Question

Consider the brain areas and connections pictured in the simplified basal ganglia circuit. Parkinson’s disease results from the degeneration of dopamine neurons in the substantia nigra pars compacta (SNc). Dopamine can inhibit or excite neurons in the putamen, a sub-division of the striatum. Describe how this damage causes a chain of effects on activity in other basal ganglia areas and the structures they ultimately output to, and how this results in hypokinesia (reduced movements) in two different ways. Make sure to refer differentially to the ‘direct’ and ‘indirect’ pathways.

Answer 1

Parkinson’s is a condition which causes the gradual loss of dopamine-producing brain cells of the substantia nigra. Dopamine is a neurotransmitter which sends impulses.loss of dopamine causes slowing of impulses due to which slow movements occurs that is hypokinesia. N

Neurons in substantia nigra pars compacta produce dopamine,that transmits signals from the substantia nigra to other parts of the brain which collectively called the “basal ganglia”. Neural Communication among substantia nigra pars compacta and basal ganglia results in smooth and purposeful movements. When the neurons in the substantia nigra are damaged in large numbers, the loss of dopamine prevents normal function in basal ganglia and causes the motor systems like Tremors, rigidity, loss of balance .The substantia nigra pars compacta contains dopamine neurons – loss of neurons produce dopamine causes impaired movement and balance.

Alpha-Synuclein is a protein found in neurons. In Parkinson's, a-Synuclein is found in globs called as Lewy bodies found in neurons. These are found in dopaminergic neurons in the substantia nigra pars compacta and contribute to death of these neurons. Lewy bodies can be found in other brain areas such as the amygdala, locus coeruleus, and raphe nucleus. These areas play role in anxiety, depression and stress.Cortex is responsible for cognition,Lewy bodies in this area of the brain are thought to cause dementia.

Lewy bodies move from one brain region to another,called Braak staging.Initially,Lewy bodies are found in the enteric nervous system, the medulla, and the olfactory bulb. The enteric nervous system that controls the gastrointestinal organs causing problems like constipation. medulla,that regulates breathing, heart functions, and digestion ,due to which patient feels blood pressure problems. Lastly,the olfactory bulb controls sense of smell. Also, presence of Lewy bodies in substantia nigra pars compacta correlates with motor symptoms. In later stages of this disease, Lewy bodies are found in the cortex causing dementia.