Lecture 17 - Basal Ganglia Flashcards
What are the 6 parts/associated structures of the basal ganglia?
- VA/VL complex of thalamus
- Subthalamic nuclei
Caudate - Putamen
- Globus pallidus
- Substania nigra pars reticula
What do dopaminergic neurons do?
- excite some medium spiny cells
- inhibit others
What characterizes medium spiny neurons?
- silent unless excited
- gabergic
What kind of inputs do medium spiny neurons receive/
-many excitatory cortical inputs
What characterizes Globus pallidus or substantia nigra?
- active unless inhibited
- gabergic
What are the 4 major parts that form connections within the basal ganglia?
- dopaminergic neuron
- medium spiny neuron
- cortical pyramidal neurons
- globus pallidus or substantia nigra
What are the two major functions of the Basal Ganglia?
- Non-Motor loops
2. Motor loops
What are motor loops?
regulate upper motor neurons that initiate + help coordinate voluntary movement
What are the 2 main motor pathways?
- direct pathway (“accelerates” movement, Huntington’s)
2. indirect pathway (“brakes” movements, Parkinson’s)
What are 3 types of non-motor loops?
- executive/prefrontal loop
- limbic loop
- oculomotor loop
What is the order of the direct pathway?
- Cortex
- Putamen
- Glob. Pal. Int.
- VA/VL Thalamus
How does the direct pathway accelerate movement?
- disinhibiting the thalamus
- also disinhibiting the upper motor neurons in the cortex
What is the order of the indirect pathway?
- Cortex excites putamen via glutamate
- Putamen inhibits glob. pal. ext. via GABA
- Glob. Pal. ext. inhibits sub thal nuc via GABA
- Sub Thal. Nuc. excites glob pal int via GABA
- Glob. Pal. Int. inhibits thalamus
- VA/VL Thalamus is inhibited
How does the indirect pathway brake movement?
-modulates the disinhibitory actions of the direct pathway
how are both the direct and indirect pathways regulated?
dopamine
Dopamine _____ the direct pathway via ____ receptors
excites, D1
Dopamine _____ the indirect pathway via _____ receptors
inhibits, D2
Overall, dopamine has a net ____ effect
excitatory
Medium spiny cells that project to the _______ are ____ by dopamine D1 receptors
Glob. Pal. Int., excited
Medium spiny cells that project to the _______ are ___ by dopamine D1 receptors
Glob. Pal. Ext., inhibited
What are an example of projection neurons in the basal ganglia?
medium spiny neurons
Projection neurons are _____
GABAergic = inhibitory
Cells in the striatum are usually ____
silent
Cells in the globus pallidus are tonically ______
active
Projection neurons in the substantia nigra, pars compacta are ____
dopaminergic
What are 2 categories of diseases of the basal ganglia?
- hyperkinesia
2. hypokinesia
What are 2 types of hyperkinesia?
- hemiballismus (loss of subthalamic nucleus)
2. huntington’s disease (loss of striatum)
What are 2 types of hypokinesia?
- associated with loss of substantia nigra pars compacta
1. Parkinson’s disease
2. drug induced (neuroleptics, MPTP)
What is Parkinson’s Disease characterized by?
loss of dopaminergic neurons in the substantia nigra
What does loss of dopaminergic neurons lead to?
- bradykinesia (slowed, impaired movement)
- rigidity
- “pill rolling” tremor
What happens when dopamine is removed from the schematic?
- glob. pal. int. goes into overdrive
- reduces excitation of motor thalamus via direct pathway or via indirect pathway
What happens when the subthalamic nucleus is loss in hemiballimus?
- activity in glob. pal. int. is reduced
- VA/L receives too little inhibition, goes into overdrive
- over excites cortex
What does the loss of striatal neurons lead to?
- subtle changes in coordination
- severe movement disorders
- Akinesia (patient can hear + understand, but not speak)
What does the loss of the ptamen do?
- reduces inhibition of glob. pal. ext.
- results in increased cortical activity
What are 5 therapies for Parkinson’s
- L Dopa
- Thalamotomy and Pallidotomy
- Deep brain stimulation of subthalamic nucleus
- Implantation of fetal dopaminergic neurons
- optically gated ion channels in damaged regions
