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

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

Where does the hyoid bone lie in relation to the thyroid cartilage?

The hyoid bone is superior to the thyroid cartilage

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 (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

• 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, 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

Rectus Capitis Anterior

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

• flexion at this joint

Rectus Capitus Lateralis

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

Longus Capitis

• runs from cervical vertebrae to occipital bone, curves superomedially

• weak flexion of head + ipsilateral rotation

Longus Colli / Longus Cervicis

• stretches along all cervical vertebrae

• stronger head flexion

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)

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

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.

Posterior Triangle