Chapter contents Overview Somatic motor component Origin, central course Intracranial course Final innervation Visceral motor component Origin and course Final innervation

Cranial Nerve III - Oculomotor Nerve Page 4 of 16 Actions of the Extraocular Muscles, continued Inferior Rectus Muscle The inferior rectus muscle originates from the tendinous ring of the orbit and inserts on the inferior surface of the eye slightly medial to the eyes vertical axis of rotation. As a result, contraction of the inferior rectus causes depression, extorsion, and adduction of the eye. The primary action of the inferior rectus muscle (depression of the eye) can be isolated by having the patient look laterally and then downwards. Figure 3-4a. Muscles that depress the eye.

		Inferior Oblique Muscle The inferior oblique muscle originates from the floor of the bony orbit and passes laterally and posteriorly to insert on the posterolateral surface of the eye slightly behind its vertical axis of rotation. Contraction of this muscle results in extorsion (outward rotation about the anterior-posterior axis of rotation), elevation, and abduction. The action of the inferior oblique muscle can be isolated by having the patient look medially and then upwards. Figure 3-4b. Muscles of abduction.

		The actions of the superior oblique and lateral rectus muscles are discussed in the modules on CN IV and CN VI, respectively. Figure 3-4c. Muscles of medial rotation.

		Figure 3-4d. Muscles of lateral rotation.

Last revised: March 22, 1998