Viscera of the Neck

Arteries

common carotid – right begins at bifurcation of brachiocephalic trunk; left begins as the 2^nd branch of aortic arch

both ascend deep to the sterno-clavicular joint within the carotid sheath
both bifurcate at the superior border of the thyroid into the internal and external carotids

internal carotid – direct continuation of the carotid, supplies 75% of blood to brain; no branches in the neck

vagus nerve lies posterolateral to the internal carotid in the carotid sheath

external carotid – supplies structures outside the skull; has six branches along its course (see below)

terminates by dividing into the superficial temporal artery and maxillary artery

Anterior Branches of External Carotid

(1) superior thyroid – most inferior branch of the internal carotid; runs inferolaterally to supply superior aspect of thyroid

also gives rise to the superior laryngeal artery which passes through the thyrohyoid membrane to supply the larynx

(2) lingual – passes along middle constrictor muscle, runs anterior-superiorly inside the mandible, deep to the stylohyoid, digastric, and hyoglossus muscles and deep to the hypoglossal nerve

terminates by branching into the sublingual and deep lingual arteries

(3) facial – may arise as a common branch with the lingual artery or branch just superior to it

passes anterior to the angle of mandible to supply the face; pulses can be felt at the inferior border of the mandible

Posterior Branches of External Carotid

(1) ascending pharyngeal–1^st posterior branch; small; sends branches to pharynx, prevertebral muscles, middle ear, meninges

(2) occipital – arises near the origin of facial a; runs inferiorly along posterior belly of digastric to end in posterior part of scalp

(3) posterior auricular – small artery superior to the occipital; supplies parotid gland, muscles of acoustic meatus, facial nerve

Branches of the Subclavian Artery

internal thoracic – inferior branch, runs along the sterno-costal margin supplying the intercostal structures

thyrocervical trunk – from 1^st part of subclavian, just medial to anterior scalene muscle; immediately gives rise to 3 arteries:

(1) suprascapular – passes over the suprascapular ligament to supply the scapular mm

may arise directly from the third part of the subclavian

(2) transverse cervical – runs laterally, 2-3 cm superior to the clavicle across the posterior triangle

supplies muscles of the posterior triangle and scapular region

(3) inferior thyroid – passes behind the common carotid to supply the inferior aspect of the thyroid

vertebral – arises from the superior part of the first part of the subclavian; ascends through the transverse foramina of the cervical vertebrae except for C7; enters skulll through foramen magnum

the right and left vertebral arteries merge to become the basilar artery of the circle of Willis

Veins

common facial – major drainage of the face; begins as junction of supraorbital vein and supratrochlear vein

runs down the face and hooks around the inferior border of the mandible to join with the internal jugular vein

internal jugular – largest vein in the neck; is the continuation of the sigmoid sinus inferior to the jugular foramen

runs in the carotid sheath and joins with the subclavian to form the brachiocephalic vein

lingual – veins of each side of tongue combine to form lingual vein which drains into either the facial or inferior ext. jugular vein

begins at angle of mandible with union of posterior auricular vein and retromandibular vein
runs obliquely along the posterior triangle, and empties into the subclavian

thyroid veins:

superior – empties into internal jugular

middle – empties into internal jugular

inferior – empties into brachiocephalic veins; potential source of bleeding during tracheotomy

subclavian – major venous drain of the upper limb

Nerves

mylohyoid (C.N. V₃) – mixed nerve; contains all the motor fibers of the trigeminal nerve; arises from trigeminal ganglia

recurrent laryngeal (C.N. X) – passes out of the skull through the foramen ovale; innervates teeth, skin in the temporal region, part of the auricle, the lower lip, lower part of the face, and most of the muscles of mastication

vagus (C.N. X) – mixed nerve; arises as rootlets in the medulla between the olive and the inferior cerebellar peduncle; descends in carotid sheath to innervate many structures in the thorax and abdomen

accessory (C.N. XI) – motor nerve; arises from spinal nucleus in lateral part of grey matter of the cervical spinal cord; passes out of the skull via the foramen magnum, runs under the sternocleidomastoid, over the scalene mm, and terminates in the trapezius; supplies muscles of soft palate, pharynx, larynx, sternocleidomastoid, trapezius muscle

hypoglossal (C.N. XII) – motor nerve; arises as 10-15 rootlets between the olive and pyramid of the medulla; leaves the skull via the hypoglassal canal in the occipital bone; supplies extrinsic and intrinsic muscles of tongue except palatoglossus

ansa cervicalis (C1-3) – nerve loop that descends from the cervical plexus to innervate the sternothyroid, sternohyoid, and omohyoid muscles; superior root from C1, inferior root from C2 and C3

superior root (descendens hypoglossi) – descendens hypoglossi is old name for the superior root of ansa cervicalis

external laryngeal – smaller of the two branches of the superior laryngeal nerve (internal laryngeal nerve is the larger, superior laryngeal nerve is derived from the vagus); external laryngeal supplies the cricothyroid muscle which is the only laryngeal muscle not innervated by the recurrent laryngeal

phrenic (C3-5) – the only motor innervation of the diaphragm; runs along the anterior scalene in the neck

sympathetic trunk – there are three cervical sympathetic ganglia in the neck

Suboccipital Triangle

Located between occipital bone of skull and upper cervical spine; each triangle contains 4 muscles (semispinalis muscle, obliquus capitis superior muscle, obliquus capitis inferior muscle, rectus capitis posterior major muscle), a vertebral artery, deep cervical vein and a suboccipital nerve

Bones

hyoid – U-shaped bone lies at C3 level, superior to thyroid cartilage

greater horn – main part of the hyoid; forms the U-shape around the larynx

lesser horn – smaller, more anterior and superior horn; provides attachment of stylohyoid ligament

temporal – formed from four fused embryonic structures – squamous, petromastoid, tympanic parts, and the styloid

mastoid process – projects antero-inferiorly and is easily palpable medial to the earlobe; one of the attachments of the sternoclieidomastoids

mandible – forms the lower jaw; largest and strongest facial bone

digastric fossa – on the inferior surface of the anterior of the mandible; anterior attachement of digastric muscle

mylohyoid groove – runs inferiorly from the mandibular foramen on the internal posterior surface of the mandible

marks the course of the mylohyoid nerve and vessels

mylohyoid line – divides the internal surface of the mandible into two parts as it runs from just posterior to the third molar, antero-inferiorly along the jaw line

submandibular fossa – lies inferior to the mylohyoid line

Membranes

thyrohyoid – connects the thyroid cartilage to the hyoid bone; median part is thickened into the thyrohyoid ligament

carotid sheath – from base of skull to root of neck; contains common carotids, internal jugular, vagus n, ansa cervicalis

Muscles

infrahyoid

sternohyoid:

attachments: manubrium and medial end of clavicle; body of hyoid bone

innervation: C1-C3 (ansa cervicalis)

action: depresses hyoid after swallowing

sternothyroid:

attachments: posterior surface of manubrium and sternum; oblique line of thyroid cartilage

innervation: C2-C3 via branch of ansa cervicalis

action: depresses hyoid bone and larynx

thyrohyoid:

attachments: oblique line of thyroid cartilage; inferior border of body and greater horn of hyoid bone

innervation: C1 via hypoglossal nerve

action: depresses hyoid, elevates larynx

omohyoid (two bellies attached at middle to the clavicle by a fascial sling):

attachments: superior border of scapula; inferior border of hyoid

innervation: C1-C3 via branch of ansa cervicalis

action: depresses, retracts, stabilizes hyoid

anterior and posterior digastric: two bellies attached in the middle to the body and greater horn of the hyoid via a sling formed by the intermediate digastric tendon

attachments: digastric fossa of mandible; mastoid notch of temporal bone

innervation: anterior belly - mylohyoid nerve; posterior belly - facial nerve

action: depresses mandible, raises hyoid and stabilizes it during speech and swallowing

Miscellaneous

carotid sinus – slight dilation of the internal carotid; area of stretch receptors for blood pressure regulation

submandibular gland – nearly fills the submandibular triangle; salivary gland

thyroid gland – largest endocrine gland; lies inferior to cricoid cartilage

right and left lobes

isthmus – connects right and left lobes; usually anterior to the 2^nd and 3^rd tracheal rings

pyramidal lobe – extra, superior lobe found in some people; remnant of distal portion of thyroglossal duct

parathyroid gland – usually four glands, but can be 2-6; lie behind the thyroid

thoracic duct – drains lymph from entire body except the right side of the head and neck

empties into the left brachiocephalic vein at the junction of the internal jugular and the left subclavian

right lymphatic trunk(s) – drains the right head and neck into the junction of the right subclavian and internal jugular