Point 23
Intro
Point: 23. Superior Colliculus
Function:
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.
Pathway:
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.
Deficits:
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.