Final answer:
The substantia nigra is responsible for controlling movement by releasing dopamine, which influences motor activity in the active and passive states of the body. It also plays roles in mood, reward, and addiction.
Step-by-step explanation:
The substantia nigra, a structure located in the midbrain contributes significantly to the control of movement. It contains dopaminergic neurons that project to the striatum influencing motor activities through the release of the neurotransmitter dopamine. Dopamine interacts with receptors that are either excitatory (D1-type) or inhibitory (D2-type). The substantia nigra pars compacta (SNc) plays a pivotal role in switching between an active state, where movement is more likely, and a passive state, where movement is less likely. This modulation of movement is crucial and disturbances in the substantia nigra, such as in Parkinson's disease, result in motor control challenges. The substantia nigra is also involved in various other functions such as mood regulation, reward processing, and addiction due to its connections with the basal nuclei and other parts of the brain.