Physiology of Hearing Flashcards
How does sound move through the air?
As sound waves
What is a sound wave?
Vibrations of molecules causing compression and rarefaction of the air particles
What is frequency?
The number of compression & rarefaction (waves) in a second.
What is the range of human hearing?
20 Hz - 20,000 Hz
What causes hearing loss - high sound pressure or low sound pressure?
High sound pressure
What is sound pressure?
Localised pressure caused by a sound wave travelling through and increasing / decreasing atmospheric pressure
What is sound pressure measured in?
Decibels
How does the hearing system hear sounds?
It converts vibrational waves (sound) to electrical neuronal impulses via mechanoreceptors in the ear.
What type of channels do mechanoreceptors contain? Where are these channels found on the mechanoreceptor?
They contain cation channels - found in the membrane of the receptors.
How do mechanoreceptors work roughly?
The vibrational sensation causes the sensory receptor in the membrane to open causing an influx of cations, causing depolarisation, thus allowing for the release of NTs OR generation of AP as a result.
What are the three parts of the outer ear?
Pinna
External auditory canal
Tympanic membrane (ear drum)
Where are the auditory ossicles found?
Middle ear
Where is the cochlea found?
Inner ear
Name the three auditory ossicles
Malleus
Incus
Stapes
What can happen to the ossicles as we get older to cause hearing loss?
They can fuse a bit, losing their ability to vibrate as much
Which ossicle is attached to the tympanic membrane?
Malleus
Which ossicle is attached to the oval window?
Stapes
How is the stapes attached to the oval window?
Annular ligament - connective tissue
What is the purpose of the middle ear?
It converts sound waves from the outer wave to fluid waves in the inner ear.
What senses is the inner ear responsible for?
Audition (hearing)
Balance
What is the cochlea made of?
Bony labyrinth & membranous labyrinth
What is the bony labyrinth filled with?
Perilymph
What is the membranous labyrinth filled with?
Endolymph?
How do perilymph and endolymph differ?
Different ion concentrations
Perilymph = high Na and low K+
Endolymph = low Na and high K+
What are the three parts of the cochlear canal?
Scala vestibuli (upper)
Scala media (middle)
Scala tympani (lower)
What does the Scala vestibuli contain?
Perilymph
Where does the Scala vestibuli end?
Oval window
What dos the Scala media contain?
Endolymph + Organ of Corti
What does the Scala tympani contain?
Perilymph
Where does the Scala tympani end?
In the round window
What does the helicotrema do?
Allows communication between the Scala vestibuli and Scala tympani
What does oscillation of the stapes do?
Causes pressure waves in the perilymph of the Scala vestibuli and Scala tympani
What does vibration in the Scala vestibuli & tympani do?
Causes vibration of the basilar membrane in the organ of corti
What is the sensory area of the auditory system called?
The organ of Corti
What does the organ of corti sit on?
Basilar membrane
What types of hair cells are found in the organ of corti?
What is the difference between them?
Outer hair cells
Inner hair cells
Outer - are found on the outer side of the organ of corti - they touch the tectorial membrane
Inner hair cells - found on the inner side - do not touch the tectorial membrane
What are hair cells?
Sensory mechanoreceptors
What are hair cells supported by?
Epithelial cells
What activates hair cells?
Vibrations of the basilar membrane
What does the organ of corti compose of?
Basilar membrane + hair cells + tectorial membrane
What do hair cells contain that respond to movement?
Stereocilia
What are stereocilia?
Projections of hair cell membrane
What are stereocilia made from?
Actin filaments
What happens when basilar membrane laterally displaces the hair cell stereocilia?
K+ influx into the hair cell from the endolymph = depolarisation
Depolarisation allows voltage-gated Ca channels to open - Ca in - leads to K+ being pumped back out of the cell by calcium-gated channels = depolarisation.
Calcium also causes a release of NTs into the synaptic cleft.
Which direction does the basilar membrane have to move in order to initiate an AP? Which direction does not initiate a hair cell AP?
Laterally = AP
Medially - no AP
What happens when there is medial displacement of the stereocilia?
Medial displacement causes hyperpolarisation and K+ efflux - does not open Ca channels.
What causes outer hair stereociliar to move?
What causes inner hair stereociliar to move?
Outer cell = bending of tectorial membrane causes them to move.
Inner cell = movement of endolymph causes them to move
Where are outer and inner hair stereociliar located in relation to the tectorial membrane?
Outer cell = embedded in the tectorial membrane
Inner cell = lie beneath the tectorial membrane
What type of nerves are the outer and inner hair cells innervated by?
What does this mean in terms of control?
Outer hair cells = afferent AND efferent nerves
Inner hair cells = afferent only.
Means that vibrations can be modulated and allows the CNS to protect the mechanoreceptors. When the vibrations are too strong - the efferent nerve to the outer hair cells can stop them moving as much and prevent damage.
How are different frequencies detected by the cochlea?
Hair cells respond to different frequencies depending on their location in the cochlea membrane.
Near the base = narrow and stiff cells - therefore only low frequency can be detected.
Near the apex = wide and flow - high frequency is detected
What is the organisation of hair cells by frequency sensitivity called?
Tonotopic organisation
Which nerve takes sound information from the cochlea?
Cochlear nerve = part of VIII
What is the name of the ganglion within the cochlea?
Spiral ganglion
Where does the spiral ganglion project to?
The ventral and dorsal cochlear nucleus (in the spinal cord)
Which complex controls the efferent nerves of the outer hair cells and receives afferent signals from the cochlear nuclei - giving the ability to distinguish sounds by time of arrival & intensity?
Superior olivary complex
Which part of the auditory pathway protects to the inferior colliculus?
The lateral lemniscus
Which part of the auditory pathway is tonotopically organised - allowing perception of high v low frequencies?
Inferior colliculus
Which part of the auditory pathway is tonotopically organised - relaying precise information on the frequency and intensity of sound?
Medial geniculate nucleus (thalamus)
Which part of the auditory pathway receives all auditory system input?
Auditory cortex
Which Brodmann area is the auditory cortex located in?
41
Which Brodmann area is the auditory association area?
42
Which area of the brain is important for interpretation of the spoken word?
Wernicke’s area
Which area of the brain is involved in speech?
Broca’s area
Which areas of the brain send descending projections (efferent nerves) to the auditory system?
Areas 41&42
What are the two main types of hearing loss?
Conductive hearing loss
Sensorineural hearing loss
What is disease in the outer ear or middle ear resulting in hearing loss called?
Conductive hearing loss
What is disease in the cochlea or neural pathways from cochlea (to brain) resulting in hearing loss known as?
Sensorineural hearing loss
What is hearing loss from a noisy work environment called? What does it do to the ear?
Occupational hearing loss - causes deterioration of the organ of Corti
What is drug induced hearing loss called? Which drugs cause this?
Ototoxic hearing loss
Streptomycin, neomycin & quinine
What is destruction of the cochlea by virus called? Which viruses can cause this?
Infectious hearing loss
Mumps, rubella or cytomegalovirus
What is hearing of a sound that has no external source called?
Tinnitus
What types of things can cause conductive hearing loss?
Earwax
Infection (outer or inner)
Perforated eardrum
Tumour in the ear canal or middle ear
Otosclerosis
What is inflammation of the middle ear called?
Otitis media
What causes otosclerosis?
What is otosclerosis?
Genetic or external factors (e.g. infection)
The temporal bone sclerosis - means stapes becomes fixed to the oval window causing impaired vibration.
What are the possible treatments for otosclerosis?
External hearing aids
Surgery & implant
What is the risk of a stapedectomy (removal of stapes?)
That it damages the branch of VII (chorda tympani) which passes through the inner ear.
Which is the most common genetic mutation for sensorineural hearing loss?
GJB2 - protein involved in K+ homeostasis.
Which is the second most common form of genetic cause for non-syndromatic hearing loss?
SLC26A4 - anion transporter issues.
