Basal Ganglia Flashcards
Basal Ganglia- movement
Regulate intensity of slow or stereotypes movements
Inhibit antagonistic + unnecessary movements
Switch motor programmes (stop or start)
Neural structures in basal ganglia
Caudate nucleus
Putamen
Globus pallidus
Caudate nucleus
C shaped nuclei in frontal lobe
Head region curves + extends to form elongated body, tapering at tail and ending in temporal lobe
Putamen
Large, rounded nuclei located in forebrain
Connected to caudate nucleus at head region of caudate
Globus pallidus
Pale body Internal segment (GPi) --> output to thalamus External segment (GPe) --> relays info between other basal ganglia nuclei + internal globus pallidus
Internal capsule
White matter structure
Separates lentiform nucleus + caudate nucleus
Caudate nucleus blood supply
Middle cerebral artery (body)
Anterior cerebral artery (anterior)
Putamen blood supply
Middle cerebral artery
Anterior cerebral artery (anterior)
Globus pallidus
Middle cerebral artery
Anterior choroidal
Internal capsule
MCA (middle)
ACA (anterior limb)
Anterior choroidal (posterior limb)
Neuronal projections into basal ganglia are from
Cerebral cortex
Substantia nigra pars compacta
Cerebral cortex projections
Almost all project directly to caudate + putamen
Majority from frontal + parietal
–> projections referred to as corticostriatal pathway
Substantia nigra pars compacta projections
Located in midbrain
Dopaminergic input to caudate nucleus + putamen
–> progressions referred to as nigrostriatal pathway
Input zone of basal ganglia
Corpus striatum- caudate nucleus + putamen
Corpus striatum neurones
75% medium spiny neurones
Inputs to medium spiny neurones
Cortical neurones (glutamatergic) Substantia nigra pars compacta neurones (dopaminergic) Local circuit neurones within corpus striatum (GABAergic)
Axons arising from medium spiny neurones converge on
Neurones in globus pallidus + substantia nigra pars reticulata
Medium spiny neurones input
Cortical + Substantia nigra pars compacta + Corpus striatum –> medium spiny neurones –> globus pallidus + substantia nigra pars reticulata
Output zone of basal ganglia
Globus pallidus
Substantia nigra pars reticulata
Output zone projections
Subthalamic nucleus
VA/VL thalamic nuclear complex
Superior colliculus –> eye movements
Subthalamic nucleus
Small paired nuclei below thalamus
Input from cerebral cortex + GPe
Projects to GPi and substantia nigra pars compacta
VA/VL thalamus complex
Input from GPi
Projects to motor areas of cerebral cortex
Direct pathway
Means for Basal ganglia to facilitate initiation of volitional movement
Direct pathway MOA
Excitatory glutamate axons project from sensory + association cortices to caudate + putamen
–> project to GPi (inhibitory)
GPi projects to motor thalamus (inhibitory)
–> disinhibition as two negatives in a row
This then projects to motor thalamus + back to supplementary motor cortex
indirect pathway
Antagonise activity of direct pathway
Stops movement
Indirect pathway MOA
Output from caudate + putamen goes to GPe and subthalamic
This then goes to GPi
Subthalamic excitatory input to GPi tonic inhibitory action increases inhibition to motor thalamus
–> motor cortex output from motor thalamus remains fixed
Rest or doing repetitive movement
Direct pathway inactive
Indirect pathway active
Change in movement
Direct pathway active
Indirect pathway inactive
D1 receptor
Increases cAMP
Increases sensitivity in corpus striatum neurones to glutamate
Projects to GPi directly via direct pathway
Activated by dopamine
D2 receptor
Decreases cAMP
Depressed by dopamine
Direct pathway receptor
D1
Indirect pathway receptor
D2
Parkinson’s
Hypokinetic
Over 80% of dopaminergic neurones have to degenerate before clinical signs of disease manifest themselves
Early PD
Levodopa
Dopamine agonist
MAO-B inhibitors
PD with motor + non-motor complications
COMT inhibitors
Apomorphine
Amantidine
Advanced PD
DBS
Huntingtons
Hyperkinetic
Autosomal dominant
Involuntary movements
Loss of GABAergic neurones in corpus striatum
Chorea
Rapid, involuntary, jerky-type movements
Athetosis
Slow, involuntary, smooth, writhing type movements
Ballismus
Rapid, involuntary, wild flinging-type movements
Huntingtons management
Amantidine- dystonia, apathy
Benzodiazepine- anxiety
Haloperidol- psychosis
Olanzapine- weight loss