Point 23
Intro
Pathway
Deficit
Overview
Problems
Contents
Anatomy
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One
of the major efferent projections of the superior colliculus
is to the CERVICAL SPINAL CORD. This
TECTOSPINAL TRACT arises from cells within the
intermediate and deep layers, crosses at midbrain levels and
courses caudally through the midbrain, pons and medulla
close to the MLF (we do not identify it in our sections).
Upon reaching the spinal cord tectospinal axons course
within the VENTRAL funiculus and terminate upon
medially placed neurons within the cervical cord. This tract
is important in reflex turning of the head in response to
visual, auditory and somatosensory stimuli. For instance, a
flash of light to your RIGHT causes you to turn your
head to the RIGHT. This reflex would involve a
projection from the retinae to the superficial layers of the
LEFT superior colliculus (retinocollicular), a short
pathway from cells in the superficial layers to cells in the
intermediate and deep layers and then the long
CROSSED tectospinal axons to the RIGHT side of
the cervical spinal cord. Spinal cord neurons on the
RIGHT side then innervate muscles such as the
splenius capitus and semispinalis capitus, which rotate your
head to the RIGHT.
Cells within the intermediate and deep layers also are
involved in the control of eye movements. We will not go
into how the collicular neurons participate in such control,
but you are already familiar with the PPRF, which is
an area of the pons involved in the control of horizontal
eye movements. For example, cells in the intermediate and
deep layers of the LEFT superior colliculus project
to the RIGHT PPRF (this pathway is not illustrated in
the coursebook). You know the circuitry from here that moves
both eyes to the RIGHT. If not, see that INFAMOUS
POINT 13 for a review!
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