Which area of the mesencephalon coatrols the body movement, and contains large aumbers of darkly pigmented cells?
A. red nuclei
B. substantia nigra
C. superior colliculi
D, cerebral peduncles
The correct answer and explanation is :
The correct answer is B. substantia nigra.
Explanation:
The substantia nigra is a region in the mesencephalon (midbrain) that plays a crucial role in controlling body movement and contains a large number of darkly pigmented cells. These cells are rich in dopamine, which is important for motor control. The substantia nigra is part of the basal ganglia system, a group of nuclei in the brain that are involved in the regulation of movement.
The substantia nigra is divided into two parts:
- Pars compacta – This area is densely packed with dopaminergic neurons that produce dopamine, a neurotransmitter that helps regulate movement. These neurons project to the striatum (part of the basal ganglia), where dopamine plays a role in modulating motor control.
- Pars reticulata – This region has fewer dopamine-producing neurons but is involved in the output of the basal ganglia.
The dark pigmentation of the substantia nigra is due to the presence of neuromelanin, a pigment that is a byproduct of dopamine metabolism. This pigmentation gives the substantia nigra its characteristic color and reflects the high levels of dopamine production in this area. The degeneration of dopaminergic neurons in the substantia nigra is a key feature in disorders such as Parkinson’s disease, which is characterized by motor symptoms like tremors, rigidity, and bradykinesia (slowness of movement).
To clarify the other options:
- A. Red nuclei are involved in motor coordination but are not heavily pigmented and do not have a primary role in the control of body movement like the substantia nigra.
- C. Superior colliculi are involved in visual processing and the coordination of eye movements, not motor control.
- D. Cerebral peduncles contain major motor pathways, but they are not involved in the regulation of movement like the substantia nigra.
Thus, the substantia nigra is the area in the mesencephalon that is crucial for controlling body movement and contains darkly pigmented cells.