Organization+of+the+Neck

toc =**Objectives**=

**Organization of the Neck**

 * 1. Describe the Posterior and Anterior Cervical Triangles.**

__Posterior Cervical Triangle__ The posterior cervical triangle is bound anteriorly by the sternocleidomastoid (SCM) muscle, posteriorly by the anterior border of trapezius, and inferiorly by the middle 1/3 of the clavicle. The roof is made of investing fascia and the floor is made by the prevertebral fascia of splenius capitus, levator scapulae, and anterior, middle, and posterior scalenes muscles. The posterior triangle is bilateral.

The inferior belly of the omohyoid muscle divides the posterior triangle into a large superior occipital triangle and a smaller inferior subclavian triangle. The accessory nerve CNXI also can be used to divide the posterior triangle, with everything above the accessory nerve called the “safe zone” and everything below it, including the subclavian triangle, called the “danger zone.”

__Occipital Triangle__ The occipital triangle contains the accessory nerve CNXI, the lateral, intermediate, and medial supraclavicular nerves, greater occipital nerve, greater auricular nerve, trunks of the brachial plexus, transverse cervical artery, parts of the external jugular vein, and superficial cervical lymph nodes.

__Subclavian Triangle__ The subclavian triangle contains part of the subclavian artery, terminal part of the jugular vein, sometimes the subclavian artery, superscapular artery, supraclavicular lymph nodes, and the parts of the brachial plexus.

__Safe and Danger Zones__ An injury to the safe zone is less dangerous than one to the danger zone because there are fewer nerves and vessels running through the safe zone. In the danger zone, just below the accessory nerve CNXI at the border of the SCM muscle is the nerve point of the neck where all the cutaneous nerves arise, including the transverse cervical nerve, supraclavicular nerves, lesser occipital nerve, and greater auricular nerve.

__Anterior Cervical Triangle__ The anterior cervical triangle is bound anteriorly by the anterior midline of the neck, posteriorly by the SCM, and superiorly by the mandible. The anterior triangle is bilateral. The anterior triangle is subdivided into the submandibular (digastric) triangle, submental triangle, carotid triangle, and muscular triangle. The submandibular, carotid, and musclar triangles are also bilateral. However the submental triangle is unilateral, spanning both the left and right anterior triangles.

__Submandibular Triangle__ The submandibular triangle is bound superiorly by the mandible, and medially and inferiorly by the lateral side of the anterior and posterior bellies of the digastric muscle, respectively. The floor of the submandibular triangle is made up of the mylohyoid muscle, hypoglossus muscle, and the middle pharyngeal constrictor muscle. It contains the submandibular gland, submandibular lymph nodes, mylohyloid nerve (C3), hypoglossal nerve CNXII, and the facial artery and vein. A pulse is palpatable from the facial artery.

__Submental Triangle__ The submental triangle spans the midline, bound superiolaterally by the medial side of the anterior belly of the digastric muscle, and inferiorly by the hyoid bone. The floor is composed of mylohyloid muscles. The submental triangle contains submental lymph nodes.

__Muscular Triangle__ The muscular triangle is bound superiorly by the hyoid bone, laterally by the medial side of omohyoid muscle superior belly, inferiorly by the SCM muscle, and medially by the anterior midline of the neck. This triangle contains the infrahyoid muscles, thyroid gland, and parathyroid glands.

__Carotid Triangle__ The carotid triangle is bound superiorly by the inferior side of the posterior belly of the digastric muscle, medially by the superior belly of the omohyoid muscle, and laterally by the SCM muscle. The floor is composed of the inferior pharyngeal constrictor muscle. It contents include: //4 arteries//: common coratid artery, internal carotid artery, external carotid artery and some branches, and the carotid body and sinus. //4 nerves//: the vagus nerve CNX, hypoglossal nerve CNXII, accessory nerve CNXI, and branches of the cervical plexus including the superior root of the ansa cervicalis. //1 vein//: the internal jugular vein and its tribularies. //Others//: deep cervical lymph nodes, the larynx, pharynx, thyroid gland, and parathyroid glands.


 * 2. Define the fascial compartments of the neck.**

There are two big cervical fascial compartments of the neck: the superficial fascia, and the deep fascia. Deep fascia is divided into four subcompartments: the investing fascia, pretrachial fascia, prevertebral fascia, and carotid sheath. The pretrachial fascia is further subdivided into the visceral part, including the buccopharyngeal fascia, and the muscular part.

__Retropharyngeal Space__ Between the buccopharyngeal fascia and prevertebral fascia is a potential space called the retropharyngeal space which extends from the base of the skull to the thorax. This space functions to facilitates movement of cervical viscera against the vertebral column and is clinically important for the spread of infection (e.g., from the nasopharyngeal tonsils).

__Superficial Fascia__ The superficial fascia contains the platysma muscle, anterior and external jugular veins, cutaneous branches of the cervical plexus, and the cervical branch of the facial nerve CNVII. The platysma is a muscle of facial expression that produces a slight wrinkling of the surface of the skin of the neck; it has the dubious distinction of being the only facial muscle found in the neck.

__Investing Fascia__ Investing fascia makes up the roof of the anterior and posterior triangles and surrounds the entire neck deep to the skin and subcutaneous fascia. It encloses trapezius, SCM, and the accessory nerve CNXI. Superiorly, it blends with the fascia of the skull and mandible and the hyoid bone. Inferiorly, it extends to the manubrium, clavicle, and scapula. Posteriorly, it is continuous with the nuchal ligament to the C7 spinous process.

__Pretracheal Fascia__ Pretracheal fascia is limited to the anterior part of the neck. It is subdivided into a visceral and a muscular part.

The visceral part encloses the neck viscera (thyroid, parathyroids, trachea, pharynx, and esophagus). Posterior to the pharynx and esophagous, the posterior visceral part of the pretracheal fascia is called the buccopharyngeal fascia which forms the anterior boundary of the retropharyngeal space.

The muscular part is bound superiorly by its attachment to the hyoid bone, inferiorly blending with the fibrous pericardium, and laterally blending with the carotid sheath. The muscular part encloses the infrahyoid muscles.

__Prevertebral Fascia__ The prevertebral fascia surrounds the vertebral column and its muscles. Laterally, it forms the axillary sheath. Superiorly, it attaches to the base of the skull, and, inferiorly, it blends with the anterior longitudinal ligament. It forms the floor of the posterior triangle and the posterior boundary of the retropharyngeal space. The sympathetic chain is in/on the anterior aspect of this fascia/

__Carotid Sheath__ The carotid sheath is a neurovascular compartment at the left and right lateral edges of the retropharyngeal space. It blends medially with the muscular part of the pretracheal fascia. It contains: //3 arteries//: Common carotid artery, internal carotid artery, and the carotid sinus and body. //It does NOT include the external carotid artery//. //1 vein//: Internal jugular vein //2 nerves//: Vagus nerve CNX and sympathetic fibers //1 lymphatic//: Deep cervical lymph nodes


 * 3. At what vertebral levels would you find the following structures:**


 * **Structure** || **Vertebral Levels** ||
 * Hyoid Bone || C3 ||
 * Carotid Bifurcation || C4 ||
 * Thyroid Cartilage || C4-C5 ||
 * Cricoid Cartilage || C6 ||
 * Thyroid Gland || C6-T1 ||

**Cervical Muscles**

 * 1. Describe the attachments, innervation, and action(s) of the following muscles.**

__Suprahyoid Muscles__
 * **Muscle** || **Origin** || **Insertion** || **Innervation** || **Action** ||
 * Mylohyoid || Mylohyoid line of mandible || Mylohyoid raphe and body of hyoid || n. to myloid || Elevates hyoid, floor of mouth and tongue during swallowing and speaking ||
 * Geniohyoid || Inferior mental spines of the mandible || Body of the hyoid bone || C1 via fibers carried by the hypoglossal nerve || Pulls hyoid anteriosuperiorly; shortens floor of mouth; widens pharynx ||
 * Stylohyoid || Styloid process of temporal bone || Body of hyoid || Stylohyoid branch of (preparotid) facial nerve (CN VII) || Elevates and retracts hyoid, thus elongating floor of mouth ||
 * Digastric || Anterior belly: digastric fossa of mandible Posterior belly: mastoid notch of temporal bone || Intermediate tendon to body and greater horn of hyoid || Anterior belly: n. to mylohyoid, a branch of inferior alveolar n. Posterior belly digastric branch of (preparotid) facial nerve (CN VII) || Working with infrahyoid muscles, depresses mandible against resistance; elevates and steadies hyoid during swallowing and speaking ||

__Infrahyoid Muscles__
 * **Muscle** || **Origin** || **Insertion** || **Innervation** || **Action** ||
 * Sternohyoid || Manubrium of sternum and medial end of clavicle || Body of hyoid || C1-C3 by a branch of ansa cervicalis || Depresses hyoid after elevation during swallowing ||
 * Omohyoid || Superior border of scapula near suprascapular notch || Inferior border of hyoid || C1-C3 by a branch of ansa cervicalis || Depresses, retracts, and steadies hyoid ||
 * Sternothyroid || Posterior surface of manubrium of sternum || Oblique line of thyroid cartilage || C2-C3 by a branch of ansa cervicalis || Depresses hyoid and larynx ||
 * Thyrohyoid || Oblique line of thyroid cartilage || Inferior border of body and greater horn of hyoid || C1 via hypoglossal n. (CN XII) ||

__Scalene Muscles__
 * **Muscle** || **Origin** || **Insertion** || **Innervation** || **Action** ||
 * Anterior scalene || Transverse processes of C3-C6 || Scalene tubercle of 1st rib || Lower cervical (C5-8) || Elevates 1st rib; bends neck ||
 * Middle scalene || Transverse processes of C2-C7 || Upper surface of 1st rib || Lower cervical (C5-8) || Elevates 1st rib; bends neck ||
 * Posterior scalene || Transverse processes of C4-C6 || Outter surface of 2nd rib || Lower cervical (C6-8) || Elevates 2nd rib; bends neck ||

__Neck Flexors__
 * **Muscle** || **Origin** || **Insertion** || **Innervation** || **Action** ||
 * longus colli || Anterior tubericle of C1; bodies of C1-C3 and transverse processes of C3-C6 || Bodies of C5-T3 || Anterior rami of C2-C6 spinal nerves || Flexes neck with rotation (torsion) to opposite side of acting unilaterally ||