Principles of Neuroscience Lecture 14 Modulation of Movement Flashcards
Describe the structure of the basal ganglia
5 discrete regions: Caudate Putamen Globus Pallidus Sub-thalamic nuclei Substantial nigra
Which two regions in the brain are modulatory centres for movement?
Basal Ganglia
Cerebellum
Describe the localisation of the basal ganglia
Caudate: runs along edge of lateral ventricles
Putamen: base of forebrain - telencephalon
Globus pallidus: next to putamen : external then internal
Sub thalamic nuclei: under thalamus
Substantial nigra: mesencephalon - midbrain
What are the functions of the basal ganglia (3)
- Initiation of movement
- Optimisation of movement, evaluation
- Selection of movements from a repertoire
What are the inputs to the Caudate-Putamen?
- Cerebral cortex
2. Substantial nigra pars compacta
What are the two output pathways from the Caudate Putamen?
Direct
Indirect
Describe the direct pathway
- Caudate putamen actively inhibits Globus pallidus internal
- GPi can no longer carry out its normal activity of inhibiting the thalamus
- Thalamus is not inhibited, so it activates the motor cortex
Describe the indirect pathway
- C-P inhibits the Globus Pallidus external
- GPe can no longer inhibit the sub - thalamic nuclei, because it has been inhibited
- Sub thalamic nucleus is not inhibited, so it excites the GPi
- The GPi is activated, so it can carry out it’s function of inhibiting the thalamus
- The thalamus is inhibited, so it can’t activate the motor cortex
What is the role of the direct pathway?
Selection and activation of the desired movements
What is the role of the indirect pathway?
Inhibition of competing movements
What are basal ganglia loops?
Such as those we see here. They talk to the cortex.
They aren’t just associated with motor function
What are the two dopamine receptors in the Caudate-Putamen?
Where is the dopamine coming from?
D1: activates direct pathway
D2: inhibits the indirect pathway
Dopamine is coming from the substantial nigra pars compacta
Describe the pathology of Parkinson’s disease?
The cells in the substantial nigra pars compacta die
Dopamine is no longer released onto the caudate-putamen
There is no longer activation of movement via the two pathways
When is a tremor first seen in Parkinson’s?
When 80% of the cells in the substantial nigra are already dead
How does the substantial nigra pars compacta activate movement? (Two ways)
- Activate the direct pathway, which is activating movement
2. Inhibits the indirect pathway, which is itself inhibitory. Thus, movement is activated
What is a treatment for Parkinson’s?
L-DOPA:
Saturate brain in dopamine
Only regions that need it respond to it
C-P now has dopamine, and movement is activated
Deep brain stimulation:
Electrical stimulation of the C-P and GP
This causes retrograde activation of the pathway
This stops the tremor
Describe the pathology of Huntington’s disease
Cells in C-P and GP die
GP normally inhibits the thalamus
No inhibition mean there are spontaneous and jerky movements
What is the striatum?
This is the caudate and the putamen
Describe deep brain stimulation?
Stimulation of the sub thalamic nucleus
Retrograde activation of the pathway, stopping the tremor and activating movement
Describe the functions of the Cerebellum (3)
- Start and stopping of movements: coordination
- Motor learning
- Plan formation
- Maintenance of muscle tone
Does not itself initiate movement
Where is the cerebellum?
Hindbrain: metencephalon
What are the inputs to the cerebellum?
Frontal cortex
Proprioception
Vestibular nuclei
What are the outputs from the cerebellum?
Motor cortex
What is ataxia?
Describe the symptoms seen in a clinical test
Ataxia: “can’t follow the path”. This is when movement is inefficient because the brain does not form a plan about where the limb should go.
Eg. Touch a spot, then touch you nose
The path is not direct
The patient does not have the feed forward information
