Organization of Reticular Projections onto Oculomotor Neurones

Abstract

This chapter describes some specific pathways from the reticular formation onto oculomotor neurones, along with the physiological evidence for their role in the control of fast eye movements. There is evidence that the paramedian pontine reticular formation (PPRF) is a major premotor area in which fast eye movements are generated. It controls the horizontal eye muscles through a projection from mainly caudal PPRF to the ipsilatera1 abducens nucleus (VI). Motoneurones of the lateral rectus, lying within VI, are intermingled with a set of internuclear neurones that project rostrally within MLF to the contralateral medial rectus motoneurones in the oculomotor nucleus (III). PPRF utilizes this internuclear system to activate medial rectus. The vertical eye movement premotor area lies in the rostral mesencephalon. A direct and compact pathway from PPRF to one nucleus in this region (rostral iMLF) could carry the coordinating signal by which PPRF can control the generation of vertical eye movements. Both rostral iMLF and the neighbouring interstitial nucleus of Cajal send direct projections to the motoneurones of inferior and superior recti, and inferior and superior oblique. A possible role for the dorsal medullary reticular formation in the inhibition of horizontal antagonists is discussed.