Neck Things to Know

Embed Size (px)

Citation preview

  • 7/23/2019 Neck Things to Know

    1/15

    Material to Learn

    Osteology of the NeckCervical Vertebrae

    Of the seven cervical vertebrae, the atlas and the axis are unique while C3-C7 share

    many common characteristics. Refer to an atlas and to the skeleton to review thedetailed structure of the cervical vertebrae.

    C1 and C2 = atypical cervical vertebrae.Atlas (C1):

    ring-likebone lacks both spinous process and vertebral body consists of two lateral massesconnected by anterior and posterior arches anterior and posterior tuberclesare located centrally on each arch the posterior arch has a groove for vertebral arteryon its superior surface the large horizontal superior articular facetslie directly medial to the transverse

    processes and articulate with the occipital condyles of the skull inferiorly C1 articulates with C2 via the densand two lateral inferior articular

    facets

    Axis (C2): has a bodywith the dens (odontoid process) projecting superiorly from it the densarticulates with the anterior arch of C1 (synovial pivot joint) has a spinous process that isusually bifid the superior articular facetslie anteromedial to the transverse processes and

    articulate with the C1 inferior articular facets via gliding synovial joints

    Typical cervical vertebrae (C3-C7): large triangular vertebral foramen vertebral bodywider from side to side than anteroposteriorly with a concave

    superior surface and convex inferior surface transverse processes with a foramen (transverse foramen) to accommodate the

    vertebral artery and vein anterior and posterior tubercleslateral to each transverse foramen obliquely orientedarticular facets that lie posteriorto the transverse processes short bifid spinous process(except for C7)

    Notice that the bodies of the cervical vertebrae have superolateral ridges called

    uncinate processes. Also, each articular processof a typical cervical vertebra formsa bulge posterior to the transverse process. On C6 the large anterior tubercle of thetransverse process is called the carotid tuberclebecause the common carotid arterycan be compressed against it and the vertebral body to control bleeding. Finally, C7, thevertebra prominens,has a very long spinous process that is not bifid.

  • 7/23/2019 Neck Things to Know

    2/15

    Hyoid Bone:U-shaped that lies in the anterior part of the neck at the level of the C3 vertebra. It issuspended by horizontally-oriented muscles attached to the mandible and styloidprocesses, and by vertically oriented muscles attached to the thyroid cartilage,manubrium and scapula. The hyoid bone consists of a bodyand right and left greater

    and lesser horns (cornua).

    Cartilages of the Anterior Neck:Thyroid cartilageis the largest and most superior of the two major cartilages of theanterior neck. It is a shield-shaped structure formed from two relatively flat plates ofcartilage (lamina) that fuse in the midline and create the laryngeal prominence. Thethyroid cartilage is open posteriorly. Superior and inferior hornsproject from the

    posterior aspect of each lamina and provide attachment sites for the thyrohyoidmembrane superiorly and the cricothyroid joint inferiorly.

    Cricoid cartilageis shaped like a signet ring with its broad laminafacing posteriorly

    and its narrow arch(band) facing anteriorly. The cricoid cartilage is the only completering of cartilage to encircle the airway! It is very strong. It is attached to the thyroidcartilage by the median cricothyroid membrane (ligament)which is easily incised to

    access the airway in an emergency. Inferiorly, the cricoid cartilage attaches to the firsttracheal ring by the cricotracheal ligament.

    Material to Learn

    Fasciae of the NeckSuperficial and deep cervical fasciaesubdivide the neck into compartments, separate

    structures, and direct the flow of fluid (e.g. infectious materials) in the neck.

    Superficial Cervical Fascia: a loose fatty layer of subcutaneous tissue that liesbetween the dermis of the skin and the investing layer of the deep cervical fascia. Thethickness of the superficial cervical fascia varies among people. It contains cutaneousnerves, blood vessels and lymphatics as well as the platysma muscle- a thin broad

    muscle that tightens the skin of the anterolateral neck.

    Deep Cervical Fascia (three layers):membranous fasciae that form compartments and

    separate muscle layers and neurovascular structures.

    Investing layer - most superficial of the deep cervical fasciae.It surrounds the entireneck just deep to the superficial cervical fascia. Posteriorly it attaches to the superiornuchal line, ligamentum nuchae and spinous processes of the cervical vertebrae.

    Anterolaterally it attaches to the mastoid processes, the zygomatic arches (of the face),the mandible and the hyoid bone. It encloses the SCM and trapezius musclesby

    splitting into superficial and deep layers around these muscles. It also encloses(surrounds) the submandibular and parotid glands.

  • 7/23/2019 Neck Things to Know

    3/15

    Pretracheal layer- found in the anterior neck. The muscular portion of pretrachealfascia is a thin, indistinct layer that encloses the infrahyoid muscles. The visceralportion of pretracheal fascia is more distinct and encloses the thyroid gland, tracheaand esophagus. Superiorly, it attaches to the hyoid boneand forms a pulley thatanchors the intertendon of the digastric muscle. Inferiorly it is continuous with the

    fibrous pericardium. Laterally it blends with the carotid sheath. Posteriorly it iscontinuous with the buccopharyngeal fasciaof the pharynx.

    Prevertebral layer- ensheaths the vertebral column and its many associated muscles:anteriorly the longus colli and capitis; posteriorly the deep (intrinsic) muscles of the back(splenius, longissimus, semispinalis etc.); and laterally the scalene muscles. Superiorlyit is attached to the cranial base. Inferiorly it blends with the anterior longitudinalandsupraspinous ligaments. At the base of the neck (near the midpoint of the clavicles)the prevertebral fascia is drawn out laterally as the axillary sheathby the nerve roots ofC5-T1 that form the brachial plexus. Posteriorly, the prevertebral fascia attaches to thespinous processes of cervical vertebrae. Anteriorly, some authors describe an additional

    layer, the alar fascia, that lies between the pretracheal and prevertebral fasciaesubdividing the retropharyngeal space. The alar fascia attaches to the carotid sheathson each side.

    Carotid sheath- a condensation of fascia that encloses the common and internalcarotid arteries, the internal jugular vein, the vagus nerveand some deep cervicallymph nodes. It extends from the base of the skull to the root of the neck and receivesfascial contributions from all three layersof deep cervical fascia.

    Material to Learn

    Suboccipital TriangleGreater occipital nerve (dorsal ramus of C2):loops around the inferior border of theinferior oblique muscle and runs posterior to the suboccipital triangle. It pierces thesemispinalis capitis and trapezius muscles and continues superiorly to innervate theposterior aspect of the scalp.

    Suboccipital triangle:a muscular triangle lying inferior to the occipital bone, deep tothe semispinalis capitis muscle. Boundaries:

    Roof:semispinalis capitis muscle

    Medial border:rectus capitis posterior major muscle Lateral border:superior oblique muscle

    Inferior border:inferior oblique muscle

    Floor: posterior arch of C1

    Contents: suboccipital nerve (dorsal ramus C1) and vertebral artery

  • 7/23/2019 Neck Things to Know

    4/15

    Rectus capitus posterior major muscle: medial border suboccipital triangle

    Attachments: Superior: inferior nuchal lineInferior: spinous process of C2

    Innervation: suboccipital nerve (dorsal ramus C1)

    Actions: unilateral - rotate the head to the same side, bilateral - extend the head

    Superior oblique muscle: lateral border suboccipital triangle

    Attachments: Superior: lateral occipital bone between superior and inferiornuchal lines Inferior: transverse process of C1

    Innervation: suboccipital nerve (dorsal ramus C1)

    Actions: unilateral - laterally bend the head, bilateralextend the head

    Inferior oblique muscle: inferior border of suboccipital triangle

    Attachments: Medial: spinous process of C2Lateral: transverse process of C1

    Innervation: suboccipital nerve (dorsal ramus C1)

    Action: strong rotator of C1 and the head to same side

    Rectus capitis posterior minor muscle: not a border of the suboccipital triangle.

    Attachments: Superior: medial aspect of the inferior nuchal lineInferior: posterior tubercle of C1

    Innervation: suboccipital nerve (dorsal ramus C1)

    Action: extend the head

    Suboccipital nerve (dorsal (posterior)ramus of C1):emerges between the occipitalbone and C1. It innervates the muscles of the suboccipital triangle plus rectus capitisposterior minor and semispinalis capitis.

    Vertebral artery:passes transversely between C1 and the occipital bone in the deep

    part of the suboccipital triangle to enter the foramen magnum. It arises as a branch ofthe subclavian artery and ascends from the root of the neck to the foramen magnum viathe transverse foramina of the cervical vertebrae (except C7). It is a main source ofblood for the brain.

    Material to Learn

    Posterior Triangle of the Neck (Lateral cervical triangle)Superficial

    Borders of the Posterior Triangle: Anterior: posterior border of sternocleidomastoid muscle Posterior: anterior border of trapezius muscle Inferior: middle third of clavicle Roof: investing layerof deep cervical fascia Floor: prevertebral layerof deep cervical fascia covering the splenius capitis,

    levator scapulae and scalene muscles

  • 7/23/2019 Neck Things to Know

    5/15

    Platysma muscle: thin subcutaneous muscle that covers the anterior and posteriortriangles of the neck

    Attachments: Superior: inferior border of mandible and related fasciaInferior: fascia over the superior aspects of the pectoralis major and deltoidmuscles

    Innervation: cervical branch of CN VII (facial nerve)

    Action: tighten the skin of the neck during certain movements of the mouth, e.g.grimace

    Sternocleidomastoid muscle: large obliquely oriented muscle that subdivides theanterolateral neck into anterior and posterior triangles.

    Attachments: Superior: mastoid process and lateral 1/2 of superior nuchal lineInferior: manubrium of the sternum and medial 1/3 of the clavicle

    Innervation: accessory nerve (CN XI) and branches of C2 and C3(proprioception)

    Action: unilateral - turn face/head to the opposite side and laterally flex the head

    and neck to the same side; bilateralextend head and, with continuedcontraction, flex inferior cervical vertebrae, chin is thrust forward; accessorymuscle of respiration.

    TIP: When one accessory nerve (CN XI) has beendamaged the head at rest will be turned toward thedamaged side.

    Accessory nerve (CN XI): is an atypical cranial nerve. It is described as having bothcranial and spinal roots. The cranial root contains motor axons that arise in the medulla

    oblongata. These axons do not exit the skull with CN XI but join the adjacent vagus

    nerve by which they are distributed to the soft palate, pharyngeal constrictors andlarynx. The spinal root consists of axons that arise from the C1 - C5 segments of the

    spinal cord. They ascend within the vertebral canal, pass through the foramen magnum,join the cranial roots for a short distance then diverge and exit the skull through thejugular foramen. These axons innervate the SCM and trapezius muscles.

    The accessory nerve appears in the superior part of the punctum nervosa (pointof nerves), traverses the posterior triangle and enters the deep surface of thetrapezius muscle which it innervates.

    Lesser occipital nerve (C2): ascends from the punctum nervosa along the posterior

    border of the SCM, and provides cutaneous innervation to the scalp posterior andsuperior to the auricle of ear.

    Great auricular nerve (C2, C3): ascends on the external surface of the SCM parallel tothe external jugular vein. It provides cutaneous innervation to the skin inferior to theauricle and to the parotid gland.

  • 7/23/2019 Neck Things to Know

    6/15

    Transverse cervical nerve (C2, C3): runs transversely across the sternocleidomastoidmuscle toward the midline of the neck and provides cutaneous innervation to skin of theanterior triangle of the neck.

    Supraclavicular nerves (C3, C4): emerge together from the posterior border of the

    sternocleidomastoid muscle then divide into medial, intermediate and lateral branchesthat supply skin along the clavicle and over the shoulder.

    Occipital artery: branch of the external carotid artery. It gives one branch to the SCMand one descending branch that anastomoses with other arteries of the area, thencontinues to supply the scalp on the back of the head as far as the vertex.

    External jugular vein: formed by the union of the posterior auricular andretromandibular (posterior division) veins. It drains smaller vessels of the scalp and faceinto the subclavian vein.

    Clinical Correlations

    The supraclavicular nerves and phrenic nerveshave common segmental origins -C3 and C4. "Referred pain"to the shoulder from pleuritis and/or abdominalinflammations that irritate branches of the phrenic nerve occurs via the supraclavicularnerves.

    If the external jugular vein (EJV)is cut near the point where it pierces the roof of theposterior triangle, its lumen is held open by the investing layer of the deep cervicalfascia. Negative pressure in the thoracic cavity will suck air into the vein resulting in avenous air embolism.Air is drawn into the right side of the heart and creates a bubblyfoam that hinders blood flow. The patient presents with a churning noise in the thorax,cyanosis (a bluish discoloration of the skin and mucous membranes resulting fromreduced oxygen in the blood) and dyspnea (shortness of breath). If pressure is appliedto the severed EJV, air can not enter the heart and the symptoms can be preventeduntil the vein is sutured.

    Under normal conditions the EJV is only slightly visible on the neck. However, whenvenous pressure is chronically elevated, for example, in congestive heart failure, theEJVs become dilated and prominent. Therefore, examination of the neck to evaluate

    the condition of the EJV is an important part of a routine physical exam.

    Material to Learn

    Posterior Triangle of the Neck (Lateral cervical triangle) - DeepSubclavian vein:drains mainly the veins of the upper limb and the external jugularvein; medially it joins the internal jugular vein to form the brachiocephalic vein

  • 7/23/2019 Neck Things to Know

    7/15

    Suprascapular vein:drains muscles around the scapula.

    Thyrocervical trunk (artery):arises from the first part of the subclavian artery andgives the following branches:

    Suprascapular artery: proximally it passes superficial to the anterior scalenemuscle, parallel and inferior to the transverse cervical artery, distally it passessuperior to the transverse scapular ligament to supply the supra- andinfraspinatus muscles.

    Transverse cervical artery:runs posterolaterally across the anterior scalene

    muscle and trunks of the brachial plexus and passes to the deep side of thetrapezius muscle to supply it and the levator scapulae and rhomboid muscles viasuperficial and deep branches.

    Inferior thyroid artery: will be dissected later. It ascends on the superficialsurface of the anterior scalene muscle, then arches inferomedially to supply thethyroid gland. It gives rise to the ascending cervical artery.

    Splenius capitis muscle:

    Attachments: Medial: ligamentum nuchae and spinous processes T1-T6Inferior: mastoid process and superior nuchal line

    Innervation: dorsal rami of mid-cervical spinal nerves Action: unilateral - laterally flex and rotate the head and neck to the same side;

    bilateralextend the head and neck

    Levator scapulae muscle: Attachments: Superior: transverse processes of C4-C6

    Inferior: superior medial border of the scapula (superior angle) Innervation: dorsal scapular nerve (C4, C5) and C3, C4 Action: elevate the scapula and tilt the glenoid fossa inferiorly (inferior rotation of

    the scapula)

    Anterior scalene muscle: Attachments: Superior: transverse processes of C4-C6

    Inferior: scalene tubercle of the 1st rib Innervation: ventral rami of C4-C6 Action: flex the neck laterally and elevate the 1st rib during inspiration

    Middle scalene muscle:

    MNEMONIC: The Army travels OVER the bridgewhile the Navy sails UNDER i.e. the suprascapularArtery travels over (superior to) the supraspinousligament while the suprascapular Nerve 'sails' under(inferior to) it. You will see this anatomy again in theupper extremity unit.

  • 7/23/2019 Neck Things to Know

    8/15

    Attachments: Superior: transverse processes of C1-C6Inferior: external surface of the 1st rib posterior to the groove for the subclavianartery

    Innervation: ventral rami of C3-C8 Action: flex the neck laterally and elevate the 1st rib during inspiration

    Posterior scalene muscle: Attachments: Superior: transverse processes of C4-C6

    Inferior: external surface of the 2nd rib Innervation: ventral rami of C6-C8 Action: flex the neck laterally and elevate the 2nd rib during inspiration

    Brachial plexus:nerves originating from the ventral rami of C5-C8 and T1. Theyinnervate the upper limb.

    Phrenic nerve:originates from the ventral rami of C3-C5. In the cervical region it lies

    on the anterior surface of the anterior scalene muscle. It provides motor innervation tothe diaphragm and sensory innervation to the pericardium, mediastinal pleura anddiaphragmatic peritoneum.

    Clinical Correlations

    The subclavian arteryand brachial plexuspass through the interscalene triangle.This pathway becomes clinically significant when the triangle is too narrow andcompresses the artery and nerve plexus. Narrowing of the triangle can occur whenmuscles are in spasm following injury (e.g. whiplash) or for other reasons such asgrowth of a tumor. Compression of the subclavian artery and brachial plexus can lead toischemia and disturbances in nerve function in the upper limb.

    Material to Learn

    Muscular Triangle of the NeckPlatysma muscle: subcutaneous muscle embedded in the superficial fascia of the neckcovering parts of the anterior and posterior triangles of the neck.

    Attachments: Superior: inferior border of mandible and fascia of the lower faceInferior: fascia over the superior parts of pectoralis major and deltoid muscles

    Innervation: cervical branch of CN VII (facial nerve) Action: tighten the skin over the neck.

    Facial artery and vein:major blood supply and drainage of the face. These vessels will

    be studied in detail in later steps.

    Anterior and communicating jugular veins:components of the jugular venoussystem. They are highly variable in size and position. The anterior jugular veins run

  • 7/23/2019 Neck Things to Know

    9/15

    vertically at the midline of the neck. The communicating veins run parallel to the anteriorborder of the SCM. Both drain venous blood from the face or suprahyoid region into theexternal jugular or subclavian veins.

    Infrahyoid muscles

    Sternohyoid: Attachments: Superior: body of hyoid bone adjacent to the midline

    Inferior: manubrium of sternum and medial end of clavicle

    Innervation: C1-C3 (ansa cervicalis)

    Action: depress the hyoid bone during swallowing and vocalization

    Omohyoid: two bellied muscle with an intertendon encircled by a fascial sling.

    Attachments: Superior: hyoid bone lateral to sternohyoidInferior: superior border of scapula medial to the scapular notch

    Innervation: C1-C3 (ansa cervicalis)

    Action: depress and retract the hyoid bone

    Sternothyroid:

    Attachments: Superior: oblique line of thyroid cartilageInferior: manubrium of sternum

    Innervation: C1-C3 (ansa cervicalis)

    Action: depress thyroid cartilage and larynx

    Thyrohyoid:

    Attachments: Superior: inferior border of the hyoid body and greater horn Inferior:oblique line of thyroid cartilage

    Innervation: C1 via hypoglossal nerve

    Actions: depress hyoid bone and/or elevate thyroid cartilage (larynx)

    Hyoid bone:lies at the angle between the floor of the mouth and superior end of theneck. It is the only bone in the body with no bony articulations.

    Thyroid cartilage:the largest cartilage of the larynx. It consists of two flat plates that liein the midline of the neck and form the laryngeal prominence (Adams apple) anteriorly.The thyroid cartilage is open posteriorly.

    Thyrohyoid membrane:joins the thyroid cartilage and hyoid bone.

    Cricoid cartilage: located inferior to the thyroid cartilage at the level of the sixth cervicalvertebra. It marks the junction of the larynx and the trachea.

    Cricothyroid membrane/ligament:joins the cricoid and thyroid cartilages. It is incisedduring cricothyrotomy.Thyroid gland:endocrine gland located in the inferior-most part of the anterior neck. It

    consists of right and left lobes joined at the midline by the isthmus which lies across thesuperior tracheal rings.

  • 7/23/2019 Neck Things to Know

    10/15

    Material to Learn

    Carotid Triangle of the Neck

    Carotid triangle: subdivision of the anterior triangle of the neck. It contains thecommon carotid artery which can be palpated and auscultated in the triangle. Otherstructures within the carotid triangle are the IJV, hypoglossal nerve, ansa cervicalis,accessory and vagus nerves and branches of the external carotid artery. Boundaries:

    superior belly of the omohyoid muscle (anteroinferior)

    posterior belly of the digastric muscle (anterosuperior)

    anterior border of the sternocleidomastoid muscle (posterior)

    Hypoglossal nerve (CN XII):supplies motor innervation to the intrinsic and extrinsic

    muscles of the tongue. It runs anterior and just superior to the tip of the greater horn of

    the hyoid bone and parallels the posterior belly of the digastric muscle during part of itspath. The muscular branch of the occipital artery to the sternocleidomastoid often hooksaround the hypoglossal nerve. Branches of C1 piggyback on the hypoglossal nerve -some will reach the thyrohyoid and geniohyoid muscles, others will descend on thecarotid sheath as the superior root of the ansa cervicalis.

    Ansa cervicalis:nerve plexus with loops formed by the union of ventral rami of C1(superior root) and C2, C3 (inferior root); innervates three of the infrahyoid muscles(omohyoid, sternohyoid and sternothyroid). The fourth muscle, thyrohyoid, is innervatedby C1 via the hypoglossal nerve.

    Superior root of ansa cervicalis (descendens hypoglossi):composed of axonsfrom C1 ventral rami that run with CN XII during part of their extra-vertebral path

    Inferior root of ansa cervicalis (descendens cervicalis):composed of axonsfrom C2 and C3 ventral rami that join C1 on the carotid sheath and innervate theinfrahyoid muscles

    Vagus nerve (CN X):lies in the posterior aspect of the carotid sheath between thecommon carotid artery and the internal jugular vein. High in the neck it gives twobranches - the pharyngeal nerve(will be identified later) and the superior laryngealnerve. Superior laryngeal descends a short distance before it divides into internal and

    external laryngeal. Internal laryngeal nerve:enters the larynx via the thyrohyoid membrane,

    provides sensory innervation to the larynx above the vocal folds External laryngeal nerve:provides motor innervation the cricothyroid muscle

    and the inferior pharyngeal constrictor muscles(Spinal) accessory nerve (CN XI):exits the jugular foramen. It is easily found on the

    deep surface of the superior portion of sternocleidomastoid muscle. It innervatessternocleidomastoid and trapezius muscles.

  • 7/23/2019 Neck Things to Know

    11/15

    Common carotid artery:ascends through the carotid triangle where it divides intointernal and external carotid arteries. The external carotid artery gives severalbranches to the neck and face (branching patterns are quite variable) and the internalcarotid enters the carotid canal on the base of the skull without giving branches in the

    neck.

    Carotid sinus and body: baroreceptor and chemoreceptor respectively are located at

    the bifurcation of the common carotid artery. The carotid sinus is in the dilation at thebase of the internal carotid artery. The carotid body is a small mass suspended betweenthe internal and external carotid arteries on the medial side of the vessels. CN IX(glossopharyngeal nerve) carries information from these receptors to the brain

    Internal carotid artery:has no branches in the neck. It ascends in the carotid sheathwith the internal jugular vein and the vagus nerve and enters the cranium via the carotidcanal.

    External carotid artery:runs from the level of the superior border of the thyroidcartilage to the neck of the mandible where it divides into the maxillary and superficialtemporal arteries. These arteries will be studied later. In the carotid triangle the externalcarotid artery gives eight branches:

    Superior thyroid artery:arises close to the tip of the greater horn of the hyoidbone, descends obliquely across the carotid triangle and passes deep to theinfrahyoid muscles to supply the thyroid gland. It gives the superior laryngealarterythat pierces the thyrohyoid membrane with the internal laryngeal nerve.

    Lingual artery:arises posterior to the tip of the greater horn of the hyoid boneand passes deep to the hyoglossus muscle to reach the tongue.

    Ascending pharyngeal artery:can be difficult to find. It arises from the deep

    surface of the external carotid artery, close to the carotid bifurcation and ascendsparallel and medial to the internal carotid artery. It supplies the pharynx.

    Facial artery:usually arises just superior to the lingual artery but in 20% of

    cases the facial and lingual arteries arise from a common branch of the externalcarotid artery.

    Occipital artery:arises from the posterior surface of the external carotid arteryjust superior to the level of the hyoid bone. It passes deep to the posterior belly ofthe digastric muscle and occupies the groove on the mastoid process. It appearsin the apex of the posterior triangle of the neck.

    Clinical Correlations

  • 7/23/2019 Neck Things to Know

    12/15

    External pressure on the carotid artery (such as taking a pulse) in people with carotidsinus hypersensitivitymay cause excessive slowing of the heart rate, a fall in bloodpressure and cardiac ischemia with syncope (fainting). Fainting results from a suddenand critical decrease in cerebral perfusion due to the response of the carotid sinusbaroreceptor to the external pressure. Consequently, this method of taking the pulse is

    not recommended for cardiac patients. Instead, the radial pulse at the wrist is preferred.

    Material to Learn

    Submandibular and Submental TrianglesSubmandibular triangle: contains the submandibular gland, facial artery and vein, CN

    XII and nerve to mylohyoid. The boundaries are: Anterior belly of digastric (anterior) Posterior belly of digastric (posterior) Inferior border of the mandible (superior)

    Digastric muscle:Anterior belly: Attachments:Anterior:digastric fossa of the mandible

    Posterior: intermediate tendon of digastric Innervation: nerve to mylohyoid (branch of the alveolar nerve, CN V3) Action: assists in depressing the mandible and elevating the hyoid bone during

    swallowing and vocalization

    Posterior belly:

    Attachments:Anterior: intermediate tendon

    Posterior: mastoid notch of the temporal bone Innervation: facial nerve (CN VII)

    Action: assists in depressing the mandible and elevating the hyoid bone duringswallowing and vocalization

    Stylohyoid muscle: Attachments: Origin: styloid process of the temporal bone

    Insertion: muscle splits around posterior belly digastric to body of the hyoid bone Innervation: facial nerve (CN VII) Action: elevates and retracts the hyoid bone

    Mylohyoid muscle: Attachments: Origin: mylohyoid line of mandible

    Insertion: mylohyoid raphe and body of the hyoid bone Innervation: mylohyoid nerve (branch of inferior alveolar nerve CN V3) Action: elevates hyoid bone, floor of mouth and tongue during swallowing

    Submandibular gland:salivary gland, palpable between the body of the mandible andmylohyoid muscle. The gland wraps around the posterior border of the mylohyoidmuscle. Thus, its superficial portionlies inferior to the mylohyoid muscle while its

  • 7/23/2019 Neck Things to Know

    13/15

    deep portionlies superior to the mylohyoid between the hyoglossus and mylohyoidmuscles. The gland is innervated by parasympathetic secretomotor fibers from the facialnerve. These axons run with the chorda tympani and lingual nerves and synapse in thesubmandibular ganglion.

    Submandibular duct(Whartons duct) opens inside the mouth at the summit of thesublingual papilla (caruncle) on either side of the frenulum of the tongue.

    Submental triangle: a single, midline triangle formed by the anterior belly of the leftand right digastric muscles. It contains only loose areolar tissue. The borders and floorare:

    Anterior belly of the left and right digastric muscles (left and right lateral) Body of the hyoid bone (base) Left and right mylohyoid muscles (floor)

    Material to Learn

    Thyroid and Parathyroid GlandsThyroid gland:

    Highly vascular endocrine gland that produces thyroxin and thyrocalcitonin Consists of right and left lobes joined in the midline by an isthmus. In 50% of

    cases a pyramidal lobe ascends from the isthmus. Supplied by:

    o Superior thyroid artery:from the external carotid arteryo Inferior thyroid artery:from the thyrocervical trunk

    Drained by:

    Superior and middle thyroid veins into the IJVs, and inferior thyroid veinsinto the brachiocephalic vein. The thyroid gland moves during swallowing. It has parathyroid glandsembedded in its lobes posteriorly.

    Parathyroid Glands: Small ovoid bodies that lie on the posterior aspect of the thyroid gland, between

    the capsule and sheath. Endocrine glands involved in the metabolism of calcium and phosphorus. Vary in number from 2 to 6 Supplied by the inferior thyroid artery.

    Clinical Correlations

    Thyroglossal Duct

  • 7/23/2019 Neck Things to Know

    14/15

    The thyroid gland develops in the floor of the embryonic pharynx at the site indicated bythe foramen cecum in the dorsum of the tongue. Subsequently, the gland descendsthrough the tongue into the neck, passing anterior to the hyoid bone, thyroid and cricoidcartilages to reach its final position anterolateral to the superior part of the trachea.During the migration process, the thyroid gland is connected to the foramen cecum by

    the thyroglossal duct. Normally, the duct obliterates and disappears as developmentprogresses. Sometimes, however, portions of the duct remain and become clinicallysignificant because they can form thyroglossal cystsat any point along the descent

    pathway.

    In addition, the thyroid gland can fail to descend completely from its embryonic origin inthe tongue. This failure results in an ectopic thyroid glandthat is located high in the

    neck below the hyoid bone. Usually this ectopic gland is the only thyroid tissue andmust be differentiated from a thyroglossal cyst. Failure to do so might result in a totalthyroidectomy in the attempt to remove a cyst. The pyramidal lobeof the thyroid gland

    that extends superiorly from the isthmus of the thyroid develops from remnants of the

    thyroglossal duct.

    Injury to the Recurrent Laryngeal NervesNear the inferior pole of the thyroid gland, the right recurrent laryngeal nerve isintimately related to the inferior thyroid arteryand its branches. Because of this closerelationship, during thyroidectomy the inferior thyroid artery is ligated some distancelateral to the thyroid gland where it is farther away from the recurrent laryngeal nerve.This prevents accidental nerve damage.

    If the recurrent laryngeal nerve is damaged, e.g. during surgery, hoarseness usuallyresults. Temporary aphonia and laryngeal spasms may also occur.

    Ectopic Parathyroid Glands

    The small, ovoid parathyroid glands usually lie external to the fibrous thyroid capsule onthe medial half of the posterior surface of each lobe of the thyroid gland. Most peoplehave four parathyroid glands, but approximately 5 % of people have more than four.The superior parathyroid glands, which are more constant in position than the inferiorones, are sometimes located as far superiorly as the thyroid cartilage or hyoid bone.The inferior parathyroids may be as far inferior as the superior mediastinum.

    Material to Learn

    Root of the NeckThoracic duct:valved lymphatic duct that runs from the cisterna chyliof theabdomen, through the aortic opening of the diaphragm, through the posteriormediastinum between the aorta and azygos vein. It arches laterally over the apex of theleft lung and empties into the junction of the left internal jugular and left subclavian veins(left venous angle).

  • 7/23/2019 Neck Things to Know

    15/15

    Branches of the first part of the subclavian artery: Vertebral artery:first and largest branch of the subclavian artery. It ascends

    between the anterior scalene and the longus colli muscles and enters thetransverse foramen of C6. From there it ascends through the transverse foraminaof C5-C1. It loops around the superior articular process of the atlas and finally

    passes through the foramen magnum into the cranial cavity. It supplies the brain.

    Thyrocervical trunk:short arterial trunk that arises lateral to the vertebral artery

    and divides into:o Inferior thyroid artery:ascends anterior to the anterior scalene muscle

    and passes posterior to the carotid sheath to supply the thyroid gland.o Transverse cervical artery:runs posterolaterally across the anterior

    scalene muscle, phrenic nerve, and trunks of the brachial plexus. Itpasses deep to the trapezius muscle to supply muscles of the scapularregion.

    o Suprascapular artery:runs anterior and lateral to the anterior scalene

    muscle, parallel to the clavicle. At the scapula it passes superior to thetransverse scapular ligament to enter the supraspinous fossa while thesuprascapular nerve passes inferior to the ligament, through the scapularnotch.

    Internal thoracic (mammary)artery:arises from the inferior aspect of thesubclavian artery and descends through the thorax parallel to the sternum andposterior to the upper six costal cartilages. It supplies the anterior thoracic wall.

    Branches of the second part of the subclavian artery: Costocervical trunk:arises from the posterior aspect of the subclavian artery

    posterior to the anterior scalene muscle. It divides into:o Deep cervical arteriessupplies the deep cervical muscleso Superior intercostal arterysupplies the first two intercostal spaces

    Sympathetic chain:runs vertically in the neck anterior to the cervical vertebrae and

    medial to the vagus nerve. It is not in the carotid sheath! It connects three cervicalganglia to each other and to the thoracic part of the chain. The inferior and middlecervical gangliaare visible in dissection. The large superior cervical ganglionwill bedissected later.