Semispinalis action is best described as which of the following?

• A. Extension of head, neck, and vertebral column
• B. Flexion of head and neck
• C. Abduction of the scapula
• D. Rotation of the humerus

Answer: (A)

Semispinalis muscles are part of the transversospinalis group that run from transverse processes to higher spinous processes. When both sides contract, they pull the spine upward and back, producing extension of the head, neck, and vertebral column. This bilateral action explains why extension is the best description for semispinalis. If contracted on one side, they would rotate the head and neck to the opposite side, not abduct the scapula or rotate the shoulder joint. Flexion of the head and neck would involve different muscles (like the sternocleidomastoid), while scapular abduction or humeral rotation are actions of other muscle groups around the shoulder and shoulder girdle.