Physiology of Hearing Flashcards
What are the functions of hearing?
- Alerts us to danger
- Recognition
- Communication
- Localising objects
What are the two attributes of sound that can be measures, and what are their units?
Frequency (Hz)
Intensity (dB)
From what intensity of sound upwards can permanent hearing damage occur?
> 90dB
What makes up the peripheral auditory system?
- Outer ear
- Middle ear
- Cochlea
- CN VIII
What are the 3 bones of the middle ear, and what is their location to each other?
Malleus (lateral)
Incus (middle)
Stapes (medial)
What is osteoclerosis, its cause, and treatment?
Osteoclerosis is hearing loss caused by the fusion of the stapes to the oval window.
It can be fixed through surgery
What is otitis media, and what population is it most common in (and also type of infection it often arises from)?
Inflammation or infection of the middle ear.
Most common in children and usually arises from respiratory tract infections
What is adhesive otitis sometimes referred to as?
Glue ear
What is adhesive otitis, what can it lead to if chronic, and what can it be treated with?
The filling of the middle ear with secreted fluids and when chronic it can lead to hearing loss.
Treated with via grommets (draining of the ear via tube that passes through the eardrum to reach middle ear).
What region the ear is the cochlea in, what shape is it, and what are its two ends?
Cochlea is in the inner ear and is a coiled structure
Has an apical end and a basal end.
What is the function of the apical and basal ends of the cochlea?
Apical end is tuned to low frequency sounds
Basal end is tuned to high frequency sounds
Where is the cochlear duct and what is its shape?
Found within the cochlea and it runs throughout the cochlea
What are the 3 parts of the cochlear duct and what type of fluid do they contain?
Scala vestibuli (perilymph)
Scala media (endolymph)
Scala tympani (perilymph)
What are the contents of perilymph and endolymph?
Perilymph (high Na+ and low K+)
Endolymph (low Na+ and high K+)
Where is the organ of corti found, and what does it detect?
Found within the Scala media
Detects the sound-induced movements of the basilar membrane (which it is next to)
What are the 2 types of sensory hair cells within the organ of corti, and what type of fibres are they innervated with?
Inner hair cells (sensory fibres)
Outer hair cells (mainly motor fibres but also some sensory fibres)
How many hair cells are in each cochlea, and can they be regenerated?
15000 in each cochlea
Can’t be regenerated once they die
What are the 2 membrane ends of the hair cells found in the organ of corti, and what fluid are they bathed in?
Apical end (bathed in endolymph)
Basolateral end (bathed in perilymph)
What are the stages of mechanotransduction in hair cells?
1) Deflection of hair cells lead to non-selective cation channels opening (which are found between hair cells)
2) Since K+ is the major cation of endolymph, it enters and depolarises the hair cells
3) Voltage-gated Ca2+ channels then open and the influx of Ca2+ activates vesicle release
4) Afferent fibres then get activated
What is electromotility, and what are the two types that can occur to hair cells?
Movement of hair cells which is caused by changes in electrical charge.
Shortening of hair cells which is caused by depolarisation
Lengthening of hair cells which is caused by hyperpolarisation
What is protein is able to modify the length of outer hair cells, and what type of protein is it?
Prestin (modified transmembrane anion transporter)
What are the 2 types of afferent fibres that innervate the hair cells, and what do they detect?
Type I which innervates inner hair cells and detects sound over a wide range of intensities
Type II which innervates outer hair cells and detects painfully loud sounds
How are inner and outer hair cells innervated by efferent fibres?
Inner hair cells: Efferent fibres from the lateral olive synapse onto Type I spiral neurons, which then synapse onto inner hair cells
Outer hair cells: Efferent fibres from the medial olive directly synapse onto them
What are the medial and lateral Oliver from?
Arise from the superior olivary complex (which is a collection of brainstem nuclei)
What are the functions of the outer and middle ear?
Outer ear collects sound and funnels it onto the tympanic membrane
Middle ear transmits the vibrations of the tympanic membrane onto the oval window of the cochlea
What is the eardrum also known as?
Tympanic membrane
What nerve do Type I and II spiral neurons neurons arise from, and what structure do they from?
Arise from the vestibulocochlear nerve
Form the cochlear ganglion
What are some factors that can cause sensorineural hearing loss?
- Noise
- Ageing
- Ototoxic drugs (e.g. some antibiotics and loop diuretics)
- Genetic mutations (half are gap junction mutations)
What are cochlear implants and some of their limitations?
Electronic devices that can provide a sense of sound to those who can’t hear.
1) Expensive (so limited to western world)
2) Speech sounds robotic
What is the route of auditory information form the cochlea to the brain?
1) Cochlear nucleus
2) Superior olivary nucleus
3) Nuclei of lateral lemniscus
4) Inferior colliculus
5) Medial geniculate
6) Primary auditory complex
On what lobe is the primary auditory complex found?
Upper surface of temporal lobe
What is sensory and motor aphasia?
Sensory aphasia: Difficulty understanding written and spoken language
Motor aphasia: Difficulty speaking or facilitating motor movements of speech
