Physiology of Hearing Flashcards
What is the function of the external ear?
receives sound
channels sound to tympanic membrane
What is the structure of the middle ear?
air filled cavity in temporal bone
What is the function of the middle ear?
amplifies sound waves and transmits them to fluid filled inner ear
Where are the ossicles located?
middle ear
What is the function of the ossicles?
conduct sound vibrations from tympanic membrane to oval window
What is impedance?
a mediums resistance to movement
pressure waves when in relation to sound
What is impedance matching?
amplification of pressure so that there is sufficient energy to move through fluid
When does impedance matching occur?
transfer of incoming vibration from the comparatively large, low impedance tympanic membrane to the much smaller high impedance oval window
What is the importance of impedance matching?
prevents sound loss
What are the oval and round windows?
two openings of the cochlea to the middle ear
What is the function of the oval and round windows?
permit transmission of pressure wave in enclosed canal and vibration of the basilar membrane
What is the cochlea?
part of the auditory system of the inner ear
shell shaped part of the bony labyrinth
What is the scala media?
endolymph filled cavity inside the cochlea between the tympanic duct and the vestibular duct
What is the ionic composition of endolymph?
high potassium concentration
low sodium concentration
negligible calcium
Where is perilymph located?
fills the scala vestibuli and tympani
What is the ionic composition of perilymph?
high sodium concentration
low potassium and calcium concentration
Where does scala vestibuli begin?
oval window
Where does scala tympani end?
round windows
What is the advantage of endolymph having a high potassium concentration and perilymph having a low potassium concentration?
only apical end of hair cells in endolymph
passive potassium influx at apical end
passive potassium efflux at other end
saves ATP
What is the organ of Corti?
sensorineural organ of the cochlea
What is the organ of Corti composed of?
supporting cells
basilar membrane
cochlear hair cells
What is transduction?
conversion of sound vibrations (mechanical energy) to electrical energy
How does transduction occur in the organ of corti?
sound waves delivered to the oval window are transmitted to the perilymph and vibrate the basilar membrane
cilia of the cochlear cells are bent by the vibration of the basilar membrane
Where are the cell bodies of the afferent fibres from the organ of Corti?
spiral ganglion of the cochlear nerve
What is the auditory pathway?
vestibulocochlear nerve (CN VIII) - cochlear nuclei - superior olivary cortex - lateral lemniscus - inferior colliculus - thalamus - primary auditory cortex
What is the pneumonic to remember the auditory pathway?
ECOLI E - Eighth CN C - Cochlear nuclei O - superior Olivary complex L - Lateral Lemniscus I - Inferior colliculus
Where is the auditory cortex located?
superior temporal gyrus
What connects the middle ear to the nasopharynx?
eustachian tube
What is the role of the eustachian tube?
opens briefly during swallowing and yawning to allow equalisation of pressure either side of the tympanic membrane
What muscles open the eustachian tube?
tensor veli palatini
levator palatine
