Structure and Function of the Abducens Nucleus - Two primary neuron types in the abducens nucleus: motorneurons and interneurons - Motorneurons drive contraction of the ipsilateral lateral rectus muscle via the abducens nerve, causing outward eye rotation (abduction) - Interneurons relay signals from the abducens nucleus to the contralateral oculomotor nucleus - Motoneurons in the oculomotor nucleus drive contraction of the ipsilateral medial rectus muscle, rotating the eye inward (adduction) - Abducens nucleus generates coordinated movements of both eyes in the same direction - Electrical stimulation of the abducens nucleus generates conjugate eye movements - Lesions to the axonal tract of interneurons disrupt conjugate eye movements through paralysis of the contralateral eye - Abducens nucleus plays a role in eye movements between distant targets - Similar discharge patterns observed in motoneurons and interneurons during slow and fast conjugate eye movements

Clinical Significance of the Abducens Nucleus - Infantile Esotropia Syndrome may be caused by problems in the firing rate of the abducens nucleus - Differences in firing rates observed in monkeys with induced strabismus - Damage to the abducens nerve causes monocular ipsilateral lateral ophthalmoparesis - Damage to the abducens nucleus causes lateral gaze palsy - Contralateral eye can still move in the direction of the lesion during convergence movements

Additional Images - Nuclei of origin of cranial motor nerves schematically represented; lateral view - Scheme showing central connections of the optic nerves and optic tracts - Figure showing the mode of innervation of the Recti medialis and lateralis of the eye - Axial section of the Brainstem (Pons) at the level of the Facial Colliculus - Vestibulo-ocular reflex - Brain stem sagittal section - Section through lower pons. Abducens nucleus is labeled #4

References - Sinnatamby, Chummy S. (2011). Lasts Anatomy (12thed.). p.478. ISBN978-0-7295-3752-0 - doi:10.1167/iovs.14-16177 Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc. www.iovs.org j - ISSN1552-5783 - Walton MMG, Mustari MJ,Willoughby CL, McLoon LK. Abnormal activity of neurons in abducens nucleus of strabismic monkeys. Invest Ophthalmol Vis Sci. 2015;56:10–19 - doi:10.1167/iovs.14-15360 - Van Horn MR, Waitzman DM, Cullen KE. Vergence neurons identified in the rostral superior colliculus code smooth eye movements in 3D space. J Neurosci. 2013;33:7274–7284

External Links - MedEd at Loyola - Neuro/frames/nlBSs/nl27fr.htm