Neck

Muscles

Sternocleidomastoid

Description: two-headed muscle on anterolateral surface of neck, prominent landmark and fleshy mass which borders delineates anterior and posterior triangles

Origin:

• clavicular head: superior surface of medial third of clavicle
• manubrial head: tendon attached to manubrium of sternum

Insertion:

• tendon to the lateral surface mastoid process of temporal bone
• thin aponeurosis to the lateral half of the superior nuchial line of occipital bone

Action:

• contracting together: prime mover of active head flexion when
• contracting in isolation: rotates head towards contralateral shoulder r laterally flexes neck to ipsilateral side

Relations: deep to platysma

Nerve supply: Accessory nerve and branches of cervical spinal nerves C₂ – C₃

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Special regions

Anterior triangle

Description:

Borders:

• Superior – inferior border of the mandible.
• Lateral – anterior border of sternocleidomastoid muscle
• Medial – midsagittal line of neck.

Contents:

• Suprahyoid muscles:
  • Stylohyoid
  • Digastric
  • Mylohyoid
  • Geniohyoid

• Infrahyoid muscles:
  • Omohyoid
  • Sternohyoid
  • Thyrohyoid
  • Sternothyroid
• Cranial nerves:
  • facial [VII], glossopharyngeal [IX], vagus [X], accessory [XI], and hypoglossal [XII]
• Vessels:
  • Common carotid artery – bifurcates within triangle into external carotid and internal carotid branches
  • Internal jugular vein

Subdivisions: carotid triangle, submental triangle, muscular triangle

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Carotid triangle

Description:

Borders:

• Superior – posterior belly of digastric muscle.
• Lateral – anterior border of sternocleidomastoid muscle.
• Inferior – superior belly of the omohyoid muscle.

Contents:

• Cranial nerves:
  • vagus [X] and hypoglossal [XII]

• Vessels:
  • Common carotid artery – bifurcates within triangle into external carotid and internal carotid branches
  • Internal jugular vein

Clinical relevance: contains carotid sinus (baroreceptors), surgical access point

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Posterior triangle

Description: an area enclosed between sternoicleidomastoid and trapezius muscle

Borders:

• Anterior – posterior border of the sternocleidomastoid.
• Posterior – anterior border of the trapezius muscle.
• Inferior – middle 1/3 of the clavicle.
• Covering – investing layer of fascia
• Floor – Prevertebral fascia
• Apex – 

Contents:

• Vessels:
  • External jugular vein – within the posterior trangle, it pierces the investing layer of fascia and empties into subclavian vein.
  • Subclavian vein –
• Muscles:

Inferior belly of omohyoid crosses lower medial part of triangle