Anatomy Week 2 - Neck Muscles and Cervical Triangles

Neck Muscles

• Divided into 3 divisions: anterior, lateral, and posterior

Anterior Neck Muscles

• divided into 4 divisions: superficial, suprahyoid, infrahyoid, and vertebral

Platysma

• inserts at multiple points on skin of the lower face

• muscle of facial expression

• vascularized by submental branch of facial artery + suprascapular branch of thyrocervical trunk

• innervation by cervical branch of facial nerve

Which nerve innervates all muscles responsible for facial expression?

Facial Nerve (CN VII)

Sternocleidomastoid

• two heads

• inserts on mastoid process

• assists with forced respiration when head and neck and fixed

• innervated by spinal accessory nerve (XI) and ventral rami

• multiple blood sources: occipital, posterior auricular, superior thyroid and suprascapular artery

Suprahyoid Muscles

• digastric, mylohyoid, geniohyoid and stylohyoid muscles

• form floor of oral cavity

• main function is to elevate the hyoid, which closes/depresses the epiglottis

Digastric Muscle

• suprahyoid muscle

• separated into an anterior and posterior belly; connected by intermediate tendon at hyoid bone

• posterior originates at mastoid process, anterior originates at mandible

Geniohyoid Muscle

• suprahyoid muscle

• short, narrow muscle

• connects from mandible to body of the hyoid

• same function as others

Mylohyoid Muscle

• suprahyoid muscle

• sheet-like muscle; forms much of the floor of the mouth

• same functions

Stylohyoid Muscle

• suprahyoid muscle

• originates on styloid process of temporal bone

Infrahyoid Muscles

• sternohyoid, omohyoid, sternothyroid and thyrohyoid muscles.

• function to depress the hyoid, reopening the airway (allowing respiration), and play a role in vocalization

Sternohyoid Muscle

• strap-like muscles; have to be moved during thyroid procedures

Omohyoid Muscle

• divided into two bellies: inferior and superior which are connected by an intermediate tendon

• inferior belly originates at superior border of scapula, superior belly originates from the tendon

• “Om(o)ha(yoid), set, hut!” Muscle is curved like a football

Sternothyroid muscle

• strap-like muscle that runs from sternum to thyroid cartilage

• doesn’t directly insert onto hyoid

Thyrohyoid Muscle

highlighted in green

• runs from thyroid cartilage to hyoid bone

• has an additional function of elevating the larynx when the hyoid bone is fixed, important for singing high notes

Vertebral Neck Muscles

• include the rectus capitis anterior, rectus capitis lateralis, longus capitis and longus colli

• mainly responsible for head flexion

• also called prevertebral muscles (surrounded by prevertebral fascia)

Rectus Capitis Anterior

• runs from anterior surface of lateral mass of C1 to occipital bone (anterior to foramen magnum)

• flexion at the atlanto-occipital joint + stabilization

Rectus Capitus Lateralis

• runs from transverse processes of C1 to inferior surface of jugular process on occipital bone

• lateral flexion of the atlanto-occipital joint, stabilization

Longus Capitis

• runs from cervical vertebrae to occipital bone, curves superomedially

• weak flexion of head (bilaterally) + ipsilateral rotation (unilaterally)

Longus Colli / Longus Cervicis

• stretches along all cervical vertebrae + upper portion of thoracic vertebrae

• stronger head flexion, weak ipsilateral flexion + contralateral rotation

Lateral Neck Muscles - Scalenes

• divided into anterior, middle, and posterior scalenes muscles

• general + lateral neck flexion

• also elevates ribs during forced inspiration (w/ fixed vertebral column)

• Notes:

  • Anterior and middle scalenes insert on 1st rib, posterior scalenes on 2nd

  • Middle scalenes is the largest, posterior scalenes is the smallest

Posterior Neck Muscles (review)

• Superficial — trapezius and splenius muscles

• Deep — transversospinalis muscles

Cervical Triangles

• The neck is divided into two large triangles by the sternocleidomastoid muscle: Anterior Triangle and Posterior

  • These main triangles are further subdivided into smaller triangles recognized by their specific boundaries and contents.

Anterior Triangle

• formed by the anterior border of sternocleidomastoid laterally, the median line of the neck medially and by the inferior border of the mandible superiorly

• further subdivided into muscular, submandibular, submental, and carotid triangles

Thoracic Outlet Syndrome

Thoracic outlet syndrome is not the name of a single entity but rather a collective title for a variety of conditions attributed to the compression of neurovascular structures as they traverse the thoracic outlet. The thoracic outlet is bordered by the scalene muscles, first rib, and clavicle.

Relevant structures: brachial plexus, subclavian artery + vein, scalenes muscles

Posterior Triangle

• borders = trapezius posteriorly, SCM anteriorly, clavicle inferiorly

• further divided into occipital triangle and supraclavicular triangle

Relevant structures of the muscular triangle

• infrahyoid muscles

• thyroid + its vessels (thyroid arteries), anterior jugular vein

• larynx, trachea, esophagus

Relevant structures of the carotid triangle

• Arteries: common, internal, external carotid (sinus at the base of internal)

• Veins: internal jugular, common facial, lingual, superior/middle thyroid

• Nerves: vagus (X), hypoglossal (XII), sympathetic trunk

Relevant structures of the submandibular triangle

• dental abscesses*

• submandibular lymph nodes, and part of the parotid gland

• facial artery + vein, submental artery + vein, lingual artery + vein

• mylohyoid nerve and hypoglossal nerve (XII)

Relevant structures of the submental triangle

Anterior jugular vein and submental lymph nodes

Relevant structures of the occipital triangle

• spinal accessory nerve (XI), cervical plexus + part of brachial plexus

• supraclavicular nerve

Relevant structures of the supraclavicular triangle

• Third part of the subclavian artery, brachial plexus trunks, nerve to subclavius muscle, lymph nodes