Ear Flashcards
(35 cards)
Intensity of sound is correlated with…..measured in……
Amplitude
Decibel
Define decibel & write its equation
It is a logarithmic ,easure of sound intensity compared to the faintest sound that can be heard.
dB=10log(I/I-0)
Pitch is correlated to……measured in…….
In human can be heard in the range……with max sensitivity between…..
Frequency of sound waves
Hertz
20-20,000
1000-2000
The pich of male is…..while female is…..
Intensity of both is….., in normal coversation
125 Hz
250 Hz
60 dB
Define masking
The presence of one sound dec the individual’s ability to hear other sounds
Enumerate functions of EAM
-Conduction of sound waves towards ear durm
-Contains ceruminous glands that secrete wax that is (1)protective (traps forgein particles, contains lysozymes & Ig) (2) lubricative to ear drum
Function of tympanic membrane
-Conduction of sound waves: vibrate in response to sound waves conducting them to bony ossicles
-Protection of the middle ear from foreign bodies (acts as a barrier)
Function of bony ossicles
-Conduction of tympanic membrane vibrations towards oval window
-Magnification of sound waves by lever system
Function of ear muscles
-Tensor tympani tenses tympanic membrane to make it read for virbatiom
-Both muscles attenuate sound for protection (acoustic tympanic reflex)
Func of cochlea is…..while that if vestibular apparatus is……
Perception of sound waves
Balance & equilibrium
Describe the magnification of sound in middle ear
- The area of tympanic membrane is 16-17 times that of oval window
- The ossicles act as a lever system, since the malleus is longer than the incus the force at stapes is inc 1.3 times. Thus middle ear causes 20-22 times magnification.
Describe the acostic tympanif refkex & its significance
The middle ear muscles contract reflexly in response to intense sounds. They pull on the malleus & the stapes outwards reducing ossicukar conduction & sound transmission.
Significance:
1. It acts to protect the auditory receptors from damage by high intensity sounds
2. The muscles contract just before chewing & vocalization which may reduce intensity of sound coming from these activities.
Mention conditions in which the auditory tube opens
- Swallowing, chewing, yawning opens tube by action of tensor palati allowing air to enter from nasophatynx to middle ear
- If pressure in middle ear exceeds that of atmosphere by 15 mmHg
What happens if auditory tube is:
1. Opened permenantly
2. Blocked (as in common cold)
- The noises of breathing will interfere with hearing
- Tympanic membrane is sucked in (due to gradual absorption of air) leading to great dec in auditory acuity
Compare fibers at base & apex of cochlea
At base, they are short & stiff & respond to high frequency sounds
At apex, they are long & lax & respond to low frequency sounds
Comapre inner & outer hair cells with respect Site & relation to tectorial membrane
I, inner side of rods of Corti, weak or absent contact with tectorial membrane
O, outer side of rods of Corti, direct contact
Inner hair cells mainly have…..fibers while outer mainly have…..
Afferent
Efferent
Comapre inner & outer hair cells with respect function
I, transducing mechanical vibration of basilar membrane into action potential
O, amplifying the sound (when depolarized) OR clarifying the sound by blocking background noise (when hyperpolarized)
Mention steps of auditory transduction
- Vibration of basilar membrane cause stereocilia to be deflected towards taller member & sheared under tectorial membrane leading to stetching the tip links & opening cation channels with K+ influx leading to depolarizing potential (cochlear microphonic) from rest (-70 mV)
- This causes Ca++ influx & release of glutamate that leads to action potential in afferent nerve
Describe how the outer hair cells perform their function?
They have electromotility. The outer hair cells shorten when depolarized causing modification of basilar membrane movement which improves stimulation of the inner ear, when hyperpolarized lengthen causing clarification by blocking bachgrounf noise.
Efferent neural impulses from brain to ear are carried by…….
Olivocochlear bundle
Describe structure & function of olivocochlear bundle
Prominent bundle of fibers present in each auditory n from ipsi&contralateral superior olivary nuclei ends primarily on outer hair cells. It releases Ach which has inhibitory effect that may function to block background noise (clarify sound). Some fibers supply middle ear muscles (attenuation reflex)
Mention theories of frequency discrimination
- Place (Helmholtz) theory: the brain detects impulses arriving from different parts of tge basilar membrane as having different frequencies.
- Travelling wave theory: the part of membrane which is maximally dispalced is maximally stimulated and excites neurons in auditory cortex
Intensity discrimination depends on……
The frequency of action potential which is directly proportional to long of intensity (Weber-Fechner law)
This depends on the degree of bending of stereocilia
