Gross Anatomy - Head and neck Summary

• The posterior cervical triangle is bounded by the trapezius, sternocleidomastoid, and clavicle and is subdivided by the posterior belly of the omohyoid into the occipital and subclavian triangles. It contains the spinal accessory nerve; external jugular vein; cervical plexus; roots and trunks of the brachial plexus; and subclavian, transverse cervical, and suprascapular arteries.
• The anterior cervical triangle is bounded by the sternocleidomastoid, mandible, and midline of the neck and is subdivided by the digastric anterior and posterior bellies and anterior belly of the omohyoid into the submandibular, carotid, muscular, and submental triangles.
• The accessory nerve runs on the levator scapulae, deep to the trapezius, and innervates the trapezius and sternocleidomastoid muscles. The superficial (cutaneous) branches of the cervical plexus include the great auricular, transverse cervical, supraclavicular, and lesser occipital nerves. The deep branches of the cervical plexus consist of the ansa cervicalis, which supplies the infrahyoid or strap muscles, and the phrenic nerve, which runs on the scalenus anterior and enters the thorax to supply the diaphragm.
• The posterior belly of the digastric and stylohyoid muscles are innervated by the facial nerve, whereas the anterior belly of the digastric and mylohyoid muscles are innervated by the trigeminal nerve. The geniohyoid and thyrohyoid muscles are innervated by C1 through the hypoglossal nerve.

• The trachea begins at the inferior border of the cricoid cartilage and ends by bifurcating into the primary bronchi at the level of sternal angle. It is kept open by a series of C-shaped hyaline cartilages.
• The esophagus is a muscular tube extending from the pharynx to the stomach. It contains smooth muscles innervated by sympathetic nerve fibers from the sympathetic trunk and branchiomeric skeletal muscles innervated by SVE fibers from the recurrent laryngeal nerves.
• The thyroid gland is an endocrine gland that secretes the hormones thyroxine and thyrocalcitonin, which regulate metabolic rate. The isthmus overlies the second to the third or the second to the fourth tracheal rings.
• The parathyroid glands are two superior and two inferior (four to six) small endocrine glands, which secrete parathyroid hormone for calcium metabolism. If there is no secretion of parathyroid hormone, fetal tetany is produced.
• The carotid sheath contains the common and internal carotid arteries, internal jugular vein, and vagus nerve. It does not contain the sympathetic trunk, which lies posterior to the carotid sheath and is embedded in the prevertebral fascia.
• The common carotid artery arises from the brachiocephalic trunk on the right and from the aortic arch on the left. It divides into the internal and external carotid arteries at the level of the upper border of the thyroid cartilage. The internal carotid artery has no named branch in the neck, and the external carotid artery has numerous branches such as the superior thyroid, ascending pharyngeal, occipital, lingual, facial, posterior auricular, maxillary, and superficial temporal arteries. The carotid body lies at the bifurcation of the common carotid artery and serves as a chemoreceptor. The carotid sinus lies at the origin of the internal carotid artery and functions as a pressoreceptor or baroreceptor. The carotid body and carotid sinus are innervated by the carotid sinus nerve of the vagus nerve and the nerve to the carotid body from the glossopharyngeal nerve.

• Muscles of facial expression are innervated by the facial nerve, and the cutaneous sensation is supplied by the trigeminal nerve. The face receives arterial blood from the facial artery, which gives rise to the inferior labial, superior labial, and lateral nasal branches and ends as the angular artery. The facial vein has the corresponding branches of the facial artery, drains into the internal jugular vein, and communicates with the pterygoid venous plexus by way of the deep facial vein.

• The scalp consists of the skin, connective tissue, aponeurosis, loose connective tissue, and pericranium (periosteum); receives sensory innervation from branches of the ophthalmic, maxillary, and mandibular nerves and the lesser, greater, and third occipital nerves; and receives blood from branches of the internal and external carotid arteries. The loose connective tissue layer is known as a dangerous layer and communicates with cranial dural venous sinuses by way of the emissary veins.

• The infraorbital fossa contains muscles of mastication, the mandibular nerve and its branches, and the maxillary artery and its branches.
• The muscles of mastication are innervated by the mandibular branch of the trigeminal nerve. The lateral pterygoid opens the jaw, and other muscles close the jaw. The mandible can be protruded by the lateral and medial pterygoid muscles, whereas it can be retracted by the temporalis and masseter muscles.
• The maxillary artery gives rise to the deep auricular, anterior tympanic, inferior alveolar, deep temporal, middle meningeal (muscles of mastication), and buccal branches in the infratemporal fossa. The middle meningeal artery passes between two roots of the auriculotemporal nerve and enters the cranial cavity through the foramen ovale. The inferior alveolar artery enters the mandibular canal and supplies the lower teeth and chin.
• The mandibular nerve gives off inferior alveolar, lingual, buccal, deep temporal, and other muscular branches. The lingual nerve is joined by the chorda tympani, which carries the preganglionic parasympathetic fibers to the submandibular ganglion and taste fibers to the anterior two thirds of the tongue. The inferior alveolar nerve gives off the mylohyoid nerve, which supplies the anterior belly of the digastric and mylohyoid muscles.
• The parotid gland secretes a large amount of watery saliva (which contains enzymes) by parasympathetic stimulation and a small amount of viscus saliva in response to sympathetic stimulation. The saliva enters the vestibule opposite the site of the upper second molar tooth by way of the parotid duct.

• The anterior cranial cavity contains numerous foramina that transmit nerves; blood vessels; and other structures including the foramen cecum (emissary vein to superior sagittal sinus), foramina of cribriform plate (olfactory nerve), posterior ethmoidal foramen (posterior ethmoidal nerve and vessels), and optic canal (optic nerve and ophthalmic artery).
• The middle cranial fossa contains the superior orbital fissure (CNs III, IV, V3, and VI and ophthalmic vein), foramen rotundum (maxillary nerve), foramen ovale (mandibular nerve, accessory meningeal artery, and lesser petrosal nerve), foramen spinosum (middle meningeal vessels and meningeal branch of mandibular nerve), foramen lacerum (upper part: internal carotid artery and plexus), hiatus of canal of lesser petrosal nerve, and hiatus of canal of greater petrosal nerve.
• The posterior cranial fossa contains the internal acoustic meatus (facial nerve, vestibulocochlear nerve, and labyrinthine artery), mastoid foramen (emissary vein), jugular foramen (CNs IX, X, and XI and internal jugular vein), condylar canal (emissary vein), hypoglossal canal (CN XII), and foramen magnum (medulla oblongata, meninges, vertebral arteries, spinal roots of CN XI).
  

• Olfactory nerve (SVA, smell).
• Optic nerve (SSA, vision).
• Oculomotor, trochlear , and abducens nerves (GSE, muscles of eye movement, SO4, LR6, and Remainder3 ).
• Trigeminal nerve (GSA, skin on face; SVE, muscles of mastication and tensor veli palatini, tensor tympani, mylohyoid, and digastric anterior belly muscles).
• Facial nerve (SVE, muscles of facial expression; SVA, taste on anterior two thirds of tongue; GVE, parasympathetic nerve to submandibular and pterygopalatine ganglia; GVA, mucous membrane on palate; GSA, external ear).
• Vestibulocochlear nerve (SSA, hearing and balance).
• Glossopharyngeal nerve (SVE, stylopharyngeus muscle; SVA, taste on posterior one third of tongue; GVE; parasympathetic nerve to otic ganglion; GVA, posterior one third of tongue; GSA, external ear).
• Vagus nerve (SVE, muscles of palate, pharynx, and larynx; SVA, taste on epiglottis; GVE, parasympathetic nerve to smooth muscles, glands, heart, and muscles in the thorax and abdomen; GVA, mucous membrane of the pharynx, larynx, middle ear cavity, and thoracic and abdominal viscera; GSA, external ear).
• Accessory nerve (SVE, trapezius and sternocleidomastoid) and hypoglossal nerve (GSE, muscles of tongue movement).

• The optic nerve mediates the afferent limb of the pupillary light reflex , whereas parasympathetic fibers in the oculomotor nerve mediate the efferent limb.
• The ophthalmic nerve mediates the afferent limb of the corneal (blink) reflex by way of the nasociliary branch, whereas the facial nerve mediates the efferent limb.
• The maxillary nerve mediates the afferent limb of the sneeze reflex (irritation of the nasal mucosa), and the vagus nerve mediates the efferent limb.
• The mandibular nerve mediates the afferent and efferent limbs of the jaw jerk reflex.
• The glossopharyngeal nerve (pharyngeal branch) mediates the afferent limb of the gag (pharyngeal) reflex , and the vagus nerve mediates the efferent limb.
• The vagus nerve mediates the afferent and efferent limbs of the cough reflex (irritation of the bronchial mucosa).

• Most veins of the brain drain into the intracranial dural venous sinuses.
• The superior sagittal sinus lies in the midline along the convex border of the falx cerebri between the cerebral hemispheres.
• The inferior sagittal sinus lies in the free edge of the falx cerebri and is joined by the great cerebral vein of Galen to form the straight sinus.
• The superior sagittal, straight, and occipital (in the falx cerebelli) sinuses join at the confluence, which is drained by the transverse sinuses.
• The transverse sinus drains into the sigmoid sinus, which becomes the internal jugular vein.
• The cavernous sinus is located on each side of the sella turcica; communicates with the ophthalmic vein, pterygoid venous plexus, and facial vein; and contains the abducens nerve and internal carotid artery in the middle and the oculomotor, trochlear, ophthalmic, and maxillary nerves in the lateral wall.

• The optic canal is formed by two roots of the lesser wing of sphenoid and transmits the optic nerve and ophthalmic artery. The superior orbital fissure is formed by the lesser and greater wings of the sphenoid bone; transmits the oculomotor, trochlear, abducens, and ophthalmic nerves and ophthalmic vein. The inferior orbital fissure lies between the greater wing and maxilla and transmits the infraorbital nerve and vessels.
• Muscles of eye movement are the levator palpebrae superioris, inferior oblique, and superior, middle, and inferior rectus muscles, which are innervated by the oculomotor nerve; the lateral rectus muscle is innervated by the abducens nerve; and the superior oblique is innervated by the trochlear nerve.
• The ophthalmic nerve divides into the lacrimal, frontal (which divides into the supraorbital and supratrochlear branches), and nasociliary nerves. The nasociliary nerve gives off a communicating branch to the ciliary ganglion and the long ciliary nerve, which contains sympathetic postganglionic fibers, and serves as afferent limb of the corneal blink reflex arc. Parasympathetic nerves supply the ciliary muscle and the sphincter pupillae muscle, and sympathetic nerves supply the dilator pupillae muscle.
• The ophthalmic artery arises from the internal carotid artery and supplies structures in the orbit and eyeball. The ophthalmic veins communicate with the cavernous sinus and the pterygoid venous plexus.
  

• The palate consists of the hard palate and soft palate. Muscles of the palate (palatoglossus, palatopharyngeus, muscular uvulae, levator veli palatine, and tensor veli palatine) are innervated by the vagus nerve, except the tensor veli palatini, which is innervated by the trigeminal nerve.

Nerves

• The maxillary teeth are innervated by the superior alveolar nerve, and the mandibular teeth are innervated by the inferior alveolar nerve.
• The outer (buccal) surface of the maxillary gingiva is innervated by the superior alveolar and infraorbital nerves, whereas the inner (lingual) surface is innervated by the greater palatine and nasopalatine nerves.
• The outer (buccal) surface of the mandibular gingiva is innervated by the buccal and mental nerves, whereas the inner (lingual) surface is innervated by the lingual nerves.

• Muscles of the tongue are innervated by the hypoglossal nerve except the palatoglossus, which is innervated by the vagus nerve. The anterior two thirds of the tongue is innervated by the lingual nerve for general sensation and by chorda tympani of the facial nerve for taste (SVA) sensation. The posterior one third of the tongue is supplied by the glossopharyngeal nerve for both general and taste sensations.

Innervation of the tongue

• GSE motor innervation to muscles of the tongue from the hypoglossal nerve.
• GSA sensation from anterior two thirds of the tongue from the lingual nerve.
• SVA taste sensation from anterior two thirds of the tongue from the chorda tympani.
• GVA and SVA sensation from posterior one third of the tongue from the glossopharyngeal nerve.
• The vallate papillae are located on the anterior two thirds of the tongue in front of the sulcus terminalis, but they are innervated by the glossopharyngeal nerve.

Glands

• The submandibular gland has a larger superficial portion, which is separated by the mylohyoid muscle from the smaller deep portion.
• The submandibular (Wharton's) duct passes medial to the lingual nerve and then superior to the nerve and opens onto the sublingual caruncle.
• The sublingual gland has numerous small ducts that open on the sublingual fold or into the submandibular duct.
• Both glands receive postganglionic parasympathetic fibers from the submandibular ganglion, which receives preganglionic parasympathetic fibers through the chorda tympani (which also contains taste fibers).
• The lingual artery arises from the external carotid artery near the greater horn of the hyoid bone and passes deep to hyoglossus muscle, but the lingual and hypoglossal nerves pass superficial to the muscle. The artery has the dorsal lingual, deep lingual, and sublingual branches.

Nasal Cavity

• The nasal cavity is divided into a vestibule , which is a dilated area inside the nostril lined by skin with hairs to filter incoming air; an olfactory region , which is the upper third of the nasal cavity lined with olfactory mucosa; and a respiratory region , which is the lower two thirds of the nasal cavity lined with vascular, glandular respiratory mucosa to warm and humidify air.
• It has a roof formed by the body of the sphenoid and sphenoid sinus; a floor formed by the hard palate; a medial wall formed by the nasal septum of the septal cartilage, perpendicular plate of ethmoid, and vomer; and a lateral wall formed by the superior and middle concha of the ethmoid and inferior concha.
• It receives GSA innervation to its mucosa by branches of the ophthalmic and maxillary nerves and receives SVA (olfaction) by the olfactory nerves. It receives blood from the sphenopalatine branch of the maxillary artery, anterior ethmoidal branch of the ophthalmic artery, and septal branch of the facial artery.

• Ganglia
• The pterygopalatine ganglion receives parasympathetic preganglionic fibers from the facial nerve through the greater petrosal nerve and the nerve of the pterygoid canal.
• Postganglionic parasympathetic fibers supply the lacrimal gland running through the maxillary, zygomatic, zygomaticotemporal, and lacrimal nerves.
• The ganglion receives branches from the maxillary nerve and then sends branches to the palate and nasal mucosae.
• Nerves
  
  • The greater petrosal nerve contains preganglionic parasympathetic GVE fibers and GVA and SVA (taste) fibers to the palate.
  • The deep petrosal nerve contains postganglionic sympathetic GVE fibers.
  • The nerve of the pterygoid canal contains preganglionic parasympathetic GVE fibers to the lacrimal gland and nasal and palatine mucosae and postganglionic sympathetic GVE fibers and GVA and SVA (taste) fibers to the palate.

• The larynx has a cartilaginous framework , consisting of the thyroid cartilage (Adam's apple, a laryngeal prominence), cricoid cartilage (signet ring shape), arytenoid cartilages (have vocal process and muscular process and rotate on the cricoid cartilage), epiglottic cartilage (leaf shaped), and corniculate and cuneiform cartilages.
• The laryngeal muscles are innervated by the recurrent laryngeal nerve except the cricothyroid, which is innervated by the external laryngeal branch of the superior laryngeal nerve. The posterior cricoarytenoid muscle abducts the vocal cord, but all other muscles adduct the vocal cord. The chief adductor is the lateral cricoarytenoid; the sole abductor is the posterior cricoarytenoid; the chief tensor is the cricothyroid; the chief relaxer is the thyroarytenoid. The lateral cricoarytenoid rotates the vocal process of the arytenoid cartilage medially, closing the rima glottidis, whereas the posterior cricoarytenoid rotates the vocal process laterally, opening the rima glottidis.
• Sensation above the vocal cord is supplied by the internal laryngeal branch of the superior laryngeal nerve, whereas sensation below the vocal cord is supplied by the recurrent laryngeal nerve. SVA (taste) sensation on the epiglottis is supplied by the internal laryngeal nerve.
• The larynx receives blood from the superior laryngeal artery of the superior thyroid artery and the inferior laryngeal artery of the inferior thyroid artery.

• The external ear consists of the auricle, which is elastic cartilage covered by skin, and is innervated by the great auricular, auriculotemporal, and lesser occipital nerves. The external acoustic meatus consists of a cartilaginous outer third and bony inner two thirds. It is innervated by the auriculotemporal branch of the trigeminal nerve and the auricular branches of the facial, vagus, and glossopharyngeal nerves.
• The tympanic membrane is covered by the skin externally and the mucosa internally. The external surface is innervated by the trigeminal, facial, glossopharyngeal, and vagus nerves, and the internal surface is innervated by the glossopharyngeal nerve.
• The auditory ossicles are the malleus (hammer), incus (anvil), and stapes (stirrup). The handle of the malleus is attached to the tympanic membrane and receives the tendon of the tensor tympani (which is innervated by the trigeminal nerve). The footplate of the stapes occupies the oval window, and its neck receives insertion of the stapedius (which is innervated by the facial nerve).
• The chorda tympani arises from the facial nerve in the facial canal, passes between the handle of the malleus and the long process of the incus, exits through the petrotympanic fissure, and joins the lingual nerve in the infratemporal fossa, carrying preganglionic parasympathetic fibers to the submandibular ganglion and taste fibers to the anterior two thirds of the tongue.
• The cochlea contains the spiral organ of Corti for hearing, the membranous cochlear duct filled with endolymph, and the scala vestibule and scala tympani filled with perilymph. The vestibule contains the membranous utricle and saccule filled with endolymph and receptors (maculae) for linear acceleration. The semicircular canals contain sensory receptors (cristae) for angular movements in the ampullae at one end of each canal.

• All of the infrahyoid muscles are innervated by the ansa cervicalis except the thyrohyoid muscle, which is innervated by C1 through the hypoglossal nerve.
• All of the muscles of facial expression are innervated by the facial nerve, and all of the muscles of mastication are innervated by the trigeminal nerve.
• All of the tongue muscles are innervated by the hypoglossal nerve except the palatoglossus muscle, which is innervated by the vagus nerve.
• All of the palate muscles are innervated by the vagus nerve except the tensor veli palatini muscle, which is innervated by the trigeminal nerve.
• All of the pharyngeal muscles are innervated by the vagus nerve except the stylopharyngeus muscle, which is innervated by the glossopharyngeal nerve.
• All of the laryngeal muscles are innervated by the recurrent laryngeal nerve except the cricothyroid muscle, which is innervated by the external laryngeal nerve.
• In addition, for the suprahyoid muscles , the stylohyoid and digastric posterior belly are innervated by the facial nerve, whereas the mylohyoid and digastric anterior belly are innervated by the trigeminal nerve, and the geniohyoid is innervated by C1 through the hypoglossal nerve.
• In the neck , the sternocleidomastoid and trapezius are innervated by the accessory nerve.
• In the middle ear , the tensor tympani and stapedius are innervated by the trigeminal and facial nerves, respectively.