Anatomy of the Ear & Hearing Flashcards
(27 cards)
3 regions of the ear
Outer, middle and inner ear
Purpose of the regions of the ear
Outer and middle ear transmit sound
Inner ear converts sound energy to fluid motion then electrical signal
what is the Pinna
- The visible part of the external ear
- Acts as a tunnel to direct sound
- Cartilage, connective tissue and fat
- Collects sound
- Provides 5-6dB amplification
Externa Ear Canal
Outer 1/3 cartilagionous: skin, hair, follicles, sebaceous & ceramunous glands
Inner 1/3 bony: thin skin over perioesteum
Tympanic Membrane
Boundary between external and middle ear. Sound waves cause vibration
Middle Ear
- Air filled cavity
- Bounded by temporal bone with ear drum laterally
- Communicates with nasopharynx via eustachian tube. Tube equalises pressure
- Contains the ossicles
- Oval and round windows on medial wall communicate with inner
Ossicles
- Malleous, Incus, Stapes
- Transmit vibration from tympanic membrane to oval window of cochlea
Inner Ear
Fluid filled sac within a bony chamber. Consists of cochlea and semi-circular canals
Cochlea
- The organ of hearing
- Spiral shape containing coiled fluid filled channels
- Sound waves are converted into fluid motion then electrical impulses
Conductive deafness
Disease of external or middle ear prevents sound wave from getting to cochlea
Causes of conductive deafness
Ear wax (cerumen), osteomata, congenital absences of external ear canal, fluid in middle ear, problems with the ossicles
Glue ear
When middle ear is filled with fluid instead of air. Common in children. Usually goes away on its own.
Haemotympanum
Bleeding within the middle ear cavity with an intact tympanic membrane. Often caused by basal skull fracture.
Problems with the ossicles
Dislocation and erosion
Sensorineural deafness
Disease of middle ear or organ of hearing. Due to damage cochlea, cochlear nerve or central centres of hearing
Causes of sensorineural deafness
Presbycusis, death of hear cells
Presbycusis
Progressive, irreversible hearing loss of ageing
How sensorineural deafness is treated
Hearing aids
How is hearing assessed
Audiogram
Tuning fork tests
- Useful bedside test
- Does not give absolute measure of hearing level
- Used to detect unilateral hearing loss and whether conductive or sensorineural
- Need a 512hz tuning fork
Weber Test
A 512hz tuning fork is struck then placed on patients forehead. Sound energy is then transmitted into the skull and to each cochlea. Ask where sound is heard.
Webers’ Test Result
- Normal: sound is heard equally in both ears
- Sensorineural deafness: sound is heard louder on the side of the intact ear
- Conductive deafness: sound is heard louder on the side of the affected ear
Rinne Test
- Bone conduction is first tested by holding fork on the tip of the mastoid bone. Tell patient to tell you when they can no longer hear the sound.
- When no sound is hear, air conduction is then tested by holding fork near pinna.
- Ask patient if they can hear the sound agan
Rinne’s Test Result
Normal result: Air conduction > Bone conduction (Rinne’s positive)
Sensorineural deafness: Air conduction > Bone conduction (Rinne’s positive) – both air and bone conduction reduced equally
Conductive deafness: Bone conduction > Air conduction (Rinne’s negative)
