Anatomy
What does the outer ear consist of? Describe briefly what thy look like (or draw)?
Pinna(or auricle)- visible part of ear
External auditory meatus(ear canal)- Sigmoid canal, 7mm in diameter, ~25mm long, running from auricle to tympanum. First ⅓ surrounded by cartilage, remaining ⅔ surrounded by bone.Hair, sebaceous and ceruminous glands in cartilaginous portion.
Tympanum (eardrum)- Collagenous membrane separating outer from middle ear. Concave externally, umbo is most depressed part of concavity. Malleus is firmly attached to medial tympanic surface
Describe function of outer ear
Converts acoustic energy to kinetic energy
Sound waves external to body are funnelled into the ear canal via the pinna, and are converted to vibrations of the eardrum.
TRUE OR FALSE?
Hearing loss can affect relations with family and friends.
True
What are the two types of hearing loss?
Conductive and sensorineural hearing loss
What are the two tests used to check impaired hearing?
Rinne test and Weber test
Describe the anatomy of the middle ear
Air-filled chamber between eardrum and inner ear. Three smallest bones in body (ossicles) connect eardrum to oval window- Malleus(hammer), incus(anvil) and stapes (stirrup)
Describe the function of the middle ear
Converts kinetic energy of tympanic membrane to hydraulic energy in inner ear, via oscillations of the ossicles.
3 ways in which hearing loss can impact one psychologically
Feelings of anger, low confidence especially in social settings, frustration, depression, communication difficulties, embarrassment, mistrustful of others, short-tempered and less tolerant of others.
Describe the two types of hearing losses
Conductive- Problem conducting sound waves through outer ear, eardrum or middle ear.
Sensorineural- Problem in cochlea (Organ of Corti), vestibulocochlearnerve or auditory cortex of the brain.
Describe a Weber test and a Rinne test
•Vibrating 256 Hz tuning fork held against middle of forehead. Patient asked to report in which ear the sound is loudest.
•Vibrating 512 Hz tuning fork held against mastoid process. When sound can no longer be heard, fork moved to 1-2cm from auditory canal.
What are the middle ear muscles and where do they attach to?
Tensor tympani: attaches to the malleus.
Stapedius: attaches to the stapes.
What is the purpose of the ossicles?
Eardrum area is 17x that of stapedial foot plate. Ossicles act like a lever (malleus= long arm; incus= short arm) with an average lever arm factor of 1.3. Thus, sound pressure is concentrated with a pressure gain of 20 or more.
3 examples of social problems people with impaired hearing may face
Conversation become less fluid, interaction in noisy places difficult, personality changes, difficulty distinguishing sounds- may feel like your ignoring them, isolated- taking part in fewer social activities, intimacy issues- feeling of inadequacy, problems getting on at work.
3 causes of conductive hearing loss
Earwax, Otitis externa, perforated ear drum, embrane tension, Otitis media, damage to small bones within the middle ear, infection, fluid in the middle ear
What does each of the test test for?
Rinne- Measures the relative conduction of sound through air and through bone.
Weber- Distinguishes between conductive and sensorineuralunilateral hearing loss.
Which two branches of the facial nerve (VII) enter the middle ear?
•The chorda tympani runs anteriorly across pars flaccida of tympanic membrane and between incus and malleus. Serves taste buds on the anterior ⅔ of the tongue.
•The stapedial nerve innervates the stapedius muscle.
Why is the contraction of the middle ear muscles beneficial?
Contraction reduces the ability of the ossiclesto vibrate and so dampens sound reaching inner ear. Both muscles contract in response to high intensity sounds or during vocalisation = acoustic reflex or attenuation reflex. Timing of reflex is 50-100 ms so it cannot protect against sudden loud sounds.
3 examples of adaptations/ aids for those with hearing loss
Doorbells- visual, extra-loud or portable doorbells
Alarms- use light or vibrations instead of sound
Theatre and cinema- audio enhancement
Televisions- customised televisions with e.g.subtitles, signing
3 causes of sensorineural hearing loss
Congenital, Presbycusis(age-related) inflammatory disease e.g. measles, mumps, meningitis, syphilis, Ménière’s disease, ototoxic drugs, physical trauma, noise-induced, benign tumours on the auditory nerve
What do the results for both tests indicate?
Rinne- If tuning fork can still be heard then air conduction > bone conduction (AC > BC). If tuning fork can no longer be heard then bone conduction > air conduction (BC > AC).
Weber- If normal ear hears sound louder, hearing loss is sensorineural. If defective ear hears sound louder, hearing loss is conductive.
Describe the anatomy of the inner ear and its contents. (Draw if easier)
Labyrinth made up of vestibular system (dedicated to balance) Bony labyrinth = surrounding petrous part of the temporal bone. Membranous labyrinth = system of tubes and chambers within bony labyrinth, filled with endolymph.
Cochlea (for hearing)-
Cochlea is a coil that makes 2¾ turns around a bony column (modiolus).Three sections: Scalamediaor cochlear duct, filled with endolymph. Scala vestibuli and Scala tympani both filled with perilymph.
What is the function of the inner ear?
Converts kinetic energy of ossicles into hydraulic energy of fluid in inner ear, and then into electrochemical signals in the vestibulocochlear nerve (VIII).Vestibular part of labyrinth uses movement of fluid to sense rotational and translational accelerations. Cochlea uses movement of fluid to sense external pressure changes (sound)