Motor Control 2 Flashcards
Where does directional tuning occur?
Primary motor cortex (area 4)
What can be said about the neurons in M1 and the direction of movement they control?
Each neuron has a preferred direction but the responses of all neurons are combined to produce a population vector
What kind of loop mechanisms control movement?
Both feedback and feedforward mechanisms control movement
What are examples of feedback mechanisms in movement?
Change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurons to correct postural instability
In addition, before movement begins brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustements to stabilise posture
In damage to descending motor pathways, what does the injury site determine?
The symptoms
In terms of movement, what does cortical damage cause?
Immediate flaccidity of contralateral muscles:
initial hypotonia due to “spinal shock” where spinal circuits are deprived of cortical input
days later spinal motor reflexes re-emerge in a consistent pattern as spared connections strengthen and new connections sprout
What is the Babinski sign?
Stimulation of lateral plantar aspect of foot leads to extension of the big toe, there may also be fanning of the other toes
What is supposed to occur with stimulation of the lateral plantar aspect of the foot in adults?
Planter flexion
When does planter extension occur on stimulation to the lateral planter aspect of the foot?
In baby or with cortical damage
What are examples of things that damage to descending motor pathways causes?
Flaccidity of contralateral muscles
Babinski sign (tendon reflexes impacted)
Loss of fine finger movement
Spasticity (due to removal of cortical suppressive influences)
What does the basal ganglia motor loop do?
Selects and initiates willed movements
What does Vlo stand for?
Ventral lateral nucleus in dorsal thalamus
Where does major subcortical input to area 6 comes from?
Ventral lateral nucleus in dorsal thalamus
Where does input to Vlo come from?
Basal ganglia
Where does input to the basal ganglia come from?
Frontal, prefrontal and parietal cortex
Explain the process of the basal ganglia motor loop?
Cortex > thalamus and basal ganglia > back to the SMA in cortex (area 6)
What are some major components of the basal ganglia?
Corpus striatum (stripped body)
This includes two principal nuclei, the caudate and the putamen
What are the input zones for the basal ganglia, and where do they recieve input from?
Caudate and putamen
From all over the cortex
What kind of inputs does the medium spiny neurons of the putamen and caudate receive?
Excitatory (glutamatergic) cortical inputs on dendrites
they have large dendritic trees and integrate massive somatosensory, premotor and motor cortical inputs
Are the axons of the putamen and caudate excitatory or inhibitory?
Inhibitory (GABAergic)
Where does the putamen and caudate project to?
Globus pallidus and to substantia nigra pars reticulata
What does the putamen fire before?
Limb/trunk movements
What does the caudate fire before?
Eye movements
The motor loop is cortex > basal ganglia > cortex, which of these pathways are excitatory and which are inhibitory?
Cortex to putamen - excitatory
Putamen to globus pallidus - inhibitory
Globus pallidus to VLo neurons - inhibitory
VLo back to SMA - excitatory
this means functional consequence of cortical activation of putamen is excitation
