Neck Anatomy: Fascia and Borders

Neck Overview

• The neck is the region between the head, shoulders and thorax.
• The superior border of the neck includes the inferior margins of the mandible and bone features on the posterior skull.
• The inferior border of the neck includes the top of the sternum, clavicle, acromion, and the line between the two acromions and the spinous process of C-VII posteriorly.

Fascia of the Neck

• Fascia of neck can be classfied into superficial and deep.
• The superficial fascia contains the platysma muscle and the cervical branch of the facial nerve.
• The deep fascia is also referred to as cervical fascia or fascia colli.
• The deep fascia has investing, prevertebral, pretracheal layers and carotid sheaths.
• The investing layer surrounds all structures.
• The prevertebral layer surrounds the vertebral column and muscles.
• The pretracheal layer surrounds respiratory and digestive organs.
• The carotid sheaths contain major neurovascular bundles.
• The investing layer attaches to the lig. nuchae and spinous process of C7 vertebra and splits to enclose the trapezius, sternocleidomastoid, and infrahyoid muscles.
• The investing layer extends as the axillary sheath of the shoulder and surrounds prevertebral mm, scalene mm, and the deep muscles of the back.
• The pretracheal layer surrounds the trachea, esophagus and thyroid gland.
• The carotid sheath surrounds the neurovascular bundle containing the common carotid artery(CCA), internal jugular vein(IJV) and vagus nerve(VN).
• Spaces are located between the fascia layers including; The pretracheal space, retropharyngeal space, and the third space located between two layers of the prevertebral layer.
• The neck has 4 longitudinal compartments: visceral, vertebral and two vascular compartments.
• The visceral compartment includes the digestive, respiratory and endocrine organs and is surrounded by the pretracheal layer.
• The vertebral compartment has cervical vertebrae, the spinal cord, cervical nerves/muscles and is covered with prevertebral layer.
• The two vascular compartments contain the common carotid artery, internal jugular vein, and vagus nerve within a carotid sheath.

Neck Triangles

• The neck divides into two triangles; anterior and posterior and their associated entities
• The anterior triangle is composed of the sternocleidomastoid m., inferior border of the mandible, and midline.
• The posterior triangle is composed of the sternocleidomastoid m., trapezius m. and the clavicle.
• The anterior triangle subdivides into the submandibular, submental, muscular, and carotid triangles.
• The submandibular triangle includes the mandible, anterior and posterior belly of the diagastric.
• The submental triangle includes the hyoid bone, anterior belly of the digastric muscle and midline.
• The muscular triangle includes the hyoid bone, superior belly of the omohyoid, sternocleidomastoid m. and midline.
• The carotid triangle includes the superior belly of the omohyoid, stylohyoid m., posterior belly of the digastric and sternocleidomastoid m.
• The submandibular triangle contains the submandibular gland and lymph nodes, hypoglossal nerve (CN-XII), mylohyoid nerve, plus the facial artery and vein.
• The submental triangle contains submental lymph nodes and small veins.
• The muscular triangle contains; muscles, thyroid/parathyroid glands, the larynx, and pharynx.
• The carotid triangle has the common carotid artery/branches, internal jugular vein, vagus nerve (X), cervical branch of the facial nerve (VII), accessory nerve (XI), hypoglossal nerve (XII), plus the superior/inferior roots of ansa cervicalis/transverse cervical nerve.
• The posterior triangle subdivides into omoclavicular and occipital triangles.
• The omoclavicular(subclavian) triangle is defined by the clavicle, sternocleidomastoid m. and inferior belly of omohyoid m.
• The occipital triangle is defined by the the Trapezius m, Sternocleidomastoid m. and Inferior belly of omohyoid m.

Muscles of The Neck

Platysma

• The platysma is a large, thin sheet of muscle in the superficial fascia of the neck.
• It originates from the upper part of the thorax and inserting into the mandible and muscles around the mouth.
• The platysma is innervated by the cervical branch of the facial nerve (CN-VII).
• Platysma’s function tenses the skin of the neck and move the lower lip and corners of the mouth down.

Suprahyoid Muscles

• The suprahyoid are located above the hyoid bone
• They include; stylohyoid m, digastric m, mylohyoid m, geniohyoid

Stylohyoid

• The stylohyoid muscle originates from the styloid process of the temporal bone, inserts into the hyoid bone and its insertion tendon splits into two parts.
• Stylohyoid innervation is through the facial nerve (CN-VII).
• The function is to pull the hyoid bone upward during swallowing.

Digastric

• Digastric m comprises of anterior and posterior bells.
• The anterior belly originates from the digastric fossa of the mandible innervated by the mylohyoid nerve (of the mandibular nerve - V3)
• The posterior belly originates from the mastoid process and is innervated by the facial nerve (CN-VII).
• The anterior belly functions to lower the mandible and open the mouth
• The posterior belly functions to pull the hyoid bone upward

Mylohyoid

• The mylohyoid muscle originates from the mylohyoid line of the mandible and inserting into the hyoid bone, and mylohoid raphe, innervated by the mylohyoid nerve (of the mandibular nerve - V3)
• The mylohyoid supports the floor of the mouth and elevates the hyoid bone.

Geniohyoid

• The geniohyoid muscle originates from the inferior mental spines of the mandible and inserts into the hyoid bone.
• It is innervated by a branch from the anterior ramus of the C1 spinal nerve (carried with the hypoglossal nerve – XII)
• It functions to elevate and pull the hyoid bone forward, and pull the mandible downward and inward.

Infrahyoid Muscles

• The Infrahyoid muscles are located below the hyoid bone also known as the strap muscles;
• They include; sternohyoid m, omohyoid m, thyrohyoid m, sternothyroid m.

Sternohyoid

• The sternohyoid muscle originates from sternoclavicular joint and the hyoid bone.
• It is innervated by ansa cervicalis.
• The sternohyoid function is to depresses the hyoid after swallowing.

Omohyoid

• The omohyoid muscle originates from the superior border of the scapula, inserting to the hyoid bone.
• It has an intermediate tendon that divides the muscle into superior and inferior bellies and is innervated by the Ansa cervicalis.
• The omohyoid functions to depress and fix the hyoid bone.

Thyrohyoid

• The thyrohyoid muscle originates from the oblique line of the thyroid cartilage and inserts into the greater horn of the hyoid bone.
• It is innervated by a branch from the anterior ramus of the C1 (carried with the hypoglossal nerve – XII)
• It functions to depresse the hyoid bone and raise the larynx (when high notes are sung).

Sternothyroid

• The sternothyroid muscle originates from the manubrium of the sternum while inserting to the oblique line of the thyroid cartilage
• The innervation by the ansa cervicalis.
• It draws the larynx downward.

Sternocleidomastoid

• The Sternocleidomastoid has sternal and clavicular heads.
• The sternal head originates from the manubrium of the sternum.
• The clavicular head originates from the medial 1/3 of the clavicle.
• The Sternocleidomastoid inserts into the mastoid process and lateral half of the superior nuchal line and innervates the accessory nerve (XI).
• It functions to tilt head toward the shoulder, and act together to draw the head forward.

Trapezius

• The trapezius originates from the superior nuchal line, external occipital protuberance, lig. nuchae and spinous processes of C-VII to T-XII.
• Trapezius’ insertion is to the lateral 1/3 of clavicle, acromion and spine of the scapula.
• It innervates by the accessory nerve (XI).
• Upper fibers elevate, middle fibers adduct, and the lower fibers depress the scapula.

Splenius Capitis

• The splenius capitis muscle originates from the lower half of the lig. nuchae and spinous processes of C-VII to T-IV while innervating the middle cervical nerves.
• The insertion is the mastoid process and the area below the lateral 1/3 of the superior nuchal line.
• Together, The splenius capitis draws the head backward or individually draw and rotate head to one side

Levator Scapulae

• Levator scapulae originates from the transverse processes of C-I to C-IV inserting to the upper part of the medial border of the scapula.
• The levator scapulae is innervates the anterior rami of C3, and C4 spinal nerves with its singular function; elevate the scapula.

Prevertebral Muscles

• The prevertebral muscles include the longus capitis, longus colli, rectus capitis anterior, and rectus capitis lateralis.
• Innervation to these muscles originates via direct (muscular) branches from anterior rami of cervical spinal nerves.

Longus Capitis

• The longus capitis originates from transverse processes of C-II to C-VI inserting in the basilar part of the occipital bone innervated via roots C1-C3.
• It’s the only muscle in cervical spine that flexes skull at the atlantooccipital join

Longus Colli

• Originating from transverse processes of C-II to C-VI inserting onto C5-7/T1-3 transverse processes and atlas tubercle innervated via C2-C6.
• The longus colli functions to flex the head anteriorly/laterally with slight opposite side rotation

Rectus Capitis Anterior

• The rectus capitis anterior originates from the lateral part of atlas and insert into the basilar part of the occipital bone and innervated via roots C1/2.
• Flexion of C0/C1 is unique to the action of prevertebrals

Rectus Capitis Lateralis

• The rectus capitis lateralis originates from the transverse process of atlas inserting the jugular process of the occipital bone innervated by C1/2.
• Performs lateral flexion on head

Scalene Muscles

• The lateral vertebral (paravertebral) muscle group is composed of the anterior, middle, and posterior scalene muscles.

Anterior Scalene

• The anterior scalene m. originates from transverse processes of C-III to C-VI, inserting the scalene tubercle of rib I
• It is innervated anaterior rami of C4 to C7
• It elevates the rib I.

Middle Scalene

• The middle scalene m. originates from transverse processes of C-II to C-VII and inserts the upper surface of rib I.
• It is innervated by anterior rami of C3 to C7.
• It elevates rib I.

Posterior Scalene

• The posterior scalene m. originates from transverse processes of C-IV to C-VI and inserts the upper surface of rib II
• It’s innervated via anterior rami of C5 to C7.
• The posterior scalen elevates rib II.
• The subclavian artery passes between the anterior and middle scalene muscles.
• The brachial plexus passes between the anterior and middle scalene muscles.
• The subclavian vein passes anterior to the anterior scalene muscle.
• The phrenic nerve passes across the anterior scalene muscle.