The distal brainstem nuclei are primarily which type of motor?

• A. Somatic motor
• B. Autonomic/parasympathetic motor
• C. Cardiac motor
• D. Visceral motor

Answer: (A)

In the nervous system, motor outputs are grouped by their targets: somatic motor to skeletal muscles, visceral motor to smooth muscles and glands (autonomic), and specific groups for cardiac control. The distal brainstem motor nuclei are the cranial nerve nuclei that project to skeletal muscles of the head and neck. Most of these distal nuclei are dedicated to somatic motor control, meaning they innervate muscles used for voluntary and reflexive movements of the face, tongue, eyes, and related structures. While autonomic (parasympathetic) nuclei exist in the brainstem to regulate things like pupil size, heart rate, and glandular activity, they are fewer in number at these distal levels. So the primary type of motor output from the distal brainstem nuclei is somatic motor.