Point 23










Point: 23. Superior Colliculus

Superior and inferior colliculi comprise the tectum or roof (dorsal to the cerebral aqueduct) of the mesencephalon or midbrain. The rostral portion of the roof consists of two bumps=superior colliculi. Superior colliculus is thought to play a role in integrating sensory information (visual, auditory, somatosensory) into motor signals that help orient the head toward various stimuli.

Visual inputs from the retina (retinocollicular) and the visual cortex (corticocollicular) reach the superficial layers of this laminated structure. Visual inputs from the right visual world reach the LEFT superior colliculus, and vice-versa. Auditory and somatosensory inputs also reach intermediate and deep layers (don't worry about how these inputs get there!). Axons that arise from cells in the intermediate and deep layers CROSS at the level of the superior colliculus, pass caudally through the brainstem (we do not identify them in our sections) and enter the VENTRAL FUNICULUS of the spinal cord. Tectospinal axons leave the ventral funiculus to synapse upon cells in the medial part of the spinal cord grey at upper cervical levels only. Pathway helps us to turn our head toward visual (and auditory and somatosensory) stimuli. The LEFT superior colliculus tells the RIGHT cervical cord motor neurons (splenius capitus, not sternocleidomastoid) to turn the head the to the right.

Lesion of the LEFT superior colliculus results in inability to turn head reflexively to the RIGHT (CONTRA.) upon visual (or somatosensory and auditory) stimuli on the RIGHT.

Other Note:
Superior colliculus is also involved in the control of eye movements.