anatomy of hearing

Question 1

what is the external ear made up of?

Answer 1

1. auricle (pinna)
2. external auditory canal
3. tympanic membrane

Question 2

what is the function and structure of auricle ?

Answer 2

it is shell shaped and composed of elastic cartilage covered with skin and some hair

function: funnel sound waves into the ear canal

Question 3

what is the function of external auditory canal ?(ear canal)

Answer 3

it is 2.5 cm and extends from auricle to ear drum
near the auricle it is cartilage and the rest is temporal bone
lined with skin bearing hair and sebaceous glands and apocrine sweat glands (ceruminous glands) for ear wax

function is to trap foreign bodies and repel insects

Question 4

what is the function and structure of tympanic membrane ?

Answer 4

1cm in diameter and sound waves that enter the canal will eventually hit the ear drum

Function: vibrates in response to pressure changes produced by sound waves and transfer the sound energy to the middle ear bone and set them vibrating

Question 5

what is the middle ear consist of ?

Answer 5

eustachian tube

Question 6

what is the function and structure of eustachian tube?

Answer 6

it connects the middle ear to nasopharynx

Function: equalize air pressure on both sides of the tympanic membrane and opens during swallowing , yawning and chewing

Question 7

what is the the internal ear made up of ? (labyrinth)

Answer 7

it lies deep into the temporal bone behind the eye socket and consist of

1. bony labyrinth
2. membranous labyrinth

Question 8

what does the bony labyrinth consist of?

Answer 8

1. vestibule
2. semicircular ducts
3. cochlea (spiral)

Question 9

what is in the vestibule ? what is its function?

Answer 9

saccule and utricle sacs

Function: part of the balancing system it use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation

Question 10

what is in the semicircular canals ? what is its function?

Answer 10

semicircular ducts (anterior posterior lateral)

At the end of each duct have ampulla that houses an equilibrium receptor

cristae ampullae are the sensory area

Question 11

what is the function of semicircular canal?

Answer 11

three tiny, fluid-filled tubes in your inner ear that help you keep your balance.
When your head moves around, the liquid inside the semicircular canals sloshes around and moves the tiny hairs that line each canal.

Question 12

what is the function of cochlea ?

Answer 12

spiral-shaped bone found in the inner ear that plays a key role in the sense of hearing and participates in the process of auditory transduction

Question 13

what is in the cochlea ?

Answer 13

cochlea duct (scale media)
houses receptor organ of hearing called the spiral lymph and contains endolymph

Question 14

what is the bony labyntinth made up of?

Answer 14

filled with perilymph (almost same as csf)

Question 15

what is the membranous labyrinth made up of?

Answer 15

filled with endolymph and surrounded by peilymph

Question 16

what is frequency of sound?

Answer 16

the higher frequency, the higher the pitch Hz

human range: 20-20,000Hz

Question 17

what is bone conduction ?

Answer 17

it when vibrating object is placed in skull can transmit sound to the peilymph

Question 18

what are the steps for a sound to be perceived?

Answer 18

1. pinna collects sound waves
2. sound waves vibrate the tympanic membrane
3. auditory ossicles vibrate and pressure is amplified
4. pressure waves created by the stapes pushing the oval window move through fluid in scala vestibuli
5. sounds with frequencies below the hearing range travel through the helicotrema and no not excite the hair cells
6. sound in the hearing range go through the cochlear duct vibrating the basilar membrane and deflecting hairs on the inner hair cells

Question 19

what is the sound pathway of nerve ?

Answer 19

first order neuron: nerve impulses in the auditory nerve
second neuron: cochlear nuclei on both sides
third order neuron : medial geniculate bodies in the thalamus