Anatomy Of The Ear Flashcards
Signs and symptoms of ear disease
- hearing loss
- tinnitus
- vertigo
- otorrhoea
- otalgia
- facial droop : rare complication of disease involving middle ear
What is tinnitus?
Sounds perceived but do not come from external source such as ringing, humming, whistling
What two things is the ear an organ of?
Hearing
Balance
What is otalgia?
Ear pain
What is otorrhoea?
Discharge from the ear
Describe the external ear region
- pinna + external auditory meatus (ear canal)
- skin-lined (keratinised squamous epithelium)
- extends as far as lateral surface of tympanic membrane
What is the external auditory meatus?
Ear canal
What is the boundary between the external and middle ear regions?
Tympanic membrane
Describe the middle ear region
- air filled cavity
- ossicles (malleus, inus + stapes)
- lined with respiratory epithelium (ciliated pseudostratified columnar epithelium)
- connected to nasopharynx via pharyngotympanic tube
What is the external ear region lined with?
Skin lined
Keratinised squamous epithelium
What is the Middle ear region lined with?
Respiratory epithelium
Ciliated pseudostratified columnar epithelium
What is the inner ear lined with?
Stereocilia
Describe the inner ear region
- fluid filled ducts
- cochlea
- semicircular canals, utricle, saccule
- lined with sterocilia
What bone is the ear associated with?
Petrous part of temporal bone
Innervation to the external ear for general sensation
Cervical spinal nerves C2/3
Trigeminal V > auriculotemporal nerve
Vagus X
Facial VII
Innervation of the middle ear cavity + medial surface of tympanic membrane
Glossopharyngeal IX (tympanic nerve)
What should you suspect if a patient presents with otalgia with no other signs suggestive of ear disease + normal ear exam?
Alternate site of pathology due to referred pain
e.g. laryngeal + pharyngeal cancers, TMJ disease, oropharyngeal disease
What nerve carries hearing from the ear?
Vestibulocochlear VIII
Function of the external ear
Collects, transmits + focuses sound waves on to tympanic membrane
Describe the external acoustic meatus
- 2.5cm long
- sigmoid shape
- outer 1/3 cartilage + inner 2/3 bone
- skin lined (keratinised squamous epithelium)
- hair + glands only in cartilage part
What glands produce ear wax?
Where are they located?
Ceruminous glands
Cartilaginous part of the eternal acoustic meatus
Describe the self cleaning function of the external acoustic meatus
Dead skin migrates laterally out from the tympanic membrane
Describe a otoscopic exam
- visualises external acoustic meatus + external surface of tympanic membrane
- pinna is pulled up + back in adults | down + back horizontally in children
Parts of the tympanic membrane
- pars tensa
- pars flaccida
- manubrium of malleus
- cone of light (way the light reflects off the TM off the otoscope)
What nerve is associated with the tympanic membrane?
Chorda tympani nerve
(From the facial nerve VII)
Why can the tympanic membrane perforate?
Loud noise
Infection building up behind it
If you see little white patches on the tympanic membrane, what are they called and what is it?
What does it indicate?
- Tympano sclerosis
- Hardening of the membrane
- Indicates trauma or irritation in past
What abnormal things may you see on the tympanic membrane?
Grommet
Perforation
Tympano sclerosis
What is a bulging + erythematous tympanic membrane indicative of?
Something is building up in the middle ear cavity which is pushing the TM up
What is a excessively retracted (pulled in medially) tympanic membrane +/- fluid behind it indicative of?
Middle ear pathology (possibly related to pharyngotympanic tube + pressure)
e.g. otitis media with effusion
What are changes to the tympanic membrane that are indicators of middle ear pathology?
- bulging + erythatmous
- excessively retracted +/- fluid behind
Function of the middle ear ossicles
Relay + amplify vibrations from tympanic membrane to oval window
What are the ossicle vibrations tampered by?
Tensor tympani
Stapedius
What is hyperacusis?
Unusual intolerance to ordinary sounds
(Normal sounds sound really loud)
What is the acoustic reflex?
When the tensor tympani + stapedius muscles contract if there’s excessive vibrations from loud noise
What does an ineffective acoustic reflex cause?
What could cause an ineffective reflex?
Hyperacusis
Facial nerve lesion related to nerve to stapedius
What does opening of the pharngotympanic tube do?
- Allows for equalisation of pressure both sides of the tympanic membrane
- ventilation
- drainage of mucous
What can dysfunction of the pharyngotympanic tube cause?
Examples
Pressure imbalances involving the middle ear
e.g. otitis media with effusion, cholesteatoma
How can infection spread from the nasopharynx to the middle ear?
Along the pharyngotympanic tube
Compare the pharngotympanic tube between children and adults
What does this mean?
In children:
- Shorter and more horizontal in infants + children
- easier passage for infection to spread between the nasopharynx + middle ear
- PT opens near pharyngeal tonsils (can get blocked if enlarged)
Important anatomical relations of middle ear
- pharyngotympanic tube
- mastoid cells
- facial nerve runs through
- sigmoid sinus behind
Why are complications in the middle ear potentially life threatening?
If they spread intracranially:
- they can involve the sigmoid sinus + cause dural venous sinus thrombosis
- they can affect the meninges > meningitis
- could form an abscess in the brain itself
Describe the fluid movement in the inner ear and what it’s perceived as
Fluid movement in:
- cochlea > perceived as sound
- semicircular canals, utricle, saccule > perceived as position sense/balance
What does a disease of the inner ear cause?
Hearing loss
Tinnitus
Balance disturbance + vertigo
What is fluid movement in the cochlea perceived as?
Sound
What is fluid movement in the semicircular canals, utricle, saccule perceived as?
Position sense/balance
What are the three sensory inputs of the balance system?
vestibular
visual
somatosensory
Describe how the body senses position + balance
- in the inner ear canal
- head movements cause movement of fluid within the vestibular system
- fluid shifts gelatinous matrix in which the stereocilia are
- stereocilia bend > AP generate > CN VIII
- signals perceived as sense of position and balance
Describe how we hear
Indicate what parts can cause hearing loss (underlined)
- pinna + external auditory meatus focus + funnel sound waves to tympanic membrane
- TM vibrates
- vibrations of ossicles > movement in cochlear fluid
- sensed by sterocilia in cochlear duct
- movement of sterocilia in organ of Corti > AP in CN VII
- primary auditory cortex make sense of the input in the temporal lobe
Conditions involving what can cause hearing loss?
- external auditory meatus
- tympanic membrane
- vibrations of ossicles
- movement of the sterocilia in organ of corti
- vestibulocochlear nerve VIII
What are the ossicles of the ear?
From TM to oval window of cochlea
Malleus
Incus
Stapes
