Sternocleidomastoid Muscle Flashcards

Examine the sternocleidomastoid muscle's two heads, attachments, innervation, actions, cervical relationships, and clinical anatomy.

Card 1 of 28Question

Where is the sternocleidomastoid muscle located?

In the anterolateral neck, extending obliquely from the sternum and clavicle to the skull.

In This Section

1. Where is the sternocleidomastoid muscle located?

In the anterolateral neck, extending obliquely from the sternum and clavicle to the skull.

2. What are the two heads of the sternocleidomastoid muscle?

The sternal head and clavicular head.

3. Where does the sternal head of the sternocleidomastoid originate?

From the anterior surface of the manubrium of the sternum.

4. Where does the clavicular head of the sternocleidomastoid originate?

From the superior surface of the medial third of the clavicle.

5. Where does the sternocleidomastoid muscle insert?

On the lateral surface of the mastoid process and lateral half of the superior nuchal line.

6. Which cranial nerve provides motor innervation to the sternocleidomastoid?

The spinal accessory nerve (cranial nerve XI).

7. Which cervical spinal nerves provide proprioceptive fibers associated with the sternocleidomastoid?

Primarily the second and third cervical spinal nerves (C2 and C3).

8. What is the primary rotational action of unilateral sternocleidomastoid contraction?

Rotation of the face toward the opposite side.

9. What lateral movement is produced by unilateral sternocleidomastoid contraction?

Ipsilateral lateral flexion of the head and neck.

10. What is the principal action of bilateral sternocleidomastoid contraction on the cervical spine?

Cervical flexion, with the exact head movement depending on posture and stabilization.

11. How does the sternocleidomastoid assist forced inspiration?

It elevates the sternum and clavicle when the head and neck are stabilized.

12. Which two major anatomical triangles are separated by the sternocleidomastoid?

The anterior and posterior cervical triangles.

13. Which border of the sternocleidomastoid forms a boundary of the anterior cervical triangle?

Its anterior border.

14. Which border of the sternocleidomastoid forms a boundary of the posterior cervical triangle?

Its posterior border.

15. What is the lesser supraclavicular fossa?

The small triangular depression between the sternal and clavicular heads of the sternocleidomastoid.

16. Which layer of deep cervical fascia encloses the sternocleidomastoid?

The investing layer of deep cervical fascia.

17. Which major vein crosses the superficial surface of the sternocleidomastoid?

The external jugular vein.

18. Which major neurovascular bundle lies deep to the sternocleidomastoid?

The carotid sheath containing the carotid artery, internal jugular vein, and vagus nerve.

19. Where does the spinal accessory nerve enter the sternocleidomastoid?

Through its deep surface in the upper part of the neck.

20. Where does the spinal accessory nerve travel after leaving the sternocleidomastoid?

Across the posterior cervical triangle toward the trapezius muscle.

21. Which cervical plexus branches emerge near the midpoint of the posterior sternocleidomastoid border?

The lesser occipital, great auricular, transverse cervical, and supraclavicular nerves.

22. Which cutaneous nerve crosses the sternocleidomastoid toward the parotid region and external ear?

The great auricular nerve.

23. Which arteries provide the principal blood supply to the sternocleidomastoid?

Branches of the occipital, superior thyroid, and suprascapular arteries, with variable contributions from neighboring vessels.

24. How is sternocleidomastoid motor function tested during a neurological examination?

By asking the patient to rotate the head against resistance while palpating the opposite sternocleidomastoid.

25. What movement is weakened by a unilateral spinal accessory nerve lesion affecting the sternocleidomastoid?

Rotation of the head toward the side opposite the affected muscle.

26. What is congenital muscular torticollis?

A condition involving shortening or fibrosis of one sternocleidomastoid, producing ipsilateral head tilt and contralateral chin rotation.

27. What is a sternocleidomastoid pseudotumor of infancy?

A benign fibrous enlargement of the sternocleidomastoid muscle associated with congenital muscular torticollis.

28. Why is the sternocleidomastoid an important landmark for internal jugular vein cannulation?

Its two inferior heads help define a surface region used to locate the internal jugular vein with ultrasound guidance.