Motor Modulation - Basal Ganglia Flashcards
the basal ganglia and cerebellum modulate motor input by influencing upper motor neurons to……?
- improve movement efficiency
- coordinate timing between muscle groups to produce fluid movements
- making movements adaptable in real time
what is the basal ganglia and its function?
a group of nuclei which function to
- select and initiate a collection of relevant movements for a given task
- inhibit competing movements for that task
why do lesions of the basal ganglia cause disturbances in initiation of a movement?
due to planning bc the BG neurons fire before a movement happens
the basal ganglia acts on the motor cortex via the …?
thalamus
when movement is needed what happens to the basal ganglia neurons?
they are transiently relieved from being tonically inhibited at rest
when the neurons of basal ganglia are stimulated, what pathways are activated?
direct pathway
indirect pathway
explain the direct pathway
- go signal
- disinhibited (releases inhibition)
- thalamic neurons that could stimulate wanted motor programs can now fire
explain the indirect pathway
- stop signal
- reinforces inhibition
- thalamic neurons that could stimulate unwanted motor programs will not fire
what are the basal ganglia brain nuclei?
- caudate
- putamen
- globus pallidus
- subthalamic nucleus
what is the basal ganglia brainstem nuclei?
substantia nigra
what is input nuclei and what does it include?
- nuclei of the basal ganglia that receives the initial stimulus from the cerebral cortex
- includes the striatum (caudate and putamen collectively)
what is the main input nucleus for motor movement?
putamen
what is output nuclei and what does it include?
- delivers the final signal to the thalamus provided via a segment of the globus pallidus
what are the two segments of the globus pallidus ?
internal and external segment
what is the function of the internal segment of the globus pallidus ?
output motor information via direct and indirect pathways
what is the function of the external segment of the globus pallidus ?
modulates projections to the subthalamic nucleus via indirect pathway only
what does the globus pallidus internal segment have high levels of?
tonic inhibitory activity acting to inhibit the thalamus in a resting state
what is a modulatory nuclei and what are the three in the basal ganglia?
nuclei that communicate only with other nuclei in the BG either to reinforce or inhibit their signals
- globus pallidus external
- subthalamic nucleus
- substantia nigra
what is happening in the direct pathway at REST?
the ability of the thalamus to excite the cortex to initiate a motor program is INHIBITED by the tonic action of the globus pallidus internal
what could cause a motor program to be activated in the direct pathway?
- stimulation of the cerebral cortex OR substantia nigra
causes the striatum to be stimulated which inhibits the GPi, freeing the thalamus to be able to stimulate the cortex
explain why hypokinetic syndromes like Parkinson’s Disease occur
- striatal neurons are hyper-polarized and need multiple excitatory inputs to reach firing threshold
- the loss of stimulatory drive from the substantia nigra causes the inability of the striatum to reach threshold
Parkinson’s Disease is associated with the degeneration of what?
dopaminergic neurons in the substania nigra
neurodegeneration normally affects what neurons?
direct pathway neurons causing loss of the go signal
how would you increase inhibitory drive to the thalamus ?
provide greater stimulus to the GPi through the subthalamic nucleus which enhances the inhibitory drive of the GPi and causes inhibition of the thalamus
which nuclei tonically inhibits the subthalamic nucleus ?
Globus pallidua external
what neurons can inhibit the globus pallidus external causing the subthalamic nucleus to fire?
striatum
explain the indirect pathway
- striatum is excited by cortical neurons and inhibits the globus pallidus external
- GPe cannot inhibit the subthalamic nucleus anymore
- subthalamic nucleus stimulates GPi which inhibits the thalamus
- thalamus inhibited = no unwanted movement
what causes Huntington’s Disease and what does it result in?
- degeneration of neurons in the striatum
- results in unwanted movements like chorea (writhing and twisting movements) and rigidity
Huntington’s disease is a genetic disorder revolving around what chromosomal mutation?
chromosome 4 mutates such that an abnormally large number of CAG repeats occurs
how is the indirect pathway modulated?
by the neurons of the substantia nigra inhibiting the striatum
neurons of which brain nuclei use dopamine as a neurotransmiter?
substantia nigra
striatal neurons associated with the direct pathway have which type of receptor?
D1 dopamine receptor that depolarizes a cell in response to dopamine
striatal neurons associated with the indirect pathway have which type of receptor?
D2 dopamine receptor that hyperpolarizes a cell in response to dopamine
the D1 and D2 dopamine receptors of the striatal neurons allows for what?
both excision of the direct pathway and inhibition of the indirect pathway
