Basal Ganglia and Dopamine Flashcards
does the basal ganglia directly synapse with LMNs?
no
what are the 5 nuclei of the basal ganglia?
- Caudate
- Putamen
- Globus pallidus (internal/external)
- substantia nigra
- sub thalamic nucleus
what pathway is the globus pallidus external?
indirect pathway
what pathway is the globus pallidus internal?
direct pathway
what structures forms the striatum?
caudate and putamen
what are the 2 parts of the substantia nigra?
substantia nigra pars compacta
substantia nigra pars reticulata
where do major inputs to the basal ganglia come from?
cerebral cortex
where do almost all inputs synapse with in the basal ganglia?
the striatum
where in the basal ganglia are most major outputs coming from?
globus pallidus internal
substantia nigra pars reticulata
are the main output pathways from the basal ganglia excitatory or inhibitory?
inhibitory (GABAergic)
where are the main targets for major outputs?
thalamus
reticular formation
superior colliculus
what is inhibition?
When a neuron inhibits another neuron meaning it cannot be excited by a different neuron
what is disinhibition?
when a neuron inhibits another neauron meaning that neuron cannot inhibit the next neuron so that neuron then gets excited (disinhibition=excitation)
what is another name for the hyperdirect pathway?
stop pathway
what is the function of the hyperdirect pathway?
it supresses ongoing movement
what is another name for the direct pathway?
go pathway
what is the function of the direct pathway?
initiation of movemnt
what is another name for the indirect pathway?
no-go pathway
what is the indirect pathway?
supression of unwanted competing movements
what gets inhibited in the hyperdirect pathway?
the internal globus pallidus inhibits the thalamus
what gets inhibited in the direct pathway?
the thalamus is less inhibited (disinhibited) therefore movement is initiated
what gets inhibited in the indirect pathway?
the subthalamic nucleus stimulates the internal globus pallidus which inhibits the thalamus
what is the function of the substantia nigra pars compacta?
It modulates activity of both the
direct and indirect pathways
through dopamine release
(dopaminergic pathway
what is the function of the D1 receptors in the striatum?
Makes the direct pathway more active
(less inhibition to the thalamus)
what is the function of the D2 receptors in the striatum?
Makes the indirect pathway less active
(less inhibition to the thalamus)
what is the net effect of the D1 and D2 receptors?
less inhibition of the thalamus
what does it mean that the effects of dopamine are transient?
the increased excitation to the cortex in the direct and indirect pathway occurs in concert with selection of a movement
what does the basal ganglia form a motor loop with?
the motor cortex in the same cerebral hemisphere
what is the function of the prefrontal loop?
Initiation and termination of
cognitive processes
what is the function of the limbic loop?
Regulates emotional and motivated behaviour
Transitions from one mood state to another
what is an example of a hyperkinetic disorder?
Huntington’s disease
Hemiballismus
what is an example of a hypokinetic disorder?
Parkinson’s Disease
what is a hyperkinetic disorder?
insufficient inhibition of the thalamus
what is a hypokinetic disorder?
excessive inhibition of the thalamus
where do clinical signs of a lesion to the basal ganglia typically present?
impairments on the contralateral side of the body
what causes Huntington’s disease?
Selective atrophy of the caudate and
putamen
what pathway is affected first in Huntington’s disease?
indirect pathway
what happens to the pathways in Huntington’s disease?
the indirect pathway is underactive so eventually the direct pathway becomes overactive
since both the direct and indirect pathways are affected in Huntington’s what does this result in?
less tonic inhibition of the thalamus
what brain structure has a lesion leading to hemiballismus?
subthalamic nucleus
what is a symptom of hemiballismus?
involuntary flinging of the limbs
which side of the body is affected by hemiballismus?
the side contralateral to the damage
what is the cause of Parkinson’s?
Progressive degeneration of dopaminergic neurons in Substantia nigra pars compacta
what are the symptoms of Parkinson’s?
T- Tremor
R- rigidity
A-akinesia
P- postural instability
what pathways are affected in parkinson’s disease?
both direct and indirect
what occurs in the D1 pathway with parkinson’s?
there is less D1 facilitation
increased inhibition to the thalamus leading to decreased movement
what occurs in the D2 pathway with Parkinson’s?
less D2 facilitation
excessive inhibition of the thalamus
what is the net effect of dopamine loss?
inhibition of the thalamus
what is Parkinson’s disease treatment?
a supplement/replace dopamine called L-dopa which is a dopamine precursor
what can’t cross the blood-brain barrier?
dopamine
what are dyskinesias?
involuntary movements
what is ‘wearing off’?
predictable decline in function
what are on-off fluctuations
Unpredictable changes in motor function
what does deep brain stimulation to treat parkinsons’s target?
Globus Pallidus internal segment
Subthalamic nuclei
