Basal Ganglia Flashcards
1
Q
Role of basal ganglia in motor control
A
- modulation of motor performance via interconnections with the motor cortices.
- major feedback loop to motor and association cortex
- in general, serve a role in motor program selection.
2
Q
Major source of input to basal ganglia
A
- Cerebral cortex
- primarily: frontal lobe areas and sensorimotor areas that have a greater role in the planning and initiation of movement.
3
Q
Characteristics of Parkinson’s disease
A
- Resting tremor, difficulty initiating movements, slowness
- etiology: loss of dopamine neurons in the substantia nigra.
4
Q
Probable mechanism of Parkinson’s
A
- Substantia nigra sends dopaminergic axons back to the striatum.
- The action of dopamine in striatum is probably largely excitatory, since Parkinson’s disease, which includes degeneration of substantia nigra neurons and loss of dopaminergic input, is marked by a paucity of movement.
5
Q
Output of basal ganglia: inhibitory vs. excitatory
A
- Inhibitory.
- GPI → (GABA -) @ Thalamus → (Glu +) Cortex.
- output of the basal ganglia is directed to the thalamus via the pallidothalamic fibers from the GPI which are GABA-nergic and from there back to the cortex.
- Basal Ganglia provide resting inhibition of the thalamus until a signal comes from the cortex causing the disinhibition of the the thalamus via the direct pathway.
6
Q
Genetic cause of Huntington’s Disease
A
- autosomal dominant
- site of mutation @ short arm of the 4th chromosome.
- Normal humans have 17-34 CAG repeats, HD have > 40.
7
Q
Characteristics/presentation of Huntington’s Disease
A
- Striatal damage produces athetosis or chorea.
- Chorea = continuous rapid movements of the face, tongue or limbs (usually distal portions).
- Athetosis indicates slow, writhing, ceaseless movements of hand, sometimes lips, tongue, neck and foot.
8
Q
HD impact on basal ganglia
A
- caudate = most affected region of basal ganglia
9
Q
“Direct path” from cortex to basal ganglia and back to cortex
A
- Cortex → excites through striatum Caudate/Putamen with glutamate
- glutamate → which inhibits GPI with GABA →
- stops inhibiting Thalamus with GABA → which can then excite the cortex with glutamate
10
Q
Stroke @ subthalamic nucleus impact
A
- subthalamic nucleus = integral piece of the indirect pathway.
- If stroke that destroyed the STN then a great degree of thalamic inhibition would be lost ==> hemiballismus
- e.g. stroke @ small ganglionic branch of posterior cerebral artery
- Disinhibition would rule, hence the flailing of arms and legs on one side.
11
Q
Type of stimulus used in deep brain stimulation for Parkinson’s patients
A
- Hyperpolarizing.
- Main problem in Parkinson’s = STN and GPI cause inhibition of the thalamus.
- DBS would work to remove such inhibition, otherwise known as encourage disinhibition.
- Hyperpolarizing the STN or GPI would do just that without the need for medications.