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THE NECK

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The neck is a tube providing continuity from the head to the trunk.

It extends anteriorly from the lower border of the mandible to the upper surface of the manubrium of sternum.

Posteriorly from the superior nuchal line on the occipital bone of the skull to the intervertebral disc between the CVII and TI vertebrae.

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• Within the tube four compartments provide longitudinal organization.

the visceral compartment is anterior and contains parts of the digestive and respiratory systems, and several endocrine glands;

the vertebral compartment is posterior and contains the cervical vertebrae, spinal cord, cervical nerves, and muscles associated with the vertebral column;

the two vascular compartments are lateral and contain the major blood vessels and the vagus nerve [X].

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• For descriptive purposes the neck is divided into anterior and posterior triangles.

• Anterior triangle; its boundaries are the anterior border of the sternocleidomastoid muscle, the inferior border of the mandible, and the midline of the neck;

• Posterior triangle; its boundaries are the posterior border of the sternocleidomastoid muscle, the anterior border of the trapezius muscle, and the middle one-third of the clavicle.

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ANTERIOR TRIANGLE OF THE NECK• The anterior triangle of the neck is outlined by

the anterior border of the sternocleidomastoid muscle laterally, the inferior border of the mandible superiorly, and the midline of the neck medially.

It is further subdivided into several smaller triangles as follows:

the submandibular triangle is outlined by the inferior border of the mandible superiorly and the anterior and posterior bellies of the digastric muscle inferiorly;

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• the submental triangle; outlined by the hyoid bone inferiorly, the anterior belly of the digastric muscle laterally, and the midline;

• the muscular triangle is outlined by the hyoid bone superiorly, the superior belly of the omohyoid muscle, and the anterior border of the sternocleidomastoid muscle laterally, and the midline;

• the carotid triangle is outlined by the superior belly of the omohyoid muscle anteroinferiorly, the stylohyoid muscle and posterior belly of the digastric superiorly, and the anterior border of the sternocleidomastoid muscle posteriorly.

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• Each of these triangles contains numerous structures that can be identified as being within a specific triangle, passing into a specific triangle from outside the area, originating in one triangle and passing to another triangle, or passing through several triangles while passing through the region.

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Muscles in anterior triangle• The muscles in the anterior triangle of the

neck can be grouped according to their location relative to the hyoid bone:

muscles superior to the hyoid are classified as suprahyoid muscles and include the stylohyoid, digastric, mylohyoid, and geniohyoid;

muscles inferior to the hyoid are infrahyoid muscles and include the omohyoid, sternohyoid, thyrohyoid, and sternothyroid.

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Suprahyoid musclesThe four suprahyoid muscles are in the

submental and submandibular triangles. They pass in a superior direction from the

hyoid bone to the skull or mandible and raise the hyoid, as occurs during swallowing.

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1. Stylohyoid; innervated by the facial nerve [VII], it pulls the hyoid bone posterosuperiorly during swallowing.

2. Digastric; has 2 bellies (anterior and posterior) connected by a tendon which attaches to the body of the hyoid bone. Innervation of the digastric muscle is from two different cranial nerves.

• Posterior belly is by facial nerve (CN VII)• Anterior belly is by trigeminal nerve (CN V)

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3. Mylohyoid; It is innervated by the trigeminal nerve [CN V]. It supports and elevates the floor of the mouth and elevates the hyoid bone.4. Geniohyoid; is innervated by a branch from the anterior ramus of C1 carried along the hypoglossal nerve [XII]. • It has two functions depending on which bone is

fixed:fixation of the mandible elevates and pulls the

hyoid bone forward; fixation of the hyoid bone pulls the mandible

downward and inward.

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• Infrahyoid muscles;The four infrahyoid muscles are in the muscular

triangle. They attach the hyoid bone to inferior

structures and depress the hyoid bone. They also provide a stable point of attachment

for the suprahyoid muscles. Because of their appearance, they are

sometimes referred to as the 'strap muscles'.

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Sternohyoid; is innervated by the anterior rami of C1 to C3 through the ansa cervicalis.

It depresses the hyoid boneOmohyoid; Lateral to the sternohyoid muscle,

This muscle consists of two bellies with an intermediate tendon in both the posterior and anterior triangles of the neck.

It is innervated by the anterior rami of C1 to C3 through the ansa cervicalis.

The omohyoid depresses and fixes the hyoid bone

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Thyrohyoid; is located deep to the superior parts of the omohyoid muscle. It is innervated by fibers from the anterior ramus of C1 that travel with the hypoglossal nerve [XII].

Sternothyroid; the last of the infrahyoid group of muscles. is innervated by the anterior rami of C1 to C3 through the ansa cervicalis.

The sternohyoid muscle draws the larynx (thyroid cartilage) downward

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Vessels in the anterior triangle

Passing through the anterior triangle of the neck are the common carotid arteries and their branches, the external and internal carotid arteries.

These vessels supply all structures of the head and neck.

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• The common carotid arteries are the beginning of the carotid system.

• the right common carotid artery originates from the brachiocephalic trunk;

• the left common carotid artery begins in the thorax as a direct branch of the arch of the aorta.

• They both ascend through the neck, lateral to the tracheal and oesophagus not giving any branch in the neck.

• Near the superior edge of the thyroid cartilage each common carotid artery divides into its two terminal branches-the external and internal carotid arteries

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Origin of the common carotid arteries

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• The superior part of each common carotid artery and its division into external and internal carotid arteries occurs in the carotid triangle.

• At the bifurcation, the common carotid artery and the beginning of the internal carotid artery are dilated.

• This dilation is the carotid sinus and contains receptors that monitor changes in blood pressure and are innervated by a branch of the glossopharyngeal nerve [IX].

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• Another accumulation of receptors in the area of the bifurcation is responsible for detecting changes in blood chemistry, primarily oxygen content.

• This is the carotid body and is innervated by branches from both the glossopharyngeal [IX] and vagus [X] nerves.

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Internal carotid arteries

• After its origin, the internal carotid artery ascends toward the base of the skull.

• It gives off no branches in the neck and enters the cranial cavity through the carotid canal in the petrous part of the temporal bone.

• The internal carotid arteries supply the cerebral hemispheres, the eyes and the contents of the orbits, and the forehead.

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External carotid arteries & its branches

Branch SuppliesSuperior thyroid artery Thyrohyoid muscle, internal structures of

the larynx, sternocleidomastoid and cricothyroid muscles, thyroid gland

Ascending pharyngeal artery Pharyngeal constrictors and stylopharyngeus muscle, palate, tonsil, pharyngotympanic tube, meninges in posterior cranial fossa

Lingual artery Muscles of the tongue, palatine tonsil, soft palate, epiglottis, floor of mouth, sublingual gland

Facial artery All structures in the face from the inferior border of the mandible anterior to the masseter muscle to the medial corner of the eye, the soft palate, palatine tonsil, pharyngotympanic tube, submandibular gland

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External carotid arteries & its branches Branch SuppliesOccipital artery Sternocleidomastoid muscle, meninges in

posterior cranial fossa, mastoid cells, deep muscles of the back, posterior scalp

Posterior auricular artery Parotid gland and nearby muscles, external ear and scalp posterior to ear, middle and inner ear structures

Superficial temporal artery Parotid gland and duct, masseter muscle, lateral face, anterior part of external ear, temporalis muscle, parietal and temporal fossae

Maxillary artery External acoustic meatus, lateral and medial surface of tympanic membrane, temporomandibular joint, dura mater on lateral wall of skull and inner table of cranial bones, trigeminal ganglion and dura in vicinity, mylohyoid muscle, mandibular teeth, skin on chin, temporalis muscle, outer table of bones of skull in temporal fossa, structures in infratemporal fossa, maxillary sinus, upper teeth and gingivae, infra-orbital skin, palate, roof of pharynx, nasal cavity

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Veins • Collecting blood from the skull, brain, superficial face,

and parts of the neck, the internal jugular vein begins as a dilated continuation of the sigmoid sinus, which is a dural venous sinus.

• The paired internal jugular veins join with the subclavian veins posterior to the sternal end of the clavicle to form the right and left brachiocephalic veins.

• Tributaries to each internal jugular vein include the inferior petrosal sinus, and the facial, lingual, pharyngeal, occipital, superior thyroid, and middle thyroid veins.

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Nerves

• Numerous cranial and peripheral nerves:pass through the anterior triangle of the neck

as they continue to their final destination; send branches to structures in or forming

boundaries of the anterior triangle of the neck;

while in the anterior triangle of the neck, send branches to nearby structures.

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The cranial nerves in these categories include: the facial [VII], glossopharyngeal [IX], vagus [X], accessory [XI], and hypoglossal [XII].

The peripheral nerves in these categories include the transverse cervical nerve from the cervical plexus and the upper and lower roots of the ansa cervicalis.

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Cranial nerves & its branches

Nerve InnervationFacial nerve [VII] the posterior belly of the digastric;

stylohyoid.

Glossopharyngeal nerve [IX] stylopharyngeus muscle, sends a branch to the carotid sinus, and supplies sensory branches to the pharynx.

Vagus nerve [X] Gives a motor branch to the pharynx, a branch to the carotid body, the superior laryngeal nerve (which divides into external and internal laryngeal branches), and possibly a cardiac branch.

Accessory nerve [XI] No branches in the anterior triangle but innervates the trapezius

Hypoglossal nerve [XII] No branches in the anterior triangle but innervates the tongue

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Glossopharyngeal nerve [IX]

Vagus nerve

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Accessory nerve Hypoglossal nerve

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Peripheral nerves & its branches

Nerve InnervationTransverse cervical nerve provides cutaneous innervation to this

area

Ansa cervicalis innervates the inferior belly of the omohyoid, and the lower parts of the sternohyoid and sternothyroid muscles.

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THYROID AND PARATHYROID GLANDS

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• They are both endocrine glands positioned anteriorly in the neck.

• Both glands begin as pharyngeal outgrowths that migrate caudally to their final position as development continues.

• The thyroid gland is a large, unpaired gland, while the parathyroid glands, usually four in number, are small and are on the posterior surface of the thyroid gland.

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Thyroid gland

• The thyroid gland is anterior in the neck below and lateral to the thyroid cartilage.

• It consists of two lateral lobes (which cover the anterolateral surfaces of the trachea, the cricoid cartilage, and the lower part of the thyroid cartilage).

• It also has the isthmus that connects the lateral lobes and crosses the anterior surfaces of the second and third tracheal cartilages.

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• It lies deep to the sternohyoid, sternothyroid, and omohyoid muscles.

• It is in the visceral compartment of the neck.• This compartment also includes the pharynx,

trachea, and esophagus and is surrounded by the pretracheal layers of fascia.

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Arterial supply• Two major arteries supplies the thyroid gland;• The superior thyroid artery and the inferior thyroid

artery.The superior thyroid artery is the first branch of the

external carotid artery, it descend along the lateral margin of thyrohyoid muscle and divides into an anterior and a posterior glandular branch at the superior pole of the gland.

Anterior glandular-supplies superior pole and anastomose with the opposite anterior glandular.

Posterior glandular- passes posterior, may anastomose with inferior thyroid artery

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Superior thyroid artery

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Inferior thyroid arteryThe inferior thyroid artery is a branch of the

thyrocervical trunk, which arises from the first part of the subclavian artery.

At the thyroid gland the inferior thyroid artery divides into an:

inferior branch, which supplies the lower part of the thyroid gland and anastomoses with the posterior branch of the superior thyroid artery;

an ascending branch, which supplies the parathyroid glands.

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Inferior thyroid artery

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Nerve supply

• The thyroid gland is closely related to and supplied by the recurrent laryngeal nerves.

• After branching from the vagus nerve [X] and looping around the subclavian artery on the right and the arch of the aorta on the left, the recurrent laryngeal nerves ascend in a groove between the trachea and esophagus.

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Recurrent laryngeal nerve

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GOODMORNING