6.1.2 Basal Ganglia Flashcards
How does Parkinson’s Disease affect the normal functions of the BG (direct and indirect pathway)?
-Normally: Direct Path: disinhibits thalamic nuclei to allow motor output. Indirect Path: inhibits thalamic nuclei to inhibit motor output
Dopamine activates the direct pathway and inhibits the indirect pathway.
In Parkinson’s disease, the loss of dopaminergic input by the SNc most significantly affects motor output via the indirect path:
- Loss of inhibition from SNc
- STN can excite GPi/SNr
- GPi/SNr can inhibit thalamic nuclei
- Cortical motor output is suppressed
What is the hyperdirect pathway?
What is Hemiballismus?
high velocity, large amplitude, involuntary movements, generally in the arms
Associated with lesions of the subthalamic nucleus
What are the characteristics of the Striatum?
Receiving or Input nuclei of BG
Made up of Putamen and Caudate nucleus
Draw a chart comparing the Normal neural circuity and a Parkinson’s Patient.
What are Choreaform Movements?
involuntary, irregular, jerky movements that are slower and smaller in amplitude than those associated with ballismus
What is given to Patients with Parkinson’s and why?
Dopamine is not capable of crossing the BBB.
Levodopa is instead prescribed as it is a permeable precursor to Dopamine
Carbidopa– peripheral dopa decarboxylase inhibitor – is co-prescribed in order to minimize the conversion of L-dopa to dopamine in peripheral tissues. Helps concentrate dopamine in the brain
What are the characteristics of Globus pallidus?
Made up of internal and external segment
Internal - output nucleus of BG
What is the underlying fault in neural circuitry for Huntington’s Disease?
- Caused by loss of the GABA neurons projecting from striatum to Gpe
- GPe is disinhibited, allowing neurons to fire at a higher rate, suppressing STN
-Suppressed STN disinhibits thalamic nuclei, causing hyperkinesia
What are the effects of dopamine on the direct and indirect pathway?
- Mixed effects of the additional pathway – the nigrostriatal – from SNc ⇒ Striatum
- Dopamine excites the Direct Route, causing disinhibition of thalamus
- Dopamine inhibits the Indirect Route, suppressing the STN and also disinhibiting the thalamus
What is Athetosis?
continuous writhing movements
What is the major function of the Basal Ganglia?
disinhibit CNS structures to allow for initiation of voluntary movement
- Accomplished by inhibitory firing from BG onto inhibitory synapses affecting the CNS
- High tonic firing rate
What are the main problems with L-dopa treatment for PD?
Severe dyskinesias
Wearing off phenomena
On-off effects
Draw out the basic circuitry and neurotransmitter of the basal ganglia (include direct and indirect pathways)
Direct pathway: By inhibiting the GPi/SNr, it can no longer inhibit the thalamus. Thus, the thalamus is disinhibited and motor output occurs
Indirect Pathway: By stimulating the GPi/SNr, inhibition of thalamus occurs. Thus, thalamus does not excite the cortex, no output
Is the the difference between the Pars reticulata and Pars Compacta?
Reticulata: Output nucleus like the GPi (for oral/face)
Compacta: Dopamine containing neurons and project to the striatum
Lesions of the Basal Ganglia affect limbs on the?
Contralateral side
Here’s why:
The projections from BG to cortex are uncrossed.
The projection from motor cortex to spinal cord is largely crossed.
Draw out the basic BG - thalamo - cortical loop.
Draw a chart comparing the neural circuitry in Huntingtons vs normal
What are the motor disorders in Parkinson’s
