Splenius cervicis action when acting unilaterally?

Splenius cervicis action when acting unilaterally?

• A. Ipsilateral flexion and rotation
• B. Contralateral rotation
• C. Bilateral head and neck extension
• D. Lateral trunk flexion

Answer: (A)

Unilateral contraction of the splenius cervicis pulls the neck toward the same side and rotates the head to that side. This happens because the muscle runs from the lower thoracic spine up to the upper cervical transverse processes, so when it contracts on one side, it shortens and pulls those cervical segments laterally and rotates them toward that same side. Bilateral contraction, in contrast, extends the neck. So the action described—ipsilateral flexion (lateral bend) and rotation with a single-side contraction—fits the anatomy. The other possibilities describe actions seen with either the opposite-side rotation, bilateral extension, or trunk-level movements, which aren’t the unilateral action of this neck muscle.

Unilateral contraction of the splenius cervicis pulls the neck toward the same side and rotates the head to that side. This happens because the muscle runs from the lower thoracic spine up to the upper cervical transverse processes, so when it contracts on one side, it shortens and pulls those cervical segments laterally and rotates them toward that same side. Bilateral contraction, in contrast, extends the neck. So the action described—ipsilateral flexion (lateral bend) and rotation with a single-side contraction—fits the anatomy. The other possibilities describe actions seen with either the opposite-side rotation, bilateral extension, or trunk-level movements, which aren’t the unilateral action of this neck muscle.