After a left hypoglossal nerve injury, the protruded tongue deviates toward the weak side. The underlying mechanism is:

• A Contraction of the paralysed geniohyoid pulling the tongue toward the lesion
• B Unopposed action of the intact contralateral genioglossus pushing the tongue toward the paralysed side ✓
• C Loss of styloglossus action on the normal side allowing the tongue to fall toward the lesion
• D Unopposed action of the ipsilateral hyoglossus drawing the tongue root backward

Explanation

Each genioglossus protrudes the tongue by pushing its own half forward and across the midline. With a left hypoglossal lesion, the right genioglossus acts unopposed, thrusting the tongue forward and toward the left, the weak side. On attempted protrusion the tongue thus points toward the lesion. Geniohyoid is supplied by C1 fibres and styloglossus retracts rather than protrudes the tongue.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.