Lecture 13- The Middle ear Flashcards
The middle ear is a
- Air filled cavity.
- Between tympanic membrane and inner air
- Contains ossicles
ossicles of the inner ear
- tiny (smaller than a coin)- from lateral to medial MIS
malleus
incus
stapes
stapes looks like a
stirrup
stapes is in contact with the
oval window
how do ossicles transmit information about sound waves to the inner ear
- vibrations from sound received on the TM
- past onto the malleus–> incus –> stapes
- Stapes looks like a stirrup
- Foot plate which communicates with the cochlear–>oval window
- Membrane will move in relation of movement to the stapes
- Transmitting vibration to waves in a fluid medium
Ossicle movement tampered by muscles
tensor tympani and stapedius
facial nerve lesion and hearing
- Nerve to Stapedius- facial nerve branch
- Related to acoustic reflex where the stapedius contracts to dampen the vibration of the footplate of the stapes in response to very loud noises
Otosclerosis
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- One of the most common causes of acquired hearing loss in young adults
- Both genetic and environmental
- Exact cause unknown
-
Ossicles fused at articulations due to abnormal bone growth particularly between base plate of stapes and oval window
- Sound vibrations cannot be transmitted effectively to cochlea
- Present with gradual unilateral or bilateral conductive hearing loss
Pharyngotympanic tube
equilibrates pressure of the middle ear with atmospheric pressure
explain how the pharygotypanic tube equilibrate pressur eof the middle ear with atmospheric pressure
- Mucous membrane of middle ear continuously reabsorbed air in the middle air causing negative pressure
- However pharyngotympanic tube (eustachian tube) allows equilibrium of pressure within the middle ear cavity with that of the atmosphere
- Also allows ventilation of and drainage if mucus from the middle ear
- If dysfunction of PT increasing build up of pressure in inner ear
- E.g. causes development of cholesteatoma or otitis media with effusion
Otitis media with effusion “glue ear” on otoscope
- looks retracted- loss of light reflex
- straw coloured
- evidence of fluid
MOA of otitis media with effusion
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- Not an actual infection- can predispose to infection
- Due to eustachian tube dysfunction
- Fluid and negative pressure in middle ear
- Decreases mobility of TM and ossicles affecting hearing
- Also draws fluid from across the mucous membrane in the middle ear
treatment of otitis media
- Most resolve spontaneously without Abx in 2/3 months
- If persists or impede speech and language development/ school performance
- Require grommets (tympanostomy tube)
- Act to maintain equilibration of pressure
acute otitis media is more common in
infants/children
- Pharyngotympanic tube is shorter and more horizontal in infants
- easier passage for infection fromt he nasopharynx to the middle ear
- tube can block more easily, compromisisng ventilation and drainage of middle ear, icnreasing risk of middle ear ifnection and glue ear
- Signs and symptoms of acute otitis media (middle ear infection) include
- Otalgia –> infants may pull or tug at ear
- Other non-specific symptoms e.g. temp
- Red +/- bulging TM and loss of normal landmarks middle ear cavity full of puss
mastoiditis
Middle ear cavity communicates via mastoid antrum with mastoid air cells
- Provides a potential route for middle ear infections to spread into the mastoid bone (mastoid air cells)
- Osteomyelitis
- Red and swollen
- Distortion of ear
important anatomical relations of the ear
signs and symptomd of acute otitis media
- Otalgia –> infants may pull or tug at ear
- Other non-specific symptoms e.g. temp
- Red +/- bulging TM and loss of normal landmarks middle ear cavity full of puss
- Mostly viral aetiology
- Occasionally bacterial
- S. penumoniae
- H. influenza
