The Oculomotor Cranial Nerves and Their Brain Stem Nuclei

The six extraocular muscles are innervated by cranial nerves III (oculomotor), IV (trochlear), and VI (abducens). Nerve IV innervates the contralateral superior oblique, nerve VI the ipsilateral lateral rectus muscle, and nerve III the remaining four extraocular muscles as well as the eye lid. The neurons giving rise to these general somatic efferents are termed oculomotor neurons (OMNs). Their cell bodies are located in three eponymous nuclei that lie in pairs along the medial longitudinal fasciculus near the midline of the brain stem: the oculomotor, trochlear, and abducens nuclei, which are often grouped and simply termed the oculomotor nuclei.

Figure 3 Axes of rotation and muscles of the eye. The eye rotates about three axes to effect horizontal, vertical, and torsional movements. These rotations are implemented via six extraocular muscles for each eye, as shown. Adduction and abduction about the z axis are accomplished by the lateral and medial rectus muscles. Raising and lowering the eyes (x axis rotations) are accomplished by the inferior and superior rectus muscles in association with the inferior and superior obliques. Likewise, torsional movements (y axis rotations) require the inferior and superior obliques together with the superior and inferior rectus muscles.

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