Anatomy and Cell Biology 3309 Lecture Notes - Lecture 32: Ear Canal, Eustachian Tube, Hair Cell
2 May 2018
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Department
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The Ear
Objectives
- Describe the anatomy of the ear
- Describe the organization of the middle ear
- Describe the organization of the cochlea (one part of the inner ear)
- Describe how the organ of Corti is designed to translate mechanic movement into electrical cell
signals
- Explain how the hair cells function
- Explain the way sound is transduced into mechanical movement in the middle ear, and into cell
signals in the cochlea
- Inner ear
o Cochlea
o Vestibular system
Ear Anatomy
- Pinna = ear outside of the head
o Mostly cartilage tissue
o Functions like a funnel
- The pinna funnels the sound waves into the ear canal (external auditory ear canal)
- The outer ear canal:
o Contains ceruminous glands that secrete ear wax
▪ Important to keep the ear canal open and clean
o Hairs in the canal prevent insects from entering the canal and expel dirt from this canal
o Ends with the ear drum = tympanic membrane
- When the sound waves enter the ear canal, they hit the tympanic membrane
o The ear drum will begin to move according to the sound waves
- Ear drum is the border between the external ear and the middle ear
- The middle ears a cavity behind the ear drum
o Air filled space
▪ Air can expand depending on pressure & temperature. This air filled space has to be
connected with the exterior, otherwise you would get high or low pressure in your
ear (ex. on airplane the middle ear hurts due to to high of air pressure in middle ear
compared to exterior world)
• Pressure on ear drum will impact hearing because you are less sensitive to
sound
• In order to have this high or low pressure adapted to the exterior air
pressure, the middle ear is connected to the nasal pharynx (mouth) by the
Eustachian tube
o Contains ossicles (3 little bones)
▪ Malleus
• Picks up the movement of the ear drum and conveys it to the incus
▪ Incus
• Connected to the stapes
▪ Stapes
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▪ Names describe how the ossicles look
▪ The ossicles pick up the movement of the ear drum and amplify it & convert it to the
movement of the stapes against the oval window
▪ 3 ossicles are connected to one another via 2 joints
• Muscles insert at these ossicles that can dampen or enhance the
transmission of sound into movement
o Ends with another window = oval window
o BORDERS= EAR DRUM & OVAL WINDOW
- Eustachian tube is not normally open
o It is collapsed
o When you crack your ear, this tube opens through the movement in the tissue release the
air pressure in your middle ear
o ONLY OPENS AT 5 MONTHS
▪ Therefore, newborns can not crack their ear. If you take them on a flight and and air
pressure drops, their ear drums would rupture (IT GROWS BACK!)
▪ If given pacifier, might crack their ear
- Middle ear infections resolve when the ear drum ruptures and inflammation can escape through a
hole in the ear drum
- IF an ear drum ruptures too often it can scar and impact hearing
o They put little tubes into the ear drum to keep it open, preventing it from rupturing and
impacting hearing later on
- Cochlea
o Only part of inner ear concerned with hearing
o Organ used for hearing
o INNERVATED! By the auditory and vestibular nerve (Joint nerve – 8th nerve that innervates
both auditory and vestibular system)
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Organization of the Auditory System
- Sound hits the ear drum making the ossicles move
- The stapes of the ossicles moves against the oval window (membrane that separates the cochlea
from the middle ear)
- From the oval window on, it is in the inner ear
- the image below shows the cochlea as if it was uncoiled
- There is a space filled with liquid, perilymph (extracellular fluid)
- Oval window is moving against the liquid
o The problem with liquid is that we can not compress liquid
o The only way the oval window can move against the perilymph is at the other end of the
structure there is a round window (membrane)
▪ As the stirrup presses against the oval window, he entire liquid moves up the coil to
the apex of the cochlea and back against the round window
▪ The round window budges in and out depending on how the stirrup presses against
the oval window
- When sound enters our ear, the stirrup presses against the perilymph filled space
o Fluid moves all the up and down the coil of the cochlea
o The perilymph space embeds another space that is filled with endolymph (high potassium
solution intracellular fluid)
- Within the Endolymph fluid, there is the Organ of Corti (SENSORY ORGAN)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Describe the organization of the middle ear. Describe the organization of the cochlea (one part of the inner ear) Describe how the organ of corti is designed to translate mechanic movement into electrical cell signals. Explain the way sound is transduced into mechanical movement in the middle ear, and into cell signals in the cochlea. Pinna = ear outside of the head: mostly cartilage tissue, functions like a funnel. The pinna funnels the sound waves into the ear canal (external auditory ear canal) The outer ear canal: contains ceruminous glands that secrete ear wax. Important to keep the ear canal open and clean: hairs in the canal prevent insects from entering the canal and expel dirt from this canal, ends with the ear drum = tympanic membrane. When the sound waves enter the ear canal, they hit the tympanic membrane: the ear drum will begin to move according to the sound waves.
