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Eccentric topic of the Week
Question 3.
3) Regarding the trochlear nerve:
A. True: It originates from the midbrain
B. True: It is the only cranial nerve that exits from the dorsal surface of the brainstem
C. False: Its lesion results in paralysis of the inferior oblique muscle
D. True: It supplies only one orbital muscle
E. False: Its palsy causes horizontal diplopia
Answer:
The trochlear nerve innervates the superior oblique muscle. Trochlear nerve palsy (weakness of the superior oblique muscle) results in torsional (palsy causes the eye to extort) and vertical diplopia; horizontal diplopia is seen in abducens nerve palsy. To compensate for the extorsion, patients with trochlear nerve palsies tilt their heads to the opposite side, in order to fuse the two images into a single visual field (by intorsion of the normal eye).*
*Snell RS. The cranial nerve nuclei and their central connections and distribution. In: Clinical Neuroanatomy for Medical Students, 4th edition. Philadelphia: Lippincott-Raven, 1997: 406.
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A. True: It originates from the midbrain
B. True: It is the only cranial nerve that exits from the dorsal surface of the brainstem
C. False: Its lesion results in paralysis of the inferior oblique muscle
D. True: It supplies only one orbital muscle
E. False: Its palsy causes horizontal diplopia
Answer:
The trochlear nerve innervates the superior oblique muscle. Trochlear nerve palsy (weakness of the superior oblique muscle) results in torsional (palsy causes the eye to extort) and vertical diplopia; horizontal diplopia is seen in abducens nerve palsy. To compensate for the extorsion, patients with trochlear nerve palsies tilt their heads to the opposite side, in order to fuse the two images into a single visual field (by intorsion of the normal eye).*
*Snell RS. The cranial nerve nuclei and their central connections and distribution. In: Clinical Neuroanatomy for Medical Students, 4th edition. Philadelphia: Lippincott-Raven, 1997: 406.
Visit:
http://www.colenpublishing.com/
for more information.
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