Which nerve innervates the omohyoid, sternohyoid, and sternothyroid muscles?

• A. Ansa cervicalis
• B. Vagus nerve
• C. Cervical sympathetic trunk
• D. Hypoglossal nerve

Answer: (A)

The nerves responsible for the motor supply to the infrahyoid (strap) muscles—omohyoid, sternohyoid, and sternothyroid—come from the ansa cervicalis. This loop of nerves in the neck is formed by branches from C1 to C3 (with C1 fibers joining the hypoglossal nerve to some muscles). The ansa cervicalis sends motor branches specifically to these three muscles to depress the hyoid and larynx after swallowing. The thyrohyoid muscle is the exception, receiving C1 fibers carried with the hypoglossal nerve, not through the ansa cervicalis. The vagus nerve and the cervical sympathetic trunk don’t innervate these infrahyoid muscles, and the hypoglossal nerve mainly supplies tongue muscles (with some C1 contribution to thyrohyoid). Hence, the innervation of omohyoid, sternohyoid, and sternothyroid is via the ansa cervicalis.