathway
reticular nuclei and superior colliculus and vestibular nuclei
What is the major component of the basal ganglia
Corpus striatum
What is the corpus striatum
two principal nuclei the caudate and the putamen
What is the function of the corpus striatum
Input zone of the basal ganglia receiving input from all over the cortex in the motor loop
What is the pathway to the basal ganglias corpus striatum called
corticostriatal pathway - multiple parallel pathways with different functions
What type of neurones are in putamen and caudate
Medium spiny neurones- which have large dendritic trees in to intergrate signals
Where do the medium spiny neurones of the putamen and caudate receive signals from
Somatosensory, premotor and motor cortical inputs
What cortical inputs are received by the medium spiny neurones dendrites
excitatory glutamatergic
What are the axons of the medium spiny neurones
Inhibitory - GABAergic
Where do the axons of the medium spiny neurone in the putamen project
Globus pallidus
Where do the axons of the medium spiny neurone in the caudate project
substantia nigra pars reticulata
When does the putamen fire its axons
Before limb/trunk movements (predictive)
When does the caudate fire its axons
Before eye movements
predictive
What is the exact process of the motor loop: cortex - basal ganglia - cortex
Cortex excites putamen
Putamen inhibits Globus Pallidus
Globus Pallidus stops inhibiting thalamus VLo neurons
VLo neurons boost SMA activity
What happens at rest of globes pallidus neurones
Spontaneously active and inhibit VLo
What arrangement is present in the basal ganglia to gate the operation of the motor loop
A chain of neurones arranged in dis-inhibitory circuit
What is the two pathways in the basal ganglia
Direct - promote movement in SMA
Indirect - suppressing competing actions to the one direct pathway
How does the indirect pathway suppress the competing actions
The Putamen+caudate (striatum) inhibits the globes pallidus external which further inhibits GPi and Subthalamic Nuclei (STN)
What occurs when cortex excites the STN
Excites GPi which inhibits the thalamus
What is two basal ganglia disorders
Parkinsons
Huntingtons
What is the cause of parkinson
degeneration of neurones in substrantia nigra (SN) and their dopaminergic (excitatory) inputs to the striatum
What is the symptoms of Parkinsons
Hypokinesia:
Slowness
Difficulty making voluntary movements
Increased Tone
Tremors of hand & jaw
What is dopamine affect on cortical inputs
Enhance cortical inputs the direct pathway
Suppress inputs through indirect pathway
What is the affect of depleted dopamine in motor control
Close down actions funnelled through the thalamus to the SMA
What is the symptoms of huntingtons disease
Hyperkinesia
Dementia
Personality
Disorders
Characteristic chorea
What is seen in characters chorea
Spontaneous, uncontrolled, rapid flicks and major movements with no purpose
What is the cause of Huntington’s
A heredity disease cause by the profound loss of caudate, putamen and globes pallidus
What is the affect of the profound loss of the basal ganglia in huntington’s disease
loss of the ongoing inhibitory effects of the basal ganglia
How much of the brain volume and CNS neurones if the cerebellum made off
Cerebellum is 10% of brain volume and 50% of CNS neurones
What can lesions of the cerebellum lead to
Uncoordinated inaccurate movements - ataxia
What is another cause of ataxia with the cerebellum
Cerebellar depression by alcohol
What information does the cerebellum send the cortex
Instructions on direction, timing and force of movements
What is the cortico-ponto-cerebellar projection
Connects the cortex, pons and cerebellum
as the cerebellum connects to the cortex via the ventrolateral thalamus
Where does the motor loop go after basal galena and VLo to achieve refinement
by a feedback loop through pons, cerebellum, thalamus and back to the cortex
How does this cortico-ponto- cerebellar projection provide refinement of motor loop
It makes use of motor learning stored in the cerebellum, based on predictions, calculations and experience,
comparing what was intended to what happens then compensating.
