Lecture 6.2: Hearing Disorders Flashcards
What is Sound?
- A compressive wave that travels at 343m/sec in air
- > 1500m/sec in water
What are the 2 properties of sounds waves?
1) Frequency = Distance = Hertz (Hz)
2) Volume = Pressure = Decibels (dB)
What is the hearing range (frequency) of humans?
20-20,000 Hz
What is normal volume of conversation in humans?
60dB
At what volume doe sound get painful for humans?
120dB
What is Hearing?
Conscious appreciation of vibration perceived as sound
What is Deafness?
Hearing loss so severe that there is very little or no functional hearing
What does it mean to be Deaf (capital D)?
- Deaf (capital D) people that have been deaf for all of
their lives, or since before they started to learn to talk * Prelingually deaf
What does it mean to be deaf (lower case d)?
- Anyone that has a severe hearing problem
- Usually postlingual
- May use hearing aids/cochlear implants
What does it mean to be hard of hearing?
Mild to moderate hearing loss
External Ear Anatomy (3)
- Pinna (Auricle)
- External Auditory Meatus
- Tympanic Membrane
Middle Ear Anatomy (4)
- Tympanic Membrane
- Ossicles
- Mastoid
- Eustachian Tube
Inner Ear Anatomy: Bony Labyrinth (4)
- Cochlea
- Vestibular Apparatus
- 3 Semicircular Canals
- Filled with perilymph
Inner Ear Anatomy: Membranous Labyrinth (4)
- Inside Bony Labyrinth
- Cochlear Duct
- Utricle and Saccule
- Semicircular Ducts
- Filled with Endolymph
Mechanism of Hearing
- The pinna collects and amplifies sound waves
- The EAM funnels them to the tympanic membrane
(TM) - The TM vibrates, transferring the vibrations
sequentially to the ossicles, the oval window and the
fluid of the inner ear - The middle ear amplifies the sound by ~30dB
- Thus the middle ear converts sound waves in air of
EAM to vibrations in fluid of inner ear - The inner ear converts mechanical signals (vibrations
in fluid) to electrical signals → auditory pathway→
brain
Function of the Inner Ear
1) Convert mechanical signals (vibrations in
fluid) to electrical signals → auditory pathway→
brain
2) Maintain balance
Inner Ear openings to Middle Ear (2)
- Oval window (connects vestibule to ME at stapes
footplate) - Round window (connects scala tympani with middle
ear)
Mechanism of Hearing in the Cochlea
- Vibration of stapes at oval window→ vibrations of
perilymph in scala vestibuli - Vibrations transmitted to endolymph in cochlear duct
and spiral organ of Corti on basilar membrane - Hair cells stimulated→impulses travel along CNVIII to
brain
Auditory Transduction: Hair Cells
- 4 rows of hair cells
- 1 inner hair cells row (provide most of the signal to CN
VIII) - 3 outer hair cell rows (role in modulating the response
of the inner hair cells)
What is the Primary (Lemniscal) Pathway?
Main pathway through which auditory information reaches the primary auditory cortex
What is the Non-Lemniscal Pathway?
Mediating unconscious perception eg. attention, emotional response, and auditory reflexes
Can supranuclear lesions cause hearing loss?
No
Where in the ear do lesions occur in conductive hearing loss?
Lesions in the outer or middle ear
Where in the ear do lesions occur in sensorineural hearing loss?
Lesions in the inner ear or vestibuloccochlear nerve (VIII)
What is Mixed hearing loss?
Lesions in the outer or middle ear AND Lesions in the inner ear or vestibuloccochlear nerve (VIII)
Where in the ear do lesions occur in Central hearing loss?
Lesion in the auditory pathway in the brain (rare)
Hearing loss usually involves sensitivity and acuity, what does this mean?
Sounds are harder to hear (sensitivity) and they are usually distorted (acuity)
What happens to the Tympanic Membrane in Conductive Hearing Loss?
- EAM/TM may look abnormal
- (except otosclerosis)
- May be temporary or treatable