Point 23


Intro

Pathway

Deficit

Overview

Problems


Contents

Anatomy

 

 

Tectospinal TractOne 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!