Basal Ganglia Flashcards
What are the components that make up the basal ganglia:
Striatum (caudate + putamen)
Globus Pallidus (external and internal)
Substantia Nigra
Subthalamic Nucleus
Describe the basal ganglia circuitry
Cortex –> striatum (putamen + caudate) –> GPi and SNr –> Thalamus –> Cortex
What two bundle fibers enter the thalamus?
Lenticular fasciculus from the globus pallidus internal, travel above the subthalamic nuclues +
Ansa Lenticularis from teh GPi, travesl below the subthalamic nucleus
Come together to enter the thalamus as the thalamic fasciculus
Input to the striatum from the cortex is ______ [inhibitory/excitatory]
Uses NT: ______
Principal output from the BG is via the ____ and _____
are _____ [inhibitory/excitatory]
Uses NT: ______
Thalamocortical projections are ______ [inhibitory/excitatory]
FXN: motor intention
Input to the striatum from the cortex is EXCITATORY
uses the NT: GLUTAMATE
Principal output from the BG is via the GPi and SNr
mostly INHIBITORY (balance of excitatory and inhibitory inputs to striatum determine whether the thalamus is suppressed)
uses GABA
Thalamocortical projections are EXCITATORY
FXN: MOTOR INTENTION
The basal ganglia has 4 major circuits. These parallel loops are concerned with…
Motor loop –>
Cognitive loop –>
Limbic loop –>
Oculomotor loop –>
Motor loop –> learned movements
Cognitive loop –> motor intention
Limbic loop –> emotional aspects of movements
Oculomotor loop –> voluntary saccades (fast eye movements)
Direct pathway:
In the end, is the cortex excited or suppressed?
Direct pathway: cortex excites the striatum –> striatum INHIBITIS GPi –> Thalamus is DISINHIBITED –> cortical activity is facilitated
excitatory input to cortex
Indirect pathway:
In the end, is the cortex excited or suppressed?
Stratium (striatal neurons with D2 R are activated by dopamine) –> GPe is inhibited (neurons of the indirect pathway have a predominantely project to the extermal segment, which normally would inhibit the GPi; if GPe is inhibited, there is less inhibition of GPi + there is less inhibition of the subthalamic nucleus; without inhibition, subthalamic nucleus excited the GPi) –> GPI is facilitated –> thalamus is INHIBITED –> cortex is suppressed
Cortical activity is suppressed
What happens during Parkinsons Disease?
There is a degeneration of the substantia nigra and the dopamine releasing centers –> normal excitation of the direct is decreased / inhibition of the indirect is less too –> GPe is inhibited –> subthalamic nucleus is activating GPi and the GPi is not being inhibited by the GPe or the direct pathway as much –> increased inhibition of the thalamus –> less excitation back to cortex / inability to initiate movment
What distinguising features can be seen in the gross brain of a patient suffering from parkinson disease?
Histology reveals loss of pigmented neurons in the substantia nigra and round, eosinophilic inclusions of alpha-synuclein/Lewy bodies in affected neurons
Huntington Disease:
_____ disorder of chromosome _____ on _____ gene
–> abnormal _____ repeat expansion
Onset about ages:
Initial sx (2):
Disease progression characteristic w/:
Huntington Disease:
AUTOSOMAL DOMINANT disorder of chromosome 4 on HUNTINGTIN gene
–> abnormal TRINUCLEOTIDE repeat expansion
Onset about ages: 30- 50 YRS
Initial sx (2): CHOREA AND ALTERNATION OF MOOD
Disease progression characteristic w/: DEMENTIA, WORSENING PERSONALITY CHANGES
What is the pathogenesis of huntington disease?
Degeneration of neurons within stiratum, particularly degeneration of GABAergic neurons in the caudate nucleus of the BG –> decrease inhibition of GPe –> increased inhibition of subthalamic nucleus and GPi –> LESS TONIC INHIBTION OF THE THALAMUS –> increased movements (chorea)
