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💀anatomy and physiology i review

Sternocleidomastoid muscle

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The sternocleidomastoid muscle is a paired muscle located in the front and side of the neck. It originates from the sternum and clavicle, and inserts on the mastoid process of the temporal bone. This muscle is responsible for rotating and laterally flexing the head, as well as assisting in neck flexion.

5 Must Know Facts For Your Next Test

  1. The sternocleidomastoid muscle is one of the most prominent muscles in the neck, forming a distinct diagonal line when contracted.
  2. This muscle plays a crucial role in the cranial nerve exam, as it is innervated by the spinal accessory nerve (cranial nerve XI).
  3. Damage or weakness of the sternocleidomastoid muscle can result in a condition called wry neck or torticollis, where the head is tilted and rotated to one side.
  4. The sternocleidomastoid muscle is often used as a landmark for palpating the carotid artery and identifying the location of the jugular vein.
  5. Tension or spasm in the sternocleidomastoid muscle can contribute to tension-type headaches and migraines.

Review Questions

  • Explain the role of the sternocleidomastoid muscle in the cranial nerve exam.
    • During the cranial nerve exam, the sternocleidomastoid muscle is assessed to evaluate the function of the spinal accessory nerve (cranial nerve XI). The examiner will ask the patient to turn their head against resistance, testing the muscle's ability to rotate and laterally flex the head. Any weakness or paralysis of the sternocleidomastoid muscle may indicate a problem with the spinal accessory nerve, which is responsible for innervating this muscle.
  • Describe how damage or weakness of the sternocleidomastoid muscle can lead to the condition of wry neck or torticollis.
    • The sternocleidomastoid muscle plays a crucial role in maintaining the proper alignment and positioning of the head. When this muscle is damaged or weakened, it can no longer effectively rotate and laterally flex the head. This results in the head being tilted and rotated to one side, a condition known as wry neck or torticollis. This abnormal head positioning can be caused by various factors, including injury, muscle spasms, or neurological disorders affecting the spinal accessory nerve.
  • Analyze the importance of the sternocleidomastoid muscle as a landmark for clinical examinations and procedures.
    • The sternocleidomastoid muscle is a valuable anatomical landmark for various clinical examinations and procedures. Its prominent position in the neck makes it easy to palpate and identify, allowing healthcare providers to locate important structures like the carotid artery and jugular vein. This muscle's proximity to these vascular structures also makes it a useful reference point for administering injections or performing other medical interventions in the neck region. Additionally, the sternocleidomastoid muscle's role in head and neck movement makes it a crucial consideration in the assessment and management of musculoskeletal disorders affecting the cervical spine.