Ear anatomy😊

External Ear

• Consists of three parts:
• Pinna.
• External auditory canal (EAC).
• Tympanic membrane.

Pinna

• Made of elastic cartilage.

• Areas without cartilage:
• Lobule
• Incisura terminalis
• Devoid of cartilage
• Space between tragus and helix
• Site of Lempert endaural incision

• Most skin is supplied by the greater auricular nerve.

External Auditory Canal (EAC)

• Continuation of the pinna.

• Length: 24mm.

• Two parts:
• Cartilaginous part:
• Lateral/outer 1/3 (8mm).
• Has hair follicles, sebaceous glands, and ceruminous glands.
• Bony part:
• Medial/inner 2/3 (16mm).
• Lacks hair follicles, sebaceous glands, and ceruminous glands.
• In newborns → bony part of the EAC is absent.

• The canal is S-shaped.

• The parotid gland is below the EAC.

Syringing direction & TM examination:

• Adults:
• pull pinna upwards,
• backwards,
• outwards.

• Children:
• pull pinna downwards,
• backwards (bony part not fully developed).

• Syncope on syringing:
• Arnold N → Parasympathetic discharge (Syncope)

Two communications with the parotid gland:

• Fissure of Santorini:
• between cartilaginous EAC and parotid.
• S → Smooth cartilagenous

• Foramen of Huschke:
• between bony EAC and parotid.
• H → Hard bony

• These communications allow infection spread.

• They usually disappear by age 5-7 years.

• Cough response from cleaning the ear canal
• Mediated by Arnold's nerve
• (auricular branch of vagus).

Tympanic Membrane (TM)

• Partition between external and middle ear.

• Obliquely placed at 45° to the EAC.

• Oval shape.

• Dimensions:
• 10 mm tall,
• 9 mm wide.

• Total surface area (TSA): 90 mm².

• Thickness: 0.1 mm.

• Effective vibrating area
• ½ TSA (45mm²)
• Peripheral portion.
• Centre
• does not vibrate
• d/t the handle of the malleus.

Parts of Tympanic Membrane

Two parts:

1. Pars Tensa:
• Tense and tight.

Has 3 layers:

• outer (ectodermal) epithelial,
• middle fibrous
• inner endothelial.
• Contains umbo and cone of light.
• Umbo
• Centre
• point where the tip of the malleus handle → attaches to the TM.

2. Pars Flaccida:
• Loose and lax.
• Has 2 layers:
• outer epithelial
• inner endothelial (lacks fibrous layer).

Two malleolar folds:

• anterior (shorter)

• posterior (longer).

Pars tensa is divided into 4 quadrants by two imaginary lines:

• 1 vertically crossing handle of malleus

• 1 horizontally through umbo
• Anterosuperior.
• Anteroinferior.
• Posterosuperior.
• Posteroinferior.

• Cone of light is in the anteroinferior quadrant of the pars tensa.
• Right TM: 3 to 6 o'clock position.
• Left TM: 6 to 9 o'clock position.

• Prussak space
• Between the pars flaccida and neck of malleus.

Middle Ear Cleft

• Function: ventilation of the middle ear.

• Components:



• Eustachian tube (anterior).
• Middle ear proper.
• Attic.
• Aditus (communication between attic and antrum).
• Mastoid air cells (posterior).

• Antrum is the largest mastoid air cell.

• Ventilatory pathway:
• Nose → nasopharynx → eustachian tube → middle ear proper → Attic → Aditus → Antrum → rest of mastoid air cells.

Anatomy of the Middle Ear Proper

• Hourglass shape.
• Anteroposterior dimension of epitympanum: 4mm
• Anteroposterior dimension of mesotympanum: 2mm.
• Anteroposterior dimension of hypotympanum: 6mm.

• Protympanum
• part of the middle ear
• around the tympanic orifice of the eustachian tube.

Walls of the Middle Ear

It has 6 walls:

• Roof:
• Tegmen tympani
• separates from middle cranial fossa

• Floor:
• Internal jugular vein
• thin bone over jugular bulb

• Lateral wall:
• Tympanic membrane and scutum
• outer attic wall

• Posterior wall:
• Pyramid (projection on posterior wall)
• aditus
• antrum.

• Anterior wall:
• Communicates with Eustachian tube (ET).
• Bone separating internal carotid artery.
• Canal for tensor tympani.

• Medial wall:
• Impression of lateral semicircular canal.
• Promontory
• impression of basal turn of cochlea
• Promontory has a tympanic plexus
• glossopharyngeal nerve
• sympathetic plexus
• High frequency → Basal turn of cochlea affected
• Low frequency → Apex of cochlea is affected
• Oval window.
• Round window.
• Facial nerve
• between
• semi-circular canal
• promontory
• Processus cochlearformis.

Nerve Supply

Pinna:

• Mnemonic: LAG 7&10.
• Lesser occipital nerve (C2).
• Auriculotemporal nerve (CN V3).
• Greater auricular nerve (C2, 3).
• Facial (7th) and Vagus (10th) nerves.

• Greater surface area
• greater auricular nerve.

• Lateral surface
• lower half: Greater auricular nerve.
• upper anterior 2/3rd: Auriculotemporal nerve.
• upper posterior 1/3rd: Lesser occipital nerve.

• Concha:
• 7th
• 10th nerve (Arnold's nerve / Aldermann’s N (Auricular branch of Vagus))
• Mnemonic: Arnold () → an Elderman () → got slapped in his ear (concha) → he coughed () afterwards cough reflex

• EAC:
• Anterior wall and roof:
• Auriculotemporal nerve.
• Posterior wall and floor:
• Facial N + Arnold's nerve / Aldermann’s N
• Auricular branch of Vagus

• Medial side of TM & Middle Ear (ME):
• Glossopharyngeal nerve (9th) → Jacobson N

• Mnemonic: 10 → 9 → 8

• Inner Ear (IE):
• Vestibulocochlear nerve (8th).
• Cochlea:
• Cochlear nerve.
• Semicircular canals (SCC) and vestibule:
• Vestibular nerve





A : Incus
B : Posterior semicircular canal
C : Lateral semicircular canal
D : Superior semicircular canal

Perforated Tympanic Membrane

• Subtotal perforation:
• includes all quadrants except the annulus.

• Structures visible through perforation:



• Handle of malleus.
• Long process of the incus.
• Head of stapes.
• Stapedial crura and Footplate
• Stapedius muscle.
• Promontory.
• Oval window (above) and round window (below) in the posteroinferior quadrant.
• Eustachian tube (ET) in the antero-inferior quadrant.
• Ossicles in the posterior superior quadrant.

Intratympanic Muscles

• Function of both: Dampen loud sound and protect the inner ear.

Muscle	Embryological Arch	Nerve Supply	Attachment
Tensor tympani	1st	Mandibular branch of trigeminal n.	Malleus neck
Stapedius	2nd	Facial nerve	Stapes neck

Facial Nerve Landmarks in the Middle Ear

• Facial nerve path:
• Makes first turn (1st genu / geniculate ganglion) from the inner ear.
• Continues horizontally in the medial wall of the middle ear.
• Takes a vertical turn (2nd genu) in the posterior wall.
• Exits through the stylomastoid foramen.
• Mnemonic:
• Facial N exits in style (stylomastoid)
• Chorda tympani exits huge (Canal of huguier)

• In the medial wall, it lies
• above oval window
• below lateral semicircular canal.

• Canal of Huguier
• exit site of chorda tympani from the middle ear.

Facial Recess and Sinus Tympani Relations

Facial recess / suprapyramidal recess:

• Superiorly:
• Fossa incudis.

• Laterally:
• Chorda tympani.

• Medially:
• Vertical segment of the facial nerve.

• Applied
1. Posterior tympanostomy
• posterior route to middle ear
• Indications
1. Cochlear implant surgery.
2. Canal wall up

Mc Evens triangle

Anatomy of Inner Ear

• Also called a labyrinth.

• Made of:
• Bony labyrinth (outer covering).
• Membranous labyrinth (content within).

Parts of Inner Ear

Vestibule (central chamber):

• Contains
• spherical recess (bony labyrinth).
• contains saccule.
• Connects to cochlear ducts anteriorly
• elliptical recess (bony labyrinth).
• contains utricle.
• Connects to SCC posteriorly

• Utricle and saccule → membranous labyrinth.

Semicircular Canals (SCC) (posterior):

• 3 canals → Parts:
1. Semi-circular duct.
2. Ampullated (dilated) end
3. non-dilated end.

• Opens into utricle
• 5 openings (not 6).
• Non-ampullated ends of → superior & posterior canals
• fuse to form the crus commune.
• → 3 ampullated ends + 2 non-dilated ends.
• Mnemonic: Communist (Crus communis) → Undilated () people → Superior () people + backward (Posterior) people

Cochlea (anterior):

Cochlear Duct /scala media/Cochlear chamber

• Spiral structure.

• Turns: 2¾ and 2½.

• Scala media rotates 2¾ around the modiolus (central axis).

Cross-Section of Cochlea:

Sound propagation

• EAC → TM → Ossicles → Oval window → scala vestibuli → scala tympani → basilar membrane against tectorial membrane → outer hair cell → inner hair cell → 8th CN → Spiral ganglion

Scala vestibuli

• perilymph.

• covered by the oval window at Basal Part

• At Apex:
• Scala vestibuli communicates with scala tympani
• at the helicotrema.

Cochlear duct (scala media)

• endolymph.

• Cochlear duct connects to saccule
• via Ductus reuniens / Canalis reuniens.

Scala tympani

• perilymph.

• covered by the round window at Basal Part

Vestibular/Reissner's membrane:

• separates scala vestibuli and scala media.

Basilar membrane:

• separates scala media and scala tympani.

Organ of Corti:

• neurosensory epithelium for hearing,

• on basilar membrane.

Others

• Tectorial membrane.

• Spiral ganglion.

• Cochlear nerve fibers.

Perilymph and Endolymph

• Perilymph:
• In scala vestibuli and scala tympani.
• Ultrafiltrate of CSF.
• Communicates with CSF via aqueduct of cochlea.
• Rich in Sodium.

• Endolymph:
• In scala media.
• Produced and reabsorbed by stria vascularis.
• Rich in Potassium.

Important Information (Inner Ear Structures)

• Saccular and utricular ducts
• form the endolymphatic duct,
• leading to the endolymphatic sac.

• Vestibular aqueduct
• bony covering
• around the endolymphatic duct.

Landmark for Endolymphatic Sac

• Donaldson's line:
• Imaginary line from lateral SCC → bisecting posterior SCC.
• Represents endolymphatic duct.
• Endolymphatic sac is inferior to Donaldson's line.
• Endolymphatic hypertension → Endolymphatic sac decompression

Embryology

• Outward structures → Pinna, Malleus, incus, stapes → from arch
• Pinna → 1, 2 arch
• Malleus, incus → 1st arch
• Stapes → 2nd arch

• TM → all three layers, cleft, pouch

• Inward structure → EAC → from Cleft (1st)

• foOT plate → OT → OTic capsule

• Embryonic layer
• EAC → Ectoderm
• Middle ear cleft → Endoderm
• All other → Mesoderm

Questions and Answers

• Q. The part of the pinna lying between the ascending crest of the helix and tragus is called the?
• Ans. Incisura terminalis.

• Q. Major part of the skin of the pinna is supplied by?
• Ans. Greater auricular nerve.

• Q. Arnold's nerve is a branch of?
• Ans. Vagus nerve.

• Q. In newborns, which part of the EAC is absent?
• Ans. Bony part.

• Q. Fissures of Santorini are seen in which part of EAC?
• Ans. Cartilaginous part.

• Q. The cough response caused while cleaning the ear canal is mediated by the stimulation of which cranial nerve?
• Ans. Auricular branch of the vagus nerve (Arnolds).

• Q. The tympanic membrane

• forms an angle of how many degrees with the external auditory canal?
• Ans. 45 degrees.

• Q. The length of the ET tube is?
• Ans. 36mm.

• Q. The structure responsible for endolymph secretion is?
• Ans. Stria Vascularis.

• Q. Duct of cochlea connecting with subarachnoid space?
• Ans. Aqueduct of cochlea.

• Q. Endolymphatic duct is formed by?
• Ans. Utricular and saccular duct.

• Q. Cochlear duct is?
• Ans. Scala media.

• Q. Cochlear duct is connected to the saccule by?
• Ans. Ductus reuniens.

• Q. Scala media is separated from scala tympani by?
• Ans. Basilar membrane.

• Q. Scala media is separated from Scala vestibular by?
• Ans. Reissner's membrane.