Housed within the mesencephalon lies the quadrigemina. The quadrigemina is responsible for the reflexes dealing with visual and auditory stimuli, as well as highly specialized nuclei which deal with the body’s movement as well as posturing. The cerebral peduncles are also within the mesencephalon.


These are comprised of tracts of fibers. The nuclei concerned with autonomic functions as well as their corresponding tracts are housed within the brain stem. This is a vital section of the brain as it attaches to the spinal cord. It also houses the midbrain, pons, and medulla oblongata.

It can be found positioned the pons and the diencephalon and is simply a small portion of the brain stem. The midbrain, houses the mesencephalic aqueduct which is responsible for the unification of the third and fourth ventricles. The mesencephalic aqueduct is also known as the aqueduct of Sylvius.


Image: Mesencephalon

The corpora quadrigemina, the cerebral peduncles, the red nucleus, and the substantia nigra are all housed within the midbrain. There are four elevated and spherical segments on the corpora quadrigemina, found along the posterior section of the midbrain. Concerned with visual reflexes, two upper eminences are found, known as the superior colliculi.

The inferior colliculi are the two lower eminences are concerned with reflexes dealing with auditory stimulation. There are two structures, appearing like cylinder stems, which are called the cerebral peduncles. They are created by the supportive fiber tracts which are responsible for creating the connection between the cerebrum and other various regions of the brain. Positioned between the cerebral peduncle and the cerebral aqueduct lies the red nucleus, found quite deep inside the midbrain.


The red nucleus is conjoined with the cerebral hemispheres and the cerebellum to work in conjuncture with these brain segments in order to regulate and control the reactions and coordination required for motor functions and posturing. It is highly vascular and receives a high level of oxygen rich blood as well as a pigment high in iron, which gives it the deep reddish color.

The pigment is actually within the cell bodies themselves. Inferior to the red nucleus is the substantia nigra. While still under conjecture, it is believed that this nucleus is responsible for the inhibiting of forced involuntary motion. The darker color if the substantia nigra is derived from the high saturation of melanin pigment.
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