By Haley Masterson
SALT ME DOWN: Six Abducts Laterally, Trochlear acts Medially Down. The oculomotor nerve is responsible for everything else.
To review: the abducens nerve (CN VI) will abduct the eye through its innervation of the lateral rectus muscle. Meanwhile, the trochlear nerve (CN IV) innervates the superior oblique muscle, which has one major action: depression – though it’s important to recognize that its effect is only clinically significant when the eye is medially adducted. Thus, the mnemonic: trochlear acts medially down.
Finally, the oculomotor nerve (CN III) innervates the medial rectus (adduction), inferior rectus (depression when not medially adducted), inferior oblique (elevation, abduction), and superior rectus muscles (elevation), as well as the levator palpebrae superioris – which does not act directly on the eye, but does function to elevate the eyelid.
1. Agarwal, Sunita. “Extraocular Muscles.” Textbook of Ophthalmology. New Delhi: Jaypee Bros., 2002.
2. Orient, Jane M., and Joseph D. Sapira. “The Neurologic Examination.” Sapira’s Art & Science of Bedside Diagnosis. Philadelphia: Lippincott Williams & Wilkins, 2005.