Basal ganglia and diencephalon Flashcards
What makes up the striatum?
Caudate and putamen
What divides the caudate and putamen?
Internal capsule
Where does the globus pallidus lie?
Medially to the putamen
Where does the STN lie?
Beneath the thalamus, above SN of midbrain
Where is the tail of caudate?
Beneath the putamen lateral to the thalamus
Where is the BG input?
Cortex to striatum
Where is the BG output?
Ascending GPi and SNr to thalamus
Descending GPi and SNr to upper brainstem
What neurons give the cortical input?
Medium spiny neurons
What type of neuron are MSNs?
Glutaminergic
Where does the striatum fire to?
Direct pathway: from striatum → SNr/GPi
Indirect pathway: from striatum → GPe → STN → SNr/GPi
Hyper-direct pathway: from cortex to STN (bypasses striatum)
What neurons are striatum projections?
GABAergic (inhibitory)
What are the two types of striatal projection neurons?
D1: Enriched in dopamine D1- receptors, substance P, dynorphin opioid
D2: Enriched in dopamine D2 receptors, A2A receptors, enkephalin opioid
When there is no striatal input how do SNr/GPi fire?
Tonically to inhibit the thalamus
When striatal input is stimulated how is motor programme released?
GABAergic inputs cause SNr/GPi to cease firing, disinhibition of the thalamus - motor programme released
What important ascending pathway is part of the basal ganglia?
Nigrostriatal dopamine input: From SNc to striatum (MSN)
How does the direct pathway affect thalamocortical relay?
Cortex excites striatum through glutaminergic
Striatal output inhibits SNr/GPi and so reduces GPi inhibition on thalamus → Disinhibition of thalamocortical relay
Overall, it facilitates movement
Direct pathway…
Facilitates movement
How does the indirect pathway affect thalamocortical relay?
Cortex excites striatum through glutaminergic
Striatal output inhibits GPe and so reduces GPe inhibition of STN.
Increased activity in STN excites GPi so increases GPi inhibition on thalamus → Inhibition of thalamocortical relay
Overall, it inhibits movements
What neurons does the STN give off?
Glutaminergic
Indirect pathway…
Inhibits movement
What is dopamines effect on the direct pathway?
D1 DA receptors on direct striatal projections facilitate pathway
And so, dopamine facilitates movement
What is dopamines effect on the indirect pathway?
D2 DA receptors on indirect striatal projections inhibit pathway
Inhibits the inhibition of movement –> facilitates movement
The movement disorder typically associated with Parkinson’s disease
Rigidity, hypokinetic
The movement disorder typically associated with degenerative lesions of the striatum..
Huntington’s
Choreiform movements
At a cellular level vascular lesions of the subthalamic nucleus results in
Loss of glutaminergic input to the globus pallidus internal segment
In Parkinson’s disease the major site of dopaminergic cell loss is the
SNc
The major drug therapy for Parkinson’s disease is L-DOPA which can
Enhance DA production by remaining DA neurons
Ballism is caused by…
Damage to the STN
