15b. Inner Ear, Hearing, Vestibular Function Flashcards
What is presbycusis?
Age-related bilateral hearing impairment
Unable to hear frequencies below 1500 Hz
What are the risk factors for presbycusis?
Noise exposure Ototoxins Infections Smoking, hypertension, vascular disease, diabetes Immunological disorders Genetics (mtDNA)
What is sensorineural presbycusis?
Degeneration of the cilia on hair cells of organ of Corti or loss of cochlear nerve fibres
What is conductive presbycusis?
Stiffening of the basilar membrane of the cochlea or ossicles
What is metabolic presbycusis?
Atrophy of the stria vascularis
Loss of resting potential of endolymph
What is the treatment for presbycusis?
Ear protection, avoid loud noises
Assistive devices
Lip reading
Amplification devices and cochlear implants
What is the function of hearing aids?
Amplify waves in the outer ear and auditory canal
What are the parts of a hearing aid?
Microphone, amplifier, speaker
What is the use of both a hearing aid and a cochlear implant called?
Electric Acoustic Stimulation
What is the function of a cochlear implant?
Capture and convert sound to electrical signals
Goes to electrode array in cochlea via a stimulator
What type of energy does the vestibular system rely on?
Hydraulic
What is the name of the sensory epithelium of the ampulla of the semi-circular canals?
Crista ampullaris
What does the crista ampullaris detect?
Angular acceleration (rotation)
What are the utricle and saccule collectively known as?
Otolith organs
What do the otolith organs detect?
Position of the head with respect to gravity (linear acceleration)
What does the superior semi-circular canal detect?
Up and down movements
What does the posterior semi-circular canal detect?
Head tilting to one shoulder
What does the horizontal semi-circular canal detect?
Head turning side to side
What is the name of the gelatinous mass that surrounds the crista ampullaris?
Cupula
What happens to the endolymph when the semi-circular canals rotate?
Endolymph stays still
Pushes against cupula which bends stereocilia of hair cells
What happens when the stereocilia are pushed against the kinocilium?
Influx of K+ and Ca+ via mechanoceptors causes depolarisation
Release of glutamate activates the vestibular nerve
What happens in the opposite ear to the one with the activated vestibular nerve?
Stereocilia bend away from the kinocilium
Hair cells hyperpolarise
What are the Otolith Organs?
Membranous labyrinths within the vestibule
What is the saccule connected to?
Scala media
What is the utricle connected to?
Semi-circular ducts
What is the name of the sensory epithelium in the otolith organs?
Macula
What is the macula composed of?
Supporting cells, sensory hair cells, vestibular dark cells
What surrounds the macula?
Otolithic membrane
Describe the make-up of the otolithic membrane
Gelatinous
Contains calcium carbonate crystals (otoliths, otoconia)
What plane do the macular hair cells project into in the utricle?
Vertical
What does the utricle respond to?
Horizontal linear acceleration
Head tilt
What plane do the macular hair cells project into in the saccule?
Horizontal
What does the saccule respond to?
Vertical linear acceleartion
Low frequency vibration
What is the resting potential of the endolymph?
80mV
What is the resting potential of the perilymph?
6mV
What transport proteins maintain the resting potential of the endolymph?
Na/K
NKCC1 (Na, K and 2Cl into cell)
K+ leak channel
What is motion sickness?
Continual movement of endolymph after head movement has stopped and visual cues tell the brain you are stationary
What is Méniere’s disease?
Unilateral fluid imbalances in inner ear due to a build-up of endolymph or a reduction of blood flow to the ear
What are the risk factors for Meniere’s disease?
Abnormal immune response
Viral infection
Genetics
What are triggers for Meniere’s disease?
Stress, overwork, fatigue, emotional distress, migraine
Autoimmune disorders
Pressure changes
High salt, caffeine, alcohol
What are the symptoms of Meniere’s disease?
Feeling of fullness in ear Low-pitched tinnitus Hyperacusis (more sensitive to changes in sound) Sensorineural hearing loss Nystagmus, vertigo, ataxia Nausea and vomiting Tumarkin's otolithic crisis
What is Tumarkin’s otolithic crisis?
Spontaneous feeling of being pushed
Patient will fall to the ground without notice
What diet changes can help with Meniere’s disease?
Reduce salt, caffeine, alcohol and smoking
What lifestyle changes can help with Meniere’s disease?
Counselling and physical therapy
What medications can help with Meniere’s disease?
Anxiolytics
Antiemetics
Diuretics
Steroid injection into inner ear (reduces inflammation)
Gentamycin injection into inner ear (purposefully damages to stop vertigo)
What surgeries can help with Meniere’s disease?
Endolymphatic sac surgery
Endolymphatic duct blockage
What is the procedure for endolymphatic sac surgery?
Bone is removed and shunt placed in endolymphatic sac to drain fluid
What is the procedure for endolymphatic duct blockage?
Bone removed and clip placed on endolymphatic sac to prevent fluid build-up in rest of inner ear