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Head & Neck Anatomy - Complete Exam Guide

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1. MANDIBLE

Anatomical Position

Parts

• Body: horizontal part; has base (inferior border) and alveolar part (superior border with teeth sockets)
• Ramus (paired): vertical plates; each has:
  • Coronoid process (anterior, triangular)
  • Condylar process (posterior) - head + neck
  • Mandibular notch between them
  • Angle of mandible (junction of body and ramus)
• Symphysis menti: midline fusion point (not a true joint in adults)

Muscle Attachments

Ligament Attachments

• Sphenomandibular ligament: spine of sphenoid → lingula of mandibular foramen
• Stylomandibular ligament: styloid process → angle of mandible
• Temporomandibular ligament (lateral ligament): zygomatic arch → neck of condyle

Nerve Supply

• Inferior alveolar nerve (branch of posterior division of mandibular nerve, V3): enters mandibular foramen, runs in mandibular canal, gives mental nerve at mental foramen
• Buccal nerve (V3): skin and mucosa over buccinator (NOT motor to buccinator - that's facial nerve)
• Lingual nerve (V3): lingual gingiva

Mental Foramen / Submental Foramen & Importance

• Located on the outer surface of the body of mandible
• Position: below the interval between premolar teeth (2nd premolar region), roughly halfway between alveolar and inferior borders
• In infants: near the inferior border (mandible not yet developed)
• In elderly (edentulous): near the alveolar border (resorption of alveolar bone)
• Contents: mental nerve, mental artery, mental vein
• Importance:
  • Local anesthetic landmark for mental nerve block
  • Surgical landmark in chin/implant procedures
  • Important for dental extractions and osteotomies
  • On X-ray, can mimic periapical pathology

TM Joint

Ossification

• Mandible ossifies in membrane (intramembranous) from a single center in the fibrous sheath of Meckel's cartilage, at the bifurcation of the inferior alveolar nerve into mental and incisive branches (~6th week of IUL)
• The condyle, coronoid process, and symphysis have secondary cartilaginous (endochondral) additions
• Symphysis fuses by end of 1st year of life

Meckel's Cartilage (Before Ossification)

• Cartilage of the 1st pharyngeal arch (mandibular arch)
• Runs from the otic capsule to the midline
• The mandible does NOT replace Meckel's cartilage - it ossifies alongside it
• Fate of Meckel's cartilage:
  • Middle portion: disappears (absorbed)
  • Posterior end: malleus and incus (middle ear ossicles)
  • Ligamentous remnant: anterior ligament of malleus and sphenomandibular ligament
  • The perichondrium near the ear → anterior malleolar ligament

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2. TONGUE

Parts

• Anterior 2/3 (oral/presulcal part): lies in the oral cavity; separated from posterior 1/3 by the sulcus terminalis (V-shaped groove)
• Posterior 1/3 (pharyngeal/postsulcal part): lies in the oropharynx
• Apex (tip): touches incisor teeth
• Dorsum: superior surface
• Inferior surface: has frenulum in the midline
• Foramen cecum: apex of the sulcus terminalis; remnant of thyroglossal duct

Extrinsic Muscles + Nerve Supply

Intrinsic Muscles + Nerve Supply

• Superior longitudinal - shortens, curls tip up
• Inferior longitudinal - shortens, curls tip down
• Transverse - narrows and elongates tongue
• Vertical - flattens and widens tongue

General Sensory Supply

• Anterior 2/3: Lingual nerve (branch of V3 - mandibular nerve)
• Posterior 1/3: Glossopharyngeal nerve (CN IX)
• Area around epiglottis (vallecula, posterior surface): Internal laryngeal nerve (branch of vagus, CN X)

Taste Supply

• Anterior 2/3: Chorda tympani (branch of facial nerve, CN VII) - carried in the lingual nerve
• Posterior 1/3: Glossopharyngeal nerve (CN IX)
• Epiglottic region: Vagus nerve (CN X) via internal laryngeal nerve

Blood Supply

• Lingual artery (branch of external carotid artery) - main supply
  • Dorsal lingual branches (posterior tongue)
  • Deep lingual artery (anterior tongue apex)
  • Sublingual artery (floor of mouth and anterior tongue)
• Venous drainage: lingual veins → internal jugular vein
• Note: The two lingual arteries do NOT anastomose across the midline in the posterior tongue (making midline incision relatively bloodless)

Lingual Nerve

• Branch of the posterior division of mandibular nerve (V3), itself a branch of the trigeminal nerve (CN V)
• Joined by the chorda tympani (from facial nerve) in the infratemporal fossa
• Carries: touch/pain/temperature (from V3) + taste and preganglionic parasympathetic fibers (from chorda tympani)
• Passes around the submandibular duct (Wharton's duct) - hooks under it ("twice around the duct")

Papillae (Types, Position, Function)

Taste Bud Structure

• Flask-shaped structures in the epithelium
• Three cell types: taste cells (neuroepithelial), sustentacular (supporting) cells, basal cells
• Each taste bud has a taste pore opening to the surface
• Microvilli (taste hairs) project through the pore
• Nerve fibers synapse at the base of taste cells
• ~50-100 taste cells per bud; ~10,000 taste buds total in humans

Anterior 2/3 of Tongue - Summary

• General sensation: Lingual nerve (V3)
• Taste: Chorda tympani (VII) via lingual nerve
• Motor: Hypoglossal nerve (XII) - all intrinsic + extrinsic (except palatoglossus)
• Papillae: Filiform, fungiform, and some foliate

Hypoglossal Nerve Injury - Deviation

• On protrusion, the tongue deviates toward the side of the lesion
• Reason: Genioglossus is the main protruder; when one side is paralyzed, the intact side pushes the tongue toward the paralyzed (injured) side
• Lower motor neuron lesion: ipsilateral deviation + wasting/fasciculation
• Upper motor neuron lesion: contralateral deviation (tongue deviates away from lesion side)

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3. LARYNX

Parts / Skeleton

• Unpaired: Thyroid, Cricoid, Epiglottis
• Paired: Arytenoid, Corniculate (of Santorini), Cuneiform (of Wrisberg)
• Thyroid cartilage: largest; two laminae meeting at ~90° (male) or ~120° (female) - explains prominent Adam's apple in males
• Cricoid cartilage: only complete ring; signet-ring shaped
• Epiglottis: leaf-shaped elastic fibrocartilage

Interior of Larynx

1. Vestibule (supraglottis): from inlet to vestibular folds
2. Vestibular folds (false cords): upper pair of folds; no vocalization function
3. Ventricle (sinus): space between vestibular and vocal folds; appendix extends superolaterally
4. Vocal folds (true cords): contain the vocal ligament; rima glottidis is the space between them
5. Infraglottis (subglottis): below vocal folds to lower border of cricoid

Epithelium

• Vestibule + posterior epiglottis + vocal folds (covering): Stratified squamous epithelium (subjected to wear)
• Rest of larynx (subglottis, tracheal surface of epiglottis): Pseudostratified ciliated columnar epithelium (respiratory epithelium)
• Watershed line: The vocal folds represent the junction between these two epithelial types

Nerve Supply

• Internal laryngeal nerve (sensory + autonomic): mucosa of larynx ABOVE vocal folds (supraglottis); enters through thyrohyoid membrane
• Recurrent laryngeal nerve (motor + sensory): ALL intrinsic muscles of larynx EXCEPT cricothyroid; sensory below vocal folds
• External laryngeal nerve: motor to cricothyroid muscle only; travels with superior thyroid artery

Watershed Line

• Above (supraglottis): lymphatics drain to upper deep cervical nodes (along internal jugular vein)
• Below (subglottis/infraglottis): lymphatics drain to lower deep cervical nodes and pretracheal nodes
• Clinical significance: spread of laryngeal carcinoma, and epithelial types differ above/below

Recurrent Laryngeal Nerve

• Right RLN: loops under the right subclavian artery in the root of the neck, then ascends in the tracheoesophageal groove to enter the larynx behind the cricothyroid joint
• Left RLN: loops under the arch of aorta (specifically around the ligamentum arteriosum), ascends in the tracheoesophageal groove - has a longer course through the thorax
• Both enter the larynx deep to the lower border of the inferior pharyngeal constrictor

• Most vulnerable at the point where it crosses the inferior thyroid artery (in the same plane or close)
• Also at risk near the ligament of Berry (posterior suspensory ligament of thyroid)
• Right RLN is more vulnerable as it may be non-recurrent in ~1% of people (loops directly to larynx from vagus)

• Unilateral RLN injury: hoarseness (rough, breathy voice); voice may compensate over time as opposite vocal cord compensates
• Bilateral RLN injury: aphonia (loss of voice) + respiratory distress/stridor (adductor paralysis → cords in paramedian position); may require tracheostomy
• Unilateral external laryngeal nerve injury: voice fatigues easily; slight loss of high-pitched tones (cricothyroid affected - tensor of vocal cords)

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4. PHARYNX

Parts

1. Nasopharynx: behind nasal cavities; above soft palate
2. Oropharynx: behind oral cavity; between soft palate and epiglottis
3. Laryngopharynx (hypopharynx): behind larynx; from epiglottis to lower border of cricoid (C6)

Extension

• Extends from the base of skull (pharyngeal tubercle on basiocciput) to the level of the lower border of cricoid cartilage (C6), where it becomes the esophagus
• Anteroposterior extent: approximately 12-14 cm

Muscles (Constrictors)

• Superior pharyngeal constrictor: 4 origins - pterygomandibular raphe, pterygoid hamulus, mandible, tongue
• Middle pharyngeal constrictor: hyoid bone (greater and lesser horns), stylohyoid ligament
• Inferior pharyngeal constrictor: thyroid and cricoid cartilages; lower part = cricopharyngeus (acts as upper esophageal sphincter)

• Stylopharyngeus (CN IX - glossopharyngeal)
• Palatopharyngeus (vagus via pharyngeal plexus)
• Salpingopharyngeus (vagus via pharyngeal plexus)

Nerve Supply

• Motor: Pharyngeal plexus (vagus CN X + glossopharyngeal CN IX + sympathetics from superior cervical ganglion) - all muscles EXCEPT stylopharyngeus (CN IX alone)
• Sensory:
  • Nasopharynx: maxillary nerve (V2)
  • Oropharynx: glossopharyngeal nerve (CN IX)
  • Laryngopharynx: vagus (CN X) via internal laryngeal nerve

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5. TONSIL

Histology (Microscopic Features)

• Covered by stratified squamous epithelium (non-keratinized)
• Epithelium dips into the substance as crypts (10-20 tonsillar crypts)
• Below epithelium: lymphoid follicles with germinal centers (B-lymphocytes)
• Between follicles: interfollicular lymphoid tissue (T-lymphocytes)
• No afferent lymphatics (tonsil is part of the primary immune barrier - antigen arrives via surface, not lymphatics)
• Has efferent lymphatics
• Connective tissue capsule on deep surface

Arterial Supply (Palatine Tonsil)

• Main supply: Tonsillar branch of facial artery (branch of external carotid)
• Other contributors:
  • Ascending palatine artery (facial artery)
  • Dorsal lingual artery (lingual artery)
  • Ascending pharyngeal artery (external carotid)
  • Descending palatine artery (maxillary artery) - to upper pole
• Para-tonsillar vein (on deep surface) - surgical hazard in tonsillectomy

Waldeyer's Ring

• Nasopharyngeal tonsil (adenoids): posterior wall of nasopharynx
• Tubal tonsils (2): around openings of Eustachian tubes
• Palatine tonsils (2): in tonsillar fossa between palatoglossal and palatopharyngeal arches
• Lingual tonsil: posterior 1/3 of tongue
• All connected by lymphoid tissue in the lateral pharyngeal bands

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6. THYROID GLAND

Type

• Endocrine gland (ductless)
• Bilobed (right and left lobes connected by isthmus); pyramidal lobe may be present (50% - remnant of thyroglossal duct)
• Enclosed in pretracheal fascia (which attaches it to larynx/trachea → gland moves with swallowing)

Histology

• Follicles: spherical units; the functional unit
• Follicular cells (thyrocytes): cuboidal/columnar; line follicles; produce T3 and T4
  • Height reflects activity: columnar = active; flat = inactive
  • Secrete thyroglobulin into the lumen
• Colloid: homogeneous eosinophilic material filling follicle lumen; composed mainly of thyroglobulin
• Parafollicular cells (C cells): located between follicles (or at periphery of follicle wall); larger, pale cells
  • Produce calcitonin (lowers blood calcium)
  • Derived from neural crest (not from thyroid diverticulum; from ultimobranchial body / 4th pharyngeal pouch)
• Stroma: thin connective tissue with rich capillary network

Draw Histology

• Round follicles of varying sizes
• Single layer of cuboidal follicular cells lining each follicle
• Central pink colloid with "scalloping" at periphery (resorption lacunae = active gland)
• C cells between follicles (larger, pale, no colloid contact)
• Thin fibrovascular connective tissue septa

Blood Supply

• Arterial:
  • Superior thyroid artery (1st branch of external carotid) → upper pole; accompanied by external laryngeal nerve
  • Inferior thyroid artery (from thyrocervical trunk of subclavian artery) → lower and posterior surface; crosses behind/near the RLN
  • Thyroidea ima artery (unpaired, inconstant ~3%): from brachiocephalic trunk or aortic arch → isthmus; important in tracheostomy
• Venous drainage:
  • Superior thyroid vein → internal jugular vein
  • Middle thyroid vein → internal jugular vein
  • Inferior thyroid veins (paired) → left brachiocephalic vein (cross in front of trachea = surgical hazard in tracheostomy)

Development

• Thyroid is the first endocrine gland to develop (at ~24 days)
• Develops from median thyroid diverticulum from the floor of the pharynx (between 1st and 2nd arch - at the site of the foramen cecum of the tongue)
• Thyroglossal duct: the track the gland descends along; normally obliterates by 7th week
• Gland descends in front of the hyoid and laryngeal cartilages to reach its final position by 7th week
• Remnant: pyramidal lobe (ascending from isthmus) + thyroglossal cysts (anywhere along the duct's path)
• Parafollicular cells derived from neural crest → ultimobranchial body → 4th pharyngeal pouch

Thyroidectomy Nerve Injury

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7. PITUITARY GLAND

Hypophyseal Fossa

• Located in the sella turcica of the sphenoid bone
• Bounded: anteriorly by tuberculum sellae; posteriorly by dorsum sellae; laterally by cavernous sinuses
• Roof: diaphragma sellae (dural fold with a central aperture for the pituitary stalk)

Parts

• Adenohypophysis (anterior pituitary, ~75%):
  • Pars distalis (anterior lobe - main bulk)
  • Pars tuberalis (wraps around pituitary stalk)
  • Pars intermedia (rudimentary in humans; between pars distalis and neurohypophysis)
• Neurohypophysis (posterior pituitary, ~25%):
  • Pars nervosa (posterior lobe)
  • Infundibular stalk (pituitary stalk)
  • Median eminence (part of hypothalamus)

Histology

• Acidophils (~40%): stain with acid dyes (eosin); two types:
  • Somatotrophs: Growth Hormone (GH)
  • Mammotrophs (lactotrophs): Prolactin
• Basophils (~10%): stain with basic dyes (PAS positive); three types:
  • Thyrotrophs: TSH
  • Gonadotrophs: LH and FSH
  • Corticotrophs: ACTH, MSH, endorphins (from POMC)

• Do not stain readily (depleted or resting cells)
• May be degranulated chromophils or stem cells
• Some are folliculostellate cells (supporting function)

Hormones of Neurohypophysis

• ADH (Antidiuretic Hormone / Vasopressin): mainly from supraoptic nuclei; increases water reabsorption in collecting ducts
• Oxytocin: mainly from paraventricular nuclei; uterine contractions and milk ejection

Control of Adenohypophysis & Neurohypophysis

• Adenohypophysis: controlled by hypothalamic releasing and inhibiting hormones delivered via the hypothalamo-hypophyseal portal system (blood-borne control)
• Neurohypophysis: controlled by direct neural connections from hypothalamus (supraoptico-hypophyseal and tuberohypophyseal tracts - axons travel down the stalk)

Hypothalamo-Hypophyseal Portal System

• A portal system is one where blood passes through two capillary beds before returning to systemic circulation
• Formation:
  1. Superior hypophyseal arteries (from internal carotid artery) form primary capillary plexus in the median eminence of hypothalamus
  2. Hypothalamic neurons secrete releasing/inhibiting hormones into these capillaries
  3. Blood drains into portal veins descending the pituitary stalk
  4. Portal veins form a secondary capillary plexus in the pars distalis (anterior pituitary)
  5. Releasing hormones act on pituitary cells here
• Significance: allows precise, direct control of anterior pituitary by tiny amounts of hypothalamic hormones without entering systemic circulation first

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8. EAR

Parts

1. External ear: Auricle (pinna) + External auditory meatus (canal) + Lateral surface of tympanic membrane
2. Middle ear (tympanic cavity): Medial surface of tympanic membrane + ossicles + Eustachian tube
3. Inner ear: Bony labyrinth (cochlea, semicircular canals, vestibule) + Membranous labyrinth within it

Functions

• Hearing (cochlea)
• Balance/Equilibrium: Static (utricle, saccule - linear acceleration/gravity) + Dynamic (semicircular canals - rotational acceleration)

External Ear

• Auricle: elastic fibrocartilage covered by skin; parts: helix, antihelix, tragus, antitragus, lobule (lobule has no cartilage - only fat and fibrous tissue)
• External auditory meatus: ~2.5 cm; outer 1/3 cartilaginous, inner 2/3 bony (temporal bone)
• Sensory supply: Great auricular nerve (C2,3), Auriculotemporal nerve (V3), Auricular branch of vagus (Arnold's nerve - irritation causes cough reflex), Facial nerve (small area)

Internal Ear

• Bony labyrinth: cavities in petrous temporal bone; contains perilymph
  • Cochlea (2.5 turns), Vestibule (contains oval and round windows), 3 Semicircular canals
• Membranous labyrinth: within bony labyrinth; contains endolymph
  • Cochlear duct (scala media), Utricle and saccule (in vestibule), 3 semicircular ducts
• Organ of Corti: in cochlear duct; rests on basilar membrane; contains hair cells for transduction

Tympanic Membrane (Parts & Function)

• Parts:
  • Pars tensa: large, taut lower portion; three layers (outer squamous, middle fibrous, inner mucosa)
  • Pars flaccida (Shrapnell's membrane): small, lax upper portion above malleolar folds; only two layers (no middle fibrous layer)
  • Cone of light: reflected light reflex at anteroinferior quadrant
  • Handle of malleus: attached to medial surface
• Function: Transmits sound vibrations from air to ossicular chain

Auditory Pathway

1. Sound waves → Tympanic membrane → Ossicular chain (malleus → incus → stapes) → Oval window → Cochlear perilymph → Basilar membrane vibration
2. Hair cells in Organ of Corti → CN VIII (cochlear division) → Cochlear nuclei (medulla)
3. → Trapezoid body → Superior olivary nuclei → Lateral lemniscus → Inferior colliculus (midbrain)
4. → Medial geniculate body (thalamus) → Auditory cortex (Heschl's gyri, superior temporal gyrus)
5. Bilateral representation above cochlear nuclei (why unilateral cortical lesion doesn't cause total deafness)

Vestibulocochlear Nerve

• CN VIII (8th cranial nerve)
• Type: Special sensory (SSA - Special Somatic Afferent)
• Two components:
  • Cochlear nerve: hearing
  • Vestibular nerve: balance
• Travels with CN VII in the internal auditory meatus (IAM)

Elastic Cartilage in Ear

• Auricle/pinna
• External auditory meatus (cartilaginous part)
• Eustachian tube (cartilaginous part)

Other Sites of Elastic Cartilage

• Epiglottis
• Corniculate cartilages (of Santorini)
• Cuneiform cartilages (of Wrisberg)
• Tip of nose (alar cartilages)

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9. TEMPORAL BONE

Anatomical Position

Parts

1. Squamous part: thin, flat, upper portion; forms part of temporal fossa
2. Petrous part: pyramid-shaped; points anteromedially toward sella turcica
3. Mastoid part: posterior; contains mastoid process
4. Tympanic part: surrounds the external auditory meatus (except roof = squamous)
5. Styloid process: projects inferiorly from inferior surface

Features

• Zygomatic process (articulates with zygomatic bone to form zygomatic arch)
• Mandibular fossa (for TMJ)
• Articular tubercle
• External acoustic meatus
• Mastoid process
• Stylomastoid foramen (between mastoid and styloid)
• Petrotympanic fissure (for chorda tympani exit)

Petrous Part

• Houses the inner ear (bony labyrinth)
• Superior surface: arcuate eminence (marks superior semicircular canal); tegmen tympani (roof of middle ear)
• Posterior surface: internal acoustic meatus (CN VII and VIII); subarcuate fossa; vestibular aqueduct opening
• Anterior surface: trigeminal impression; greater and lesser petrosal nerve grooves; opening for canal for tensor tympani
• Apex: foramen lacerum (covered by fibrocartilage in life); carotid canal opens

Muscle Attachments

• Sternocleidomastoid: mastoid process (lateral surface)
• Splenius capitis: mastoid process
• Longissimus capitis: mastoid process
• Posterior belly of digastric: mastoid notch (medial to mastoid process)
• Occipitalis: supreme nuchal line area

Mastoid Process Formation

• Present at birth as a flat surface
• Develops after birth due to pull of sternocleidomastoid muscle
• Well formed by 2 years of age
• Contains mastoid air cells (communicates with middle ear via aditus ad antrum)

Petrous Foramina & Contents

Sutures Formed

• Squamosal suture: with parietal bone
• Parietomastoid suture: mastoid part with parietal bone
• Occipitomastoid suture: mastoid part with occipital bone
• Petrosquamosal suture: between petrous and squamous parts (internal)
• Sphenosquamosal suture: squamous with greater wing of sphenoid
• Petro-occipital fissure: petrous part with basiocciput

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10. SPHENOID BONE

Anatomical Position

Parts

1. Body: central; contains sphenoidal sinuses; superior surface = sella turcica
2. Lesser wings (paired): project anterolaterally from superoanterior body
3. Greater wings (paired): project laterally and superiorly from sides of body
4. Pterygoid processes (paired): project inferiorly from junction of body and greater wings; each has medial and lateral pterygoid plates

Surfaces of Body

• Superior: sella turcica (hypophyseal fossa, anterior and posterior clinoid processes, tuberculum sellae, dorsum sellae), optic chiasm groove, limbus sphenoidale
• Posterior: fused with basiocciput (basilar part) to form clivus
• Anterior: rostrum, openings of sphenoidal sinuses, cribriform-like area
• Lateral: carotid sulcus

Carotid Sulcus Contents

• Internal carotid artery (siphon/cavernous part)
• Surrounded by the cavernous sinus

Greater Wing

• Three surfaces: cerebral (middle cranial fossa floor), temporal (temporal fossa), orbital (lateral wall of orbit)
• Foramina in greater wing:
  • Foramen rotundum: maxillary nerve (V2)
  • Foramen ovale: mandibular nerve (V3), accessory meningeal artery, lesser petrosal nerve (sometimes)
  • Foramen spinosum: middle meningeal artery and vein, meningeal branch of mandibular nerve
  • Foramen of Vesalius (emissary sphenoidal foramen, inconstant): small emissary vein

Lesser Wing

• Forms posterior boundary of anterior cranial fossa
• Anterior clinoid processes are the posterior ends of lesser wings
• Optic canal (between lesser wing and body): optic nerve (CN II) + ophthalmic artery

All Foramina & Contents

Posterior Articulation

• With the occipital bone (basiocciput) via sphenooccipital synchondrosis
• Type of joint: Cartilaginous joint (primary cartilaginous/synchondrosis) → fuses at ~18-25 years of age (used as a skeletal age marker)

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11. OCCIPITAL BONE

Parts

1. Basilar part (basiocciput): anterior; fuses with sphenoid at spheno-occipital synchondrosis; forms part of clivus
2. Condylar parts (lateral/exoccipital): paired; bear the occipital condyles (articulate with atlas C1)
3. Squamous part: posterior and largest; forms the posterior cranial fossa and back of skull

Ossification

• Squamous part above highest nuchal line: intramembranous (interparietal bone)
• Rest: endochondral (from cartilage)
• Squamous part below highest nuchal line (supraoccipital): endochondral
• Basiocciput: endochondral
• Exoccipital (condylar parts): endochondral
• Ossification centers: Multiple; fuse during childhood; basiocciput fuses with sphenoid at ~18-25 years

Foramen Magnum Contents

• Medulla oblongata (junction of medulla and spinal cord at upper border of C1)
• Vertebral arteries (bilateral)
• Anterior and posterior spinal arteries
• Spinal accessory nerve (CN XI) - ascending rootlets
• Meninges (dural sheath extending into spinal canal)
• Alar ligaments and apical ligament of dens (in the foramen)

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12. FRONTAL BONE

Parts

1. Squamous part: vertical frontal plate; forms forehead and part of anterior cranial fossa floor
2. Orbital parts (horizontal plates): form the roof of the orbits (floor of anterior cranial fossa)
3. Nasal part: articulates with nasal bones

Frontal Sinus

• Paired air-filled spaces within the squamous part (between outer and inner tables)
• Separated by a septum (rarely in the midline)
• Drains into the middle meatus via the frontonasal duct (infundibulum of ethmoid)
• Absent at birth; develops from ~2 years; adult size by puberty
• Highly variable in size; may be absent unilaterally

Functions of Paranasal Sinuses

• Lighten the skull (reduce weight)
• Resonance of voice (amplification)
• Warm and humidify inspired air (disputed)
• Mucus production (drainage to nasal cavity)
• Shock absorption (buffer the orbit and anterior cranial fossa)
• Increase surface area of nasal mucosa for olfaction (disputed)

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13. CERVICAL VERTEBRAE

Axis (C2)

• Dens (odontoid process): projects superiorly from the body; represents the "stolen" body of C1 (atlas); held against anterior arch of atlas by transverse ligament
• Atlas-axis joint: atlantoaxial joint - allows ~50% of all neck rotation
• Superior articular facets face superolaterally (for atlas lateral mass)
• No disc between C1 and C2

• Body: from 1 center (at birth)
• Dens: from 2 centers that fuse at ~7th month of fetal life; dens tip has a secondary center that appears ~3 years, fuses ~12 years
• Subdental synchondrosis: between dens and body; fuses by ~3-6 years (important radiologically)

• Rectus capitis posterior major: spinous process
• Obliquus capitis inferior: spinous process
• Semispinalis cervicis: spinous process
• Longus colli: body

7th Cervical Vertebra (C7)

• Vertebra prominens: has the longest and most prominent spinous process (palpable landmark, used to count vertebrae)
• Spinous process is not bifid (unlike typical C3-6)
• Has small or absent foramen transversarium (or contains accessory vertebral vein only; vertebral artery does NOT pass through C7 foramen transversarium normally)
• Larger body than typical cervical vertebrae
• Transitional features between cervical and thoracic vertebrae

Typical Cervical Vertebra (C3-C6)

• Small, wide body (broader transversely)
• Large triangular vertebral foramen
• Bifid spinous process
• Transverse processes with foramen transversarium (for vertebral artery, vein, and sympathetic plexus)
• Uncinate processes (uncus) on lateral body margins → uncovertebral joints (Luschka)
• Superior articular facets face superoposteriorly (45° to horizontal)
• Short pedicles

• Vertebral artery (C1-C6 only)
• Vertebral vein (C1-C7)
• Sympathetic nerve plexus (from inferior cervical ganglion)

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14. SKULL BASE & CRANIAL FOSSAE

Cranial Fossae

Contents of Cranial Fossae

Base of Skull - Key Foramina (summary)

Jugular Foramen

• Between petrous temporal bone and occipital bone
• Divided by fibrous or bony partition into:
  • Nervous part (anteromedial): CN IX (glossopharyngeal), CN X (vagus), CN XI (accessory), inferior petrosal sinus
  • Venous part (posterolateral): Sigmoid sinus continues as internal jugular vein; posterior meningeal artery

Cavernous Sinus

• Paired venous spaces on either side of sella turcica
• Contents (from lateral wall to medial):
  • CN III (oculomotor) - in lateral wall
  • CN IV (trochlear) - in lateral wall
  • CN V1 (ophthalmic) - in lateral wall
  • CN V2 (maxillary) - in lateral wall
  • CN VI (abducens) - runs free inside the sinus (most medial - first affected by raised ICP)
  • Internal carotid artery (siphon) + surrounding sympathetic plexus - runs through the sinus
• Receives blood from superior/inferior ophthalmic veins, sphenoparietal sinus, superficial middle cerebral vein
• Drains via superior and inferior petrosal sinuses to sigmoid sinus / jugular vein

Superior Sagittal Sinus

• Runs in the upper border (convex border) of the falx cerebri
• From the crista galli anteriorly to the internal occipital protuberance posteriorly
• Drains cortical veins and arachnoid granulations
• Turns right (usually) → right transverse sinus at the confluens sinuum (torcular Herophili)

Inferior Sagittal Sinus

• Runs in the lower (free) border of the falx cerebri
• Smaller than superior sagittal sinus
• Joins the great cerebral vein (of Galen) to form the straight sinus at the junction of falx cerebri and tentorium cerebelli

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15. ORBIT

Identification

Formation (Walls)

Contents

• Eyeball + fat
• Extraocular muscles (7 including levator palpebrae superioris)
• CN II (optic nerve) + ophthalmic artery
• CN III, IV, VI (motor nerves to muscles)
• CN V1 (sensory: lacrimal, frontal, nasociliary branches)
• Ciliary ganglion (between optic nerve and lateral rectus)
• Lacrimal gland (superolateral)
• Superior ophthalmic vein

Extraocular Muscles

Lacrimal Apparatus

• Lacrimal gland: secretes tears; in superolateral orbit; innervated by CN VII (via greater petrosal nerve → pterygopalatine ganglion → zygomatic nerve → lacrimal nerve)

Tear Drainage Pathway

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16. HARD PALATE

Identification

Formation

• Greater palatine foramen: anterolateral (greater palatine nerve and artery emerge here)
• Lesser palatine foramina: posterior (lesser palatine nerves)
• Incisive foramen: midline anteriorly (nasopalatine nerve + ascending branches of greater palatine artery)
• Median palatine suture (midline)
• Transverse palatine suture: junction of the two bones

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17. MUSCLES

Muscles of Facial Expression

• Frontalis: raises eyebrows (temporal branch)
• Orbicularis oculi: closes eye; has orbital and palpebral parts (temporal + zygomatic branches)
• Orbicularis oris: closes lips (buccal + marginal mandibular)
• Buccinator: compresses cheek; keeps food between teeth (buccal branch) - note: buccinator is a muscle of facial expression, NOT mastication, though it assists chewing
• Zygomaticus major and minor: raise angle of mouth (zygomatic + buccal)
• Mentalis: raises and protrudes lower lip (marginal mandibular)
• Platysma: depresses mandible and lower lip; wrinkles neck skin (cervical branch)

Sternocleidomastoid (SCM)

• Origin:
  • Sternal head: anterior surface of manubrium sterni
  • Clavicular head: medial 1/3 of clavicle
• Insertion: Lateral surface of mastoid process + lateral half of superior nuchal line of occipital bone
• Nerve supply: Spinal accessory nerve (CN XI) (motor) + C2, C3 (proprioception/sensation)
• Actions:
  • Unilateral: tilts (laterally flexes) head to same side + rotates face to opposite side (sternomastoid torticollis)
  • Bilateral: flexes neck + extends head (at atlanto-occipital joint); elevates thorax in forced inspiration
• Clinical note: In torticollis, the sternocleidomastoid is shortened/fibrotic on the affected side → head tilts toward and face rotates away from the affected side

Extraocular Muscles - see Orbit section above

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18. NERVES

Vestibulocochlear Nerve (CN VIII)

• Special sensory (SSA)
• Cochlear division: hearing; cell bodies in spiral ganglion of cochlea
• Vestibular division: balance; cell bodies in vestibular (Scarpa's) ganglion
• Passes through internal acoustic meatus with CN VII

Lingual Nerve

• Branch of posterior division of mandibular nerve (V3)
• Enters infratemporal fossa medial to lateral pterygoid; joined by chorda tympani (CN VII branch)
• Crosses the floor of the mouth (hooks around submandibular duct)
• Supplies: general sensation to anterior 2/3 of tongue, floor of mouth, lingual gingiva; taste fibers (from chorda tympani) to anterior 2/3

Hypoglossal Nerve (CN XII)

• Purely motor nerve to all intrinsic + extrinsic tongue muscles (except palatoglossus)
• Exits through hypoglossal canal of occipital bone
• Loops around the occipital artery; passes between internal carotid artery and internal jugular vein; crosses external carotid artery; passes over hyoglossus to reach the tongue
• In the neck, carries C1 fibers (for ansa cervicalis): gives off branch to thyrohyoid and geniohyoid (C1) and forms ansa cervicalis (C1,2,3)

Recurrent Laryngeal Nerve - see Larynx section

Facial Nerve (CN VII)

• Mixed nerve: SVE (motor - facial expression), GVE (parasympathetic), SVA (taste anterior 2/3 tongue), GSA (skin of ear)
• Exits brainstem at cerebellopontine angle → internal acoustic meatus → facial canal (petrous temporal bone)
• Branches in petrous bone: greater petrosal nerve (parasympathetic to lacrimal gland, palate, nasal glands); nerve to stapedius; chorda tympani (taste + parasympathetic to submandibular and sublingual glands)
• Exits via stylomastoid foramen → parotid gland → 5 terminal branches (Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical)

Laryngeal Nerve Supply - see Larynx section

Tongue Nerve Supply Summary

• General sensation anterior 2/3: lingual nerve (V3)
• Taste anterior 2/3: chorda tympani (VII)
• Motor all intrinsic and extrinsic: hypoglossal (XII) (except palatoglossus = vagus X)
• General sensation posterior 1/3: glossopharyngeal (IX)
• Taste posterior 1/3: glossopharyngeal (IX)
• Epiglottic region (sensory + taste): internal laryngeal nerve (X)

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19. HISTOLOGY

Tonsil

• Non-keratinized stratified squamous epithelium
• Crypts (invaginations of epithelium)
• Lymphoid follicles with germinal centers (B cells)
• Interfollicular zones (T cells)
• Fibrous capsule on deep surface
• No afferent lymphatics

Thyroid

• Follicles lined by cuboidal follicular cells (thyrocytes)
• Central eosinophilic colloid (thyroglobulin)
• "Scalloping" of colloid at active borders (resorption lacunae)
• Parafollicular (C) cells - pale, between follicles
• Rich vascular stroma between follicles

Pituitary

• Cells arranged in cords/clusters around sinusoids
• Acidophils (~40%): eosinophilic cytoplasm (GH, prolactin)
• Basophils (~10%): basophilic/PAS+ (TSH, LH, FSH, ACTH)
• Chromophobes (~50%): pale, degranulated Neurohypophysis (pars nervosa):
• Axons + axon terminals (Herring bodies = storage granules)
• Pituicytes (supportive glial cells)
• Fenestrated capillaries
• No nerve cell bodies (just axon terminals from hypothalamic neurons)

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20. JOINTS

TM Joint

• Synovial joint (condyloid/modified hinge)
• Articular surfaces: head of mandibular condyle + articular tubercle/mandibular fossa of temporal bone
• Articular disc (fibrocartilaginous) divides into upper (gliding) and lower (hinge) compartments
• Capsule reinforced by:
  • Lateral (temporomandibular) ligament - main ligament
  • Sphenomandibular ligament (accessory)
  • Stylomandibular ligament (accessory)
• Movements: depression/elevation (lower compartment), protrusion/retraction (upper compartment), side-to-side

Fibrous Joints

• Serrate (interdigitating, e.g., sagittal suture)
• Squamous (overlapping, e.g., temporal-parietal)
• Plane (flat, e.g., palatine bones)
• Denticulate (tooth-like projections)

Fibrous Joints in Skull

• Coronal, sagittal, lambdoid, squamosal, and others
• In adulthood → obliterate (cranial sutures become synostoses after ~30 years)

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21. OSSIFICATION

Mandible

• Intramembranous ossification (primarily)
• Single ossification center per side at ~6 weeks IUL (bifurcation of inferior alveolar nerve)
• Secondary cartilaginous additions: condylar process (main growth center, endochondral), coronoid process, symphysis
• Symphysis menti fuses during 1st year of life

Occipital Bone

• Multiple centers; combination of membranous and endochondral
• Squamous above highest nuchal line (interparietal): membranous
• Rest: endochondral
• Fusion complete by early childhood; sphenooccipital synchondrosis fuses at ~18-25 years

Skull

• Neurocranium (braincase): intramembranous (vault bones) + endochondral (base of skull)
• Viscerocranium (facial bones): mostly intramembranous; some endochondral (synchondroses)

Fontanelles

• Bulging: raised intracranial pressure (meningitis, hydrocephalus)
• Sunken: dehydration
• Delayed closure: hypothyroidism, rickets, hydrocephalus, Down syndrome
• Premature closure: craniosynostosis

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22. CARTILAGE

Elastic Cartilage Distribution

• Ear: Auricle, external auditory meatus, auditory tube (partial), cartilaginous part of Eustachian tube
• Larynx: Epiglottis, corniculate cartilages (of Santorini), cuneiform cartilages (of Wrisberg)
• Nose: Alar cartilages (tip of nose)

Meckel's Cartilage

• Cartilage of the 1st branchial (pharyngeal) arch
• Extends from otic capsule to midline symphysis
• The mandible ossifies in the mesenchyme around Meckel's cartilage (not by replacing it)
• Fate (from medial to lateral):
  • Dorsal end: malleus (head and neck) and incus (body and short process) - middle ear ossicles
  • Intermediate: anterior malleolar ligament + sphenomandibular ligament (perichondrium persists)
  • Middle portion: resorbs (disappears)
  • Note: The Meckel's cartilage in the mandible disappears as the bone forms around it

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23. BLOOD SUPPLY

Tongue

• Lingual artery (branch of external carotid artery):
  • Dorsal lingual arteries
  • Deep lingual artery (profunda linguae)
  • Sublingual artery
• Venous: dorsal lingual vein + deep lingual vein → lingual vein → facial vein OR internal jugular vein

Tonsil

• Tonsillar branch of facial artery (main)
• Ascending palatine artery (facial artery)
• Dorsal lingual artery (lingual artery) - lower pole
• Ascending pharyngeal artery (external carotid)
• Descending palatine artery (maxillary artery) - upper pole

Thyroid Gland

• Superior thyroid artery (1st branch of external carotid artery) → upper pole
• Inferior thyroid artery (thyrocervical trunk from 1st part of subclavian artery) → lower pole
• Thyroidea ima (inconstant, ~3%) → isthmus
• Venous: Superior + middle thyroid veins → internal jugular vein; Inferior thyroid veins → left brachiocephalic vein

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24. IMPORTANT MODEL IDENTIFICATION TIPS

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1. Tongue deviates toward the side of hypoglossal nerve lesion (LMN)
2. RLN loops under subclavian (right) / aortic arch (left); injured near inferior thyroid artery in thyroidectomy
3. All intrinsic laryngeal muscles = RLN, EXCEPT cricothyroid = external laryngeal nerve
4. All tongue muscles = XII, EXCEPT palatoglossus = X
5. Anterior 2/3 tongue sensation = V3 (lingual nerve); taste = VII (chorda tympani)
6. Posterior 1/3 tongue sensation + taste = IX (glossopharyngeal)
7. Parafollicular (C) cells of thyroid → calcitonin → derived from neural crest (not thyroid diverticulum)
8. Adenohypophysis: Acidophils = GH, Prolactin; Basophils = TSH, LH, FSH, ACTH; Chromophobes = resting
9. Neurohypophysis: ADH + Oxytocin (made in hypothalamus, stored here)
10. Anterior fontanelle closes at 18 months; posterior fontanelle at 6-8 weeks
11. Meckel's cartilage → malleus + incus + sphenomandibular ligament; mandible forms around it (intramembranous)
12. Foramen magnum: medulla, vertebral arteries, anterior/posterior spinal arteries, spinal roots of CN XI
13. Cavernous sinus: CN III, IV, V1, V2 (in lateral wall); CN VI + ICA (free in sinus)
14. Mental foramen moves superiorly with age (as alveolar bone resorbs in edentulous patients)
15. Waldeyer's ring: nasopharyngeal tonsil + tubal tonsils (2) + palatine tonsils (2) + lingual tonsil