THE EAR AND HEARING Flashcards
what is humans frequency range for sound?
20-20,000 Hz
what is the part of the ear we can see called?
the pinna aka auricle
what is the name of the ear canal?
external auditory meatus
whats the name of the ear drum?
the tympanum
whats the function of the pinna?
to funnel sound into thr external auditory meatus and filters sounds
in other mammals what other roles does the pinna have?
signalling mood and assisting with thermoregulation
outline the structure of the external auditory meatus?
a sigmoid shaped tube that extends from the deep part of the concha to the tympanic membrane. The walls of the external 1/3 are formed by cartilage, whereas the inner 2/3 are formed by the temporal bone.
the tympanic membrane is a concave structure, what do we call the most depressed region?
the umbo - also where the handle of the malleus attached
whats the function of the tympanum?
vibrate in response to sound pressure waves and thus transmit sound energy into the middle ear
whats the blood supply of the external ear?
posterior auricular branch of the external carotid artery.
what nerves innervate the skin of the auricle?
greater auricular nerve
lesser occipital nerve
auriculotemporal nerve
what innervates the external auditory meatus?
auriculotemporal nerve and branches of facial and vagus nerves
what inervates the deeper aspect of the auricle?
branches of facial and vagus nerves
why do some individuals complain of an involuntary cough when cleaning their ears?
due to stimulation of the auricular branch of the vagus nerve which is also responsible for the cough reflex
what is within the middle ear?
ossicles and eustachian tube
whats the function of the ossicles?
transmit sound and amplify it
what are the 3 ossicles?
malleus (hammer)
incus (anvil)
stapes (stirrup)
why are mammals much better at hearing than birds?
as mammals have 3 ossicles and birds have 1
whats the function of the Eustachian tube?
to allow pressure equilisation between middle ear and outside world - important to prevent damage to tympanic membrane
how can you open the Eustachian tube?
lower and protrude the jaw
what are the 2 middle ear muscles and where do they attach?
tensor tympani attaches to malleus
strapedius atached to the stapes
whats the function of tensor tympani and stapedius muscles?
pulls the eardrum inward and decreases the area over which sound energy may be collected. = acoustic reflex
what is the acoustic reflex?
the contraction of the stapedius muscle elicited by the presentation of an acoustically loud sound
what is tensor tympani innervated by?
branch of mandibular nere
what is the stapedius muscle innervated by?
facial nerve
whats the 2 main functions of the inner ear?
converting mechanical signals from the middle ear into electrical signals
to maintain balance by detecting position and motion
where is the inner ear located?
in the petrous part of the temporal bone
what are the 2 main components of the inner ear?
bony labyrinth and membranous labyrinth
what is within the bony labyrinth?
cochlea, vestibule and 3 semicircular canals
what is within the membranous labyrinth?
cochlear duct, semi-circular ducts, utricle and saccule
whats the fluid in the bony labyrinth?
perilymph
whats the fluid in the membranous labyrinth?
endolymph
what are the 2 openings in the inner ear that connect to the middle ear?
oval window - separates middle ear and vestibule
round window - separates middle ear from scala tympani
what is the vestibule?
the central part of the bony labyrinth in the inner ear that is separated from the middle ear bu the oval window
contains the saccule and utricle
what is the cochlea?
a bony structure that twists around the modulus and contains the cochlea duct of the membranous labyrinth. Its presence creates the scala vestibuli and scala tympani which are 2 perilymph filled chambers
where is the scaal vestibule?
superior to the cochlear duct
where is the scala tympani?
inferor to cochlear duct - terminates at the roudn window
what are the 3 semicircular canals and what do they contain and what is their function?
anterior lateral and posterior
contain the semi-circular ducts
responsible for balance along with utricle and saccule
whats hold the cochlear duct in place?
the spiral lamina
what is the organ of Corti?
the basilar membrane with contains epithelial cells of hearing
it produces nerve impulses in response to sound vibrations.
whats the difference in electrokyte balance within endolymph and perilymph?
endolymph is rich in K+ and perilymph is rich in Na+
what liquid can be found in the scala media, scala vestibuli and scala tympani?
scala media - endolymph
scala vestibuli and scala tympani - perilymph
what separates the scala vestibuli and media?
reissners membrane
what separates the scala media and scala tympani?
Baslar membrane
how does the ear detect movements in 3D space?
as the 3 semicircular canals are positioned at right angles to one another
what in the ear detects angular acceleration?
semicircular canals
outline how the semicircular canals detect angular acceleration?
when the head rotates, the inertia of the endolymph causes it to lag, exerting a pressure that deflects the capula in the opposite direction. This deflections stimulates hair cells by bending their stereocilia in the opposite direction. Bending the stereocilia towards kinocilium depolarizes the hair cell and bending away causes hyperpolarization and decreases firing
This causes the hair cell neurones to fire and send the information down the vestibular branch of the vestibular cochlea nerve (CN 8)
how do we detect linear acceleration?
The otolith organs have hair cells embedded in a matrix with is weighed down by calcium carbonate crystals. this allows them to detect linear acceleration in the horizontal (utricle) and vertical plane (saccule) Again if the stereocili move towards kinocilium then we get depolarization and if hair cells are bent away you get hyperpolarizarion
outline how we hear
sound waves travel through air, and into ear where they set up vibrations in tympani and this causes ossilations in the ossicles. this moves the stapes in and out causing a wave in the perilymph which moves down the cochlear and, depending on frequency, at some point crosses sets up vibratons in the basilar membrane which results in sound waves in the scala tympani. These waves then travel in the reverse direction until it reaches the round window which absorbs the sound waves. Crossing the basilar membrane also causes vbration of organ or corti which leads to displacement of hair cells
which areas in the brain are for hearing?
brodmann areas 41 and 42 in the temporal lobe
which nerve transmits sound from the inner ear to the brain?
The vestibulocochlear nerve
outline how frequency alters where the sound waves start displacing the basilar membrane?
close to the base of the cochlear the basilar membrane is very stiff but at the helicotrema its way more flexible so the point at which the sound waves cross depends on frewuency and having enough energy to displace this membrane
what can detect the time lag between acoustical signals entering the two ears?
medial superior olivary nucleus
what detects which direction sound is coming from?
lateral superior olivary nucleus
why on recording do people tend to not like the sound of their voice?
as recordings only pick up air conducted sound so you cannot hear the bone conducted sound you get when you are speaking
why does your voice sounds lower than people perceive it to be?
as bones conduct lower frequencies better than higher ones and other people only hear the air conducted sound whilst you hear air conducted and bone conducted
what are the 2 types of hearing loss?
conductive - problems conducting sound waves through ear
sensorineural - problems in cochlea, vestibulocochlear nerve or auditory cortex of brain
what are common causes of conductive hearing loss?
ear wax
otitis externa or media
perforated ear drum
membrane tenson
what are some causes of sensorineural hearing loss?
congenital presbycusis - age related inflammatory disease menieres disease ototoxic drugs physical trauma noise induced
what are the 2 main hearing tests?
rinne test
weber test
how does rinne test work?
Place the base of a struck tuning fork on the mastoid bone behind the ear. Have the patient indicate when sound is no longer heard. Move fork (held at base) beside ear and ask if now audible. In a normal test, AC > BC; patient can hear fork at ear.
what does it mean if patient in rinne test cannot hear tuning fork at ear?
bone conduction > air conduction = conductive hearing loss
what does it mean if patient in rinne test can hear tuning fork at ear?
air conduction > bone conduction
normal hearing or sensorineural hearing
how do you carry out the weber test?
Tap the tuning fork strongly on your palm and then press the butt of the instrument on the top of the patient’s head in the midline and ask the patient where they hear the sound. Normally, the sound is heard in the center of the head or equally in both ears.
what does it mean if, during the weber test, sound is hear louder in affected ear?
conductive hearing loss
what does it mean if, during the weber test, sound is heard loudest in unaffected ear?
hearing loss in sensorineural
whats the problem with the weber test?
you need to know which ear is affected to be able to carry out this test
whats the purpose of the weber test?
to distinguish between conductive and sensorineural unilateral hearing loss
what innervates the meatus side of the tympanum?
auriculotemporal nerve
what innervates the lateral aspect of the external ear?
greater auricular nerve
what innervates the concha of the external ear?
auricular branch of vagus nerve
what innervates the most medial half of the external ear?
auriculotemporal
