Damage to the structure paralyzes which muscle (AIIMS 2016)
Damage to the structure producing the elevation marked
leads to paralysis of which of the following muscle
(AIIMS 2016)
a. Lateral rectus
b. Risorius
c. Levator palpebrae superioris
d. Superior oblique
Ans. b. Risorius and a. Lateral rectus
Note: b. Risorius is a better answer than a. Lateral rectus
Explanation: The diagram shows the floor of the fourth ventricle, with the arrow showing the facial colliculus.
Facial colliculus is a rounded elevation formed by the axons of facial nerve winding around the abducent nucleus.
Damage to the facial nerve axons paralyzes muscles of facial expression like risorius.
In facial colliculus syndrome, even the deeper abducent nucleus may be damaged, leading to paralysis of lateral rectus muscle.