Anterior Thorax and Neck -

LO 8

8. Identify and detail the muscles of the anterior neck: sternocleidomastoid m., infrahyoid mm.

Sternocleidomastoid m.

Superior attachments:
- Mastoid process of temporal bone & occipital bone
Inferior attachments:
- Manubrium of sternum
- Medial clavicle
Actions:
- Bilateral contractions: flexes cervical vertebrae
- Unilateral contraction: lateral flexes the neck & rotates the head in the opposite direction
Innervation:
- Efferent: Accessory n. (CN XI)
- Afferent: C2 & C3 fibers
- It is uncommon that separate nerves provide afferent and efferent innervation to a muscle.
Anatomical relationships:
- Prominently visible and palpable landmark in the neck
- External jugular v. typically runs anterior/superficial to this muscle

Infrahyoid mm.

The infrahyoid muscles are a set of 4 muscles (sternohyoid, omohyoid, sternothyroid, and thyrohyoid mm.) located inferior to the hyoid bone. This set of muscles is often referred to as strap muscles due to their ribbon/strap-like shape.

The names of the muscles indicate the attachment points:
- Omo-: means shoulder (in this case, attached on the scapula)
- Thyro(id): indicates the thyroid cartilage, not thyroid gland
Actions
- Stabilization or depression of hyoid
- Dependent on muscles, will pull larynx either superiorly, or inferiorly
Innervation
- Ansa cervicalis (cervical plexus) for 3 of the 4 muscles
Anatomical relationships:
- Arranged in two layers
  - Superficial: sternohyoid & omohyoid
  - Deep: sternothyroid & thyrohyoid
- To access the thyroid gland, these muscles have to be reflected or moved