The mesencephalon or midbrain is the portion of the brainstem that connects the hindbrain and the forebrain. A number of nerve tracts run through the midbrain that connect the cerebrum with the cerebellum and other hindbrain structures. A major function of the midbrain is to aid in movement as well as visual and auditory processing. Damage to certain areas of the mesencephalon have been linked to the development of Parkinson's disease.
Functions of the mesencephalon include:
- Controlling Responses to Sight
- Eye Movement
- Pupil Dilation
- Regulate Muscle Movement
The mesencephalon is the most rostral portion of the brainstem. It is located between the forebrain and the hindbrain.
A number of structures are located in the mesencephalon including the tectum, tegmentum, cerebral peduncle, substantia nigra, crus cerebri, and cranial nerves (oculomotor and trochlear). The tectum consists of rounded bulges called colliculi that are involved in vision and hearing processes. The cerebral peduncle is a bundle of nerve fibers that connect the forebrain and hindbrain. The cerebral peduncle includes the tegementum (forms the base of the midbrain) and the crus cerebri (nerve tracts that that connect the cerebrum with the cerebellum). The substantia nigra has nerve connections with the frontal lobes and other areas of the brain involved in motor function. Cells in the substantia nigra also produce dopamine, a chemical messenger that helps to coordinate muscle movement.
Neurodegeneration of nerve cells in the substantia nigra results in a drop off of dopamine production. Significant loss in dopamine levels (60-80%) may result in the development of Parkinson's disease. Parkinson's disease is a nervous system disorder that results in the loss of motor control and coordination. Symptoms include tremors, slowness of movement, muscle stiffness, and trouble with balance.
More Mesencephalon Information:
Divisions of the Brain
- Forebrain - encompasses the cerebral cortex and brain lobes.
- Midbrain - connects the forebrain to the hindbrain.
- Hindbrain - regulates autonomic functions and coordinates movement.