Core Curriculum Syllabus: Review of Anatomy
The anatomy of the head and neck can be divided into the following sections:
The temporal bone contains the sensory organs of hearing and balance, and structurally contributes to the cranial vault. The temporal bone consists of five parts: the squamous, the mastoid, the tympanic, zygomatic and petrous segment. It contains portions of the carotid artery and jugular venous drainage system, and is intimately related to the dura of the middle and posterior fossa. Anteriorly, it articulates with the condyle of the mandible. Posteriorly, and superiorly, the mastoid air cell system communicates with the middle ear. The facial nerve passes through the temporal bone en route to the muscles of facial expression.
Both functionally and anatomically, it can be divided into three parts.
A. External Ear - that portion external to the tympanic membrane. It serves chiefly to protect the tympanic membrane, but also collects and directs sound waves and plays a role in sound localization. The skin of the external ear normally migrates laterally from the umbo of the malleus in the tympanic membrane to the external auditory meatus (at a rate of 2-3 mm per day). This is a unique and essential mechanism for maintaining patency of the canal.
- The Auricle - elastic cartilage covered with closely adherent skin. The configuration is intricate, and extremely difficult to duplicate.
- External Auditory Canal
- Lateral Portion - cartilaginous with thick, loosely applied skin containing ceruminous and sebaceous glands.
- Medial Portion- very thin skin directly over bone, no skin appendages. Curves anteriorly and medially in adults, which may obscure the anterior tympanic membrane. It comprises two-thirds of the total canal in adults, less in infants and children.
B. The Middle Ear - This is an air-containing space which communicates with the nasopharynx via the eustachian tube. It is normally sealed laterally by the tympanic membrane. Its function is to transmit and amplify sound waves from tympanic membrane to the stapes footplate converting energy from air medium to a fluid medium of the membranous labyrinth. The relationship of the three ossicles is depicted below.
Left ear viewed posteriorly
- The tympanic membrane is an ovoid, three-layered structure consisting of squamous epithelium laterally, respiratory mucosa medially, and an intervening fibrous layer. It normally has a conical shape, with the apex maintained medially by the support of the malleus. The fibrous layer thickens laterally to form the annulus, an incomplete ring which is attached to surrounding bone. Superior to the lateral process of the malleus, this ring is deficient, and this area is known as the pars flaccida. The majority of the drum is composed of the pars tensa.
Left ear viewed externally
- Ossicles - three small bones which are involved in sound conduction. From lateral to medial, these are the malleus, the incus, and the stapes. The handle and lateral process of the malleus is attached to the tympanic membrane and can be easily seen on physical exam. The long process of the incus can often be seen through the posterior superior quadrant of the membrane. The stapes is attached to a foot plate which is in direct contact with the fluid of the inner ear. (See diagrams 1 and 3).
- Spaces - the middle ear cleft is wider than the tympanic membrane, and is conventionally divided into spaces in reference to the annulus.
- Epitympanum - superior to the tympanic membrane. Contains the body of the incus and the head of the malleus. Communicates with the mastoid via the aditus.
- Mesotympanum - on a level with the ear drum. The oval and round windows, located posterosuperiorly on the medial wall, communicate with the inner ear. The long process of the incus projects into the posterior quadrant to articulate with the stapes which sits in the oval window. The facial nerve, usually covered by a bony canal, crosses the posterior superior quadrant superior to the stapes, then courses inferiorly between the middle ear and mastoid air cells.
- Protympanum - in this anterior recess of the middle ear, the eustachian tube exits to communicate with the nasopharynx. This tube runs in close proximity to the carotid artery.
- Hypotympanum - the jugular bulb curves through the hypotympanum. It is usually covered by bone, but may be dehiscent and extend into the middle ear space.
C. Inner Ear - consists of a fluid-filled labyrinth which functions to convert mechanical energy into neural impulses. The bony labyrinth is subdivided into smaller compartments by the membranous labyrinth. Fluid surrounding the membranous labyrinth is called perilymph; fluid within is called endolymph. There are three main divisions of the bony labyrinth.
- Vestibule - just medial to the oval window, and contains the utricle and the saccule, two organs of balance. The vestibule is an antechamber, leading to both the cochlear and the semicircular canal.
- The Cochlea - a snail-shaped chamber anterior to the vestibule. It bulges into the middle ear and its bony covering is the promontory. The cochlea also communicates with the middle ear via the round window. In this organ, sound waves are converted into neural impulses with elaborate coding.
- The Semicircular Canals - three in number; project posteriorly from the vestibule. These organs detect angular acceleration. They consist of a superior, posterior and lateral, or horizontal canals.
The nerve fibers from the labyrinth make up the auditory nerve which consists of a cochlear nerve and a superior and inferior vestibular with both afferent and efferent fibers from the respective sensory end organs. This nerve enters the cranial cavity via the internal auditory canal.
The nose is the air conditioner of the body, responsible for warming and saturating inspired air, removing bacteria and particulate debris, as well as conserving heat and moisture from expired air. Nasal breathing is important for optimal pulmonary function. It is also a prominent cosmetic feature of the face.
A. External Nose - the anterior, caudal portion of the nose is cartilaginous, while posteriorly and superiorly it is bony.
- Cartilages: greater alar (lower lateral), septal, lateral nasal (upper lateral), lesser alar, sesamoid.
- Bones: Nasal, maxillary, frontal
- Musculature: Nasalis, depressor septi, procerus, dilator naris. Blood supply
- External carotid
- External maxillary: lateral nasal, angular, alar, septal, external nasal.
- Internal carotid: Ophthalmic, which gives rise to anterior ethmoid, posterior ethmoid, and dorsal nasal vessels.
- External carotid
- Lymphatics: facial artery, submandibular, parotid nodal drainage.
- Nerve supply
- Sensory trigeminal
- Ophthalmic division: Nasociliary, external nasal, infratrochlear.
- Maxillary division: infraorbital
- Motor facial: Buccal, zygomatic branches
- Sensory trigeminal
B. Internal Nose:
- Floor - the floor of the nose is formed by the hard palate. The nasal cavity extends as far back as the soft palate, where the posterior choanae opens into the nasopharynx.
- Roof - the roof of the nose is adjacent to the anterior cranial fossa. The cribriform plate contains numerous tiny perforations which transmit sensory fibers to the olfactory bulbs. The sensation of smell is limited in man to a very small area of mucosa in the superior recesses of the nose. Posteriorly, the roof slants downward as the anterior wall of the sphenoid sinus.
- Lateral Walls - the turbinates, three or sometimes four bony shelves covered by erectile mucosa, project from the lateral wall of the nose. These processes serve to increase the interior surface area of the nose to facilitate heat and water exchange. They constantly engorge or shrink to accommodate changing physiologic requirements. They are also the chief structures involved in pathologic obstruction. A series of spaces are created by the overhanging edge of these turbinates.
- Inferior Meatus - inferior to the inferior turbinate. Contains orifice of nasolacrimal duct.
- Middle Meatus - inferior to the middle turbinate. Contains semilunar hiatus, with openings of the maxillary, frontal, and anterior ethmoidal sinuses.
- Superior Meatus - drains posterior ethmoid cells.
- Spheno-ethmoid recess - orifice of sphenoid sinus
- Blood Supply
- Anterior ethmoid - to roof and anterior superior portion of septum and lateral wall
- Sphenopalatine - to lateral wall of nose
- Nasopalatine - supplies roof, septum, and floor
- Lateral nasal - supplies lateral nasal wall anteriorly.
- Descending palatine - supplies the lateral nasal wall posteriorly.
- Pharyngeal - supplies roof posteriorly
- Posterior ethmoid - supplies septum and lateral nasal wall superiorly
- Septal - supplies septum inferiorly and floor
- Nerve supply
- Medial internal nasal - to septum, anterosuperiorly
- Lateral internal nasal - to lateral wall, anterosuperiorly
- External nasal - to skin of back of nose
- Posterior superior nasal - supplies septum and lateral wall posteroinferiorly, to middle turbinate
- Posterior inferior nasal - to floor and inferior turbinate
- Pharyngeal - to choana
- Anterior superior alveolar - to inferior meatus
- Infraorbital - to vestibule
- Lymphatics: drained by
- Facial venous drainage Retropharyngeal Superior deep cervical
These are air-filled, mucosal-lined cavities which develop in facial and cranial bones. The spaces communicate with the nasal airway. Their function is unknown but has been subject to a great deal of speculation. They could serve to decrease the weight of the skull or to function as resonators for the voice. In lower animals with a more acute sense of smell, the sinuses are largely lined by olfactory epithelium. Sinuses may have originally developed to increase the available surface area for the sense of smell. Therefore, in humans, with olfaction limited to a much smaller area, sinuses may be vestigial anachronisms.Though their function is obscure, their medical significance is not. Sinuses frequently become infected due to obstruction of normal drainage, and negative pressure in a sinus can cause headache. Neoplasms which arise in the sinuses can be occult for quite a long time, so that they are usually very advanced at the time of diagnosis. There are four groups of sinuses:
- Frontal - Paired, in frontal bone. Posterior wall is adjacent to anterior cranial fossa. Usually asymmetrical, occasionally absent.
- Maxillary - Paired, in maxilla. Superior wall - floor of orbit. Medial wall - lateral wall of nose. Inferiorly related to tooth-bearing area of maxilla.
- Ethmoid - Numerous cells in superior and lateral walls of nose, and in medial walls of orbits.
- Sphenoid - Paired, in sphenoid bone. Sella turcica projects into this space.
Designed for articulation in speech and mastication of food, the oral cavity also functions as an alternate airway.
- Anterior - the lips
- Posterior - the anterior tonsillar pillars
- Roof - hard and soft palate
- Floor - mucosa overlying sublingual and submandibular glands.
- Walls - buccal mucosa
- Alveolar processes and teeth
- Anterior tongue to circumvallate papilla
- Orifice of parotid gland (Stenson's duct) in buccal mucosa opposite upper second molars
- Orifice of submandibular duct (Wharton's duct) in anterior floor of mouth
- Orifices of sublingual glands
A. Nasopharynx - extends from posterior choanae of the nose to the soft palate. Related posteriorly to the base of the skull. Contains adenoid tissue and the orifices of the eustachian tubes. This area is not accessible to direct inspection and must be examined by mirrors or optical instruments.
B. Oropharynx - that portion which is visible via the mouth. Extends from soft palate superiorly to vallecula inferiorly. Posterior and lateral walls are formed by the superior and middle pharyngeal constrictors.
C. The Palatine Tonsils are lymphoid aggregates between the mucosal folds created by the palatoglossus and palatopharyngeus muscles. They are covered by stratified squamous epithelium, which continues down into deep crypts. Tonsils vary widely in size and may be sessile or pedunculated.
D. Hypopharynx - Is the portion of the pharynx that lies inferior to the tip of epiglottis. The posterior and lateral walls are formed by middle and inferior pharyngeal constrictors. It extends inferiorly to the cricopharyngeus, where the pharynx empties into the cervical esophagus. Anteriorly, it extends from the valleculae and contains the epiglottis and the larynx. Lateral to the larynx are the pyriform sinuses, two mucosal pouches whose medial borders are the lateral walls of the larynx. The posterior aspect of the hypopharynx contains the posterior pharyngeal wall and post cricoid mucosa.
The larynx is a valve separating the trachea from the upper aerodigestive tract. It is primarily thought of as an organ of communication--the "voice box"--but it is also an important regulator of respiration, and is necessary for an effective cough or valsalva maneuver, and prevents aspiration during swallowing.
- Hyoid Bone - attachment to epiglottis and strap muscles.
- Thyroid Cartilage - anterior attachment of vocal folds. Posterior articulation with cricoid cartilage.
- Cricoid Cartilage - complete ring. Articulates with thyroid and arytenoid cartilages.
- Arytenoids - two cartilages which glide along the posterior cricoid and attach to posterior ends of vocal folds.
- Supraglottis - usually covered with respiratory epithelium containing mucous glands.
- Epiglottis - leaf-shaped mucosal-covered cartilage, which projects over larynx.
- Aryepiglottic folds - extend from the lateral epiglottis to the arytenoids.
- False vocal cords - mucosal folds superior to the true glottis. Separated from true vocal folds by the ventricle.
- Ventricle - mucosal-lined sac, variable in size which separates the supraglottis from the glottis.
- Glottis - the true vocal folds attach to the thyroid cartilage at the anterior commissure. The posterior commissure is mobile, as the vocal folds attach to the arytenoids. Motion of the arytenoids effects abduction or adduction of the larynx. The bulk of the vocal fold is made up of muscle covered by mucosa. The free edge is characterized by stratified squamous epithelium. The vocal folds abduct for inspiration and adduct for phonation, cough, and valsalva.
- Subglottis - below the vocal folds, extending to the inferior border of the cricoid cartilage.
C. Innervation - branches of the vagus nerve.
- Superior Laryngeal Nerve - sensation of the glottis and supraglottis. Motor fibers to the cricothyroid muscle, which tenses the vocal folds. This nerve leaves the vagus high in the neck.
- Recurrent Laryngeal Nerve - sensation of the subglottis, and motor fibers to intrinsic muscles of the larynx. This nerve branches from the vagus in the mediastinum, then turns back up into the neck. On the right, it travels inferior to the subclavian artery and on the left, the aorta.
A. Parotid Gland
- Located on side of face, anterior to mastoid tip and external auditory canal, inferior to zygomatic arch, and superior to the lower border of the angle of the mandible. Anteriorly, it overlaps the masseter muscle.
- Stenson's duct enters oral cavity through buccal mucosa opposite upper second molar.
- Parasympathetic secretory afferents to the parotid leave the inferior salivary nucleus with the glossopharyngeal nerve and travel via Jacobson's plexus in the middle ear to synapse in the otic ganglion. Post-synaptic fibers are distributed to the parotid by the auriculotemporal nerve.
- Facial nerve passes through this gland.
B. Submandibular Gland
- Beneath floor of the mouth, inferior to mylohyoid muscles and superior to digastric muscle.
- Marginal mandibular branch of the facial nerve travels in the fascia on the lateral surface of this gland.
- Parasympathetic secretory afferents to the submandibular gland arise from the superior salivatory nucleus, and leave the brainstem in the facial nerve. They exit the facial nerve at the geniculate ganglion and travel via the chorda tympani to the lingual nerve. Fibers synapse in the submandibular ganglion, and post-synaptic fibers then enter the gland.
- The lingual and hypoglossal nerves lie deep to this gland.
- Wharton's duct enters the floor of the mouth near the lingual frenula.
C. Sublingual Glands - located below the mucous membrane of the floor of the mouth, adjacent to mandible and mylohyoid muscle. Ten to twelve small caliber ducts drain the gland, some emptying into the submandibular duct, and others draining directly into the floor of the mouth.
D. Minor Salivary Glands - small collections of salivary gland tissues are scattered throughout the oral mucosa, and can also be seen in the pharynx, supraglottis, nose and sinuses.
The neck contains important communications between the head and the body, including air and food passages, major blood vessels and nerves, and the spinal cord. Many vital structures are compressed into a narrow area which is engineered for maximal mobility to permit variation in head position relative to body.
A. Skeleton - primarily composed of the vertebral column. Anteriorly, the hyoid bone, and laryngeal and tracheal cartilages support the aerodigestive spaces. These are suspended from the mandible and base of skull by a system of muscles and ligaments.
B. Muscles - anteriorly, strap muscles connect the respiratory skeleton and sternum. There are also muscular attachments from the hyoid to the tongue, mandible, and styloid. The digastric muscle passes forward from the mastoid, attaches to the hyoid, then ascends to the anterior mandible. The sternocleidomastoid (SCM) divides the neck into anterior and posterior triangles. The posterior triangle is largely muscular. The anterior triangle which contains most of the vital structures, can be divided into smaller triangles by muscles.
The anterior and posterior bellies of the digastric form the submandibular triangle. The submental triangle is in the midline, between the anterior bellies. The vascular or carotid triangle is inferior to the digastric and hyoid.
The omohyoid is a small muscle, running at roughly 90 degrees to the SCM, from the hyoid to the scapula.
C. Nerves - the neck contains major branches of cranial nerves, as well as cervical roots.
- Cranial Nerves
- VII - the marginal mandibular branch dips down into the neck in the fascia overlying the submandibular gland. In addition to the muscles of facial expression, branches of VII innervate the platysma, the stylohyoid and the posterior belly of the digastric.
- X - the vagus nerve exits the jugular foramen and travels inferiorly in the carotid sheath. It carries the parasympathetic fibers of the thoracic cavity and much of the GI tract, as well as laryngeal and pharyngeal sensory and motor branches.
- The Spinal Accessory Nerve (XI) - supplies the trapezius and sternocleidomastoid muscles. It exits the jugular foramen, then runs posteriorly.
- The Hypoglossal Nerve (XII) - supplies the muscles of the tongue. The nerve exits the skull through its own canal, runs downward in the carotid sheath, then curves forward superficially to the carotid at the level of the occipital artery to reach the tongue.
- Cervical Nerves
- Cervical plexus - anterior roots of C1-4
- Ansa cervicalis - to strap muscles (some travel with XII)
- Branches to phrenic nerve
- Phrenic nerve - C3-5
- Brachial Plexus C5-T1
- Posterior rami - to posterior muscles and skin
- Cervical sympathetic chain - travels in carotid sheath
- Cervical plexus - anterior roots of C1-4
D. Major Vascular Structures
- Carotid Artery - bifurcates into:
- Internal (intracranial) - no branches in the neck
- External (extracranial) - branches:
- Superior thyroid
- Ascending pharyngeal
- Superficial temporal
- Internal maxillary
- Thyrocervical trunk
- Transverse cervical
- Inferior thyroid
- Vertebral artery
- Internal jugular vein (within carotid sheath)
- External jugular vein
E. Visceral Column - pharynx, larynx, trachea, and esophagus.
F. Thyroid Gland
- Developmentally derived from pharyngeal floor
- Located anterior and lateral to the trachea
- Closely related to recurrent laryngeal nerve and parathyroid glands
- Blood supply
- Superior thyroid artery (branch of external carotid)
- Inferior thyroid artery (branch of thyrocervical trunk)
- Thyroid "ima" artery (variable)
- Superior thyroid vein
- Middle thyroid vein
- Inferior thyroid vein
G. Parathyroid Glands
- Four glands: two on each side
- Derived from branchial pouches III and IV: Superior parathyroid glands from pouch IV and inferior parathyroid gland from pouch III.
- Glands usually related to posterior surface of thyroid gland, but may be found as inferior as mediastinum
H. Anatomic triangles (superimposed on superficial neck anatomy):
The neck can be divided into two major triangles, with multiple smaller triangles:
a. Anterior triangle - bordered by the anterior border of the SCM, midline of the neck, and the mandible
- muscular triangle--formed by the midline, superior belly of the omohyoid, and SCM
- carotid triangle--formed by the superior belly of the omohyoid, SCM, and posterior belly of the digastric
- submental triangle--formed by the anterior belly of the digastric, hyoid, and midline
- submandibular triangle--formed by the mandible, posterior belly of the digastric, and anterior belly of the digastric
b. Posterior triangle - bordered by the posterior border of the SCM, trapezius, and clavicle
- supraclavicular triangle--formed by the inferior belly of the omohyoid, clavicle, and SCM
- occipital triangle--formed by inferior belly of the omohyoid, trapezius, and SCM
I. Lymphatic drainage: major head and neck lymph node groups.
The lymph nodes of the neck can be divided into six levels within the defined anatomic triangles. These groups and the areas that they drain are particularly important when locating and working up a "neck mass" or possible malignancy. The groups and drainage areas are as follows:
- I--Submental and submandibular nodes
- II--Upper jugulodigastric group
- III--Middle jugular nodes draining the naso- and oropharynx, oral cavity, hypopharynx, larynx.
- IV--Inferior jugular nodes draining the hypopharynx, subglottic larynx, thyroid, and esophagus.
- V-- Posterior triangle group
- VI--Anterior compartment group
Individual Lymph Nodes in the Head and Neck: