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You are watching: This extrinsic eye muscle elevates the eye and turns it medially.
Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. Second edition. Sunderland (MA): Sinauer Associates; 2001.
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Three antagonistic pairs of muscles manage eye movements: the lateral and also medial rectus muscles, the superior and also inferior rectus muscles, and the superior and also inferior slope muscles. This muscles room responsible for activities of the eye follow me three various axes: horizontal, either towards the nose (adduction) or away from the nose (abduction); vertical, one of two people elevation or depression; and torsional, activities that lug the height of the eye towards the sleep (intorsion) or far from the nose (extorsion). Horizontal movements are managed entirely by the medial and lateral rectus muscles; the medial rectus muscle is responsible because that adduction, the lateral rectus muscle for abduction. Vertical motions require the coordinated activity of the superior and inferior rectus muscles, and also the slope muscles. The family member contribution the the rectus and oblique teams depends ~ above the horizontal place of the eye (Figure 20.2). In the primary position (eyes right ahead), both of these groups contribute to vertical movements. Elevation is as result of the activity of the exceptional rectus and inferior slope muscles, when depression is as result of the action of the worse rectus and superior tilt muscles. When the eye is abducted, the rectus muscles are the prime vertical movers. Elevation is as result of the activity of the superior rectus, and also depression is due to the action of the worse rectus. When the eye is adducted, the slope muscles space the prime vertical movers. Elevation is because of the action of the inferior oblique muscle, while depression is as result of the activity of the premium oblique muscle. The oblique muscle are additionally primarily responsible because that torsional movements.
Figure 20.2
The contributions of the six extraocular muscles to vertical and horizontal eye movements. Horizontal activities are mediated by the medial and lateral rectus muscles, while vertical movements are mediated through the superior and also inferior rectus and the remarkable (more...)
The extraocular muscles room innervated by reduced motor neurons that type three cranial nerves: the abducens, the trochlear, and also the oculomotor (Figure 20.3). The abducens nerve (cranial nerve VI) exit the brainstem indigenous the pons-medullary junction and also innervates the lateral rectus muscle. The trochlear nerve (IV) exit from the caudal portion of the midbrain and supplies the premium oblique muscle. In distinction to all various other cranial nerves, the trochlear nerve exit from the dorsal surface ar of the brainstem and crosses the midline come innervate the superior oblique muscle on the contralateral side. The oculomotor nerve (III), which exits from the rostral midbrain near the cerebral peduncle, provides all the rest of the extraocular muscles. Back the oculomotor nerve governs several different muscles, each receives that innervation from a separate group of lower motor neurons in ~ the 3rd nerve nucleus.
Figure 20.3
Organization that the several cranial nerve nuclei that govern eye movements, mirroring their innervation the the extraocular muscles. The abducens cell nucleus innervates the lateral rectus muscle; the trochlear nucleus innervates the superior oblique muscle; (more...)
In enhancement to providing the extraocular muscles, a distinct cell group within the oculomotor cell nucleus innervates the levator muscles of the eyelid; the axons from this neurons likewise travel in the 3rd nerve. Finally, the third nerve carries axons indigenous the surrounding Edinger-Westphal nucleus that room responsible because that pupillary constriction (see chapter 12). Thus, damage to the third nerve outcomes in 3 characteristic deficits: impairment of eye movements, drooping the the eyelid (ptosis), and pupillary dilation.
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