What is the primary function of the sternocleidomastoid muscle?

The primary function of the sternocleidomastoid muscle is to facilitate the rotation of the head to the opposite side. This muscle, which is located on each side of the neck, has two functions when acting unilaterally. When one side contracts, it causes the head to rotate towards the opposite side while also tilting it to the same side. This action is essential for various movements of the head and is a crucial part of turning the head to look in different directions.

In addition to its role in head rotation, the sternocleidomastoid contributes to other movements of the head and neck, such as flexion and extension. However, these functions are secondary to its primary role in rotation. Understanding the specific actions of this muscle is important for recognizing its significance in neck movements and the overall biomechanics of the cervical spine.