Unit 14 — Ear (Vestibulocochlear Organ) · Question Bank

TMU Anatomy · External Ear · Middle Ear · Inner Ear · Hearing & Balance
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Q1
What is the correct order of auditory ossicles from lateral (tympanic membrane) to medial (oval window)?
TMU Slides Unit 14
A. Malleus → incus → stapes
B. Incus → malleus → stapes
C. Stapes → incus → malleus
D. Malleus → stapes → incus
✓ Answer: A — Malleus → Incus → Stapes
The handle (manubrium) of the malleus is attached to the tympanic membrane laterally. The malleus articulates with the incus, which in turn articulates with the stapes. The base (footplate) of the stapes sits in the fenestra vestibuli (oval window) medially. Sound vibrations pass: tympanic membrane → malleus → incus → stapes → oval window → inner ear.
⚠ Mnemonic: MIS (Malleus → Incus → Stapes), lateral to medial. The malleus is the most lateral (touches drum); the stapes is the most medial (touches oval window).
Q2
The ossicles of the middle ear are notable because they are:
TMU Slides Unit 14
A. The largest bones in the body
B. The smallest bones in the human body
C. The only sesamoid bones in the skull
D. The only bones lacking a periosteum
✓ Answer: B — Smallest bones in the human body
The three auditory ossicles (malleus, incus, stapes) are collectively the smallest bones in the human body. The stapes is the smallest individual bone (~3 mm). They are housed within the tympanic cavity of the middle ear and function to transmit and amplify sound vibrations from the tympanic membrane to the oval window.
⚠ The stapes alone is the single smallest bone. All three ossicles are often cited as the smallest bones in the body as a group. They are not sesamoid bones (sesamoid bones are embedded in tendons, e.g. patella).
Q3
The auditory (Eustachian) tube connects the tympanic cavity to the:
TMU Slides Unit 14
A. Oropharynx
B. Nasal cavity directly
C. Nasopharynx
D. Mastoid antrum
✓ Answer: C — Nasopharynx
The auditory tube (~3.5–4.5 cm long) is the channel through which the tympanic cavity communicates with the nasopharynx. Its lateral 1/3 is bony (opens on the anterior wall of the tympanic cavity); its medial 2/3 is cartilaginous (opens into the nasopharynx). During swallowing the pharyngeal orifice opens, allowing air in to equalise pressure on both sides of the tympanic membrane, ensuring free vibration.
⚠ The tube opens into the NASOPHARYNX (not oropharynx). The mastoid antrum communicates with the middle ear via the aditus, not via the auditory tube.
Q4
Why are children more susceptible to otitis media (middle ear infection) than adults?
TMU Slides Unit 14
A. The tympanic membrane is thinner in children
B. The mastoid air cells are not yet pneumatised
C. The oval window is more exposed in children
D. The auditory tube in children is shorter, wider, and more horizontal
✓ Answer: D — Shorter, wider, and more horizontal auditory tube
In childhood, the auditory tube is shorter, wider, and more horizontal than in adults. This means pharyngeal inflammation (e.g. from a common cold) can spread more readily along the auditory tube into the tympanic cavity, causing otitis media. In adults, the tube is longer, narrower, and more oblique, offering more resistance to ascending infection.
⚠ The key phrase is all three: shorter + wider + more horizontal. Any one of these alone would increase infection risk; together they make children highly susceptible. This is a favourite exam point.
Q5
To inspect the tympanic membrane of an adult using an otoscope, the auricle should be pulled in which direction?
TMU Slides Unit 14
A. Upward, backward, and lateral
B. Downward and forward
C. Downward, backward, and medial
D. Forward and medial only
✓ Answer: A — Upward, backward, and lateral
In the adult, the external acoustic meatus is convex upward and backward. To straighten this S-shaped canal for otoscopic examination, the auricle must be pulled upward, backward, and lateral. This manoeuvre aligns the cartilaginous and bony portions of the meatus and brings the tympanic membrane into view.
⚠ In infants (under 2 years), pull the auricle downward and backward (the meatus curves differently). In adults: UP, BACK, LATERAL. This distinction frequently appears in clinical exams.
Q6
On otoscopic examination of a healthy tympanic membrane, the cone of light is seen:
TMU Slides Unit 14
A. Posterosuperior to the umbo
B. Anteroinferior to the umbo
C. At the centre of the umbo directly
D. In the flaccid part (Shrapnell's membrane) superiorly
✓ Answer: B — Anteroinferior to the umbo
The umbo is the central depression on the outer surface of the tympanic membrane, formed by the traction of the lower end of the handle of malleus. The cone of light (light reflex) is a bright triangular reflection seen anteroinferior to the umbo when the otoscope light strikes the concave tympanic membrane. Loss or distortion of the cone of light suggests middle ear pathology.
⚠ The cone of light points anteroinferiorly (toward 5 o'clock on the right drum, 7 o'clock on the left). It is a reflection from the concave surface of the drum. It lies BELOW and in FRONT of the umbo, not at the umbo itself.
Q7
Which statement about the tympanic membrane is CORRECT?
TMU Slides Unit 14
A. It is circular and lies perpendicular to the floor of the meatus
B. The flaccid part is the larger lower portion of the membrane
C. It is pearly-grey, oval, forms a 55° angle with the meatus floor, and has a tense part and a flaccid part (Shrapnell's membrane)
D. It is formed entirely of fibrous tissue with no epithelial layers
✓ Answer: C — Pearly-grey, oval, 55°, tense + flaccid parts
The tympanic membrane is: pearly-grey in colour; oval in shape; thin and semi-transparent; inclined at ~55° to the floor of the meatus (anterior and inferior walls of meatus are therefore longer). It has two parts: the tense part (pars tensa) — the large lower portion, tightly stretched; and the flaccid part (pars flaccida / Shrapnell's membrane) — the small superior portion above the malleolar folds, lax and thin.
⚠ The FLACCID part (Shrapnell's) is small and SUPERIOR. The TENSE part is large and inferior. Cholesteatoma typically originates in the flaccid part. The drum is three-layered: outer squamous epithelium, middle fibrous layer, inner mucous membrane.
Q8
Which part of the auricle (pinna) lacks cartilage?
TMU Slides Unit 14
A. Helix
B. Antihelix
C. Tragus
D. Lobule (ear lobe)
✓ Answer: D — Lobule (ear lobe)
The auricle is composed of elastic fibrocartilage covered with skin, giving it its shape and resilience. The single exception is the auricular lobule (ear lobe), which lies below the auricle and is composed of fibrous and adipose (fat) tissue only — no cartilage. This is why the ear lobe is soft and flexible, and why it is the preferred site for ear-piercing.
⚠ Helix, antihelix, tragus, antitragus, concha — all contain elastic fibrocartilage. Only the lobule is cartilage-free. The lobule has no auricular muscles attached to it.
Q9
The bony labyrinth of the inner ear consists of which three parts?
TMU Slides Unit 14
A. Cochlea, vestibule, semicircular canals
B. Cochlear duct, utricle, saccule
C. Scala vestibuli, scala tympani, cochlear duct
D. Modiolus, helicotrema, osseous spiral lamina
✓ Answer: A — Cochlea, vestibule, semicircular canals
The bony labyrinth (housed in the petrous temporal bone) is divided into three communicating parts from anterior to posterior: (1) cochlea (hearing); (2) vestibule (central part — contains openings of semicircular canals and oval/round windows); (3) bony semicircular canals (3 in number: anterior, posterior, lateral). They all communicate with each other and are filled with perilymph.
⚠ The bony labyrinth is the OUTER bony shell; the membranous labyrinth lies inside it. The three parts of the membranous labyrinth are different: cochlear duct, utricle + saccule, membranous semicircular ducts. Do not confuse the two systems.
Q10
Which statement about the cochlea is CORRECT?
TMU Slides Unit 14
A. The cochlea makes 1.5 turns around the modiolus
B. The cochlea makes 2.5 turns; the organ of Corti lies on the basilar membrane
C. The organ of Corti lies on the vestibular membrane
D. The scala vestibuli and scala tympani do not communicate
✓ Answer: B — 2.5 turns; organ of Corti on basilar membrane
The cochlear spiral canal winds 2.5 turns around the central modiolus. The osseous spiral lamina projects from the modiolus and divides the cochlear canal into scala vestibuli (above) and scala tympani (below) with the cochlear duct in between. The organ of Corti (spiral organ) is the receptor for auditory sensation and lies on the basilar membrane (inferior wall of the cochlear duct). The scala vestibuli and scala tympani communicate at the apex via the helicotrema.
⚠ The vestibular membrane (Reissner's membrane) forms the SUPERIOR wall of the cochlear duct, separating it from the scala vestibuli. The organ of Corti is on the BASILAR membrane (INFERIOR wall). The scala tympani is closed at its basal end by the secondary tympanic membrane (round window).
Q11
Which fluid fills the membranous labyrinth, and which fluid fills the space between the membranous and bony labyrinths?
TMU Slides Unit 14
A. Membranous labyrinth = perilymph; surrounding space = endolymph
B. Both spaces contain endolymph
C. Membranous labyrinth = endolymph; surrounding space = perilymph
D. Both spaces contain perilymph
✓ Answer: C — Membranous = endolymph; surrounding space = perilymph
The membranous labyrinth is a closed system of channels filled with endolymph (high K+, low Na+ — similar to intracellular fluid; produced by the lateral wall/stria vascularis of the cochlear duct). The perilymph (high Na+, low K+ — similar to CSF/extracellular fluid) fills the space between the membranous and bony labyrinths. The two fluids do not communicate.
⚠ Memory aid: Endo is INside (membranous labyrinth); Peri is around (periLabyrinthine space). In Ménière's disease, excess endolymph (endolymphatic hydrops) disrupts this balance.
Q12
Regarding the organ of Corti (spiral organ), which statement is CORRECT?
TMU Slides Unit 14
A. It detects angular acceleration and is located in the semicircular ducts
B. It is the receptor for auditory sensation; inner hair cells outnumber outer hair cells 3:1
C. It lies on the vestibular membrane and detects low-frequency sounds at the base
D. It is the receptor for auditory sensation; high-frequency sounds are detected at the base of the cochlea (tonotopic organisation)
✓ Answer: D — Auditory receptor; high freq at base (tonotopic)
The organ of Corti (spiral organ) is the receptor for auditory sensation, situated on the basilar membrane. It contains inner and outer hair cells (outer hair cells outnumber inner ~3:1 but inner hair cells do ~95% of afferent transmission). It is tonotopically organised: high-frequency sounds stimulate hair cells at the base of the cochlea (near the oval window); low-frequency sounds stimulate hair cells at the apex (near helicotrema). This is because the basilar membrane is narrower and stiffer at the base.
⚠ Angular acceleration = ampullary crests in semicircular ducts. Static balance/gravity = maculae of utricle and saccule. Tonotopy: BASE = HIGH, APEX = LOW. Noise-induced hearing loss typically affects high frequencies first (4 kHz notch) because basal hair cells are damaged first.
Q13
The three bony semicircular canals detect:
TMU Slides Unit 14
A. Angular (rotational) acceleration of the head
B. Linear acceleration and deceleration of the head
C. Gravity and static head position
D. Sound vibrations transmitted from the tympanic membrane
✓ Answer: A — Angular (rotational) acceleration
There are 3 bony semicircular canals: anterior (superior), posterior, and lateral (horizontal). Each lies in a different plane approximately at right angles to the others, allowing detection of rotation in any direction. The receptor is the ampullary crest (crista ampullaris) located within the membranous ampulla of each duct. These are the organs of kinetic (dynamic) balance, stimulated by angular acceleration of the head.
⚠ Angular acceleration = semicircular canals (via ampullary crests). Linear acceleration + gravity = utricle and saccule (via maculae). The anterior and posterior canals are in vertical planes; the lateral canal is nearly horizontal.
Q14
The utricle and saccule detect:
TMU Slides Unit 14
A. Angular rotation of the head only
B. Gravity, static head position, and linear acceleration/deceleration
C. High-frequency sounds via the basilar membrane
D. Pressure changes in the scala tympani
✓ Answer: B — Gravity, static head position, linear acceleration
Both the utricle and saccule lie in the vestibule of the bony labyrinth. Their receptor organs are the maculae (macula utriculi and macula sacculi), which are the organs of static balance. They are stimulated by: (1) changes of head position relative to gravity; (2) linear acceleration and deceleration of the head. They do NOT detect angular (rotational) acceleration (that is the role of the semicircular canal ampullary crests).
⚠ Mnemonic: UTILS = UTricle + sacc = Linear + Static. The maculae contain otoliths (crystals of calcium carbonate) embedded in a gelatinous membrane that deflect hair cells in response to gravity and linear motion.
Q15
CN VIII (vestibulocochlear nerve) consists of two divisions. Which statement is CORRECT?
TMU Slides Unit 14
A. Cochlear division (balance) + vestibular division (hearing)
B. Both divisions carry motor fibres to the stapedius muscle
C. Cochlear division (hearing) + vestibular division (balance)
D. CN VIII carries only parasympathetic fibres to the inner ear
✓ Answer: C — Cochlear = hearing; vestibular = balance
CN VIII (vestibulocochlear nerve) has two purely sensory divisions: (1) Cochlear (auditory) division: carries impulses from the organ of Corti → hearing; (2) Vestibular division: carries impulses from the utricle, saccule, and semicircular canal ampullary crests → balance and spatial orientation. Both divisions travel through the internal acoustic meatus alongside CN VII (facial nerve).
⚠ CN VIII is purely SENSORY (special somatic afferent). The stapedius muscle is supplied by CN VII (facial nerve), not CN VIII. Damage to the cochlear division = sensorineural deafness. Damage to vestibular division = vertigo, imbalance, nystagmus.
Q16
The inner ear is housed within which part of the temporal bone?
TMU Slides Unit 14
A. Squamous part
B. Tympanic part
C. Mastoid part
D. Petrous part
✓ Answer: D — Petrous part
The inner ear (bony labyrinth) lies within the petrous part of the temporal bone. The petrous temporal bone is a dense pyramid of compact bone forming the floor and lateral wall of the middle cranial fossa. It is described as the hardest bone in the body, which provides excellent protection for the delicate inner ear structures. The term “petrous” derives from Latin petra = rock.
⚠ The temporal bone has four parts: squamous (lateral skull wall), petrous (houses inner ear + internal acoustic meatus), mastoid (mastoid process + air cells), and tympanic (forms the floor and anterior wall of the external acoustic meatus). Only the petrous part houses the inner ear.
Q17
Which nerves pass through the internal acoustic meatus?
TMU Slides Unit 14
A. CN VII (facial) and CN VIII (vestibulocochlear)
B. CN V (trigeminal) and CN VIII (vestibulocochlear)
C. CN IX (glossopharyngeal) and CN VIII only
D. CN VII alone
✓ Answer: A — CN VII (facial) and CN VIII (vestibulocochlear)
The internal acoustic meatus is a short canal within the petrous temporal bone, running from the internal acoustic pore to its fundus. Through it pass: (1) CN VII (facial nerve) — proceeding to enter the facial canal; (2) CN VIII (vestibulocochlear nerve) — cochlear and vestibular branches entering the inner ear; (3) the labyrinthine artery and vein.
⚠ A tumour of CN VIII in the internal acoustic meatus (acoustic neuroma / vestibular schwannoma) will also compress CN VII, causing facial palsy as a late sign — because both nerves share the same canal. This is clinically important.
Q18
The mastoid antrum is an air sinus that communicates with the tympanic cavity via the:
TMU Slides Unit 14
A. Auditory tube
B. Aditus (opening in the mastoid wall of the tympanic cavity)
C. Oval window
D. Round window membrane
✓ Answer: B — Aditus in the mastoid (posterior) wall
The mastoid antrum is an air sinus in the petrous part of the temporal bone. It communicates with the tympanic cavity (middle ear) via the aditus, an opening situated in the superior part of the posterior wall (mastoid wall) of the tympanic cavity, leading back from the epitympanic recess. The mastoid air cells communicate with the antrum through multiple openings in its floor. Infection spreading from the middle ear can cause mastoiditis.
⚠ The auditory tube connects the tympanic cavity to the nasopharynx (anteriorly). The aditus connects the epitympanic recess to the mastoid antrum (posteriorly). These are two separate communication routes, in opposite directions.
Q19
Ménière's disease is caused by:
TMU Slides Unit 14 / Gray's 4e
A. Otosclerosis of the stapes footplate (conductive deafness)
B. Acoustic neuroma compressing CN VIII in the internal acoustic meatus
C. Endolymphatic hydrops (excess endolymph) causing sensorineural deafness, tinnitus, and episodic vertigo
D. Rupture of the secondary tympanic membrane (round window)
✓ Answer: C — Endolymphatic hydrops
Ménière's disease is caused by endolymphatic hydrops — abnormal increase in the volume and pressure of endolymph within the membranous labyrinth. This distension disrupts both cochlear and vestibular function, producing the classic triad: (1) episodic vertigo (attacks lasting 20 min to several hours); (2) sensorineural hearing loss (low-frequency initially, later all frequencies); (3) tinnitus (ringing in the ear); often accompanied by a sense of aural fullness.
⚠ Otosclerosis = conductive deafness from stapes fixation (footplate immobile in oval window). Acoustic neuroma (vestibular schwannoma) = unilateral sensorineural deafness + tinnitus without episodic vertigo (grows slowly in internal acoustic meatus). Ménière's = episodic attacks distinguishes it.
Q20
The tegmen tympani is:
TMU Slides Unit 14
A. The floor of the tympanic cavity, related to the jugular fossa
B. The medial wall of the tympanic cavity, related to the inner ear
C. The posterior wall of the tympanic cavity, related to the mastoid process
D. The thin bony roof of the tympanic cavity, separating it from the middle cranial fossa
✓ Answer: D — Thin bony roof; separates from middle cranial fossa
The tegmen tympani (tegmental wall) is the superior wall (roof) of the tympanic cavity. It is a thin plate of compact bone that separates the tympanic cavity from the middle cranial fossa (and therefore from the temporal lobe of the brain). Because it is thin, middle ear infections can erode through it, causing intracranial complications (meningitis, temporal lobe abscess).
⚠ The six walls of the tympanic cavity: Tegmental (roof) = middle cranial fossa; Jugular (floor) = internal jugular vein; Carotid (anterior) = internal carotid artery + auditory tube; Mastoid (posterior) = mastoid process + aditus; Membranous (lateral) = tympanic membrane; Labyrinthine (medial) = inner ear.
D1 Tympanic Membrane +
The tympanic membrane is a thin, semi-transparent, oval membrane that separates the external acoustic meatus from the tympanic cavity (middle ear). It is pearly-grey in the living subject and inclines at approximately 55° to the floor of the meatus (so the anterior and inferior walls of the meatus are longer). It consists of three layers: an outer squamous epithelium, a middle fibrous layer, and an inner mucosal layer. It is divided into the large tense part (pars tensa) and the small superior flaccid part (pars flaccida / Shrapnell's membrane). The central depression, the umbo, is formed by the tip of the handle of malleus. The cone of light (light reflex) is visible anteroinferior to the umbo on otoscopy. Function: converts sound waves into mechanical vibrations for transmission via the ossicular chain.
Source: TMU Slides Unit 14, Slides 13–16
D2 Organ of Corti (Spiral Organ) +
The organ of Corti (spiral organ) is the receptor organ for auditory sensation, situated on the basilar membrane of the cochlear duct. It consists of inner hair cells (one row; ~3,500) and outer hair cells (three rows; ~12,000), supported by various supporting cells, all covered by the overlying tectorial membrane. When the basilar membrane vibrates, hair-cell stereocilia deflect against the tectorial membrane, generating nerve impulses transmitted by the cochlear division of CN VIII. The organ exhibits tonotopic organisation: high-frequency sounds activate hair cells at the base of the cochlea (narrow, stiff basilar membrane); low-frequency sounds activate hair cells at the apex (wider, more flexible).
Source: TMU Slides Unit 14, Slides 51–53
D3 Endolymph vs Perilymph +
Endolymph fills the membranous labyrinth (inside). It is high in potassium (K+) and low in sodium (Na+), resembling intracellular fluid. It is produced by the stria vascularis (lateral wall of the cochlear duct) and reabsorbed by the endolymphatic sac. It is continuous throughout the utricle, saccule, cochlear duct, and semicircular ducts.

Perilymph fills the space between the membranous and bony labyrinths (outside). It is high in Na+ and low in K+, resembling CSF/extracellular fluid, and is thought to communicate with the subarachnoid space via the perilymphatic duct.

The two fluids do not communicate. In Ménière's disease, excess endolymph (endolymphatic hydrops) distends the membranous labyrinth causing sensorineural hearing loss, tinnitus, and vertigo.
Source: TMU Slides Unit 14, Slide 40
D4 Auditory Tube (Eustachian Tube) +
The auditory tube (pharyngotympanic / Eustachian tube) is the channel connecting the tympanic cavity (middle ear) to the nasopharynx. It is approximately 3.5–4.5 cm long, with a lateral bony part (~one-third, opening on the anterior wall of the tympanic cavity) and a medial cartilaginous part (~two-thirds, opening into the nasopharynx). The pharyngeal orifice is normally closed; it opens during swallowing and yawning, admitting air into the tympanic cavity to equalise pressure on both sides of the tympanic membrane. In children, the tube is shorter, wider, and more horizontal, increasing the risk of ascending infection from the pharynx causing otitis media.
Source: TMU Slides Unit 14, Slides 33–36
D5 Tonotopic Organisation +
Tonotopic organisation refers to the spatial arrangement of hair cells along the basilar membrane of the cochlea such that different sound frequencies activate different regions. The basilar membrane varies in width and stiffness from base to apex: it is narrow and stiff at the base (near the oval window) and wide and flexible at the apex (near the helicotrema). As a result, high-frequency sounds cause maximal vibration at the base, and low-frequency sounds cause maximal vibration at the apex. This tonotopic map is preserved throughout the auditory pathway from the cochlea to the auditory cortex (Heschl's gyri, superior temporal gyrus). Clinical relevance: noise-induced hearing loss preferentially damages high-frequency (4 kHz) hair cells at the cochlear base first.
Source: TMU Slides Unit 14, Slide 53; Gray's Anatomy 4e
D6 Bony vs Membranous Labyrinth +
The bony labyrinth is a series of cavities within the petrous temporal bone, lined by periosteum and filled with perilymph. It has three parts: cochlea (anterior), vestibule (central), and three bony semicircular canals (posterior). All three parts communicate with each other.

The membranous labyrinth is a closed system of ducts and sacs lying within the bony labyrinth, filled with endolymph. Its three parts are: cochlear duct (in the cochlea), utricle and saccule (in the vestibule), and membranous semicircular ducts (within the bony canals). The membranous labyrinth is suspended within the perilymph-filled bony shell.

The membranous labyrinth contains all the receptor organs: organ of Corti (hearing), maculae of utricle/saccule (static balance/gravity/linear acceleration), and ampullary crests (kinetic balance/angular acceleration).
Source: TMU Slides Unit 14, Slides 40–53
Essay 1
Describe the external ear: the auricle, the external acoustic meatus, and the tympanic membrane. Include structure, divisions, and clinical relevance.
8 marks

Auricle

  • Composed of elastic fibrocartilage covered with skin, giving shape and resilience.
  • Landmarks: helix, antihelix, tragus, antitragus, concha, scaphoid fossa.
  • Auricular lobule (ear lobe): only part without cartilage; composed of fibrous and adipose tissue — soft, flexible, preferred site for ear-piercing.
  • Function: collects and funnels sound waves into the external acoustic meatus; assists with sound localisation.

External Acoustic Meatus

  • Extends from the external acoustic pore to the tympanic membrane; ~2.5–3.5 cm in length.
  • Lateral 1/3: cartilaginous; medial 2/3: bony (housed in temporal bone).
  • In adults, the meatus is convex upward and backward; to inspect the drum, pull the auricle upward, backward, and lateral to straighten it.
  • In infants: pull auricle downward and backward.
  • Clinical: site of otitis externa (infection of meatus skin); foreign bodies lodge here.

Tympanic Membrane

  • Pearly-grey, oval, thin, semi-transparent; separates external meatus from middle ear.
  • Inclined at ~55° to the meatus floor (anterior and inferior walls of meatus are longer).
  • Tense part (pars tensa): large, lower portion, tightly stretched; contains middle fibrous layer.
  • Flaccid part (Shrapnell's membrane / pars flaccida): small, superior, lax; lacks middle fibrous layer; site of cholesteatoma formation.
  • Umbo: central depression formed by the tip of the handle of malleus.
  • Cone of light: bright triangular reflection, visible anteroinferior to umbo on otoscopy; loss suggests effusion or retraction.
Marking (8 marks): Auricle structure + lobule (1.5) · Meatus divisions (1/3 cartilaginous, 2/3 bony) (1) · Adult otoscopy technique (1) · Tympanic membrane colour/angle (1) · Tense and flaccid parts named + difference (1.5) · Umbo + cone of light (1) · Clinical relevance stated (1)
Essay 2
Describe the middle ear (tympanic cavity): its six walls with key relations, the auditory ossicles (names, order, attachments, function), and the auditory tube.
10 marks

Six Walls of the Tympanic Cavity

  • Tegmental wall (roof / superior): tegmen tympani — thin bone; separates from middle cranial fossa. Erosion → intracranial complications.
  • Jugular wall (floor / inferior): thin bone; separates from internal jugular vein (may be deficient, separated only by mucosa).
  • Carotid wall (anterior): related to internal carotid artery; bears two parallel semicanals — upper for tensor tympani, lower for auditory tube.
  • Mastoid wall (posterior): related to mastoid process; bears opening of mastoid antrum (aditus) superiorly; pyramidal eminence contains stapedius.
  • Membranous wall (lateral): formed largely by tympanic membrane; epitympanic recess above (houses malleus head and incus body).
  • Labyrinthine wall (medial): lateral wall of inner ear; bears tympanic promontory (from basal cochlear turn); fenestra vestibuli (oval window) posterosuperiorly — closed by stapes base; fenestra cochleae (round window) posteroinferiorly — closed by secondary tympanic membrane. Facial canal prominence crosses this wall.

Auditory Ossicles

  • Three smallest bones in body: malleus (hammer), incus (anvil), stapes (stirrup).
  • Order (lateral to medial): malleus → incus → stapes.
  • Malleus: handle attached to tympanic membrane; head articulates with incus.
  • Incus: lies between malleus and stapes; long process articulates with stapes.
  • Stapes: footplate (base) closes the fenestra vestibuli (oval window).
  • Function: transmit and amplify vibrations. Sound → tympanic membrane → malleus → incus → stapes → oval window → inner ear.
  • Tensor tympani (acts on malleus, tenses drum) + stapedius (acts on stapes, dampens oscillation, protects inner ear from loud sounds; supplied by CN VII).

Auditory Tube

  • ~3.5–4.5 cm; lateral bony 1/3 + medial cartilaginous 2/3.
  • Connects tympanic cavity to nasopharynx; normally closed; opens during swallowing/yawning to equalise pressure.
  • In children: shorter, wider, more horizontal → otitis media risk.
Marking (10 marks): All 6 walls named with correct relations (3) · Oval + round windows on labyrinthine wall (0.5) · Tegmen tympani clinical significance (0.5) · Ossicles names + order (1) · Attachments (malleus to drum; stapes to oval window) (1) · Sound transmission pathway stated (1) · Muscles named (tensor tympani + stapedius) (0.5) · Auditory tube structure, function, children's difference (2.5)
Essay 3
Describe the inner ear: distinguish bony from membranous labyrinth, describe the cochlea (structure and hearing receptor), and the vestibular apparatus (balance receptors).
10 marks

Bony vs Membranous Labyrinth

  • Bony labyrinth: series of cavities in the petrous temporal bone, filled with perilymph (high Na+). Three parts: cochlea, vestibule, 3 semicircular canals.
  • Membranous labyrinth: lies within the bony labyrinth, filled with endolymph (high K+). Three parts: cochlear duct, utricle + saccule, membranous semicircular ducts. The two fluids do not communicate.

Cochlea — Hearing

  • Cochlear spiral canal winds 2.5 turns around the central modiolus.
  • Osseous spiral lamina divides canal into: scala vestibuli (above) and scala tympani (below), communicating at the apex via the helicotrema. The cochlear duct lies between them.
  • Cochlear duct walls: superior = vestibular membrane (Reissner's); lateral = stria vascularis (produces endolymph); inferior = basilar membrane.
  • Organ of Corti on basilar membrane: inner hair cells (1 row) + outer hair cells (3 rows); covered by tectorial membrane. Tonotopic: high frequency → base; low frequency → apex.
  • Impulses travel via cochlear division of CN VIII.

Vestibular Apparatus — Balance

  • Utricle and saccule (lie in vestibule): contain maculae — organs of static balance; detect gravity and linear acceleration/deceleration via otoliths on gelatinous membrane.
  • Membranous semicircular ducts (3 ducts within 3 bony canals; anterior, posterior, lateral): each has an ampulla containing the ampullary crest (crista ampullaris) — organ of kinetic (dynamic) balance; detects angular (rotational) acceleration.
  • Impulses travel via vestibular division of CN VIII.
Marking (10 marks): Bony vs membranous labyrinth clearly distinguished + correct fluids (2) · Cochlea: 2.5 turns, modiolus, three scalae (1.5) · Cochlear duct walls: vestibular + basilar membranes (1) · Organ of Corti location + tonotopy (1.5) · CN VIII cochlear division stated (0.5) · Utricle/saccule: maculae + static balance + linear acceleration (1.5) · Semicircular ducts: ampullary crests + angular acceleration (1.5) · CN VIII vestibular division (0.5)
Essay 4
Describe the pathway by which sound waves are conducted from the external environment to nerve impulses in the auditory cortex (hearing pathway).
8 marks

1. External Ear (Air Conduction — Normal Pathway)

  • Sound waves enter the external acoustic meatus and strike the tympanic membrane.
  • The tympanic membrane vibrates, converting air pressure waves into mechanical movement.

2. Middle Ear (Ossicular Chain)

  • Vibrations pass via the ossicular chain: malleus → incus → stapes.
  • The ossicular chain acts as a mechanical amplifier (impedance matching): transforms low-pressure air vibrations into high-pressure fluid vibrations (area reduction tympanic membrane → oval window, plus lever action of ossicles → ~20-fold amplification).
  • The base of the stapes pushes on the fenestra vestibuli (oval window).

3. Inner Ear (Cochlea)

  • Stapes movement sets perilymph in the scala vestibuli into motion.
  • Pressure wave travels through perilymph → through the vestibular membrane → into endolymph of the cochlear duct → vibrates the basilar membrane.
  • Basilar membrane displacement deflects hair cell stereocilia in the organ of Corti against the tectorial membrane → mechanotransduction → nerve impulse.
  • Pressure wave dissipates at the fenestra cochleae (round window), which bulges into the tympanic cavity via the secondary tympanic membrane.
  • Tonotopic activation: high-frequency → basal hair cells; low-frequency → apical hair cells.

4. Neural Pathway

  • Impulses travel via cochlear division of CN VIII → cochlear nuclei (pontomedullary junction) → superior olivary nucleus → inferior colliculus (midbrain) → medial geniculate nucleus (thalamus) → primary auditory cortex (Heschl's gyri, superior temporal gyrus, Brodmann areas 41, 42).

Bone Conduction (Alternative Pathway)

  • Sound waves → skull → bony labyrinth → perilymph → endolymph → organ of Corti → nerve impulse. Used in hearing aid devices and Weber/Rinne testing.
Marking (8 marks): Sound wave to tympanic membrane (0.5) · Ossicular chain in correct order (1) · Amplification/impedance matching concept (0.5) · Oval window named (0.5) · Perilymph → endolymph → basilar membrane (1) · Organ of Corti: mechanotransduction + tonotopy (1.5) · Round window pressure dissipation (0.5) · CN VIII cochlear branch stated (0.5) · Central pathway to cortex (named nuclei) (1.5) · Bone conduction mentioned (0.5)
Essay 5
Write notes on the clinical correlations of ear anatomy: (a) otitis media and the auditory tube, (b) Ménière's disease, (c) conductive vs sensorineural deafness.
8 marks

(a) Otitis Media — Role of the Auditory Tube

  • Otitis media = infection of the middle ear (tympanic cavity).
  • In children, the auditory tube is shorter, wider, and more horizontal than in adults. Upper respiratory tract infections cause nasopharyngeal inflammation that ascends readily along the tube into the tympanic cavity.
  • Signs: fever, otalgia, conductive hearing loss, bulging red tympanic membrane on otoscopy. May perforate → otorrhoea.
  • Complication of spread: mastoiditis (via aditus to mastoid antrum); intracranial infection (erosion of tegmen tympani → meningitis/abscess); facial palsy (facial canal in labyrinthine wall is thin/incomplete).

(b) Ménière's Disease

  • Caused by endolymphatic hydrops (excess endolymph in membranous labyrinth).
  • Classic triad: (1) episodic vertigo (attacks 20 min – several hours); (2) sensorineural hearing loss (low-frequency initially); (3) tinnitus (roaring or ringing); often with aural fullness.
  • Distension affects both cochlea (hearing) and vestibular end-organs (balance) simultaneously.
  • Management: salt restriction, betahistine, diuretics; endolymphatic sac decompression in refractory cases.

(c) Conductive vs Sensorineural Deafness

  • Conductive deafness: problem in the external or middle ear preventing sound transmission to the inner ear. Causes: impacted cerumen (wax), otitis media with effusion (“glue ear”), tympanic membrane perforation, otosclerosis (bony ankylosis of stapes footplate in oval window). Rinne test: BC > AC in the affected ear. Weber lateralises to the worse ear. Treatable (hearing aid, surgery).
  • Sensorineural deafness: problem in the cochlea (hair cells) or CN VIII. Causes: noise-induced damage (high-frequency loss, 4 kHz notch), Ménière's disease, presbycusis (age-related), acoustic neuroma (vestibular schwannoma in internal acoustic meatus), ototoxic drugs (aminoglycosides, cisplatin). Rinne test: AC > BC but both reduced. Weber lateralises to the better ear.
Marking (8 marks): Otitis media + anatomical basis (auditory tube difference in children) (2) · Complications of otitis media: mastoiditis + intracranial (1) · Ménière's: endolymphatic hydrops + correct triad (2) · Conductive deafness: definition + 2 causes + Rinne finding (1.5) · Sensorineural deafness: definition + 2 causes + Rinne finding (1.5)
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