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 3 of 16 Actions of the Extraocular Muscles The actions of all six extraocular muscles are summarized in the table below: Muscle Innervation Primary action Secondary action Tertiary action Medial rectus CN III Adduction -- -- Superior rectus CN III Elevation Intortion Adduction Inferior rectus CN III Depression Extortion Adduction Inferior oblique CN III Extorsion Elevation Abduction Superior oblique CN IV Intorsion Depression Abduction Lateral rectus CN VI Abduction -- -- A knowledge of the origins and points of insertion of the extraocular muscles on the eye relative to the axes of motion of the eye is critical to understanding the actions of these muscles. Figure 3-3a. Muscles of the orbit.

		Medial Rectus Muscle The medial rectus muscle originates from the tendinous ring of the orbit and inserts on the medial border of the eye. Contraction of this muscles leads to adduction of the eye. Figure 3-3b. Muscles of adduction.

		Superior Rectus Muscle The superior rectus muscle originates from the tendinous ring of the orbit and inserts on the superior surface of the eye slightly medial to the eyes vertical axis of rotation. Due to these factors, contraction of the superior rectus results in elevation, intorsion, and adduction of the eye. The primary action of the superior rectus muscle (elevation of the eye) can be isolated by having the patient look laterally and then upwards. Figure 3-3c. Muscles of elevation.

Last revised: March 22, 1998