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Anatomy of neck Dr. Muslim Kandel 2016 Surface anatomy Skin Superficial fascia Anatomy of neck platesma muscle cutenous br of cervical plexus superfecial veins Deep fascia Investing f , pretrachial f ,Carotid sheath , Prevertebral f ,Parotid f ,Pharyngo-basilar f ,Bucco-pharyngial f , supraplural membrane, legementum nuchae Muscular triangles Ant. Triangle(sub divided into small triangles) Post. Triangle(sub divided into small triangles) Glands Salivary glands Thyroid & parathyroid glands Superficial Fascia The superficial fascia of the neck forms a thin layer that encloses the platysma muscle. Also embedded in it are the cutaneous nerves the superficial veins, and the superficial lymph nodes. Platysma Its important muscular sheet embedded in the superficial fascia Origin :fascia covering pectorals major & deltoid Insertion: lower border of mandible &skin of face Nerve supply :-cervical br. of facial N Action:-wrinkle of skin of neck -depress of mandible Superficial Veins 1-External Jugular Vein begins just behind the angle of the mandible by the union of the posterior auricular vein with the posterior division of the retromandibular vein. It descends obliquely across the sternocleidomastoid muscle and, drains into the subclavian vein Branches -Posterior auricular vein -Posterior division of the retromandibular vein -Transverse cervical vein -Suprascapular vein -Anterior jugular vein EXTERNAL JUGUAR VEIN Superficial temporal v. Maxillary v. Facial v. Posterior auricular v. External jugular v. Retromandibular v. Common facial v. (to IJV) Transverse cervical v. Suprascapular v. Subclavian v. Anterior jugular v. jugular arch 2-Anterior Jugular Vein --Formed just below the chin, by the union of several small veins . It runs down the neck close to the midline. Just above the suprasternal notch, the veins of the two sides are united by a transverse trunk called the jugular arch. --drain into the external jugular vein Cutaneous nerves of neck Arse from branches of cervical plexus Lesser occipital n from ant. Rami of C2 supply upper part of skin of inner surface of auricle & adjescent part of skin of scalp Greet auricular n from ant. Rami of C2,C3 supply lower part of skin of inner surface of auricle , skin over parotid gl & skin over angle of mandible Supraclavicular n from C3, C4 supply skin of post. Triangle , skin of tip of shoulder& skin of chest down to 2nd rib Transverse nerve of neck from C2,C3 supply of skin of ant. triangle Cutaneous nerves Lesser occipital n. External jugular vein Greet auricular n. Transverse nerve of neck Anterior jugular vein Supraclavicular n. Superficial Lymph Nodes Its lie along the external jugular vein superficial to the sternocleidomastoid muscle - receive lymph vessels from the occipital and mastoid lymph nodes - drain into the deep cervical lymph nodes Deep Cervical Fascia Its supports the muscles, the vessels, and the viscera of the neck . In certain areas, it is condensed to form welldefined, fibrous sheets called the investing layer, the pretracheal layer, the prevertebral layer. It is also condensed to form the carotid sheath Investing fascia Retropharyngeal space Pretracheal fascia * Buccopharyngeal fascia * Carotid sheath Common carotid a. Internal jugular v. Vagus n. Prevertebral fascia * = Component of visceral fascia Investing Layer Its is a thick layer that encircles the neck.(like collar ) It splits to enclose the trapezius and the sternocleidomastoid muscles.its form base of ant. & post. Triangles Attachment –postlegemantum nuchae --ant. hyoid bone , thyroid cartlage , --inf. maniberium , clavicle , acromian processes & spin of scapula -- sup mandible , then splite to involve parotid gland to attached to ext. audetory meatus Pretracheal Layer It is a thin layer that is attached above to the laryngeal cartilages It surrounds the thyroid and the parathyroid glands, forming a sheath for them, and encloses the infrahyoid muscles. Prevertebral Layer The prevertebral layer is a thick layer that passes like a septum across the neck -- behind the pharynx and the esophagus -- in front of the prevertebral muscles and the vertebral column ,extend from base of skull to 3rd Thoracic vertebrate. --It forms the fascial floor of the posterior triangle, -- it extends laterally over the first rib cross scalenous ant. into the axilla to Axillary Sheath All the anterior rami of the cervical nerves that emerge in the interval between the scalenus anterior and scalenus medius muscles lie at first deep to the prevertebral fascia. As the subclavian artery and the brachial plexus emerge in the interval between the scalenus anterior and the scalenus medius muscles, they carry with them a sheath of the fascia, which extends into the axilla and is called the axillary sheath Parotid f Its derived from investing f superficial layer attach to zygomatic arch Deep layer attach to petrous ,temporal, styloid and mastoid Pharyngo –basilar f Tough f connect pharynx to base of skull nasopharynx patent Bucco-parhngial f Cover muscles of pharynx Supra plural membrane Cover apex of lung Base of skull Buccopharyngeal fascia Retropharyngeal space Prevertebral fascia Mediastinum Ligamentum Nuchae Strong Triangalar leg. Its upper continuation of supraspinus & infraspinus leg Attachement Above (base)occipital protrberance and crest below (apex)spine of C7 Ant. all cervical spines Post. free Clinical Significance of the Deep Fascia of the Neck Acute Infections Dental infections lower molar teeth. The infection spreads medially from the mandible into the submandibular spaces and pushes the tongue forward and upward. Further spread downward may lead to edema of the vocal cords and airway obstruction. Ludwig's angina is an acute infection of the submandibular fascial space and is commonly secondary to dental infection Chronic Infection Tuberculous TB of the deep cervical lymph nodes can result in liquefaction and destruction of one or more of the nodes. collarstud abscess. The clinician is aware of the superficial abscess but must not forget the existence of the deeply placed abscess Muscular Triangles of the Neck Generally the neck divided into 2 large triangles ant. & post. Triangles by sternomastoid muscle Anterior Triangle bounded above by the body of the mandible posteriorly by the sternocleidomastoid anteriorly by the midline . roof :……formed by: platysma investing layer of deep cervical fascia It is further subdivided by : digastric anterior and posterior bellies into , the submental triangle, the digastric triangle omohyoid superior belly into the carotid triangle the muscular triangle Posterior Triangle bounded posteriorly by the trapezius muscle, anteriorly by the sternocleidomastoid muscle, inferiorly by the clavicle . It is further subdivided by the inferior belly of the omohyoid muscle into :---a large occipital triangle above --- a small supraclavicular triangle below roof ………formed by : platysma • investing (superficial) layer of deep cervical fascia. floor :…….formed by : • splenius capitis levator scapulae muscles anterior, middle, posterior scalene muscles Contains of post triangle: accessory nerve, cutaneous branches of cervical plexus, external jugular vein, transverse cervical suprascapular vessels, subclavian vein & artery, Inferior belly of omohyoid, roots and trunks of brachial plexus. nerve to subclavius dorsal scapular, suprascapular, long thoracic nerves Sternocleidomastoid Muscle When the sternocleidomastoid muscle contracts, it appears as an oblique band crossing the side of the neck from the sternoclavicular joint to the mastoid process of the skull. Relation It divides the neck into anterior and posterior triangles . Post carotid arteries, the internal jugular vein, and the deep cervical lymph nodes; it also overlaps the thyroid gland. The deep surface of the posterior border is related to the cervical plexus of nerves, the phrenic nerve, and the upper part of the brachial plexus Ant skin, fascia, the platysma muscle, and the external jugular vein. . The origin have 2 heads Manubrium sterni medial third of clavicle, insertion Mastoid process of temporal bone and occipital bone , nerve supply Spinal part of accessory nerve and C2 and 3, Action Two muscles acting together extend head and flex neck; one muscle rotates head to opposite side . TRAPEZIUS MUSCLE Origin: Superior nuchal line, ext. occipital protuberance, lig. nuchae, spines of C7 – T12 Insertion: Lateral 1/3 of clavicle, acromion, spine of scapula Functions: --elevation of scapula (sup. fibers), depression of scapula (inf. fibers), retraction of scapula (middle fibers), superior rotation of glenoid fossa of scapula (sup. + inferior fibers). Scalenus Anterior Muscle The scalenus anterior muscle is a key muscle in understanding the root of the neck .It is deeply placed and it descends almost vertically from the vertebral column to the first rib. Origin Transverse processes of third, fourth, fifth, and sixth cervical vertebrae Insertion First rib Nerve supply C4, 5, and 6 Action Elevates first rib; laterally flexes and rotates cervical part of vertebral column SCALENE MUSCLES Anterior scalene m. Middle scalene m. Posterior scalene m. Rib 1 Important Relations Anteriorly: Related to the carotid arteries, the vagus nerve, the internal jugular vein, and the deep cervical lymph nodes .The transverse cervical and suprascapular arteries and the prevertebral layer of deep cervical fascia bind the phrenic nerve to the muscle. Posteriorly: Related to the pleura, the origin of the brachial plexus, and the second part of the subclavian artery .The scalenus medius muscle lies behind the scalenus anterior muscle. Medially: Related to the vertebral artery and vein and the sympathetic trunk . On the left side, the medial border is related to the thoracic duct. Laterally: Related to the emerging branches of the cervical plexus, the roots of the brachial plexus, and the third part of the subclavian artery Scalenous medius Largest of all scalenous m Origin :post tubercle of all C. vertebrae Insertion : 1st rib behind subclavian groove N. supply:all cervical nn Action flexion of neck &fixation of1st rib Scalenous post. Smallest of all scalenous Scalenous minimous v. Small m arise from transverse process of C7 inserted at plural memberan Nerves in posterior triangle 1-Cervical plexus 2-Brachial plexus 1- four muscular branches Roots , trunks and their branches 2- four cutaneous branches 1- dorsal scapular nerve – c5(nerve to rhomboids ) 2- nerve to subclavius – c5 &c6 3- nerve to serratus anterior – c5,6 &7 Suprascapular nerve –c5&6 3- spinal root of accessory nerve (11th cranial nerve ) It is the most important structure in the occipital triangle Digastric & submandibular trianglar boundaries Above ….lower border of mandible Below & infront ..anterior belly of Digastric muscle Below & behind ..posterior belly of Digastric & stylohyoid muscles . Floor : Anteriorly : ……..mylohyoid muscle Posteriorly ………part of hyoglossus muscle Contents of Digastric triangle submandibular salivary gland submandibular lymph nodes lie on the surface of the gland facial artery deep to posterior end of submandibular salivary gland facial vein lies superficial to submandibular salivary gland hypoglossal nerve nerve to mylohyoid muscle digastric muscle consists of two muscular bellies united by an intermediate rounded tendon. Posterior belly longer than the anterior belly, arises from the mastoid notch Insertion at Intermediate tendon is held to hyoid by fascial sling Nerve supply Facial nerve Anterior belly Arise from Body of mandible have same insertion at Intermediate tendon is held to hyoid by fascial sling s held in connection with the side of the body and the greater cornu of the hyoid N supply Nerve to mylohyoid Action of both belly Depresses mandible or elevates hyoid bone Mylohyoid muscle is a paired muscle , flat and triangular, and is situated immediately superior to the anterior belly of the digastric muscle running from the mandible to the hyoid bone, forming the floor of the oral cavity of the mouth arise from the mandible at the mylohyoid line, (which extends from the mandibular symphysis in front to the last molar tooth behind) Insertion --The posterior fibers pass inferomedially and insert at anterior surface of the hyoid bone. -- The medial fibres of the two mylohyoid muscles unite in a midline raphe (where the two muscles intermesh) N supply branch of the mandibular nerve through inf . Alvolaer N Function its elevates the hyoid and the tongue. & support of floor of mouth This is particularly important during swallowing and speaking Mylohyoid muscle Geniohyoid Its small muscle deep ( above) to mylohyoid m Arise from Inferior mental spine of mandible Inserted Body of hyoid bone N supply First cervical nerve Function Elevates hyoid bone or depresses mandible Genoglossus muscle Between genial tubercle and tongue Styloglossus muscle from styloid process to the tongue Hyoid bone The hyoid bone (lingual bone) The hyoid bone is U shaped and consists of a body and two greater and two lesser cornua , unlike other bones, not articulate to other bones by muscles or ligaments. The hyoid is anchored by muscles from all directions, situated in the anterior midline of the neck between the chin and the thyroid cartilage . At rest, it lies at the level of the base of the mandible in the front and the (C3) behind. attachment -to the skull by the stylohyoid ligament - to the thyroid cartilage by the thyrohyoid membrane. -forms a base for the tongue and is suspended in position by muscles that connect it to the mandible, to the styloid process of the temporal bone, to the thyroid cartilage, to the sternum, and to the scapula function is aids in tongue movement and swallowing. The hyoid bone provides attachment to the muscles of the floor of the mouth and the tongue above, the larynx below, and the epiglutis and pharynx behind. Styloid process Is a slender projection of variable length extends downward & forward from temporal bone. Gives origin to : A- three muscles: stylohyoid, styloglossus, Stylopharyngeus B-two ligaments : stylohyoid stylomandibular. Carotid triangle boundary : Behind : …………..sternomastoid muscle Infront & above : posterior belly of digastric muscle Infront&below : superior belly of omohyoid muscle Floor : infont : hyoglossus muscle ( above ) and the thyrohyoid muscle (below) Behind: the middle constrictor muscle of the pharynx (above ) and the inferior constrictor muscle of the pharynx (below ) Carotid Sheath The carotid sheath is a local condensation of the prevertebral, the pretracheal, and the investing layers of the deep fascia Attached - above At base of skull surround caroted &jagular foramens - below blend with adventecia of arch of aorta Contents :- its surround the a- in the upper part(above post belly of digastric m) internal carotid artery the internal jugular vein, 4 cranial NN (9,10,11,12 ) deep cervical lymph nodes . b-in the lower part (below post belly of digastric m) .common internal carotid arteries the internal jugular vein, Vegus between CCA&IJV) Note:-- sympathetic chain embeded in post layer of sheath -- 2 limbs of ansa cervicalis at ant. Wall -- sheath thick over art. While thin over vein Contents of the Carotid triangle 1- The carotid sheath and its contents : 2- the external carotid artery :gives most of its branches in the carotid triangle ( superior thyroid artery ,lingual artery ,facial artery , ascending pharyngeal artery and occipital artery ) 3- hypoglossal nerve 4- Descendes cervicalis (C2,3) anterior to carotid sheath. 5- sympathetic trunk adherent to the posterior wall of carotid sheath the Submental triangle boundaries Posterior (to the back) by the anterior belly of the digastricus, Anterior (to the front) by the midline of the neck between the mandible and the hyoid bone; Inferior (below) by the body of the hyoid bone floor is formed by the mylohyoid. Contents of the Submental triangle 1- submental lymph nodes 2- beginning of the anterior jugular vein Suprahyoid muscles 1- digastric muscle 2- mylohyoid muscle 3- hyoglossus muscle 4- geniohyoid muscle 5- stylohyoid muscle The hyoglossus Its thin and quadrilateral muscle , arises from the side of the body of hyoid bone and from the whole length of the greater cornu, and passes almost vertically upward to enter the side of the tongue, between the styloglossus and the inferior longitudinal muscle of the tongue. It forms a part of the floor of submandibular triangle Relations of hypogossus medial/deep the glossopharyngeal nerve (cranial nerve 9) the stylohyoid ligament the lingual artery and vein.The lingual vein passes medial to the hyoglossus, and the lingual artery passes deep to the hyoglossus. Laterally, in between the hyoglossus muscle and the mylohyoid muscle lay several important structures (from upper to lower): sublingual gland, submandibular duct, lingual nerve, vena comitans of hypoglossal nerve, the hypoglossal nerve. Note, posteriorly, the lingual nerve is superior to the submandibular duct and a portion of the submandibular salivary gland protrudes into the space between the hyoglossus and mylohyoid muscles Geniohyoid muscle Hyoglossus Submendibular gland Digastric Accessory n. Hypoglossal n. Superior thyroid a. Ansa cervicalis Sternothyroid Sternohyoid Vagus n. Cervical plexus Phrenic n. Omohyoid The Styloglossus the shortest and smallest of the three styloid muscles, arises from the anterior and lateral surfaces of the styloid process near its apex, and from the stylomandibular ligament. Insertion Passing downward and forward between the internal and external carotid arteries, it divides upon the side of the tongue near its dorsal surface, blending with the fibers of the Longitudinalis inferior in front of the Hyoglossus; the other, oblique, overlaps the Hyoglossus and decussates with its fibers. N supply the Hypoglossal nerve (CN XII) like all muscles of the tongue except palatoglossus which is innervated by the Pharyngeal plexus of vagus nerve Action draws up the sides of the tongue to create a trough for swallowing. As a pair they also aid in retracting the tongue The geniohyoid muscle is a narrow muscle situated superior to the medial border of the mylohyoid muscle It arises from the inferior mental spine, on the back of the mandibular symphysis, insertion its runs backward and slightly downward, to be inserted into the anterior surface of the body of the hyoid bone N supply The geniohyoid muscle is innervated by fibres from the first cervical nerve travelling alongside the hypoglossal nerve.These fibers are called ansa cervicalis. Action its brings the hyoid bone forward and upwards. This dilates the upper airway, assisting respiration. submandibular glands The paired submandibular glands are major salivary glands located beneath the floor of the mouth. At diagastric triangle --wedge shape about 15 gr and produce 60–67% of saliva secretion; Its divided into superficial (large) and deep lobes ( small), which are separated by the mylohyoid muscle ,together continue at post . free border of mylohyoid submandibular duct arise from medial surface of superfecial lobe about 5 cm length, The excretory ducts are then crossed by the lingual nerve, and ultimately drain into the sublingual caruncles on either side of the lingual frenulum a Blood supply. is supplied by sublingual and submental arteries branches from the facial and lingual arteries drained by common facial and lingual veins The lymphatics drain into submandibular LN and subsequently into jugulo - digastric lymph nodes Nerve supply Sensery N from lingual N through ganglion without relay while Secretmotor regulated directly by the parasympathetic and indirectly by the sympathetic (through arterial supply). Parasympathetic is provided by the superior salivatory nucleus via the chorda tympani, a branch of the facial nerve, that becomes part of the trigeminal nerve's lingual nerve prior to synapsing on the submandibular ganglion. -Increased parasympathetic activity promotes the secretion of saliva. The sympathetic --through the arteries that supply it. Increased sympathetic activity vasoconsitructionreduces bloodflowdecreasing the volume of secretions, producing an enzyme rich mucous saliva. -- direct stimulation of sympathetic nerves will cause an increase in salivary enzymatic secretions. In sum, the volume decreases Note:- The submandibular gland accounts for 80% of all salivary duct calculi because viscous nature of the saliva that it produces and the tortuous travel of the submandibular Sublingual gland They are the smallest, most diffuse, and the only unencapsulated major salivary glands. They provide only 3-5% of the total salivary volume They lie anterior to the submandibular gland inferior to the tongue, as well as beneath the mucous membrane of the floor of the mouth They are drained by 8-20 excretory ducts called the ducts of Rivinus N supply :- branches from lingual N containing sensory fibers , sympathetic ¶sympathetic f blood supply sublingual and submental arteries. Lymph drainage the sublingual salivary gland drains into the submandibular LN the Muscular triangle is bounded in front, by the median line of the neck from the hyoid bone to the sternum; behind, by the anterior margin of the sternocleidomastoid; above, by the superior belly of the omohyoid Contents A-infrahyoid muscles They consist of 4 muscles arranged into 2 layers : 1- superficial layer : -- sternohyoid -- omohyoid 2- deep layer: -- sternothyroid -- thyrohyoid B-lat. Lobe of thyroid gl .leing deep tosternohyoid &sternothyroid sternohyoid Origin : back of maniberium & back of clavicle Insertion :- lower border of hyoid bone along midline N supply :-ansa cervicalis Action :1-depresion of hyoid bone after deglutision 2-fixation of hyoid bone during movement of tongue omohyoid Origin :- it has 2 bellis 1-sup. Belly —lower border of hyoid body lat. To sternohyoid 1-inf. Belly –upper border of scapula &suprascapular leg Insertion :-intermediate tendon lies on IJV &held in position by facial sling connect it to clavicle N supply ansa cervicalis Action like sternohyoid & pull deep facia around Ext. J V sternothyroid Origin back of memberain & costal cartlage Insertion Oblique line on lamina of thyroid cartilage N supply Ansa cervicalis; C1, 2, and 3 action Depresses larynx in second phase of diglution thyrohyoid Origin :- Oblique line on lamina of thyroid cartilage Insertion :-Lower border of body of hyoid bone N supply 1st cervical n C1(hypoglusal n) action Depresses hyoid bone or elevates larynx • Ansa cervicalis Its nerve loop formed of 2 descending nn & supply 3 infrahyoid mm Site :- lies infront of carotid sheath Formation : its formed by union of 2 descending nn 1-descending hypoglussi( sup . Limbe of ansa ) Its fibers aris from C1 join hypoglussal n then leave it its turn forwareds across carotid sheath 20 descending cervicalis ( inf. Limb of ansa): Its fiber arise from C2,3 its began behind IJV then descend along its ant. Surface to join descending hypoglussi infront caroted sheath( thus the ansa cervicalis arise from C1,2 ,3) Branches of ansa cervicalis Aris from convixity of loop and supply 3 of • infrahyoid mm (the two belly of omohyoid ,sterno hyoid &sternothyroid)except thyrohyoid (from C1 through hypoglossal n) Cervical Ligaments Stylohyoid ligament: Connects the styloid process to the lesser cornu of the hyoid bone Stylomandibular ligament: Connects the styloid process to the angle of the mandible Sphenomandibular ligament: Connects the spine of the sphenoid bone to the lingula of the mandible Pterygomandibular ligament: Connects the hamular process of the medial pterygoid plate to the posterior end of the mylohyoid line of the mandible. It gives attachment to the superior constrictor and the buccinator muscles Thyroid Gland Its largest endocrine gland in body about 25 gr The thyroid gland butterfly in shape consists of right and left lat. lobes connected by a narrow isthmus at mid ant. Triangle . pyramidal lobe is often present, and it projects upward from the isthmus, usually to the left of the midline. A fibrous or muscular(levator glandulae thyroideae) band frequently connects the pyramidal lobe to the hyoid bone Capsules :1- true capsule adherent to gland 2- false capsule derived from the pretracheal layer of deep fascia. The sheath attaches the gland to the larynx and the trachea. So thyroid move with deglutition Each lobe is pear shaped, with its apex being directed upward as far as the oblique line on the lamina of the thyroid cartilage; its base lies below at the level of the fourth or fifth tracheal ring. The isthmus extends across the midline in front of the second, third, and fourth tracheal rings Relations of the Lobes Anterolaterally: The sternothyroid, the superior belly of the omohyoid, the sternohyoid, and the anterior border of the sternocleidomastoid (Fig. 11-49) Posterolaterally: The carotid sheath with the common carotid artery, the internal jugular vein, and the vagus nerve (Fig. 11-49) Medially: The larynx, the trachea, the pharynx, and the esophagus. Associated with these structures are the cricothyroid muscle and its nerve supply, the external laryngeal nerve. In the groove between the esophagus and the trachea is the recurrent laryngeal nerve (Fig. 11-49). The rounded posterior border of each lobe is related posteriorly to the superior and inferior parathyroid glands (Fig. 11-110) and the anastomosis between the superior and inferior thyroid arteries. Relations of the Isthmus Anteriorly: The sternothyroids, sternohyoids, anterior jugular veins, fascia, and skin Posteriorly: The second, third, and fourth rings of the trachea The terminal branches of the superior thyroid arteries anastomose along its upper border. Blood Supply The arteries to the thyroid gland are the superior thyroid artery, the inferior thyroid artery, and sometimes the thyroidea ima. The arteries anastomose profusely with one another over the surface of the gland. The superior thyroid artery, a branch of the external carotid artery, descends to the upper pole of each lobe, accompanied by the external laryngeal nerve (Fig. 11-110). The inferior thyroid artery, a branch of the thyrocervical trunk, ascends behind the gland to the level of the cricoid cartilage. It then turns medially and downward to reach the posterior border of the gland. The recurrent laryngeal nerve crosses either in front of or behind the artery, or it may pass between its branches. The thyroidea ima, if present, may arise from the brachiocephalic artery or the arch of the aorta. It ascends in front of the trachea to the isthmus (Fig. 11-110). The veins from the thyroid gland are the superior thyroid, which drains into the internal jugular vein; the middle thyroid, which drains into the internal jugular vein; and the inferior thyroid (Fig. 11-110). The inferior thyroid veins of the two sides anastomose with one another as they descend in front of the trachea. They drain into the left brachiocephalic vein in the thorax. Lymph Drainage The lymph from the thyroid gland drains mainly laterally into the deep cervical lymph nodes. A few lymph vessels descend to the paratracheal nodes. Nerve Supply Superior, middle, and inferior cervical sympathetic ganglia Functions of the Thyroid Gland The thyroid hormones, thyroxine and triiodothyronine, increase the metabolic activity of most cells in the body. The parafollicular cells produce the hormone thyrocalcitonin, which lowers the level of blood calcium Parathyroid Glands Location and Description The parathyroid glands are ovoid bodies measuring about 6 mm long in their greatest diameter. They are four in number and are closely related to the posterior border of the thyroid gland, lying within its fascial capsule . The two superior parathyroid glands are the more constant in position and lie at the level of the middle of the posterior border of the thyroid gland. The two inferior parathyroid glands usually lie close to the inferior poles of the thyroid gland. They may lie within the fascial sheath, embedded in the thyroid substance, or outside the fascial sheath. Sometimes they are found some distance caudal to the thyroid gland, in association with the inferior thyroid veins, or they may even reside in the superior mediastinum in the thorax. Blood Supply The arterial supply to the parathyroid glands is from the superior and inferior thyroid arteries. The venous drainage is into the superior, middle, and inferior thyroid veins. Lymph Drainage Deep cervical and paratracheal lymph nodes Nerve Supply Superior or middle cervical sympathetic ganglia Thyroid gland Arteries of the Head and Neck Common Carotid Artery The right common carotid artery arises from the brachiocephalic artery behind the right sternoclavicular joint (Figs. 11-57 and 11-59). The left artery arises from the arch of the aorta in the superior mediastinum (see page 125). The common carotid artery runs upward through the neck under cover of the anterior border of the sternocleidomastoid muscle, from the sternoclavicular joint to the upper border of the thyroid cartilage. Here it divides into the external and internal carotid arteries (Figs. 11-55 and 11-60). Carotid Sinus At its point of division, the terminal part of the common carotid artery or the beginning of the internal carotid artery shows a localized dilatation, called the carotid sinus (Fig. 11-60). The tunica media of the sinus is thinner than elsewhere, but the adventitia is relatively thick and contains numerous nerve endings derived from the glossopharyngeal nerve. The carotid sinus serves as a reflex pressoreceptor mechanism: A rise in blood pressure causes a slowing of the heart rate and vasodilatation of the arterioles Carotid Body The carotid body is a small structure that lies posterior to the point of bifurcation of the common carotid artery (Fig. 11-60). It is innervated by the glossopharyngeal nerve. The carotid body is a chemoreceptor, being sensitive to excess carbon dioxide and reduced oxygen tension in the blood. Such a stimulus reflexly produces a rise in blood pressure and heart rate and an increase in respiratory movements. The common carotid artery is embedded in a connective tissue sheath, called the carotid sheath, throughout its course and is closely related to the internal jugular vein and vagus nerve • • • • • • • Relations of the Common Carotid Artery Anterolaterally: The skin, the fascia, the sternocleidomastoid, the sternohyoid, the sternothyroid, and the superior belly of the omohyoid (Fig. 11-55) Posteriorly: The transverse processes of the lower four cervical vertebrae, the prevertebral muscles, and the sympathetic trunk (Fig. 11-57). In the lower part of the neck are the vertebral vessels. Medially: The larynx and pharynx and, below these, the trachea and esophagus (Fig. 11-49). The lobe of the thyroid gland also lies medially. Laterally: The internal jugular vein and, posterolaterally, the vagus nerve (Fig. 11-49) Branches of the Common Carotid Artery Apart from the two terminal branches, the common carotid artery gives off no branches Branches of the Internal Carotid Artery There are no branches in the neck. Many important branches, however, are given off in the skull Branches of the External Carotid Artery Superior thyroid artery Ascending pharyngeal artery Lingual artery Facial artery Occipital artery Posterior auricular artery Superficial temporal artery Maxillary artery Subclavian Arteries Right Subclavian Artery The right subclavian artery arises from the brachiocephalic artery, behind the right sternoclavicular joint (Figs. 11-57 and 11-59). It arches upward and laterally over the pleura and between the scalenus anterior and medius muscles. At the outer border of the first rib, it becomes the axillary artery. Left Subclavian Artery The left subclavian artery arises from the arch of the aorta in the thorax. It ascends to the root of the neck and then arches laterally in a manner similar to that of the right subclavian artery . The scalenus anterior muscle passes anterior to the artery on each side and divides it into three parts First Part of the Subclavian Artery The first part of the subclavian artery extends from the origin of the subclavian artery to the medial border of the scalenus anterior muscle (Fig. 11-57). This part gives off the vertebral artery, the thyrocervical trunk, and the internal thoracic artery. Branches The vertebral artery ascends in the neck through the foramina in the transverse processes of the upper six cervical vertebrae (Fig. 11-57). It passes medially above the posterior arch of the atlas and then ascends through the foramen magnum into the skull. On reaching the anterior surface of the medulla oblongata of the brain at the level of the lower border of the pons, it joins the vessel of the opposite side to form the basilar artery. The basilar artery (Fig. 11-15) ascends in a groove on the anterior surface of the pons. It gives off branches to the pons, the cerebellum, and the internal ear. It finally divides into the two posterior cerebral arteries. On each side, the posterior cerebral artery (Fig. 11-15) curves laterally and backward around the midbrain. Cortical branches supply the inferolateral surfaces of the temporal lobe and the visual cortex on the lateral and the medial surfaces of the occipital lobe. Branches in the neck: Spinal and muscular arteries Branches in the skull: Meningeal, anterior and posterior spinal, posterior inferior cerebellar, medullary arteries The thyrocervical trunk is a short trunk that gives off three terminal branches (Fig. 11-57). The inferior thyroid artery ascends to the posterior surface of the thyroid gland, where it is closely related to the recurrent laryngeal nerve. It supplies the thyroid and the inferior parathyroid glands. The superficial cervical artery is a small branch that crosses the brachial plexus (Fig. 11-57). The suprascapular artery runs laterally over the brachial plexus and follows the suprascapular nerve onto the back of the scapula (Fig. 11-57). The internal thoracic artery descends into the thorax behind the first costal cartilage and in front of the pleura (Fig. 11-57). It descends vertically one fingerbreadth lateral to the sternum; in the sixth intercostal space, it divides into the superior epigastric and the musculophrenic arteries. Second Part of the Subclavian Artery The second part of the subclavian artery lies behind the scalenus anterior muscle (Fig. 11-57). Branches The costocervical trunk runs backward over the dome of the pleura and divides into the superior intercostal artery, which supplies the first and the second intercostal spaces, and the deep cervical artery, which supplies the deep muscles of the neck. Third Part of the Subclavian Artery The third part of the subclavian artery extends from the lateral border of the scalenus anterior muscle (Fig. 11-57) across the posterior triangle of the neck to the lateral border of the first rib, where it becomes the axillary artery. Here, in the root of the neck, it is closely related to the nerves of the brachial plexus. Branches The third part of the subclavian artery usually has no branches. Occasionally, however, the superficial cervical arteries, the suprascapular arteries, or both arise from this part. Veins of the Face and the Neck Facial Vein The facial vein is formed at the medial angle of the eye by the union of the supraorbital and supratrochlear veins (Fig. 11-39). It is connected through the ophthalmic veins with the cavernous sinus. The facial vein descends down the face with the facial artery and passes around the lateral side of the mouth. It then crosses the mandible, is joined by the anterior division of the retromandibular vein, and drains into the internal jugular vein. Superficial Temporal Vein The superficial temporal vein is formed on the side of the scalp (Fig. 11-39). It follows the superficial temporal artery and the auriculotemporal nerve and then enters the parotid salivary gland, where it joins the maxillary vein to form the retromandibular vein. Maxillary Vein The maxillary vein is formed in the infratemporal fossa from the pterygoid venous plexus (Fig. 11-39). The maxillary vein joins the superficial temporal vein to form the retromandibular vein Retromandibular Vein The retromandibular vein is formed by the union of the superficial temporal and the maxillary veins (Fig. 11-39). On leaving the parotid salivary gland, it divides into an anterior branch, which joins the facial vein, and a posterior branch, which joins the posterior auricular vein to form the external jugular vein. External Jugular Vein The external jugular vein is formed behind the angle of the jaw by the union of the posterior auricular vein with the posterior division of the retromandibular vein (Fig. 11-39). It descends across the sternocleidomastoid muscle and beneath the platysma muscle, and it drains into the subclavian vein behind the middle of the clavicle. Tributaries Posterior external jugular vein from the back of the scalp Transverse cervical vein from the skin and the fascia over the posterior triangle Suprascapular vein from the back of the scapula Anterior jugular vein Anterior Jugular Vein The anterior jugular vein descends in the front of the neck close to the midline (Fig. 11-39). Just above the sternum, it is joined to the opposite vein by the jugular arch. The anterior jugular vein joins the external jugular vein deep to the sternocleidomastoid muscle. Internal Jugular Vein The internal jugular vein is a large vein that receives blood from the brain, face, and neck (Fig. 11-39). It starts as a continuation of the sigmoid sinus and leaves the skull through the jugular foramen. It then descends through the neck in the carotid sheath lateral to the vagus nerve and the internal and common carotid arteries. It ends by joining the subclavian vein behind the medial end of the clavicle to form the brachiocephalic vein. Throughout its course, it is closely related to the deep cervical lymph nodes. The vein has a dilatation at its upper end called the superior bulb and another near its termination called the inferior bulb. Directly above the inferior bulb is a bicuspid valve Tributaries of the Internal Jugular Vein Inferior petrosal sinus Facial vein ( Pharyngeal veins Lingual vein Superior thyroid vein ( Middle thyroid vein Subclavian Vein The subclavian vein is a continuation of the axillary vein at the outer border of the first rib .It joins the internal jugular vein to form the brachiocephalic vein, and it receives the external jugular vein. In addition, it often receives the thoracic duct on the left side and the right lymphatic duct on the right. Relations Anteriorly: The clavicle Posteriorly: The scalenus anterior muscle and the phrenic nerve Inferiorly: The upper surface of the first rib Lymph Drainage of the Head and Neck The lymph nodes of the head and neck (Fig. 11-40) are arranged as a regional collar that extends from below the chin to the back of the head and as a deep vertical terminal group that is embedded in the carotid sheath in the neck (Fig. 11-55). Regional Nodes The regional nodes are arranged as follows: Occipital nodes: These are situated over the occipital bone on the back of the skull. They receive lymph from the back of the scalp. Retroauricular (mastoid) nodes: These lie behind the ear over the mastoid process. They receive lymph from the scalp above the ear, the auricle, and the external auditory meatus. Parotid nodes: These are situated on or within the parotid salivary gland. They receive lymph from the scalp above the parotid gland, the eyelids, the parotid gland, the auricle, and the external auditory meatus. Buccal (facial) nodes: One or two nodes lie in the cheek over the buccinator muscle. They drain lymph that ultimately passes into the submandibular nodes. Submandibular nodes: These lie superficial to the submandibular salivary gland just below the lower margin of the jaw. They receive lymph from the front of the scalp; the nose; the cheek; the upper lip and the lower lip (except the central part); the frontal, maxillary, and ethmoid sinuses; the upper and lower teeth (except the lower incisors); the anterior two thirds of the tongue (except the tip); the floor of the mouth and vestibule; and the gums Submental nodes: These lie in the submental triangle just below the chin . They drain lymph from the tip of the tongue, the floor of the anterior part of the mouth, the incisor teeth, the center part of the lower lip, and the skin over the chin. Anterior cervical nodes: These lie along the course of the anterior jugular veins in the front of the neck. They receive lymph from the skin and superficial tissues of the front of the neck. Superficial cervical nodes: These lie along the course of the external jugular vein on the side of the neck. They drain lymph from the skin over the angle of the jaw, the skin over the lower part of the parotid gland, and the lobe of the ear. Retropharyngeal nodes: These lie behind the pharynx and in front of the vertebral column. They receive lymph from the nasal pharynx, the auditory tube, and the vertebral column. Laryngeal nodes: These lie in front of the larynx. They receive lymph from the larynx. Tracheal (paratracheal) nodes: These lie alongside the trachea. They receive lymph from neighboring structures, including the thyroid gland. Deep Cervical Nodes The deep cervical nodes form a vertical chain along the course of the internal jugular vein within the carotid sheath . They receive lymph from all the groups of regional nodes. The jugulodigastric node, which is located below and behind the angle of the jaw, is mainly concerned with drainage of the tonsil and the tongue. The juguloomohyoid node, which is situated close to the omohyoid muscle, is mainly associated with drainage of the tongue. The efferent lymph vessels from the deep cervical lymph nodes join to form the jugular trunk, which drains into the thoracic duct or the right lymphatic duct Main Nerves of the Neck Cervical Plexus The cervical plexus is formed by the anterior rami of the first four cervical nerves. The rami are joined by connecting branches, which form loops that lie in front of the origins of the levator scapulae and the scalenus medius muscles (Fig. 11-57). The plexus is covered in front by the prevertebral layer of deep cervical fascia and is related to the internal jugular vein within the carotid sheath. The cervical plexus supplies the skin and the muscles of the head, the neck, and the shoulders. Branches Cutaneous branches The lesser occipital nerve (C2), which supplies the back of the scalp and the auricle The greater auricular nerve (C2 and3), which supplies the skin over the angle of the mandible The transverse cervical nerve (C2 and 3), which supplies the skin over the front of the neck The supraclavicular nerves (C3 and 4). The medial, and intermediate, and lateral branches supply the skin over the shoulder region. These nerves are important clinically, because pain may be referred along them from the phrenic nerve (gallbladder disease). Muscular branches to the neck muscles. Prevertebral muscles, sternocleidomastoid (proprioceptive, C2 and 3), levator scapulae (C3 and 4), and trapezius (proprioceptive, C3 and 4). A branch from C1 joins the hypoglossal nerve. Some of these C1 fibers later leave the hypoglossal as the descending branch, which unites with the descending cervical nerve (C2 and 3), to form the ansa cervicalis (Fig. 11-60). The first, second, and third cervical nerve fibers within the ansa cervicalis supply the omohyoid, sternohyoid, and sternothyroid muscles. Other C1 fibers within the hypoglossal nerve leave it as the nerve to the thyrohyoid and geniohyoid. Muscular branch to the diaphragm. Phrenic nerve Phrenic Nerve The phrenic nerve arises in the neck from the third, fourth, and fifth cervical nerves of the cervical plexus. It runs vertically downward across the front of the scalenus anterior muscle (Fig. 11-57) and enters the thorax by passing in front of the subclavian artery. Its further course in the thorax is described on page 127. The phrenic nerve is the only motor nerve supply to the diaphragm. It also sends sensory branches to the pericardium, the mediastinal parietal pleura, and the pleura and peritoneum covering the upper and lower surfaces of the central part of the diaphragm Brachial Plexus The brachial plexus is formed in the posterior triangle of the neck by the union of the anterior rami of the fifth, sixth, seventh, and eighth cervical and the first thoracic spinal nerves (Fig. 11-71). This plexus is divided into roots, trunks, divisions, and cords. The roots of C5 and 6 unite to form the upper trunk, the root of C7 continues as the middle trunk, and the roots of C8 and T1 unite to form the lower trunk. Each trunk then divides into anterior and posterior divisions. The anterior divisions of the upper and middle trunks unite to form the lateral cord, the anterior division of the lower trunk continues as the medial cord, and the posterior divisions of all three trunks join to form the posterior cord. The roots of the brachial plexus enter the base of the neck between the scalenus anterior and the scalenus medius muscles (Fig. 11-57). The trunks and divisions cross the posterior triangle of the neck, and the cords become arranged around the axillary artery in the axilla (see Fig. 920). Here, the brachial plexus and the axillary artery and vein are enclosed in the axillary sheath