Answer
The mid brain develops from the mesencephalon. It comprises the cerebral aqueduct, parts of the medial lemniscus, parts of the RF, and the motor nuclei of the oculomotor nerve and the trochlear nerve--concerned with eye movements.
The tectum is the part of the midbrain on the posterior aspect of the cerebral aqueduct . It displays as a pair of ovoid upper and lower bulges; these are called the superior colliculi and the inferior colliculi , respectively.
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The superior colliculi are concerned with functions related to visual attention , such as visual tracking of moving objects; visual reflexes related to blinking; focusing; pupillary dilation, and pupillary constriction; preripheral vision processes.
The inferior colliculi relay signal from the inner inner ear to other parts of the brain; they also mediate the reflex turning of the head to a sound, and the jump startle reflex.
Anterior to the cerebral aqueduct the three cerebral peduncles anchor the cererbrum to the brainstem. The two important parts of a cerebral peduncle are the tegmentum, and the substantia nigra. The rubrospinal tract of the red nucleus of the tegmentum goes to the cerebellum and facilitates fine motor control of muscles. The substantia nigra , a dark gray pigmented nucleus, sends inhibitory signals to the thalamus, and basal nuclei. These inhibitory signals prevent unwanted body movements.
The gray matter that surrounds the cerebral aqueduct is called the central or periaqueductal gray matter. Together with the reticulospinal tract, the central gray matter is concerned with pain awareness.
