Quick Facts
The midbrain, or mesencephalon, is the portion of the central nervous system that lies above the hindbrain, or rhombencephalon, and below the diencephalon, connecting the two. It is involved with sensory integration, control of motor and sleep functions and in the regulation of temperature.
The midbrain is somewhat primitive as a neural structure. It was one of the first to evolve in vertebrates and it is present in most of the early vertebrate brains. The midbrain consists of the tectum that makes up the roof, or dorsal aspect of the midbrain, and the cerebral peduncle that primarily makes up the floor, or ventral aspect of the midbrain.
The tectum consists of the inferior colliculus, which is involved in auditory processing and reflexes, and the superior colliculus, which is involved in visual processing and reflexive control of eye movements.
The cerebral peduncle consists of the tegmentum and crus cerebri that contains a nucleus called the substantia nigra. The substantia nigra is involved with motor control and reward. This part of the brain is the one primarily affected by Parkinson's disease, giving rise to its characteristic motor dysfunctions. The tegmentum also contains many pathways that are involved with homeostasis and reflexes.
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Mesencephalon
The ventral part of the mesencephalon is the region through which the major tracts of nerve processes that connect centers in the cerebral cortex with specific sites in the spinal cord pass.
