Which muscle action includes rotating the head and neck to the same side?

Which muscle action includes rotating the head and neck to the same side?

• A. Splenius capitis
• B. Rectus abdominis
• C. Transverse abdominis
• D. Quadratus lumborum

Answer: (A)

Unilateral contraction of the splenius capitis rotates the head and neck to the same side. This muscle runs from the upper spine up to the skull behind the ear, so when it tightens on one side, pulls the head toward that same side, producing rotation (and, if both sides contract, extension). The abdominal muscles listed don’t affect head rotation—rectus abdominis and transverse abdominis mainly flex or compress the trunk. The quadratus lumborum supports the lumbar spine and can lateral bend the trunk, but it doesn’t rotate the head.

Unilateral contraction of the splenius capitis rotates the head and neck to the same side. This muscle runs from the upper spine up to the skull behind the ear, so when it tightens on one side, pulls the head toward that same side, producing rotation (and, if both sides contract, extension). The abdominal muscles listed don’t affect head rotation—rectus abdominis and transverse abdominis mainly flex or compress the trunk. The quadratus lumborum supports the lumbar spine and can lateral bend the trunk, but it doesn’t rotate the head.