The Auditory system
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What (briefly) makes up the outer, middle and inner ear?
• Outer - pinna + canal • Middle - tympanic membrane, ossicles • Inner - cochlea, oval window
What are the differences between perilymph and endolymph?
• Perilymph - normal ECF conc (high Na, low K), surrounds the cochlear duct. • Endolymph - Unusual ECF conc (high K, low Na), separated from perilymph by membranes and is within cochlear duct.
What membranes surround the spiral organ?
• tectorial membrane (on top) • basilar membrane (bottom) - separates from scala tympani
What happens to the stereocilia to depolarise the hair cell?
• Sterocilia tilt in direction of longest one • More potassium channels open • K+ influx • Depolarises (-40mv)
What happens to the stereocilia to hyperpolarise the hair cell?
• Sterocilia move in direction of smallest one • More K channels close • Inner membrane remains negative • Hyperpolarised
What are (3) vulnerabilities in transduction and function of the auditory system?
• Conduction of sound wave can be blocked leading to conductive hearing loss • Production and removal of endolymph must be balanced, can become imbalanced • Destroyed hair cells can’t be replaced
What is the physiology of loud sounds in the ear? How is this damaging?
• Large vibrations • Bigger receptor potentials • More transmitter released -> more APs • Strong vibrations can damage sterocilia / kill hair cells
How are we able to listen to different pitches?
Each pitch activates a characteristic set of receptors and labelled-lines.
What is the primary auditory pathway?
• cochlear nerve • cochlear nuclei • inferior colliculus • medial geniculate nucleus • primary auditory cortex (temporal lobe)
What is presbyacusis?
When old people lose high frequency hearing
What is the difference in function between the lateral and medial superior olivary nuclei?
• Lateral - compares loudness of sounds in two ears (for high frequency) • Medial - compares moment when sound reaches two ears (for low frequency)
How many inner hair cells per ear do we have?
~3,500