The Auditory System?

Front 1

What are the three main structures of the ear?

Back 1

The external ear –collects sound waves and channels them inward.
• The middle ear –conveys signals to the oval window.
• The inner ear –contains the receptors for hearing and equilibrium (balance).

Front 2

What are the components of the external ear?

Back 2

• •The auricle
• •The external auditory canal
• •The tympanic membrane

Front 3

What is the tympanic membrane?

Back 3

• •The tympanic membrane is also referred to as the eardrum.
• It is a thin layer of connective tissue covered by skin on the external side and mucus on the internal side
• •It separates the external canal from the middle ear

Front 4

What do the ceruminous glands secrete and what is its function?

Back 4

• •The ceruminou s glands are located near the exterior opening of the external canal.
• •They secrete cerumen(or earwax).
• •The hairs and cerumenin the external canal help to prevent the dust and foreign objects from entering the ear.
• •Cerumen also protects the skin of the external ear canal from water and insects.

Front 5

Where is the middle ear located?

Back 5

• The middle ear is a small air-filled cavity located in the temporal bone.
• It is separated from the inner ear by two membrane-covered openings:
• •The oval window
• •The round window

Front 6

What are the names of the auditory ossicles?

Back 6

• •The auditory ossiclesare the smallest bones in the body and they extend across the middle ear.
• •The malleus(hammer)
• •The incus(anvil)
• •The stapes (stirrup)

Front 7

What membranes do the maleus, the incus and the staples connect to?

Back 7

• The “handle” of the malleus attaches to the internal surface of the tympanic membrane.
• The base of the stapes fits into the oval window.
• What membrane does the stapes connect to the oval window

Front 8

What is the function of the tensor tympani and the stapedius?

Back 8

• The tensor tympani and the stapedius are tiny skeletal muscles attached to the auditory ossicles.
• •The tensor tympani limits movement and increases the tension of the tympanic membrane to prevent damage from loud noises.
• •The stapedius muscle acts to dampen large vibrations of the stapes due to loud noises.
• •As such, it protects the oval window from damage.

Front 9

What does the opening of the eustachian tube allow?

Back 9

• During swallowing and yawning it opens and allows the air pressure in the middle ear to equalise with the atmospheric pressure
• •The outer bony labyrinth

Front 10

What are the two main divisions of the inner ear?

Back 10

• •The outer bony labyrinth
• •The inner membranous labyrinth

Front 11

What are the three portions of the bony labyrinth?

Back 11

• The semicircular canals
• The vestibule
• The cochlea

Front 12

What is the name of the fluid inside the bony labyrinth?

Back 12

• The bony labyrinth contains a fluid similar in composition to CSF called the perilymph.
• The membranous labyrinth contains a fluid called the endolymph

Front 13

What is the name of the fluid inside the membranous labyrinth?

Back 13

• the endolymph

Front 14

What are the three channels of the cochlea?

Back 14

• The cochlea duct–continuation of the membranous labyrinth, filled with endolymph.
• The scala vestibuli–a channel above the cochlea duct. It ends in the oval window. It is filled with perilymph.
• The scala vestibuliis separated from the cochlea duct by the vestibular membrane.

Front 15

What is the spiral organ?

Back 15

• The spiral organ (organ of Corti) rests on the basilar membrane.

Front 16

What are hair cells and hair cell bundles?

Back 16

• Hair cells are the receptors for hearing.
• At the apical tip of each hair cell are the hair cell bundles. These consist of 40-80 hair-like microvilli that extend into the endolymph of the cochlea duct.

Front 17

What do hair cells synapse onto? Where are the cell bodies of these neurons located?

Back 17

• Hair cells synapse onto sensory neurons that form the cochlea branch of the vestibulocochlear nerve. The cell bodies of these sensory neurons are located in the spiral ganglion.

Front 18

What is the tectorial membrane?

Back 18

• The tectorial membrane is a gelatinous membrane that projects over and makes contact with the hair cells of the spiral organ.

Front 19

What are the events that lead to auditory nerve impulses?

Back 19

• The auricle directs sound waves into the external auditory canal.
• Sound waves hit the tympanic membrane causing it to vibrate.
• Vibrations of the tympanic membrane are transferred to the malleus then to the incus and then to the stapes.
• Movement of the stapes pushes the membrane of the oval window back and forth
• Movement of the oval window pushes on the perilymph of the scalavestibulica using pressure waves.
• Pressure waves are transferred from the scalavestibuli to the scalatympani and then absorbed by the membrane of the round window.
• Movement of the scalavestibuli and the scalatympani cause the vestibular membrane to move back and forth creating pressure waves in the endolymph of the cochlea duct.
• Pressure waves in the endolymph cause the basilar membrane to vibrate. This moves the hair cells of the spiral organ against the tectorial membrane.
• The bending of hair cell microvilli against the tectorial membrane opens ion channels that lead to depolarising graded pot

Front 20

How does the structure of the basilar membrane determine the frequency of sound it responds to?

Back 20

• The basilar membrane changes from wider and flexible at one end TO narrower and stiffer at the other end.
• This structural property means that the basilar membrane vibrates at different locations depending on the frequency of sound it is exposed to.
• The narrow end vibrates in response to high frequencies.
• The wider end vibrates in response to low frequencies.
• Hair cells are located along the basilar membrane.
• So which hair cells are activated depends on which segment of the basilar membrane is vibrating i.e. what frequency of sound it has been exposed to.