18, 19, 20 HEARING Flashcards
Give essential reasons for hearing
Education, learning, social engagement, mobility, health/ well being
What percentage of people have hearing loss in NZ
13-18%
Describe some etiological factors in hearing loss
Age Noise exposure Genetic Trauma Tumours Anti cancer drugs, amino glycoside antibiotics
Describe a common tumour that effects hearing
acoustic neuroma/ vestibular schwannoma
Non malignant.
Grows in vestibular cochlear nerve schwann cells
Impact of hearing and hearing impairment
Poor speech Language and cognitive impairment Literacy, learning and employment impairment Social isolation Depression Tinnitus
Describe frequency
Number of sound waves per second.
Describe amplitude
magnitude of the vibration considered as pressure or intensity
How is amplitude measure
In decibels (sound pressure level) using logarithmic scale
Describe features of the outer ear
Pinna are cartilaginous folds which amplifies and direct sound.
External auditory meatus is cartilage tubing whereby cerumen gland within it secrete earwax which is cleaning and antibacterial and reeks water/ traps debris.
Describe the anatomy of middle ear
Air filled cavity.
Starts at tympanic membrane-
Contains three auditory ossicles; malleus, incus, stapes joined by synovial joints and ligaments.
Has eustachian tube for pressure equalisation and aeration.
Oval window at base of stapes.
Round window (pressure release) inferior to oval
What are the two small inner ear muscle called, what nerve innervate them and what are their functions
The stapedius and the tensor tympani. Attached to the stapes and malleus and innervated by the facial and trigeminal nerves respectively. Muscle contractions initiated by loud noises stiffen the ossicular chain and protect the inner ear from loud noises. called middle ear reflex.
What nerve sits between the malleus and the incus
The chords tympani, a branch of the facial nerve that senses taste
Why do we need a middle ear?
The middle ear acts as a transformer to match the low impedance of air to high impedance of inner ear fluid. The large surface eardrum and shape of the ossicles means that movements in the larger bones (malleus) are transmitted to more forceful movements in the stapes (snow boot/ high heel) to do with distribution of energy.
Where is the inner ear situated in the skull
In the petrous part of the temporal bone
Describe the anatomy of the cochlea
Connected at its basal end to the middle ear via the oval window. Coiled bony structure with three inner tubes; scala vestibuli, scala media, scala tympani. Bisected by the cochlear partition from basal to almost apical end, just before the apical end is the helicotrema a gap where the scala vestibular scala tympani mis their perilymph. The scala media sits within the cochlear partition. The cochlear partition supports the basilar and tectorial membranes.
The organ of corti sits on the basilar membrane. The organ of corti is made up of sensory hair cells
Describe the anatomy of the organ of corti
Sits on the basilar membrane which is wider and more flexible at the apical end.
How does the travelling wave transmit sound signals
The travelling wave results in the stereocillia of inner hair cells being bent against the tectorial membrane. Tip links join adjacent stereocillia. Stretching of the tip links (that occurs in the wave) opens mechanically gated ion channels depolarising the hair cells which in turn leads to an action potential on CVIII.
Describe how the cochlear determines different frequencies of sound
The difference in width and flexibility of the basilar membrane means that it vibrates maximally at different positions. This is what results in the tonotopical distinction of frequencies. With high frequencies best detected at the stiffer narrow basal end and low frequencies at the apical end. The travelling wave reaches a point of maximum displacement (in relation to the width/ flexibility of the basilar membrane) at this point the energy is transmitted into the sensory cells the hair cells.
What is the function of outer hair cells
Connected with efferent fibres from the superior olivary complex. Thought to have an important role in modulating basilar membrane motions and as a cochlear amplifier.
Describe the composition of perilymph and endolymph and the function of this
Perilymph is similar to normal extracellular fluid with high Na+ and low K+. Endolymph as high K+. Assists in creating electrochemical gradient conducive with fast ion transduction and minimal energy consumption by hair cells. Also voltage differences acts as sound amplifier
What produces the endolymph
The stria vascularis
What is Meniere’s disease
An fluid imbalance with excess fluid in the labyrinth of the inner ear. Causes hearing loss, tinnitus and balance disorders.
What is a major cause of congenital deafness
A genetic abnormality in the production of Cx26, a protein that forms gap junctions imprtotant in the recycling of K+ to the stria vascularis.
Define a conductive hearing loss
Hearing loss as a result of conduction of sound waves along the outer, middle ear, and tympanic membrane.
