What are the distal motor nuclei of the brainstem? (4)

• A. Trigeminal motor nucleus, facial motor nucleus, nucleus ambiguus, accessory nucleus
• B. Trigeminal motor nucleus, facial motor nucleus, nucleus ambiguus, hypoglossal nucleus
• C. Trigeminal sensory nucleus, facial motor nucleus, nucleus ambiguus, accessory nucleus
• D. Trigeminal motor nucleus, abducens nucleus, nucleus ambiguus, accessory nucleus

Answer: (A)

In the brainstem, motor nuclei are organized by the muscles they innervate, with a key distinction between branchial (distal) motor to muscles derived from the pharyngeal arches and somatic motor to other skeletal muscles. The distal/branchial motor group includes nuclei that control muscles of mastication and facial expression, as well as the pharynx, larynx, and certain neck muscles.

Specifically, the trigeminal motor nucleus supplies the muscles of mastication; the facial motor nucleus controls the muscles of facial expression; the nucleus ambiguus innervates the pharyngeal and laryngeal muscles via IX and X; and the accessory nucleus provides motor input to the sternocleidomastoid and trapezius. These four nuclei form the distal/branchial motor set.

The other options mix in a sensory nucleus (which is not motor), or include nuclei that innervate muscles not from the pharyngeal arches (for example, tongue muscles via the hypoglossal nucleus or eye muscles via the abducens nucleus). Thus they don’t fit the distal/branchial motor group.