6) The Ear Flashcards
The ear is divided into which 3 parts?
External ear
Middle ear
Internal ear
What separates the external and middle ear?
Tympanic membrane
Which tube joins the middle ear to the nasopharynx?
Pharyngotympanic/Eustachian/Auditory tube
What is the external ear comprised of?
Auricle (Pinna) - elastic cartilage covered by skin
External acoustic meatus
What structures comprise the auricle (pinna)?
Helix (outer rim)
Tragus (flap guarding external acoustic meatus)
Non-cartilaginous lobule (lobe)
What is the blood supply to the external ear?
Posterior Auricular & Superficial Temporal arteries (ECA)
Which nerves provide sensory innervation to the auricle?
Anterior to the external auditory meatus - Auriculotemporal nerve (branch of mandibular Viii)
Rest of auricle - Great Auricular nerve
What is the external auditory meatus?
Cartilaginous tube/canal lateral 1/3 Bony canal medial 2/3 Lies in temporal bone Lined by skin secreting cerumen (modified sebum) Sigmoid shaped
What is ear wax comprised of?
Discarded skin cells & cerumen of external auditory meatus
What is the tympanic membrane?
Partition between external & middle ear
Shallow cone, apex points medially
Thin, oval, semi-transparent, pearly-grey membrane
Which nerves supply the tympanic membrane?
External surface: Auriculotemporal nerve (branch of Viii)
Auricular branch of vagus nerve
Internal surface: Glossopharyngeal nerve
What is the Ear-Cough reflex?
Stimulation of Auricular branch of Vagus
e.g. insertion of cotton bud
Produces cough reflex, some even vomit
Over-sensitivity
How can the tympanic membrane be affected in disease?
Dull & becomes red/yellow
Dilated blood vessels - injection of drum
Dense, white plaques - Tympanosclerosis
Bulging - Pus/fluid in middle ear
Retracted - Infratympanic cavity pressure reduced, obstruction of Eustachian tube
Perforation - Trauma, Infection
What makes up the middle ear?
Narrow air-filled chamber in petrous part of temporal bone
Tympanic cavity proper
Epitympanic recess
What is the tympanic membrane proper?
Space directly internal to tympanic membrane
Connected to nasopharynx & mastoid air cells
What is the epitympanic recess?
Space superior to the tympanic membrane
Is the Auditory tube usually open or closed?
Closed
Intermittently opened by pull of attached palate muscles when swallowing
What are the contents of the middle ear?
Auditory ossicles: Malleus, Incus, Stapes
Stapedius & Tensor Tympani muscles
Chorda Tympani nerve
Tympanic plexus of nerves
What are the auditory ossicles?
Malleus
Incus
Stapes
What is the function of the auditory ossicles?
Relay vibrations encountered by tympanic membrane to inner ear
Amplify & concentrate sound energy to oval window
What is the function of the tensor tympani muscle?
Inserts into handle of malleus, pulls handle medially
Tenses tympanic membrane, reducing amplitude of oscillations
Prevents damage to inner ear when exposed to loud sounds
What is the function of the stapedius muscle?
Pulls stapes posteriorly, tilts its base over oval window
Tightens anular ligament, reduces oscillatory range
Prevents excessive movement of stapes
Innervated by nerve to stapedius (facial)
What is the relationship of the facial nerve and the middle ear?
CN VII lies in the facial canal
separated from tympanic cavity by thin bony partition
Middle ear infection may cause lesion
What is the inner ear?
Labyrinth
Channels hollowed out of the Petrous temporal bone,
surrounding the membranous labyrinth
Which structures are contained within the middle ear?
Vestibule Semi-circular ducts & canals Cochlea Cochlear duct Organ of Corti
What are the main functions of the inner ear?
Receptors that respond to rotational acceleration & static pull of gravity
Receptors of auditory apparatus
What is an auricular haematoma?
Trauma resulting in bleeding within auricle
Blood collects between perichondrium & auricular cartilage
Distorts contours of auricle
If blood not aspirated - fibrosis (Cauliflower’s ear)
What congenital pinna deformities can occur?
Antihelix deformity
Pinna malformation
Pre-auricular pit
Pre-auricular skin tag
What is acute otitis externa?
Infection/inflammation of the external acoustic meatus
Common in swimmers
Itching & pain in external ear
What is otitis media?
Infection of the middle ear
Often secondary to URTIs via Eustachian tube
More common in children - shorter, more horizontal eustachian tube
Earache, bulging red tympanic membrane (pus/fluid)
Inflammation of mucous membrane may cause blockage of eustachian tube
Name some causes of a perforated tympanic membrane
Otitis media, insertion of foreign bodies, trauma, excessive pressure (scuba diving)
Middle ear deafness, often heal spontaneously
What is mastoiditis?
Infection of mastoid antrum & mastoid air cells
Results from otitis media
- inflammation of mastoid process (swelling behind ear)
- may spread into middle cranial fossa in children (osteomyelitis)
How might the Eustachian tube be blocked?
Swelling of mucous membrane e.g. infections
Low pressure in tympanic cavity, retraction of tympanic membrane
Hearing affected
Adenoidal hypertrophy (children, EBV)
What is hyperacusis?
Loss of protective action against loud noises
e.g. lesion of facial nerve, paralysis of stapedius
How does motion sickness occur?
Discordance between vestibular & visual stimulation
What 3 symptoms do injuries of the peripheral auditory system cause?
Hearing loss
Vertigo
Tinnitus
How does conductive hearing loss occur?
Anything in external or middle ear that interferes with conduction of sound or movement of oval or round windows
People will speak with a soft voice
Surgery/hearing device
How does sensorineural hearing loss occur?
Defects in pathway from cochlea to brain
cochlea, cochlea nerve, brainstem
Cochlear implants
What is Ménière syndrome?
Blockage of cochlear aqueduct
Recurrent tinnitus, hearing loss & vertigo
Sense of pressure in ear, distortion of sounds & sensitivity to noise
What is cholesteatoma?
Necrotic mass of dead skin caused by:
Blockage of eustachian tube
Negative middle ear pressure leads to retraction pockets
Dead skin cells accumulate
Erosion of middle ear structures & bone via lytic enzymes
What is otalgia?
Ear pain
Infection/Inflammation around ear
Pain from teeth, pharynx or cervical spine commonly referred to the ear
What is pruritus?
Itching
Primary disorder of external ear, or middle ear discharge
What is otorrhoea?
Discharge from the ear
Indicates acute or chronic infection
Blood/CSF discharge associated with skull fracture
