DIAG: external, middle, inner ear

• Eardrum: boundary between ME and IE

DIAG: temporal bone (left)

• Different parts of temporal bone

DIAG: external ear

• Pinna and ear canal
• Pinna: collect sound, less important in humans
• Canal: cartilaginous (outer) + bony (inner)
• Both lined by skin, therefore all skin problems can occur in canal
• Ear has good cleansing properties

DIAG: structure of pinna

DIAG: normal eardrum

• Margin of eardrum: fibrous annulus, bony
• Eardrum semi-transparent, paper-thin
• Lateral process of malleus divides eardrum into upper and lower
• Anterior and posterior malleolar folds joining malleus to eardrum
• Pars flaccida: lower: inner and outer epithelial lining, fibrous layer in between
• Pars tensa: upper: no middle fibrous layer

DIAG: ME

• 3 ossicles: malleus, incus, stapes (air-filled)

DIAG: ME lateral view

• Facial nerve (VII): from BS, medial wall of ME (horizontal segment), vertical segment in mastoid process
• Anterior: internal carotid
• Posterior: internal jugular vein (from jugular bulb)
• Disease: BV exposed to ME (therefore careful of puncturing during ME procedure)

DIAG: labyrinth (IE)

• Ant: Eustachian tube
• Medial: oval and round window
• Cochlea (anterior)
• Vestibule + semicircular canals (posterior)

DIAG: bony and membranous labyrinth

• N = bony labyrinth fused with temporal bone
• Membranous labyrinth: floating in bony labyrinth (same configuration)

DIAG: Organ of Corti

• Cochlea has 3 tubes going together

1. Scala vestibuli (connected to oval window)
2. Scala tympani (round window)
3. Scala media

DIAG: sensory end-organs for vestibular function

• Anterior cochlea: hearing
• Posterior: balance
• Linear velocity: saccule + utricle (end in macula)
• Angular velocity: semicircular canals (end in ampulla cristi)

DIAG: semicircular canals on both sides

• Work in pairs

DIAG: CN VIII

• Vestibular
• Cochlear
• Go into internal auditory meatus with CN VII (therefore problems affecting both are common)

DIAG: middle cranial fossa

• Internal canal in line with external canal

DIAG: internal acoustic meatus

• Cerebellopontine angle
• Closeness of VII/ VIII, V, and IX/ X/ XI

• Both VII and VIII through internal auditory measure and canal
• Near parotid gland

DIAG: facial n (intracranial segment)

• Medial wall, covered by bone
• Congenital/ disease: facial n exposed in ME air (dehiscent facial n)
• After passing past oval window, turns sharply downward (labyrinthal segment to mastoid segment) -> then exits skull (extracranial portion)

DIAG: facial n (extracranial course)

DIAG: facial n and parotid gland

• Through stylomastoid foramen to exit skull, through parotid gland (divides parotid into deep and superficial)
• Parotid gland lesion can cause facial n palsy

DIAG: facial n branches

Hear with our brains

• Absorb energy of the stimulus
• Bring about changes in the state of the sensory cell
• Initiating electrical impulses in the n leading from the sensory organ to CNS

• N are multitude of individual fibres
• Each fibre arises from an individual neurone
• Receptive and sensory neurones

• All or none response of excited sensory neurone
• Spike rate (frequency) increases and stimulus intensity increases and vice versa
• Plateau: once a certain level reached, increase in loudness will not result in increased firing, will remain at same rate (but hearing will be painful long before this point)

External ear: flattened, so collection of sound not so important, but contours amplify high-frequency sounds

Movement of stapes on oval window

1. Quiet sound: rocking action

2. Loud sound: piston action

As stapes pressure on oval window, round window bulges out (fluid inside and surrounding bone are incompressible)

• Cochlea has 2 1/4 turns
• Coils around modiouls - a bony and hollow core
• Modiolus contains CN VIII and bipolar cell bodies - spiral ganglion

3 fluid-filled columns

• Scala vestibuli filled with perilymph
• Scala media (cochlear duct) filled with endolymph
• Scala tympani filled with perilymph

Endolymphatic hydrops = Meniere's disease

• Sensory epithelium of hearing
• Inner and outer hair cells
• Pillar cells
• Tunnel of Corti (filled with perilymph)
• Inner and outer supporting hair cells

3-4 rows of outer hair cells (cylindrical)

1 row of inner hair cells (flask-shaped)

• Inner supporting hair cells lie on osseous spiral lamin
• Flask-shaped
• Stereocilia arrange in one row
• Rootlets in circular plate
• During development, IHC has kinocilium but lost during maturation
• No contact with tectorial membrane (controversial)
• Cf. Outer hair cells with embed in tectorial membrane

• Outer supporting cell (Deiters' cell) has cup-shaped depression that supports base of OHC
• OHC are cylindrical-shaped
• OHC's line up 3 or 4 W-shaped rows
• Kinocilia is at bottom of W
• Top of the kinocilia are embedded in the tectorial membrane (shearing)
• When stimulated at resonant frequency OHC actually vibrates (active process)

• Hair cell bents towards kinocilia: more firing (excitation)
• Bends away from kinocilia (inhibition)

• Mechanical transmission of sound from stapes to a specific place along the cochlear duct (travelling wave)
• Amplification of the vibrations at the most excited portion (maxima) of the cochlear duct
• Maxima: tonotopic arrangement of cochlea (frequency and amplitude)
• Once the energy has passed through the place of matching resonance, the travelling wave stops suddenly
• If slowed down slowly, we would hear other frequencies as well (frequency selectivity)
• Transduction of mechanical vibration into nerve impulses

Basal part: next to stapes (ME), high-frequency

Apical part: low-frequency 50 Hz

• Cochlear hair cells are innervated by peripheral processes of spiral ganglion cells
• 3x as many OHC and IHC
• 95% of spiral ganglion neurones innervate only IHC
• 5% go to OHC making small afferent sensory synapses with OHC
• Problem if you have IHC damage
• Mild-mod hearing loss: OHC damaged only
• Severe-profound hearing loss: IHC damaged (hearing-aid cannot help, only amplifies the sound - eg. Elderly)

• Angular: 3 semicircular canals
• Linear: utricule + saccule

• Cristae ampullares in the semicircular canals
• Maculae in the utriculus and the sacculus

• VHC are either flask-shaped (type I) or columnar (Type II)
• Type I cells have large synaptic endings called calyces
• Type II cells have mouton-type terminals synapsing on their base
• Projected stereocilia and kinocilia
• Analogy: piano pendulum; adjusting height of weight
• Weight at top: more sensitive to gravity (therefore wider at top)

• Anchored in cuticular plate
• Each stereocilium widens at top
• Contained parallel molecules of actin (same protein in m cells)
• Kinocilium has no actin
• All cilia are bound together to form ciliary tuft

• Composed of supporting cells and hair cells
• Embedded in an otolithic membrane (gelatinous structure containing many crystals of calcium carbonate)
• Crystals adds weight to the membrane
• Half of the kinocilia point in the opposite direction
• Ear stones: when crystals dislodge

• Composed of supporting cells and hair cells
• Stereocilia and kinocilia embedded in gelatinous membrane, cupula
• Cupula do not contain otolith
• Bending of ciliary tufts openings the potassium......

• Hearing loss: conductive, sensorineural, mixed
• Otorrhoea: serous, purulent, blood-stained (pus = infection; blood = inflam, neoplastic, traumatic)
• Otalgia: ear-pain; inflam, trauma, neoplastic, referred from other H&N region
• Tinnitus: Pt hears sound not present in environment; non-specific; assoc. with all types of hearing loss
• Mx: underlying problem? Hearing loss?
• Vertigo: subjective, objective; Hallucination of movt; Subjective (Pt feels he is rotating) + Objective (Pt feels surroundings are rotating)

• Otoscope: most common, convenient
• Camera into ear canal - look at monitor
• Systematic approach: EE, ME, IE
• Eg. If you suspect perforated eardrum, don't just inspect IE

• Pinna
• External auditory meatus
• Also any facial anomalies

• Level
• Anomalies: eg. Pinnal cartilage

1. Congenital abnormalities: microtia (small pinna), bat-ear (pinna sticking out; operable), preauricular sinus, accessory auricle (more than a pinna), low-set ear, cup ear (congested)
2. Acquired abnormalities: skin ulcers, haematoma, swellings, surgical scar, deformity

• Mass lesion: benign, malignant, all skin lesions
• Surgical scar: eg. Inflammatory, neoplastic diseases in past (commonest: postaural, anaural, incision at meatus)
• "Tenderness": pain on touch, test for pain, eg. Otitis externa

Tenderness, swelling, lymph node, subcutaneous/subperiosteal abscess

• Size of meatus: meatoplasty (enlarged through surgery), meatal atresia/ stenosis (congenital or acquired - scarring after infection/ trauma/ surgery)
• Wax impaction
• Discharge
• Foreign body: insects
• Mass lesion
• Inflammation; Furunculosis, otitis externa, soft tissue and bony swellings

Integrity of the ear-drum

• Inflammation, tympanosclerosis
• Cone of light to assess the position of the eardrum
• Retraction pockets
• Fluid/mass behind the eardrum

• Site and kind of ear-drum perforation
• Active or inactive infection, fungal growth mucus and status of the middle ear mucosa

Facial nerve function

Evidence of sensorineural hearing loss

Nystagmus: 1^°, 2^°, 3 ^°

Facial nerve function: paralysis, dyskinesia

Hallpike's manoeuvre (BPPV with chronic dizziness/vertigo)

Cerebellar sign/ trigeminal nerve

Other examinations:

Examination of:

• Nasopharynx
• Palate
• Cervical lymph node

Fork tests (512 Hz)

Rinne's test

Weber test (unilateral hearing loss)

Speech tests:

Listen

Whispering, conversational voice, shouting voice; masking

Dr. Dennis Au, Audiologist

1. Conductive,
2. Sensorineural,
3. Mixed & functional

Terms: audiogram, frequencies, decibel, degree of hearing loss

Adult

1. Pure-tone audiometry,
2. Speech tests

Children

1. >2.5 yo - Play audiometry
2. 1.5-2.5 yo - Visual reinforcement audiometry
3. 1 mo-1.5 yo - Distraction test

Evoked response audiometry - auditory brainstem response, cortical evoked response audiometry (hearing and neurological assessments)

Otoacoustic emissions (outer hair cells)

Impedance audiometry (ear canal volume, middle-ear pressure, middle-ear compliance, acoustic reflex and Eustachian tube function)

Terms: vertigo, dizziness, light-headedness, horizontal and rotary nystagmus

Multi-sensory inputs (vision, proprioception and vestibular) with co-ordinated, automatic muscle outputs (muscles of postural control)

Electronystagmography - ocular-motor and vestibulo-ocular systems (tracking, smooth pursuit, position optokinetic test, gaze test, caloric tests and fixation index)

Dynamic posturography - vestibular-spinal system

Rotational chair - frequency-specific vestibular functions

Hallpike test - benign paroxysmal positional vertigo

Systematic vestibular and postural exercise for central compensation and adaptation