These nuclei relay sensory information on the state of stretch of muscles and joints to the cerebellum. Other visible structures on the exterior of the medulla include the olives, which are swellings caused by folds of gray matter of the underlying inferior olivary nuclei. This crossing over is the cause of the contralateral control exerted by the brain over most of the body. Most of the fibers cross to the opposite side before descending into the spinal cord at a point known as the decussation of the pyramids. Large corticospinal tracts from the motor cortex create pyramids, two longitudinal ridges on flanking the midline of the medulla's ventral aspect. The fourth ventricle's ventral wall is indeed formed by the medulla and the pons. The cavity of the fourth ventricle is formed by the central canal of the spinal cord proceeding upward into the medulla. While the exact fusion point between the medulla and spinal cord is not discernible, it is considered to be at the foramen magnum of the skull. The medulla oblongata, or medulla, is the most inferior part of the brain stem. They are embedded in a system of small nuclei scattered through the core of the brain stem called the reticular formation and are primarily responsible for acting as relay nuclei in some descending motor pathways that effect limb flexion. It is found deep to the substania nigra and acquires its reddish hue because it has a rich blood supply and a relatively high level of iron pigment within its neurons. Another embedded nucleus is the oval-shaped red nucleus. These neurons are highly responsible for releasing the neurotransmitter dopamine and are functionally linked to the basal nuclei and are usually considered part of the basal nuclear complex. The bandlike substantia nigra are also embedded in each side of the midbrain white matter, deep to the cerebral peduncle. They also act in reflexive response to sound, such as in the startle reflex, which causes you to turn your head toward an unexpected sound. The inferior colliculi form a corresponding part of the auditory reflex from the hearing receptors of the ear to the sensory cortex. The superior colliculi (the superior pair) are visual reflex centers that coordinate head and eye movements when we visually follow a moving object, even if we don't consciously intend to look at the object. They raise four domelike protrusions on the dorsal midbrain surface. The corpora quadrigemina are the largest of these nuclei. The aqueduct is surrounded by the periaqueductal gray matter, which is involved in pain suppression and serves as the link between fear-perceiving amygdala and ANS pathway that controls the 'fight-or-flight' response.ДЄs previously mentioned, gray matter nuclei are scattered throughout the surrounding white matter. The third and fourth ventricles are connected by the hollow cerebral aqueduct, which delineates the cerebral peduncles ventrally from the tectum (the midbrain's roof). The midbrain is connected to the cerebellum dorsally by the superior cerebellar peduncles, which are also fiber tracts. Each peduncle's crus cerebri contains a large pyramidal motor tract descending to the spinal cord. They are vertical pillars that appear to hold up the cerebrum. Two cerebral peduncles are found on its ventral aspect. The midbrain is found between the diencephalon and the pons.

Brain stem parts