anatomy of the neck

ANATOMY OF THE NECK

Kaan Yücel M.D., Ph.D. 24. October. 2011 Monday

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The neck is the transitional area between the base of the cranium superiorly and the clavicles inferiorly.

Neck is a passageway for many important structures extending between the head and the trunk such as the larynx and the thyroid and parathyroid glands.

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The neck is relatively slender to allow the flexibility necessary to position the head to maximize the efficiency of its sensory organs (mainly the eyeballs but also the ears, mouth, and nose).

Thus many important structures are crowded together in the neck, such as muscles, glands, arteries, veins, nerves, lymphatics, trachea, esophagus, and vertebrae.

Consequently, the neck is a well-known region of vulnerability.

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The main arterial blood flow to the head and neck (the carotid arteries) and the principal venous drainage (the jugular veins) lie anterolaterally in the neck.

Carotid/jugular blood vessels are the major structures commonly injured in penetrating wounds of the neck.

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The brachial plexuses of nerves originate in the neck and pass inferolaterally to enter the axillae and continue into and supply the upper limbs.

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Bones of the Neck The skeleton of the neck is formed by the cervical vertebrae, hyoid

bone, manubrium of the sternum, and clavicles.

These bones are parts of the axial skeleton except the clavicles, which are part of the appendicular skeleton.

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Cervical Vertebrae 7 cervical vertebrae form the cervical region of the vertebral column,

which encloses the spinal cord and meninges.

The centrally placed vertebral bodies

Support the head, and the intervertebral (IV) articulationsespecially the craniovertebral joints at its superior end

Provide the flexibility necessary to allow positioning of the head.

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Hyoid Bone (Hyoid)Lies in the anterior part of the neck at the level of the C3 in the angle between the mandible and the thyroid cartilage.

Suspended by muscles that connect it to the mandible, styloid processes, thyroid cartilage, manubrium, and scapulae.

Does not articulate with any other bone.

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It is suspended from the styloid processes of the temporal bones by the stylohyoid ligaments and is firmly bound to the thyroid cartilage.

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The hyoid consists of a body and greater and lesser horns (L. cornua; the lesser horn is the attachment for the sytlohyoid ligament.).

Functionally, the hyoid serves as an attachment for anterior neck muscles and a prop to keep the airway open.

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Fascia of the Neck

Structures in the neck are surrounded by a layer of subcutaneous tissue (superficial fascia) and are compartmentalized by layers of deep cervical fascia.

The knowledge of the organization of the cervical fascia is critical in figuring out where the infections of this region may spread.

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Superficial cervical fascia

Layer of fatty connective tissue that lies between the dermis of the skin and the investing layer of deep cervical fascia. This tissue is usually thinner than in other regions, especially anteriorly.

Contains cutaneous nerves, blood and lymphatic vessels, superficial lymph nodes, and variable amounts of fat. Anterolaterally, it contains the platysma.

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The platysma (G. flat plate) is a broad, thin sheet of muscle in the subcutaneous tissue of the neck.

The external jugular vein (EJV) and the main cutaneous nerves of the neck are deep to the platysma.

The platysma covers the anterolateral aspect of the neck.

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Acting from its superior attachment, the platysma tenses the skin, producing vertical skin ridges and releasing pressure on the superficial veins.

Acting from its inferior attachment, the platysma helps depress the mandible and draw the corners of the mouth inferiorly.

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As a muscle of facial expression, the platysma serves to convey tension or stress.

The platysma is supplied by the cervical branch of CN VII.

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Deep cervical fasciaThe deep cervical fascia consists of three fascial layers (sheaths): investing, pretracheal, and prevertebral layers support the viscera (e.g., the thyroid gland), muscles, vessels, and deep lymph nodes.

The deep cervical fascia also condenses around the common carotid arteries, internal jugular veins (IJVs), and vagus nerves to form the carotid sheath.

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Investing layer of deep cervical fasciaMost superficial deep fascial layer,

Surrounds the entire neck deep to the skin and subcutaneous tissue.

Anteriorly, surrounds the infrahyoid muscles.

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The investing fascia is attached: Superiorly to the external occipital protuberance and the superior

nuchal line; Laterally to the mastoid process and zygomatic arch; and Inferiorly to the spine of the scapula, the acromion, the clavicle, and

the manubrium of sternum.

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Pretracheal layer of deep cervical fascia Extends between the hyoid bone and thorax.

At the thorax blends with the fibrous pericardium.

Has two layers: Muscular layer encloses the infrahyoid muscles Visceral layer encloses the thyroid gland, trachea and esophagus.

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Posteriorly, the pretracheal layer is referred to as the buccopharyngeal fascia (a fascia enclosing the pharynx, superior continuation of the fascia covering the buccinator muscle) and separates the pharynx and the esophagus from the prevertebral layer.

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The buccopharyngeal fascia begins superiorly at the base of the skull and ends inferiorly in the thoracic cavity.

Laterally, it blends with the carotid sheath.

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Prevertebral layer of deep cervical fascia

Forms a tubular sheath for the vertebral column and the muscles associated with it.

Extends between the base of the skull and T3 vertebra.

Attached posteriorly along the length of the ligamentum nuchae, and superiorly forms a continuous circular line attaching to the base of the skull.

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The prevertebral layer of deep fascia is fixed to the cranial base superiorly.

Infero-laterally it extends to axilla and continuous with the axillary sheath enclosing the axillary vessels and the brachial plexus.

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Carotid SheathTubular fascial investment ;extends from the cranial base to the root of the neck. Contains :1) Common and internal carotid arteries.2) Internal jugular vein.3) Vagus nerve (CN X).4) Some deep cervical lymph nodes.5) Carotid sinus nerve.6) Sympathetic nerve fibers (carotid periarterial plexuses)

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The carotid sheath and pretracheal fascia communicate freely with the mediastinum of the thorax inferiorly and the cranial cavity superiorly.

These communications represent potential pathways for the spread of infection and extravasated blood.

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Fascial spacesBetween the fascial layers in the neck are spaces that may provide a conduit for the spread of infections from the neck to the mediastinum. Three spaces could be involved in this process: 1) Pretracheal space between the investing layer of cervical

fascia and the pretracheal fascia,which passes between the neck and the anterior part of the superior mediastinum;

2) Retropharyngeal space 3) Within the prevertebral layer covering the anterior surface of

the transverse processes and bodies of the cervical vertebrae.

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Retropharyngeal space

Largest and most important interfascial space in the neck.

Potential space that consists of loose connective tissue between the visceral part of the prevertebral layer of deep cervical fascia and the buccopharyngeal fascia surrounding the pharynx superficially.

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It permits the movement of pharynx, larynx and esophagus

The retropharyngeal space is closed with the skull base superiorly and the carotid sheath laterally.

It extends from the base of the skull to the upper part of the posterior mediastinum.

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Cervical RegionsTo allow clear communication regarding the location of structures, injuries, or pathologies, the neck is divided into regions.

Between the cranium (mandible anteriorly and occipital bone posteriorly) and the clavicles, the neck is divided into 4 major regions.

Based on the usually visible and/or palpable borders of the large and relatively superficial SCM and trapezius muscles.

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Sternocleidomastoid RegionThe sternocleidomastoid (SCM) muscle is a key muscular landmark in the neck, forming the sternocleidomastoid region [1].

The SCM visibly divides each side of the neck into the anterior [2] and lateral cervical [3] regions (anterior and posterior triangles).

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The SCM is a broad, strap-like muscle that has two heads: Sternal head attaches to the manubriumClavicular head attaches to the clavicle

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The SCMs produce movement at the craniovertebral joints, the cervical intervertebral joints, or at both.

The cranial attachments of the SCMs lie posterior to the axis of the atlanto-occipital (AO) joints.

Bilateral contraction of the SCMs will cause extension of the head at the AO joints, elevating the chin

Acting bilaterally, the SCMs can also flex the neck.

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Posterior Cervical RegionThe region posterior to the anterior borders of (i.e., corresponding to the area of) the trapezius is the posterior cervical region.

The suboccipital region is deep to the superior part of this region.

The trapezius is a large, flat triangular muscle that covers the posterolateral aspect of the neck and thorax.

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The trapezius is a:Superficial muscle of the back Posterior axioappendicular muscle, that acts on the pectoral girdleCervical muscle, that can produce movement of the cranium.

The trapezius attaches the pectoral girdle to the cranium and the vertebral column and assists in suspending it.

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Lateral Cervical RegionThe lateral cervical region (posterior triangle) is bounded:

Anteriorly by the posterior border of the SCM.Posteriorly by the anterior border of the trapezius.Inferiorly by the middle third of the clavicle between the trapezius and the SCM.

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Muscles in the Lateral Cervical Region

The floor of the lateral cervical region is usually formed by the prevertebral fascia overlying four muscles: splenius capitis, levator scapulae, middle scalene (L. scalenus medius), and posterior scalene (L. scalenus posterior).

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Nerves of the Lateral Cervical RegionThe spinal accessory nerve (CN XI) passes deep to the SCM, supplying it before entering the lateral cervical region at or inferior to the junction of the superior and middle thirds of the posterior border of the SCM.

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The roots of the brachial plexus (anterior rami of C5-C8 and T1) appear between the anterior and the middle scalene muscles.

The five rami unite to form the three trunks of the brachial plexus, which descend inferolaterally through the lateral cervical region.

The plexus then enters the axilla, providing innervation for most of the upper limb.

Vessels in theLateral Cervical Region

1) The lateral branches of the thyrocervical trunk2) The third part of the subclavian artery3) Part of the occipital artery

Veins in lateral cervical regionThe external jugular vein (EJV) is formed by the union of the

posterior division of the retromandibular vein with the posterior auricular vein.

The EJV terminates in and drains into the subclavian vein.

The subclavian vein, the major venous channel draining the upper limb unites with the IJV to form the brachiocephalic vein.

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Lymph nodes in the Lateral Cervical Region Lymph from superficial tissues in the lateral cervical region enters the superficial cervical lymph nodes.

Efferent vessels from these nodes drain into the deep cervical lymph nodes, which form a chain embedded in the fascia of the carotid sheath.

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Anterior Cervical RegionThe anterior cervical region (anterior triangle) has the following:

An anterior boundary formed by the median line of the neck.A posterior boundary formed by the anterior border of the SCM.A superior boundary formed by the inferior border of the mandible.An apex located at the jugular notch in the manubrium.A roof formed by subcutaneous tissue containing the platysma.A floor formed by the pharynx, larynx, and thyroid gland.

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For more precise localization of structures, the anterior cervical region is subdivided into four smaller triangles by the digastric and omohyoid muscles: the unpaired submental triangle and three small paired triangles—submandibular, carotid, and muscular.

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Submental triangle Inferior to the chin A suprahyoid area bounded inferiorly by the body of the hyoid and

laterally by the right and left anterior bellies of the digastric muscles. The floor formed by the two mylohyoid muscles, which meet in a

median fibrous raphe. The apex at the mandibular symphysis Its base formed by the hyoidContains several small submental lymph nodes and small veins that unite to form the anterior jugular vein.

Anterior digastric muscles (abd) Mylohyoid muscle (mh)

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Submandibular triangleA glandular area between the inferior border of the mandible and the anterior and posterior bellies of the digastric muscle. Submandibular lymph nodes Hypoglossal nerve (CN XII) Nerve to the mylohyoid muscle (a branch of CN V3, which also supplies the anterior

belly of the digastric) Parts of the facial artery and vein Submental artery (a branch of the facial artery)

anterior belly of digastric (abd)posterior belly of digastric (pbd)

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MUSCLES IN ANTERIOR CERVICAL REGIONIn the anterolateral part of the neck, the hyoid provides

attachments for the suprahyoid muscles superior to it and the infrahyoid muscles inferior to it.

These hyoid muscles steady or move the hyoid and larynx. For descriptive purposes, they are divided into suprahyoid and infrahyoid muscles.

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Muscles superior to the hyoid are classified as suprahyoid musclesstylohyoiddigastricmylohyoid geniohyoid

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Muscles inferior to the hyoid are infrahyoid musclesomohyoid (superficial plane)sternohyoid (superficial plane)thyrohyoid (deep plane)sternothyroid (deep plane)

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Anterior Cervical RegionArteries in anterior cervical region

The anterior cervical region contains the carotid system of arteries, consisting of the common carotid artery and its terminal branches, the internal and external carotid arteries. It also contains the IJV and its tributaries and the anterior jugular veins.

Common carotid artery

The common carotid artery arises from the brachiocephalic trunk on the right side and from the arch of aorta on the left side.

The common carotid artery and one of its terminal branches, the external carotid artery, are the main arterial vessels in the carotid triangle.

The carotid triangle is bounded: posteriorly by the sternocleidomastoideus; inferiorly, by the superior belly of the omohyoideus superiorly, by the stylohyoideus and the posterior belly of the

digastricus.

Each common carotid artery ascends within the carotid sheath with the IJV and vagus nerve to the level of the superior border of the thyroid cartilage.

Here, each common carotid artery terminates by dividing into the internal and external carotid arteries.

The internal carotid artery has no branches in the neck; the external carotid has several.

The right common carotid artery begins at the bifurcation of the brachiocephalic trunk.

The right subclavian artery is the other branch of this trunk.

From the arch of the aorta, the left common carotid artery ascends into the neck.

The internal carotid arteries are direct continuations of the common carotids superior to the origin of the external carotid artery, at the level of the superior border of the thyroid cartilage.

The carotid body (carotid glomus or glomus caroticum) is located in the cleft between the internal and the external carotid arteries.

While the carotid bodies contain chemoreceptors, the carotid sinus, a slight dilatation of the proximal part of internal carotid artery, contains baroreceptors. The carotid sinus is sensitive to blood pressure changes.

Role of the carotid bodies

Carotid bodies are sensitive to decreased O2 and increased CO2 content of the blood

In both cases visseral reflexes are activated leading to increased ventilation (increased depth and rate of repiration) and as well as rise of heart rate and blood pressure

Both the afferent and efferent pathways for this reflex is through the vagus and glossopharyngeal nerves.

Internal carotid artery

The internal carotid arteries enter the cranium through the carotid canals in the petrous parts of the temporal bones and become the main arteries of the brain and structures in the orbits.

No named branches arise from the internal carotid arteries in the neck.

The internal carotid artery supplies the brain together with the vertebral artery which is a branch of the subclavian artery.

After entering the cranial vault it forms the polygon of Willis together with the vertebral artery.

External carotid artery Supplies most structures external to the cranium; the orbit and the

part of the forehead and scalp supplied by the supraorbital artery are the major exceptions.

Extends to the level of the parotid gland. Terminates by dividing into two branches, the maxillary artery and the superficial temporal artery within the tissue of the parotid gland

Veins in anterior cervical region Most veins in the anterior cervical region are tributaries of the

internal jugular vein (IJV), typically the largest vein in the neck.

Internal jugular vein is the main vein draining the intracranial veins, as well as the head and neck.

Veins in anterior cervical region

It commences at the jugular foramen in the posterior cranial fossa as the direct continuation of the sigmoid sinus.

IJV unites with the subclavian vein to from the brachiocephalic vein.

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NERVES IN ANTERIOR CERVICAL REGIONSeveral nerves, including branches of cranial nerves, are located in the anterior cervical region.Transverse cervical nerve (C2 and C3): supplies the skin covering the anterior cervical region.

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Hypoglossal nerve (CN XII): the motor nerve of the tongue, enters the submandibular triangle deep to the posterior belly of the digastric muscle to supply the intrinsic and four of the five extrinsic muscles of the tongue.

The nerve gives off the superior root of the ansa cervicalis and then a branch to the geniohyoid muscle.

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Branches of the glossopharyngeal (CN IX) and vagus (CN X) nerves: in the submandibular and carotid triangles. CN IX is primarily related to the tongue and pharynx. In the neck, CN X gives rise to pharyngeal, laryngeal, and cardiac branches.

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ROOT OF THE NECK Junctional area between the thorax and the neck. Cervical side of the superior thoracic aperture, through which pass all

structures going from the thorax to the head or upper limb and vice versa.

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The inferior boundary of the root of the neck is the superior thoracic aperture, formed laterally by the 1st pair of ribs and their costal cartilages, anteriorly by the manubrium of the sternum, and posteriorly by the body of T1 vertebra.

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NERVES IN ROOT OF NECKThere are three pairs of major nerves in the root of the neck: (1) vagus nerves(2) phrenic nerves(3) sympathetic trunks

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Vagus Nerves (CN X)

After its exit from the jugular

foramen, each vagus nerve passes inferiorly in the

neck within the

posterior part of the carotid sheath in the angle between the

IJV and the common carotid

artery.

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The right vagus nerve passes anterior to the first part of the subclavian artery and posterior to the brachiocephalic vein and to enter the thorax.

The left vagus nerve descends between the left common carotid and the left subclavian arteries to enter the thorax.

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The recurrent laryngeal nerves arise from the vagus nerves in the inferior part of the neck.

The cardiac branches of CN X originate in the neck as well as in the thorax and convey presynaptic parasympathetic and visceral afferent fibers to the cardiac plexus of nerves.

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Phrenic NervesThe phrenic nerves pass under the prevertebral layer of deep cervical fascia, between the subclavian arteries and veins, and proceed to the thorax to supply the diaphragm.

The phrenic nerves are important because, in addition to their sensory distribution, they provide the sole motor supply to their own half of the diaphragm.

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Sympathetic Trunks

Each sympathetic trunks descend at the antero-lateral parts of the vertebral column. Sympathetic trunks are formed of sympathetic ganglia and nerve fibers extending between them.

The cervical portion of the sympathetic trunks lies anterolateral to the vertebral column, extending superiorly to the level of the C1 vertebra or cranial base.

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The sympathetic trunks receive no white rami communicantes in the neck (white rami associated with cervical spinal nerves).

The cervical portion of the trunks includes three cervical sympathetic ganglia: superior, middle, and inferior.

These ganglia receive presynaptic fibers conveyed to the trunk by the superior thoracic spinal nerves and their associated white rami communicantes, which then ascend through the sympathetic trunk to the ganglia.

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After synapsing with the postsynaptic neuron in the cervical sympathetic ganglia, postsynaptic neurons send fibers to the:Cervical spinal nerves via gray rami communicantesThoracic viscera via cardiopulmonary splanchnic nervesHead and viscera of the neck via cephalic arterial branches (rami)

Root of NeckArteries in root of neck

The brachiocephalic trunk is covered anteriorly by the right sternohyoid and sternothyroid muscles; it is the largest branch of the arch of the aorta.

It arises in the midline from the beginning of the arch of the aorta.

It passes superolaterally to the right where it divides into the right common carotid and right subclavian arteries.

The brachiocephalic trunk usually has no branches.

Subclavian artery The subclavian arteries supply the upper limbs; they also send

branches to the neck and brain.

The right subclavian artery arises from the brachiocephalic trunk.

The left subclavian artery arises from the arch of the aorta distal to the left common carotid artery.

Veins in root of neckTwo large veins terminating in the root of the neck are the external jugular vein (EJV), draining blood received mostly from the scalp and face, and the variable anterior jugular vein (AJV), usually the smallest of the jugular veins.

The right and left AJVs commonly unite across the midline to form the jugular venous arch.

The subclavian vein, the continuation of the axillary vein, begins at the lateral border of the 1st rib and ends when it unites with the internal jugular vein (IJV).

The subclavian vein is separated from the subclavian artery by the anterior scalene muscle. It usually has only one named tributary, the EJV.

The internal jugular vein (IJV) is the main vein draining the intracranial veins, as well as the head and neck.

It ends posterior by uniting with the subclavian vein to form the brachiocephalic vein.

This union is commonly referred to as the venous angle and is the site where the thoracic duct (left side) and the right lymphatic trunk (right side) drain lymph collected throughout the body into the venous circulation.

Right and left brachiocephalic veins unite to form the superior vena cava (opens into the right atrium of the heart).

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VISCERA OF NECKThe cervical viscera are disposed in three layers, named for their primary function. Superficial to deep, they are the: Endocrine layer: the thyroid and parathyroid glands. Respiratory layer: the larynx and trachea. Alimentary layer: the pharynx and esophagus

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Endocrine Layer of Cervical VisceraThe cervical organs in the endocrine layer are part of the body's endocrine system of ductless, hormone-secreting glands.

The thyroid gland is the body's largest endocrine gland. It produces thyroid hormone, which controls the rate of metabolism, and calcitonin, a hormone controlling calcium metabolism.

The thyroid gland affects all areas of the body except itself and the spleen, testes, and uterus.

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The hormone produced by the parathyroid glands, parathormone (PTH), controls the metabolism of phosphorus and calcium in the blood.

The parathyroid glands target the skeleton, kidneys, and intestine.

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THYROID GLANDThe thyroid gland lies deep to the sternothyroid and sternohyoid muscles, located anteriorly in the neck.

It consists primarily of right and left lobes, anterolateral to the larynx and trachea.

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A relatively thin isthmus unites the lobes over the trachea, usually anterior to the second and third tracheal rings.

A pyramidal lobe is often present, and it projects upward from the isthmus, usually to the left of the midline.

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Vasculature of the Thyroid GlandThe highly vascular thyroid gland is supplied by the superior and inferior thyroid arteries.

These vessels lie between the fibrous capsule and the loose fascial sheath.

Three pairs of thyroid veins usually form a thyroid plexus of veins on the anterior surface of the thyroid gland.

The lymph from the thyroid gland drains into superficial and deep cervical lymph nodes.

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Nerves of Thyroid Gland The nerves of the thyroid gland are derived from the superior,

middle, and inferior cervical (sympathetic) ganglia.

They reach the gland through the cardiac and superior and inferior thyroid periarterial plexuses that accompany the thyroid arteries.

These fibers are vasomotor, not secretomotor. They cause constriction of blood vessels. Endocrine secretion from the thyroid gland is hormonally regulated by the pituitary gland.

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PARATHYROID GLANDS

The small flattened, oval parathyroid glands usually lie external to the thyroid capsule on the medial half of the posterior surface of each lobe of the thyroid gland, inside its sheath.

Most people have four parathyroid glands.

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Vessels of the Parathyroid Glands Because the inferior thyroid arteries provide the primary blood

supply to the posterior aspect of the thyroid gland where the parathyroid glands are located.

Parathyroid veins drain into the thyroid plexus of veins of the thyroid gland and trachea.

Lymphatic vessels drain into deep cervical lymph nodes and paratracheal lymph nodes.

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Nerves of the Parathyroid Glands

The nerve supply of the parathyroid glands is abundant; it is derived from thyroid branches of the cervical (sympathetic) ganglia.

Like the nerves to the thyroid, they are vasomotor rather than secretomotor because these glands are hormonally regulated.