Describe the unilateral action of the highlighted muscle. Lateral flexion of neck Rotation of head to same side Retraction of scapula Rotation of head to opposite side Extension of head and neck Rotation of head so face turns to opposite side Depression of scapula Reset Zoom
The correct answer and explanation is :
The correct answer to the unilateral action described is Lateral flexion of neck.
Explanation:
The unilateral action of a muscle refers to its activity when one side of the muscle contracts, as opposed to when both sides contract together. In the context of the neck and head, many muscles perform complex actions depending on their position, attachment, and function.
The muscle responsible for lateral flexion of the neck is typically the sternocleidomastoid (SCM). When the SCM on one side contracts, it causes the head and neck to bend toward that side. The muscle originates from the sternum and clavicle and inserts into the mastoid process of the temporal bone in the skull. When acting unilaterally (one side only), it pulls the head toward the same side, causing lateral flexion.
For example, when you tilt your head toward your right shoulder, it’s the right SCM that contracts, and the left SCM relaxes. This action is different from when both SCM muscles work together, which results in neck flexion (bringing the chin down toward the chest).
Other Actions in the List:
- Rotation of head to same side: This action is also performed by the sternocleidomastoid, but it involves a different movement than lateral flexion. When one side contracts, the head rotates to that side (e.g., rotating the head to the right if the right SCM contracts).
- Retraction of scapula: This is performed by the rhomboid major and minor muscles, which retract the scapula, pulling it toward the spine.
- Rotation of head to opposite side: This involves muscles such as the sternocleidomastoid on one side, which rotates the head to the opposite side.
- Extension of head and neck: This involves the splenius capitis and semispinalis muscles, which extend the neck and head.
- Depression of scapula: This action is generally performed by muscles like the lower trapezius and pectoralis minor, which help lower the scapula.
Conclusion:
Lateral flexion of the neck occurs when a muscle on one side, such as the sternocleidomastoid, contracts unilaterally, causing the head to tilt toward the same side. This specific action is essential for movements such as looking to the side or tilting your head in various directions.