Basal Ganglia - Lecture 2 Flashcards
What are the Basal ganglia?
A collection of subcortical nuclei extending into the midbrain
Caudate, putamen, globus pallidus (internal and external), substantia nigra (pars reticular and pars compacts), subthalamic nucleus
What are the input nuclei of the BG?
The striatum (caudate and putamen) receives direct and indirect connections from the cortex.
Afferent connections from the cortex and thalamus are directed to the striatum
What are the output nuclei of the BG?
The Gpi and SNpr both provide tonic inhibitory output to the thalamus
What is a secondary role of the substantia nigra pars reticula?
SNpr also influences saccadic eye movements via the superior colliculus
When referring to internal connections within the basal ganglia, what does the striatum project to?
The globus pallidus (striato-pallidal pathway)
The substantia nigra (striato-nigral pathway)
The subthalamic nucleus forms an indirect pathway with what part of the BG?
Between the GPe and the GPi/SNpr
When discussing the direct and indirect pathways, what neurotransmitters are involved and what effects do they have?
Excitatory neurotransmitters - glutamate
Inhibitory neurotransmitters- gaba, substance P, enkephalin
Mixed effect - dopamine
Dopamine is known to have a mixed effect on the direct/indirect pathway, explain this
When dopamine acts on the D1 receptor, the direct pathway is excited. When acting on the D2 receptor, the indirect pathway is inhibited. Both of these effects disinhibit thalamic output, hence facilitating movement
Basal ganglia is involved with the strategic aspects of movement, what are some cardinal symptoms of Parkinson’s ?
Bradykinesia (slowness of movement) Akinesia (inability to initiate movement) Rigidity (increased muscle tone) Tremor Postural instability
A loss of dopaminergic cells in the substantia nigra can be seen
In reference to the direct/indirect pathways, what happens in Parkinsons and Huntingtons?
In Parkinson’s, indriect pathway is over active hence movement is restricted
In huntingtons, direct pathway is over active hence movement facilitation
Give a detailed description of the treatments available in Parkinson’s?
L-dopa - a dopamine precursor promotes the manufacture of dopamine in the distal end of SNpc neurons (in striatum)
Pallidotomy - heat ablation of the GPi, reduces inhibitory output of BG
STN stimulation - disrupts the function of STN, inhibits indirect pathway
Discuss concept of paradoxical movement in Parkinson’s.
Sensory cues (beeps on floor) can be implemented to overcome akenesia, this overrides the basal ganglia and emphasise it’s normal role in self-triggered movement.
What are some symptoms of Huntington’s disease and effects it has on the basal ganglia?
Rapid jerky motions, with choreiform with no clear purpose.
Causes selective atrophy of the caudate and the putamen
