Parkinson disease involves the destruction of the substantia nigra and the nigrostriatal pathway. Where are these structures anatomically?

Motor activity occurs as a result of integrating the actions of the cerebral cortex, basal ganglia, and cerebellum. The basal ganglia are a group of neurons located in the cerebrum, at the base of the brain, near the lateral ventricles. When the basal gaglia are stimulated they secrete of two major neurotransmitters to accomplish the movement process, dopamine and acetylcholine (ACh)[Ign17]. Dopamine is produced by the substantia nigra, as well as the adrenal glands, and transmitted to the basal ganglia. ACh is produced and secreted by the basal ganglia and in the nerve endings in the peripheral body. ACh transmits excitatory messages, whereas dopamine inhibits the function of the neurons, thus allows control over voluntary movement[Ign17]. When there is degeneration of the substantia nigra it decreases the amounts of dopamine in the brain, thus the patient loses the ability to refine voluntary movement[Ign17]. As a result of the imbalance of dopamine to ACh, with larger amount of ACh, results in the inability to depress or control motor function.