1. Parkinson’s disease (PD) is chronic progressive nervous system disorder that
ID: 3504905 • Letter: 1
Question
1. Parkinson’s disease (PD) is chronic progressive nervous system disorder that affects movements. Describe:
a) How dopaminergic neurons in substantia nigra are thought to control the direct and indirect pathways of the basal ganglia (2 marks) and what is overall effect of dopaminergic neurons in the substantia nigra on the basal ganglia outflow in normal individuals? (1 mark)
b) In patients with Parkinson’s disease that have akinesia, describe the changes that occur in nigrostriatal pathways (1 mark); and in the direct & indirect pathways of the cortex-basal ganglia-cortex motor loop, underlying this motor symptom. (3 marks)
Explanation / Answer
ANS.
a). Dopaminergic neuron in substantia nigra control the direct and indirect pathway of basal ganglia in a balanced manner. These two pathways have opposite effects on thalamic target structures. Excitation of direct pathway, excites thalamic neuron which make excitatory connections on to cortical neurons whereas excitation of indirect pathway has effect of inhibiting thalamic neuron due to which motor cortex neurons are not excited. An Imbalance between direct and indirect pathway results in motor dysfunctions which leads to extrapyrimidal effects. Direct pathway striatial neurons have D1 dopamine receptors which causes depolarization of the cell in response to dopamine whereas indirect pathway striatal neurons have D2 dopamine receptors which causes hyperpolarization of the cell in response to dopamine.
b). The cause of Parkinson Disease that have Akinesia is due to loss of dopaminergic neuron in substantia nigra. The nigrostriatal pathway excites the direct pathway and inhibits the indirect pathway, the loss of this, changes the balance in favor of activity in the indirect pathway because of which the GPint neurons becomes abnormally active which keeps thalamic neurons inhibited and hence in absence of the thalamic input, the motor cortex neurons are not excited.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.