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Anatomy of the Ear

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1. External (Outer) Ear

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2. Middle Ear (Tympanic Cavity)

The ossicles act as a mechanical transformer, amplifying vibrations from air (low impedance) to fluid (high impedance) in the inner ear. (Bailey & Love, p. 771)

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3. Inner Ear (Labyrinth)

• Spiral, snail-shaped structure; ~2.5 turns
• Contains three fluid-filled ducts:
  • Scala vestibuli — filled with perilymph
  • Scala tympani — filled with perilymph
  • Scala media (cochlear duct) — filled with endolymph
• Organ of Corti — sits on the basilar membrane; contains inner and outer hair cells (mechanoreceptors)
• Tectorial membrane — overlies hair cells; deflects them during sound waves
• Auditory nerve (CN VIII) — carries signals to brainstem

• Semicircular canals (3 — anterior, posterior, lateral): detect rotational/angular movement
• Utricle and Saccule: detect linear acceleration and gravity (via otoliths)

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Sound Transmission Pathway

Sound wave
    ↓
Pinna → EAC → Tympanic Membrane
    ↓
Malleus → Incus → Stapes
    ↓
Oval Window → Perilymph (scala vestibuli)
    ↓
Basilar Membrane vibration → Hair cells (Organ of Corti)
    ↓
Endolymph wave → Round Window (pressure relief)
    ↓
Auditory nerve (CN VIII) → Brainstem → Auditory Cortex

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Simple Diagram to Draw

        OUTER EAR        MIDDLE EAR       INNER EAR
  ________________    _______________    ___________
 |                |  |               |  |           |
 |   PINNA        |  | Malleus       |  |  Cochlea  |
 |    \           |  |  \            |  |  (snail   |
 |     EAR        |~~|   Incus       |~~|   shape)  |
 |     CANAL      |  |    \          |  |           |
 |                |  |     Stapes ===|==| Oval Win  |
 |________________|  |  Eustachian   |  |___________|
         ↓            |  Tube ↓      |
      Eardrum         |  (throat)    |
    (tympanic         |______________|
     membrane)

1. Draw a large C-shape (pinna) on the left
2. Draw a short horizontal tube (EAC) going right
3. Draw a slightly angled oval at the end = tympanic membrane
4. Inside the middle ear box, sketch 3 tiny bones in an L/chain shape: hammer → anvil → stirrup
5. The stirrup touches a small oval on the right wall = oval window
6. To the right, draw a snail/spiral = cochlea
7. Add a tube going down from the middle ear = Eustachian tube
8. Label all parts

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"MIS" — Malleus, Incus, Stapes (in order from eardrum inward) "3 S's" — Sound → Stirrup → Scala (cochlea)

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Anatomy of the Ear

1. Surface Anatomy

Auricle (Pinna) Landmarks

Simple Drawing Guide — Surface Anatomy

         Helix (outer rim)
        /
       /    Triangular
      |      Fossa
      |  Antihelix
      | /
      |/  Scapha
     ( )  ← Concha (cymba above, cavum below)
      |\ 
      | Tragus   Antitragus
      |___|___|
        Lobule

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2. Regional Anatomy

A. External Ear

• Auricle: fibrocartilage skeleton (elastic cartilage) covered by skin; attached to skull by ligaments and muscles
• External Auditory Canal (EAC):
  • Length: ~2.5 cm
  • Outer 1/3: cartilaginous (soft), contains hair follicles + ceruminous (wax) glands
  • Inner 2/3: bony (tympanic part of temporal bone), thinner skin, no glands
  • Slightly S-shaped; straightened for otoscopy by pulling pinna up and back (adults) or down and back (children)
• Tympanic Membrane (Eardrum):
  • Boundary between external and middle ear
  • Diameter: ~9–10 mm; oriented obliquely (not perpendicular)
  • Pars tensa (lower 2/3): taut, pearly grey — main functional part (Harrison's, p. 1036)
  • Pars flaccida (upper 1/3): lax, above the short process of malleus — important site for cholesteatoma

B. Middle Ear (Tympanic Cavity)

• Air-filled cavity within the petrous part of temporal bone
• Walls (6 relations):

• Ossicles: Malleus → Incus → Stapes (suspended by ligaments)
• Muscles: Tensor tympani (CN V3), Stapedius (CN VII — facial nerve)
• Eustachian Tube: 35–40 mm long; connects to nasopharynx; normally closed, opens on swallowing/yawning
• Chorda tympani: branch of CN VII crossing the middle ear; carries taste from anterior 2/3 tongue

C. Inner Ear (Bony & Membranous Labyrinth)

• Utricle & Saccule (in vestibule): linear acceleration/gravity detection (otolith organs)
• Semicircular ducts (in canals): angular/rotational acceleration
• Cochlear duct (scala media): hearing

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3. Gross Anatomy

Cochlea (Cross-Section — Gross)

         ___________
        /           \
       | Scala       |   ← Perilymph
       | Vestibuli   |
        \___________/
        /           \
       | Scala       |   ← Endolymph  (cochlear duct)
       | Media       |
        \___________/
        /           \
       | Scala       |   ← Perilymph
       | Tympani     |
        \___________/

• Modiolus: central bony axis of cochlea; carries the spiral ganglion and cochlear nerve fibers
• Helicotrema: apex of cochlea where scala vestibuli and scala tympani communicate
• Oval window: stapes footplate inserts here → scala vestibuli
• Round window: base of scala tympani; covered by secondary tympanic membrane; acts as pressure relief

Ossicles — Gross Features

Tympanic Membrane — Gross

• Umbo: central cone-shaped depression; tip of malleus handle
• Light reflex: cone of light seen inferoanteriorly on otoscopy (5 o'clock in right, 7 o'clock in left)
• Annulus: fibrocartilaginous ring anchoring TM to temporal bone

Internal Acoustic Meatus (IAM)

• Canal in petrous bone transmitting:
  • CN VIII (vestibulocochlear): cochlear + superior/inferior vestibular divisions
  • CN VII (facial nerve)
  • Labyrinthine artery (branch of AICA)

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4. Histology

A. Tympanic Membrane — 3 Layers

B. External Auditory Canal

• Outer 1/3: keratinizing stratified squamous epithelium + hair follicles + sebaceous glands + ceruminous glands (modified apocrine sweat glands producing cerumen/wax)
• Inner 2/3: thin stratified squamous epithelium directly over periosteum; no glands

C. Eustachian Tube

• Pseudostratified ciliated columnar epithelium (respiratory type) with goblet cells
• Cilia beat toward nasopharynx → mucus clearance from middle ear

D. Cochlea — Key Histological Layers

         ORGAN OF CORTI (on Basilar Membrane)
    ________________________________________
   |  Tectorial  |   ← Gelatinous membrane overlying hair cells
   |  Membrane   |
   |_____________|
   |  Outer Hair |  ← 3 rows; active amplification (electromotility)
   |  Cells (3)  |
   |_____________|
   |  Inner Hair |  ← 1 row; primary sensory transduction (~95% of afferent fibers)
   |  Cells (1)  |
   |_____________|
   |  Basilar    |  ← Stiff at base (high freq), flexible at apex (low freq)
   |  Membrane   |
   |_____________|

E. Vestibular Sensory Epithelium

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Summary Table

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The Ear — Complete Multi-Disciplinary Overview

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1. Physiology

A. Physiology of Hearing (Mechanotransduction)

• Without the ossicular chain, 99.9% of sound energy would be reflected at the air-fluid interface
• The eardrum + ossicles boost sound energy ~200-fold before it reaches the inner ear (Harrison's, p. 1019)
• Achieved by: Area ratio (TM vs. oval window = 17:1) + Lever action of ossicles

Base of cochlea → High frequency (20,000 Hz) → narrow, stiff
Apex of cochlea → Low frequency (20 Hz)      → wide, flexible

• Loud sound → CN VIII → brainstem → CN VII (stapedius) + CN V3 (tensor tympani)
• Muscles stiffen ossicular chain → attenuates loud sounds → protects inner ear

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B. Physiology of Balance (Vestibular System)

• Head moves → vestibular signal → compensatory eye movement in opposite direction
• Keeps visual field stable during head movement

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2. Biochemistry

A. Endolymph vs. Perilymph Composition

B. Endocochlear Potential (EP)

• Stria vascularis generates a +80 mV resting potential in endolymph
• This is the driving force for K⁺ to rush into hair cells when stereocilia channels open
• Essential for mechanotransduction — loss of EP = sensorineural deafness

C. Hair Cell Mechanotransduction — Ion Channels

Stereocilia deflect toward tallest → tip links stretch
→ MET channels (MYO7A, TMHS, LHFPL5) open
→ K⁺ + Ca²⁺ influx → depolarization
→ Voltage-gated Ca²⁺ channels open at base
→ Vesicle release (glutamate) → CN VIII

D. Prestin (SLC26A5) — Outer Hair Cell Motor

• Prestin is a piezoelectric motor protein in OHC lateral wall
• Changes cell length in response to voltage changes (electromotility)
• Amplifies basilar membrane movement up to 1000×
• Loss of prestin → 40–60 dB hearing loss

E. Cerumen (Earwax) Biochemistry

• Produced by ceruminous (apocrine) glands in outer EAC
• Composition: long-chain fatty acids, alcohols, squalene, lysozyme, IgA
• Functions: antimicrobial, lubricating, waterproofing, acidic pH (6.1) → inhibits bacterial/fungal growth

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3. Pathology

A. Conductive Hearing Loss (CHL) — Outer/Middle Ear

B. Sensorineural Hearing Loss (SNHL) — Inner Ear/Nerve

C. Other Pathologies

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4. Microbiology

Acute Otitis Media (AOM)

Otitis Externa (Acute)

Malignant Otitis Externa

• Pseudomonas aeruginosa almost exclusively
• Osteomyelitis of skull base; can involve CN VII → facial palsy
• Risk: Diabetics, elderly, HIV+

Chronic Suppurative OM

• Polymicrobial: Pseudomonas aeruginosa + S. aureus (including MRSA) + anaerobes

Fungal OE (Otomycosis)

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5. Clinical Presentation

Hearing Loss

Ménière's Disease — Triad

"VHT": Vertigo (episodic, 20 min–24 hrs) + Hearing loss (fluctuating, low-frequency SNHL) + Tinnitus (low-pitched roaring) ± aural fullness

Acute Otitis Media

• Ear pain (otalgia), fever, irritability (children)
• Otoscopy: red, bulging, opaque TM; loss of light reflex
• May progress to: TM perforation (pain relief), mastoiditis, meningitis

Otitis Externa

• Intense itching → pain → discharge
• Tragal tenderness and pain on jaw movement (pathognomonic)
• Canal edematous, erythematous, debris-filled

Acoustic Neuroma

• Unilateral SNHL + tinnitus + imbalance
• Absent corneal reflex (CN V involvement)
• Diagnosed on MRI with gadolinium (IAM)

Otosclerosis

• Progressive conductive hearing loss in young adult
• Family history; worsens in pregnancy (estrogen accelerates bone remodeling)
• Otoscopy: Schwartze sign (flamingo pink blush through TM — active otospongiosis)
• Audiogram: Carhart's notch at 2000 Hz

Cholesteatoma

• Foul-smelling discharge + hearing loss
• Otoscopy: pearly white mass in pars flaccida/posterior-superior quadrant
• Complications: ossicular erosion, labyrinthine fistula, facial palsy, meningitis, brain abscess

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6. Medicine (Clinical Medicine)

Audiological Tests

Tympanogram Types

Complications of OM

• Mastoiditis (most common)
• Facial palsy (CN VII in Fallopian canal)
• Labyrinthitis → SNHL
• Petrositis (Gradenigo's syndrome: deep ear pain + CN VI palsy + retro-orbital pain)

• Meningitis, brain abscess, lateral sinus thrombosis, subdural empyema

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7. Pharmacology

A. Topical Ear Drops

B. Systemic Antibiotics for OM

C. Ototoxic Drugs (Critical!)

Mnemonic — Ototoxic drugs: "AGAIN" Aminoglycosides · General anesthetics (loop diuretics) · Antimalarials · Indomethacin-like (salicylates) · Neoplastic agents (cisplatin)

D. Ménière's Disease Treatment

E. Otosclerosis Treatment

• Sodium fluoride: slows active otospongiosis (inhibits osteoclast activity)
• Bisphosphonates: used investigationally
• Definitive: Stapedectomy / Stapedotomy — surgical removal/laser perforation of stapes

F. Vestibular Suppressants

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Summary Overview Table

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The Nose — Complete Multi-Disciplinary Overview

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1. Surface Anatomy

External Nose Landmarks

Simple Drawing — External Nose

        Nasion (top)
          |
     _____|_____
    |  Dorsum   |
    |           |
    |___ Tip __/
   /  Columella  \
  /               \
 Ala(L)  Naris  Ala(R)
          |
     Subnasale

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2. Regional Anatomy

A. Nasal Cavity

• Upper bony part: perpendicular plate of ethmoid
• Lower bony part: vomer
• Anterior cartilaginous: quadrilateral (septal) cartilage
• Common site for septal deviation (most common anatomical variation)

The ostiomeatal complex (OMC) — the area under the middle turbinate — is the key functional drainage site; obstruction here causes sinusitis.

• Anterior entry zone just inside nostril; contains vibrissae (nasal hairs) filtering large particles

• Narrowest part of the airway (~90° angle between septum and upper lateral cartilage)
• Most common site of nasal airflow resistance

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B. Paranasal Sinuses

Frontal sinus absent in up to 10% of normal individuals (Murray & Nadel, p. 1613)

• Force dissipation in facial trauma
• Vocal resonance
• Mucus production and immune surveillance
• Contribution to facial aesthetics

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C. Blood Supply — Key for Epistaxis

• Anteroinferior septum where all 5 vessels anastomose
• Site of 90% of anterior nosebleeds

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D. Nerve Supply

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3. Gross Anatomy

Nasal Skeleton

        BONY FRAMEWORK                 CARTILAGINOUS FRAMEWORK
   ___________________              ________________________
  | Nasal bones (2)   |            | Upper lateral          |
  | Frontal process   |            | cartilages (2)         |
  | of maxilla        |            | Lower lateral (alar)   |
  |___________________|            | cartilages (2)         |
                                   | Septal cartilage       |
                                   | Sesamoid cartilages    |
                                   |________________________|

• Nasion to rhinion: bony dorsum (nasal bones)
• Rhinion to tip: cartilaginous dorsum (upper lateral cartilages)
• Tip: defined by lower lateral (greater alar) cartilages — medial + lateral crura

Turbinate Gross Appearance

• Scroll-shaped bony projections covered by thick, vascular mucosa
• Erectile tissue (venous sinusoids) → nasal cycle: alternating congestion/decongestion every 2–6 hours
• Inferior turbinate: largest; most significant in nasal obstruction

Choanae

• Posterior opening of each nasal cavity into the nasopharynx
• Width ~1 cm in adults
• Choanal atresia: congenital bony/membranous obstruction → neonatal respiratory distress

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4. Histology

A. Nasal Mucosa — Two Zones

• Ciliated columnar cells (most abundant): ~200 cilia/cell; beat 1000×/min; mucociliary clearance
• Goblet cells: mucin-secreting; form upper gel layer of mucus blanket
• Basal cells: stem cells; regenerate epithelium
• Brush cells: chemosensory
• Club cells (formerly Clara): detoxification

B. Nasal Glands (Seromucinous)

• Seromucous glands: serous + mucous components; produce the sol layer (periciliary fluid) and gel layer (mucus blanket)
• Innervated by parasympathetic fibers (CN VII → pterygopalatine ganglion → VIP/ACh)
• Stimulation → watery secretion (rhinorrhea)

C. Paranasal Sinus Histology

• Lined by ciliated pseudostratified columnar epithelium (thinner than nasal mucosa)
• Fewer goblet cells and glands than nasal cavity
• Cilia beat toward ostium → mucociliary drainage into nasal cavity (Murray & Nadel, p. 1613)

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5. Physiology

A. Nasal Airflow & Conditioning

• Nose handles ~90% of inspired air at rest
• Functions: Filter, Warm, Humidify

B. Mucociliary Clearance (MCC)

• Two-layer mucus blanket:
  • Sol layer (periciliary, low viscosity): cilia beat freely within this
  • Gel layer (upper, viscous): traps particles and pathogens
• Ciliary beat: effective stroke (forward, moves gel layer) + recovery stroke (backward, within sol layer)
• Clearance rate: ~6 mm/min; mucus blanket replaced every 10–15 minutes
• Entire nasal mucus cleared in ~30 minutes to nasopharynx → swallowed

C. Nasal Cycle

• Alternating unilateral nasal congestion/decongestion (~2–7 hours cycle)
• Mediated by sympathetic tone controlling erectile venous sinusoids
• Total nasal resistance remains relatively constant (one side opens as other closes)

D. Olfaction (Smell)

Odorant molecule (volatile, hydrophobic)
    ↓
Dissolves in Bowman's gland secretion
    ↓
Binds olfactory receptor proteins (G-protein coupled)
    ↓
Adenylyl cyclase → ↑cAMP
    ↓
cAMP-gated Na⁺/Ca²⁺ channels open → depolarization
    ↓
Action potential → olfactory nerve (CN I) → cribriform plate
    ↓
Olfactory bulb → olfactory tract → piriform cortex, amygdala, hypothalamus
    (No thalamic relay — direct limbic access → explains emotion-smell link)

E. Sneezing Reflex

• Trigger: irritation of nasal mucosa → CN V afferents → brainstem sneeze center
• Response: deep inspiration → glottis closes → explosive expiration (up to 160 km/h)
• Clears nasal cavity of irritants

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6. Biochemistry

A. Nasal Mucus Composition

B. Olfactory Receptor Biochemistry

• ~400 functional olfactory receptor (OR) genes in humans (largest gene family; ~3% of genome)
• Each ORN expresses one type of OR (one-receptor-one-neuron rule)
• OR activation → Golf protein → adenylyl cyclase III → ↑cAMP → CNGA2 channels open → Na⁺/Ca²⁺ influx
• Ca²⁺ also activates Cl⁻ channels → amplification

C. Nitric Oxide (NO) in the Nose

• Paranasal sinuses (especially maxillary) produce high concentrations of NO
• Nasal NO: ~250 ppb (highest in body)
• Functions: vasodilation, ciliary beat stimulation, antimicrobial, bronchodilation in lower airways
• Reduced nasal NO = marker of primary ciliary dyskinesia (PCD)

D. Inflammatory Mediators in Allergic Rhinitis

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7. Pathology

A. Inflammatory Conditions

B. Structural Pathology

C. Destructive & Neoplastic

D. Rhinosinusitis — Diagnostic Criteria (Murray & Nadel, p. 1613)

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8. Microbiology

Acute Rhinosinusitis (Bacterial)

Chronic Rhinosinusitis

• Polymicrobial: Staphylococcus aureus (dominant, including MRSA), coagulase-negative staph, Pseudomonas, anaerobes
• S. aureus superantigen hypothesis: drives eosinophilic inflammation in CRS with polyps

Fungal Sinusitis

Rhinoscleroma

• Caused by Klebsiella rhinoscleromatis
• Chronic granulomatous infection; causes nasal sclerosis
• Mikulicz cells (foamy macrophages with Russell bodies) on histology

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9. Clinical Presentation

Symptom Framework — "PODS"

Purulent discharge · Obstruction · Dysosmia · Sinus pain/pressure/fullness

Key Presentations

Anterior Rhinoscopy (Clinical Exam)

• Inspect: septum deviation, turbinate hypertrophy, mucosa color/edema, polyps, discharge
• Allergic salute: horizontal nasal crease from repeated upward wiping
• Allergic shiners: infraorbital darkening from venous congestion

Nasal Endoscopy (Key Findings)

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10. Medicine (Clinical)

Investigations

Complications of Sinusitis

• Preseptal cellulitis → orbital cellulitis → subperiosteal abscess → orbital abscess → cavernous sinus thrombosis
• Chandler classification (I–V)

• Meningitis, epidural/subdural abscess, brain abscess, Pott's puffy tumour (frontal osteomyelitis with forehead swelling)

• Mucus-filled expansion of sinus (usually frontal); erodes bone; pushes orbit laterally

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11. Pharmacology

A. Intranasal Corticosteroids (INCS) — First-Line for AR & CRS

Mechanism: reduce Th2 cytokines (IL-4, IL-5, IL-13), inhibit mast cells, reduce eosinophils, decrease goblet cell hyperplasia

B. Antihistamines

C. Decongestants

D. Leukotriene Modifiers

E. Biologics (Severe CRS with Polyps)

F. Antibiotics for Rhinosinusitis

G. Antifungals

H. Immunotherapy

• Allergen immunotherapy (AIT): subcutaneous (SCIT) or sublingual (SLIT)
• Mechanism: shifts Th2 → Th1/Treg; increases blocking IgG4; induces tolerance
• Indication: allergic rhinitis not controlled by medications
• Only treatment that modifies disease course rather than just controlling symptoms

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Summary Table

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The Throat — Complete Multi-Disciplinary Overview

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1. Surface Anatomy

External Landmarks (Anterior Neck)

Simple Drawing Guide — Surface Anatomy

        Mandible
           |
       Hyoid bone  ← C3 (palpable, moves with swallowing)
           |
    Thyroid notch
    [THYROID CART.] ← C4-5 (Adam's apple)
           |
    Cricothyroid membrane ← Emergency airway here
    [CRICOID CART.] ← C6
           |
    Tracheal rings

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2. Regional Anatomy

A. The Pharynx

i. Nasopharynx (Epipharynx)

• Boundaries: Skull base (sphenoid/occipital) → soft palate
• Key structures:
  • Eustachian tube orifice (lateral wall, at level of inferior turbinate) → middle ear communication
  • Fossa of Rosenmüller (pharyngeal recess) — commonest site for nasopharyngeal carcinoma (NPC)
  • Adenoids (pharyngeal tonsil) — posterior wall; prominent in children; regresses by puberty
  • Pharyngobasilar fascia — strong fibrous roof

ii. Oropharynx

• Boundaries: Soft palate → tip of epiglottis/hyoid bone
• Key structures:

Lymphatics from palatine tonsils drain to jugulodigastric nodes (Level II); spread also to Levels III, IV, V and retropharyngeal nodes (nodes of Rouvière) (Cummings, p. 1809)

iii. Hypopharynx (Laryngopharynx)

• Boundaries: Tip of epiglottis → lower border of cricoid (C6)
• Key structures:

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B. The Larynx

• Cricothyroid joint: thyroid tilts forward → lengthens/tenses vocal cords → higher pitch
• Cricoarytenoid joint: rotates arytenoids → abducts/adducts vocal cords

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C. Nerve Supply

RLN vulnerability: Left RLN loops under aortic arch (longer course) → more at risk in thoracic/mediastinal pathology. Right RLN loops under subclavian artery.

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D. Blood Supply

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3. Gross Anatomy

Tonsillar Ring (Waldeyer's Ring)

        Adenoids (pharyngeal tonsil) ← posterior nasopharynx
               /              \
    Tubal tonsils          Tubal tonsils  ← around Eustachian tube openings
         |                        |
    Palatine tonsils ← bilateral; between pillars
               \              /
         Lingual tonsil ← base of tongue

Palatine Tonsil — Gross Features

• Oval mass in tonsillar fossa
• Crypts: branching recesses in surface epithelium (~10–20); trap food debris → tonsilloliths
• Capsule: fibrous; separates tonsil from superior constrictor muscle
• No lymphatics in germinal centres (unlike other lymph nodes); subepithelial lymphatics drain to jugulodigastric nodes (Cummings, p. 1809)

Epiglottis — Gross

• Leaf-shaped elastic cartilage; attached to hyoid by hyoepiglottic ligament and to thyroid cartilage by thyroepiglottic ligament
• Vallecula: space between lingual surface of epiglottis and base of tongue — site of foreign body impaction
• Petiole: inferior narrow stalk; attaches at thyroid cartilage

Vocal Cords — Gross

• True vocal cords (vocal folds): pearly white; vibratory edge = free margin
• False vocal cords (vestibular folds): pink; no vibratory function; protective
• Glottis: opening between true cords — anterior commissure (anterior) + posterior commissure (arytenoids, posterior)
• Rima glottidis: ~60% membranous, ~40% cartilaginous (between arytenoids)

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4. Histology

A. Pharyngeal Epithelium — Varies by Region

B. Tonsil Histology

C. Laryngeal Epithelium — Varies by Zone

D. Vocal Cord — Microanatomy (Reinke's Space)

    ____________________________________
   |  Stratified squamous epithelium    |  ← Surface
   |____________________________________|
   |  Superficial lamina propria        |  ← Reinke's space (loose connective tissue)
   |   (loose fibrous tissue)           |    Oedema here = Reinke's oedema
   |____________________________________|
   |  Intermediate + deep lamina propria|  ← Vocal ligament (collagen + elastin)
   |____________________________________|
   |  Vocalis muscle (thyroarytenoid)   |  ← Body of vocal fold
   |____________________________________|

• Mucosa-cover model: superficial layer (mucosa/cover) vibrates over deeper body (vocalis muscle)
• Reinke's space: potential space in superficial LP; fluid accumulates here in Reinke's oedema (smoker's polypoid corditis)

E. Epiglottis Histology

• Elastic cartilage core (not hyaline — does NOT calcify)
• Laryngeal surface (posterior, airway-facing): stratified squamous epithelium
• Lingual surface (anterior, tongue-facing): respiratory (ciliated columnar) epithelium
• Mucous glands in lamina propria

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5. Physiology

A. Swallowing (Deglutition) — 3 Phases

• Tongue shapes food into bolus, pushes it posteriorly against palate
• Soft palate elevates → seals nasopharynx (levator veli palatini, CN X)

Bolus touches fauces/posterior pharyngeal wall
    ↓
Swallowing centre (medulla — nucleus tractus solitarius)
    ↓
Sequence of coordinated events:
  1. Soft palate rises → closes nasopharynx
  2. Hyoid + larynx elevate anterosuperiorly
  3. Epiglottis folds back → covers laryngeal inlet
  4. True + false vocal cords adduct → close glottis
  5. Pharyngeal constrictors contract (superior → inferior)
  6. Upper oesophageal sphincter (cricopharyngeus) relaxes
    ↓
Bolus passes into oesophagus

• Entire pharyngeal phase in <1 second
• Respiration inhibited during swallowing (apnoea)

• Peristaltic waves carry bolus to stomach
• Lower oesophageal sphincter relaxes

B. Voice Production (Phonation)

Subglottic air pressure builds up
    ↓
Overcomes adducted vocal cord tension
    ↓
Cords blown apart (Bernoulli effect sucks them back)
    ↓
Rapid opening/closing cycles = mucosal wave
    ↓
Air pulsed into supraglottic resonating chambers
    ↓
Sound modified by: pharynx, palate, tongue, lips, teeth

C. Laryngeal Protective Functions

D. Adenotonsillar Physiology

• Waldeyer's ring = first line immunological barrier to inhaled/ingested antigens
• Tonsils process antigens → generate secretory IgA + systemic antibody response
• Peak immunological activity: ages 4–10 years
• Function diminishes after puberty (atrophy)

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6. Biochemistry

A. Saliva & Pharyngeal Mucus

B. Vocal Cord Biochemistry

• Hyaluronic acid: abundant in Reinke's space → maintains viscoelasticity and pliability of vocal fold cover
• Fibronectin, collagen I/III: vocal ligament; provide tensile strength
• Elastin: allows recoil after vibration
• Loss of hyaluronic acid (scarring, ageing) → voice dysphonia, reduced mucosal wave

C. Inflammatory Mediators — Tonsillitis

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7. Pathology

A. Pharyngeal Pathology

B. Laryngeal Pathology

C. Hypopharyngeal Pathology

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8. Microbiology

Pharyngitis / Tonsillitis

Acute Epiglottitis

Deep Space Neck Infections

• Peritonsillar abscess: GAS + oral anaerobes (Prevotella, Fusobacterium, Peptostreptococcus)
• Retropharyngeal abscess: Staphylococcus, GAS, anaerobes, H. influenzae (children)
• Ludwig's angina: submandibular space infection; mixed oral flora; floor of mouth

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9. Clinical Presentation

Symptom Framework — Throat

Centor/McIsaac Score (Bacterial Tonsillitis)

Score ≥4: treat with antibiotics / rapid strep test positive → treat

Epiglottitis — Classic Presentation (Emergency!)

• "4 Ds": Drooling · Dysphagia · Dysphonia · Distress
• Child sits leaning forward ("tripod position")
• Lateral neck X-ray: "Thumb sign" (enlarged epiglottis)
• Do NOT examine throat with tongue depressor → may precipitate airway obstruction

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10. Medicine (Clinical)

Investigations

Complications of Tonsillitis/Pharyngitis

• Peritonsillar abscess (quinsy) — most common
• Parapharyngeal/retropharyngeal abscess
• Otitis media (Eustachian tube dysfunction)

• Rheumatic fever (2–4 weeks after GAS pharyngitis): carditis, arthritis, chorea, subcutaneous nodules, erythema marginatum (Jones criteria)
• Post-streptococcal glomerulonephritis (1–3 weeks): haematuria, oedema, hypertension
• PANDAS: paediatric autoimmune neuropsychiatric disorder

• F. necrophorum → peritonsillar abscess → IJV thrombophlebitis → septic pulmonary emboli → sepsis
• Young adults; often mistaken for "glandular fever"

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11. Pharmacology

A. Antibiotics for Throat Infections

B. Steroids

C. Inhaled / Nebulised Agents

D. Voice & Laryngeal Pharmacology

E. Biologics / Targeted Therapy

F. Rheumatic Fever Prophylaxis

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Summary Table

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The Eye — Complete Multi-Disciplinary Overview

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1. Surface Anatomy

External Eye Landmarks

Simple Drawing Guide

        Superior lid
           _____
    /     |     |     \
   /  Upper fornix     \   ← Conjunctival sac
  |  Bulbar conjunctiva |
  |   [white sclera]    |
  |  [coloured iris]    |
  |    [black pupil]    |
   \                   /
    \ Limbus (ring)   /
       ¯¯¯¯¯¯¯¯¯¯¯
        Inferior lid
   Lacrimal punctum (medial)

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2. Regional Anatomy

A. Eyeball (Globe) — Three Concentric Coats

        OUTER COAT           MIDDLE COAT (UVEA)     INNER COAT
   ___________________    ___________________    _______________
  | Cornea (anterior) |  | Iris              |  | Retina        |
  |                   |  | Ciliary body      |  | (sensory)     |
  | Sclera (posterior)|  | Choroid           |  |               |
  |___________________|  |___________________|  |_______________|

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B. Anterior Segment

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C. Posterior Segment

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D. Extraocular Muscles & Nerve Supply

Mnemonic: "LR6SO4" — Lateral Rectus = CN VI, Superior Oblique = CN IV, all others = CN III

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E. Lacrimal System

Lacrimal gland (superolateral orbit)
    ↓ (tears)
Tear film over cornea/conjunctiva
    ↓
Upper + lower lacrimal puncta (medial lids)
    ↓
Canaliculi → common canaliculus
    ↓
Lacrimal sac (medial orbital wall)
    ↓
Nasolacrimal duct → inferior meatus of nose

• Lacrimal gland: serous + mucous secretion; innervated by CN VII (parasympathetic via pterygopalatine ganglion)
• Tear film: 3 layers: lipid (Meibomian) + aqueous (lacrimal) + mucin (goblet cells)

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F. Orbital Anatomy

• Bony orbit: 7 bones — frontal, zygomatic, maxilla, palatine, lacrimal, ethmoid, sphenoid
• Optic canal (sphenoid): transmits CN II (optic nerve) + ophthalmic artery
• Superior orbital fissure: CN III, IV, V1 (ophthalmic), VI + superior ophthalmic vein
• Inferior orbital fissure: CN V2 (maxillary), inferior ophthalmic vein

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3. Gross Anatomy

Cornea — 5 Layers (Gross to Micro)

1. Epithelium (stratified squamous, 5–6 cell layers)
2. Bowman's layer (acellular condensed stroma)
3. Stroma (90% of corneal thickness; collagen lamellae)
4. Descemet's membrane (basement membrane of endothelium)
5. Endothelium (single layer; maintains corneal dehydration/clarity)

• Total thickness: ~0.5 mm centrally, ~0.7 mm peripherally
• Avascular — nourished by aqueous humour (anterior) and tear film (anterior surface)
• Innervation: densely innervated by CN V1 (ophthalmic) — most sensitive tissue in the body

Lens — Gross Features

• Three components: capsule (elastic basement membrane) + epithelium (anterior only) + lens fibres (crystallins)
• No nucleus in mature fibres; no blood supply; nourished by aqueous/vitreous
• Zonules of Zinn: suspensory ligaments from ciliary body

Optic Nerve

• ~50 mm long; 4 segments: intraocular (1 mm) → intraorbital (25–30 mm) → intracanalicular (6–9 mm) → intracranial (10 mm)
• Surrounded by meningeal sheaths (dura, arachnoid, pia) → subarachnoid space continues → raised ICP → papilloedema
• Contains ~1.2 million nerve fibres (retinal ganglion cell axons)

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4. Histology

A. Retinal Layers (10 layers, outer → inner)

B. Rods vs Cones

C. Corneal Histology

• Epithelium: 5–6 layers non-keratinizing stratified squamous; rapid turnover (7–10 days); stem cells at limbus
• Bowman's layer: acellular collagen mesh; does NOT regenerate if damaged
• Stroma: 200+ regularly arranged collagen lamellae (type I) + keratocytes; regular arrangement = transparency
• Descemet's membrane: thick (~10 µm in adults); produced by endothelium
• Endothelium: single layer of hexagonal cells (~2,500 cells/mm²); pump fluid out of stroma (Na⁺/K⁺-ATPase); does NOT regenerate — cell density decreases with age

D. Iris Histology

• Anterior: loose collagen stroma with melanocytes (iris colour)
• Posterior: double layer of pigmented epithelium (continuation of ciliary epithelium)
• Sphincter pupillae: smooth muscle ring at pupillary margin (parasympathetic — CN III)
• Dilator pupillae: radial myoepithelial cells (sympathetic)

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5. Physiology

A. Aqueous Humour Dynamics

Ciliary epithelium (non-pigmented layer)
    ↓ secretion (~2–3 µL/min; active transport + ultrafiltration)
Posterior chamber
    ↓ (through pupil)
Anterior chamber
    ↓
Trabecular meshwork (conventional, 90%)
    ↓
Canal of Schlemm → episcleral veins
    (Uveoscleral pathway: 10%)

• Normal intraocular pressure (IOP): 10–21 mmHg
• IOP = Rate of aqueous production / Facility of outflow (resistance of trabecular meshwork)
• Aqueous provides nutrients (glucose, O₂, amino acids) to avascular cornea and lens

B. Accommodation (Near Focus)

Near object → ciliary muscle CONTRACTS (CN III parasympathetic)
    ↓
Zonule fibres RELAX (become slack)
    ↓
Lens becomes MORE CONVEX (elastic recoil)
    ↓
Increased refracting power → near focus

• Presbyopia: age-related loss of accommodation; lens hardening reduces elasticity (typically >40 years)
• Accommodation reflex triad: convergence + accommodation + miosis

C. Pupillary Light Reflex

Light → Retinal ganglion cells (intrinsically photosensitive: melanopsin/ipRGCs)
    ↓ CN II (afferent)
Pretectal nucleus (midbrain)
    ↓ (bilateral projection)
Edinger-Westphal nucleus (CN III parasympathetic)
    ↓ CN III (efferent)
Ciliary ganglion → short ciliary nerve → sphincter pupillae → miosis

• Direct reflex: light in same eye → constriction in same eye
• Consensual reflex: light in one eye → constriction in both eyes (bilateral pretectal projection)
• RAPD (Relative Afferent Pupillary Defect): swinging flashlight test; affected eye shows paradoxical dilation when light swings to it → optic nerve lesion

D. Phototransduction (Visual Transduction)

Light → rhodopsin (11-cis retinal → all-trans retinal)
    ↓
Opsin activates transducin (Gα protein)
    ↓
Phosphodiesterase (PDE) activated → cGMP hydrolysed
    ↓
cGMP-gated Na⁺/Ca²⁺ channels CLOSE → hyperpolarization
    ↓
Less glutamate released at photoreceptor synapse → bipolar cell activation
    ↓
Retinal ganglion cell fires → optic nerve → visual cortex

Note: photoreceptors are depolarized in the dark (Na⁺ influx via cGMP channels = "dark current") and hyperpolarize in light — opposite to most sensory systems.

E. Visual Pathway

Retina → Optic nerve (CN II)
    ↓
Optic chiasm (nasal fibres decussate; temporal fibres stay ipsilateral)
    ↓
Optic tract → Lateral Geniculate Nucleus (LGN) of thalamus
    ↓
Optic radiation (Meyer's loop inferiorly through temporal lobe)
    ↓
Primary visual cortex (V1) — calcarine fissure, occipital lobe

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6. Biochemistry

A. Visual Cycle (Retinoid Cycle)

All-trans retinal (after light activation)
    ↓ (reduced to all-trans retinol)
Transported to RPE
    ↓ (RPE isomerase)
11-cis retinal regenerated
    ↓
Transported back to photoreceptor outer segment
    ↓ + opsin → rhodopsin (dark-adapted)

• Vitamin A (retinol) is essential — deficiency → night blindness (nyctalopia)
• RPE is central to visual cycle — RPE dysfunction → photoreceptor death

B. Lens Biochemistry

• Cataract formation: oxidative damage to crystallins → protein aggregation → opacification
• Lens relies on anaerobic glycolysis (no mitochondria in mature fibres) → high sorbitol in diabetes (polyol pathway) → osmotic cataract

C. Aqueous Humour Biochemistry

• High ascorbic acid (antioxidant; ~20× plasma concentration)
• High hyaluronic acid in vitreous
• Low protein (unlike blood) → maintains optical clarity
• Tryptophan metabolites → absorb UV radiation (protecting lens/retina)

D. Intraocular Pressure — Molecular Regulation

• Prostaglandins (PGF2α): increase uveoscleral outflow → lower IOP
• Beta-blockers: decrease aqueous secretion (inhibit β-adrenergic receptors on ciliary epithelium)
• Carbonic anhydrase: produces HCO₃⁻ essential for active secretion of aqueous → inhibition lowers IOP

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7. Pathology

A. Corneal Pathology

B. Lens Pathology

C. Glaucoma

D. Retinal Pathology

E. Optic Nerve Pathology

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8. Microbiology

Conjunctivitis

Endophthalmitis

• Post-surgical: S. epidermidis, S. aureus, Gram-negative rods
• Post-traumatic: Bacillus cereus (soil/vegetable matter injury — very virulent)
• Endogenous (haematogenous): Candida, Aspergillus, Klebsiella (diabetics in Asia)

Toxoplasmosis (Posterior Uveitis)

• Toxoplasma gondii; most common cause of posterior uveitis worldwide
• "Headlight in fog": white fluffy retinal lesion adjacent to old pigmented scar
• Reactivation of congenital or acquired infection

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9. Clinical Presentation

Red Eye — Differential Diagnosis

Sudden Visual Loss — Framework

Marcus Gunn (RAPD) Test

• Swinging flashlight: light in normal eye → both pupils constrict
• Light swings to affected eye → both pupils dilate (paradoxical response)
• Indicates ipsilateral optic nerve or extensive retinal disease

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10. Medicine (Clinical)

Ophthalmic Investigations

Diabetic Eye Disease Grading (ETDRS / UK NSC)

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11. Pharmacology

A. Glaucoma Treatments (Lowering IOP)

B. Age-Related Macular Degeneration (Wet AMD) — Anti-VEGF

C. Diabetic Macular Oedema (DMO) — Same anti-VEGF drugs; also:

• Intravitreal corticosteroids: dexamethasone implant (Ozurdex), fluocinolone acetonide (Iluvien) — for pseudophakic or unresponsive cases; SE: cataract + raised IOP

D. Infection / Inflammation

⚠️ Steroids in the eye: can cause steroid-induced glaucoma (IOP rise) and posterior subcapsular cataract with prolonged use

E. Mydriatics / Cycloplegics

⚠️ Avoid mydriatics in known narrow angles — risk of precipitating acute angle closure

F. Lubricants (Dry Eye Disease)

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Summary Table