Which of the following muscles is associated with neck movement?

The sternocleidomastoid muscle plays a crucial role in neck movement. It is a prominent muscle located on both sides of the neck and is responsible for several movements, including rotation of the head, lateral flexion of the neck, and flexing the neck forward. When one side of the sternocleidomastoid contracts, it causes the head to turn to the opposite side, while contraction of both sides will result in the forward flexion of the neck.

While the trapezius muscle also contributes to neck movement by elevating and rotating the scapula and assisting with the extension of the neck, the sternocleidomastoid is more directly responsible for the specific motion of turning and tilting the head. The rectus abdominis, primarily involved in flexing the lumbar spine, and the deltoid, which mainly facilitates shoulder movements, do not play an active role in neck movement. Thus, the sternocleidomastoid stands out as the correct choice in the context of muscles specifically associated with movements of the neck.