Which nucleus is described as controlling somatic motor - active/voluntary movement?

• A. Trigeminal motor nucleus
• B. Facial motor nucleus
• C. Nucleus ambiguus
• D. Principal sensory nucleus

Answer: (C)

The key idea is how motor nuclei are tied to the muscles they control. Nuclei that send signals to skeletal muscles used for active, voluntary movements are the somatic (or branchial/SVE) motor nuclei for head and neck muscles.

Nucleus ambiguus. It contains neurons that send efferent fibers to muscles of the pharynx, larynx, and soft palate via cranial nerves IX and X. Those muscles are involved in swallowing and phonation—clear examples of active, voluntary movements of the throat and voice. So this nucleus is described as governing somatic motor activity that enables purposeful actions like speaking and swallowing.

The other options don’t fit as neatly for this specific description. The trigeminal motor nucleus does control jaw muscles for chewing, which is also voluntary movement, but the nucleus ambiguus is the key source for the pharyngeal and laryngeal muscles that execute important voluntary actions in swallowing and voice. The facial motor nucleus governs facial expression, which is voluntary but serves a different muscle group. The principal sensory nucleus is sensory, not motor.