**Parkinson's Disease and Dopamine Dysfunction**

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive motor symptoms such as tremors, rigidity, bradykinesia (slowness of movement), and postural instability. These symptoms result from the degeneration of dopaminergic neurons in a region of the brain called the substantia nigra. Dopamine is a neurotransmitter that plays a crucial role in movement control and coordination, as well as other functions such as reward, motivation, and mood regulation.

**Defective Action of Dopamine in Parkinson's Disease**

The defective action of dopamine in the brain is primarily responsible for the motor symptoms observed in Parkinson's disease. Dopamine is released by dopaminergic neurons in the substantia nigra and acts as a chemical messenger, transmitting signals between neurons in the brain. It binds to specific receptors called dopamine receptors, located on the surface of target cells, and activates them.

In Parkinson's disease, the degeneration of dopaminergic neurons leads to a significant reduction in the production and release of dopamine in the brain. This decrease in dopamine levels disrupts the normal functioning of the basal ganglia, a group of structures involved in motor control. The basal ganglia help coordinate movements by facilitating or inhibiting signals that are transmitted from the cerebral cortex to the muscles.

**Role of Dopamine in Motor Control**

Dopamine has an inhibitory effect on the basal ganglia circuitry. It helps balance the activity of two major pathways within the basal ganglia: the direct pathway and the indirect pathway. The direct pathway facilitates movement, while the indirect pathway inhibits movement. Dopamine acts to modulate the activity of these pathways, ensuring the smooth initiation and execution of voluntary movements.

In Parkinson's disease, the lack of dopamine leads to an imbalance between the direct and indirect pathways, resulting in excessive inhibition of movement. This disruption in the basal ganglia circuitry contributes to the motor symptoms characteristic of Parkinson's disease, such as tremors, rigidity, and bradykinesia.

**Conclusion**

In summary, the defective action of dopamine in the brain is responsible for the motor symptoms observed in Parkinson's disease. The degeneration of dopaminergic neurons in the substantia nigra leads to a decrease in dopamine levels, disrupting the balance of the basal ganglia circuitry and impairing motor control. Understanding the role of dopamine in Parkinson's disease has led to the development of medications that can help alleviate symptoms by increasing dopamine levels or mimicking its effects.

Parkinson's disease is a neural dysfunction disease. It is caused due to loss of neurotransmitter i.e. Dopamine in the area of the brain called substantia nigra. The causes of Parkinson's disease is not completely understood but a known cause is the degeneration of a group of nerves in the centre of the brain. These nerves produce a chemical messenger called dopamine. When 80% of dopamine is lost, the symptoms of the disease is produced. Symptoms of feeling drained, unmotivated, impaired balance, and lack of voluntary movement affect the person adversely affected by this disorder. As their olfactory nerves get impaired, the person also experiences the deterioration in smelling ability.