Detailed Notes on Neck Muscles and Anatomy

Overview of the Neck Musculature
  • The neck houses several important muscles that can be categorized into anterior, lateral, and posterior groups.
Learning Objective
  • Describe the anatomical layout of the main muscles of the neck, specifically focusing on the anterior and posterior compartments as well as the triangles of the neck.
Categories of Neck Muscles
Anterior Muscles

  • Suprahyoids: Located above the hyoid bone, they elevate the hyoid and assist in swallowing.

    • Examples include Digastric, Stylohyoid, Mylohyoid, Geniohyoid.

  • Infrahyoids: Located below the hyoid bone, they stabilize and depress the hyoid and larynx.

    • Examples include Sternohyoid, Omohyoid, Sternothyroid, Thyrohyoid.
Lateral Muscles
  • Involved in lateral flexion, rotation and flexion of the neck.
Posterior Muscles
  • Responsible for neck extension, lateral flexion and rotation.
Neck Triangles
Anterior Triangle
  • Boundaries:
    • Laterally: Anterior border of the sternocleidomastoid (SCM) muscle.
    • Superiorly: Inferior border of the mandible.
    • Medially: Midline of the neck.
  • Subdivisions:
    • Submandibular triangle
    • Submental triangle
    • Muscular triangle
    • Carotid triangle
  • Contents: Muscles, arteries, veins, nerves, lymph nodes and viscera pertinent to the anterior region of the neck.
Posterior Triangle
  • Boundaries:
    • Anteriorly: Posterior edge of SCM.
    • Posteriorly: Anterior edge of trapezius.
    • Base: Middle third of the clavicle.
    • Apex: Occipital bone posterior to mastoid process.
  • Muscular Floor: Splenius capitis, levator scapulae, and scalene muscles.
Hyoid Bone
  • Structure: An unpaired bone in the neck with no direct connections to other bones, comprised of:
    • Body
    • Greater cornu
    • Lesser cornu
  • Function: Acts as an attachment site for larynx, pharynx, and tongue muscles, making it vital for speech and swallowing.
Larynx
  • Location: Between pharynx and trachea, comprising various hyaline cartilages (Thyroid, Cricoid, Epiglottis).
  • Function: Keeps airway open while allowing phonation.
Muscle Anatomy: Sternocleidomastoid (SCM)
  • Origin: Manubrium of sternum, clavicle.
  • Insertion: Mastoid Process.
  • Nerve Supply: Accessory nerve (CN XI) and C2-C4.
  • Action:
    • Unilateral: Lateral flexion and head rotation to the opposite side.
    • Bilateral: Flexes the neck.
Suprahyoid Muscles
  • Functions: Elevation of hyoid and depression of mandible.
    • Digastric: 2 bellies (anterior from mandible, posterior from mastoid process).
    • Innervation: Anterior belly via mylohyoid nerve (CN V3), posterior via facial nerve (CN VII).
    • Stylohyoid: Elevates and retracts hyoid.
    • Mylohyoid: Forms the floor of the mouth.
    • Geniohyoid: Elevates hyoid or depresses mandible.
Infrahyoid Muscles
  • Positioned below hyoid, involved mainly in hyoid stabilization and depression:
    • Sternohyoid: Depresses hyoid, innervated by ansa cervicalis (C1-C3).
    • Omohyoid: Has superior and inferior bellies, stabilizes or depresses hyoid.
    • Thyrohyoid: Connects thyroid cartilage to hyoid, can depress hyoid or elevate thyroid.
    • Sternothyroid: Depresses thyroid cartilage only, not connected to hyoid.
Ansa Cervicalis
  • A loop of nerve fibers from C1-C3, innervates the infrahyoid muscles, contributing to muscle functions in the anterior triangle of the neck.
Scalenes Muscles
  • Anterior, Middle, and Posterior Scalenes: Elevate ribs and flex the neck laterally, located between the cervical vertebrae and their respective insertion points into the ribs.