Basal ganglia Flashcards
In what way does the basal ganglia regulate movement?
- regulates the intensity of slow movement
- inhibits antagonist and unnecessary movements
- switch motor programs
Name the neural structures that make up the basal ganglia.
Caudate
Putamen
(make the corpus striatum)
Globus pallidus internal + external
(makes the lenticular nucleus with the putamen)
Also has motor associations with subthalamic nucleus + substantia nigra
In what region/s is the caudate nucleus located?
Frontal lobe and temporal lobe
In what region is the putamen located?
Forebrain
What two structures does the internal capsule separate?
Lentiform nucleus and caudate nucleus
What artery/ies supply the putamen?
MCA and ACA (penetrating branches such as the recurrent artery of Heubner)
What artery/ies supply the caudate?
MCA (body) and ACA (anterior)
also supplied by lenticulostriate arteries
What artery/ies supply the thalamus?
Branches of posterior cerebral and basilar arteries –> posterior choroidal, thalamogeniculate, and thalamoperforator arteries
What artery/ies supply the globus pallidus?
Anterior choroidal artery and middle cerebral artery
What artery/ies supply the internal capsule?
MCA (middle), ACA (anterior limb), anterior choroidal (posterior limb)
Which pathway involves projections from the cerebral cortex to the putamen and caudate? What NT is involved?
Corticostriatal pathway
Glutamate (excitatory)
Which pathway involves projections from the substantia nigra pars compacta to the putamen and caudate? what NT is involved?
Nigrostriatal pathway
Dopamine
What NT is involved with the local circuit neurones within the corpus striatum?
Gamma-AminoButyric Acid (inhibitory)
Describe how initiation of volitional movement occurs through the direct pathway.
- cerebral cortex projects to the corpus striatum via excitatory glutamate neurones
- when the corpus striatum is ‘excited’ it releases GABA
- corpus striatum projects to the GPi and inhibits it via GABA
- this prevents GPi from inhibiting the VA/VL complex (therefore it is disinhibited)
- there is excitation of UMNs in the frontal cortex
Describe how the indirect pathway works.
Acts to antagonise the activity of the direct pathway
- output from the caudate and putamen goes through the GPe and the subthalamic nucleus (before GPi)
- tonic inhibitory actions of the GPi are increased by excitatory input from subthalamic nucleus
- Motor thalamus remains fixed and supplementary motor cortex output remains fixed
During rest or repetitive movement, what is the state of the direct and indirect pathways? (i.e. active or inactive?)
direct pathway = inactive
indirect pathway = active
What is the effect of dopamine on the direct and indirect pathways?
Dopamine increases the action of the direct pathway (via D1 receptors)
Dopamine decreases the action of the indirect pathway (via D2 receptors)
How are D1 receptors able to increase the action of the direct pathway?
The D1 receptor increases cAMP
this increases the sensitivity of the corpus striatum neurones to glutamate
increases the inhibition of the GPi
What would happen if there was no dopamine in this system? (i.e. as in hypo kinetic disorders)
There would be no activation of D1 receptors and no depression of D2 receptor - system is ‘stuck’ = unable to stop/start movement properly
What are the characteristics of Parkinson’s?
resting tremor
slowness of movement (bradykinesia)
muscular rigidity
minimal facial expressions
In PD, what causes the defects in motor function?
Loss of dopaminergic neurones in the substantial nigra pars compacta - shift to indirect pathway
What kinds of drugs are used to treat early PD?
Levodopa
Dopamine agonists
MAO-B inhibitors
What kinds of drugs are used to treat PD with motor and non-motor complications?
COMT inhibitors
Apomorphine
Amantadine
What treatment method is used to treat life-limiting PD?
DBS
What gene is mutated in Huntington’s disease?
Hungtingtin
What is responsible for the hyperkinetic movements seen in Huntington’s?
Loss of GABAergic neurones in the corpus striatum
What is chorea?
rapid, involuntary, jerky-type movements that are more distal
What is athetosis?
slow, involuntary, smooth, writhing-type movements that are more distal
What is ballismus?
rapid, involuntary, wild-flinging type movements that are more proximal
What drugs would you use to treat a Huntington’s patient with no other symptom but chorea?
Tetrabenazine
Amantadine
What drugs would you use to treat a Huntington’s patient with chorea and weight loss?
Olanzapine
Cannabinoids
What drugs would you use to treat a Huntington’s patient with chorea, psychosis, aggression/impulsivity?
Aripiprazole Haloperidol Olanzapine Risperidone (+ many others)
What is the inheritance pattern of Huntington’s?
Autosomal dominant
