Week 6 -- Structures and function of the ear

What are the three regions of the ear?

External ear (Collects soundwaves and channels them inward), Middle ear, Internal ear (Houses receptors for hearing and equillibrum)

Parts of the external ear

• Auricle = flap of elastic cartilage shaped like the end of a trumpet (covered in skin)

• External Auditory Canal = curved tube 2.5cm long that leads to the tympanic membrane (Contains a few hair cells & ear wax)

• Tympanic membrane (ear drum) = boundary between inner and outer ear

Parts of the middle ear

• When ear drum is vibrating, the auditory ossicles vibrate and then passes that to the inner ear. (Moves the fluid in the inner ear/cochlea)

• The round window is there so that cochlea fluid has space to move around

• Auditory canal (a tube made of bone & elastic cartilage), connects middle ear with nasal tharynx (top part of throat). Allows air to enter/leave the middle ear to equalise the pressure.

Internal Ear

What is Equillibrium? (Balance)

A state of balance and stability maintained by vestibular system (vestibule & semicircular canals)

Inner ear parts that contribute to equilibrium detection

• Vestibule and semicircular canals house receptors for equilibrium

• Vestibule (utricle and saccule) monitor static equilibrium (body movement, head position)

• Semicircular canals monitor dynamic equilibrium (shaking head, spinning)

What causes receptor potentials for static equilibrium

• Sitting on top of hair cells is the otolithic membrane and otoliths

• Tilting head/linear movement = otoliths move

• This movement drags the membrane, bends hair cells and causes a receptor potential

What causes receptor potentials for dynamic equilibrium

• Within each semicircular ducts ampulla is a small elevation called the crista

• Hair cells cover crista, and are surrounded by gelatinous cupula

• As the head moves, so do the hairs and cupula, but endolymph in semicircular ducts lags

• This causes bending of hair cells and generation of receptor potential

How do hearing receptors work

1. Sound waves enter outer ear

2. Travel thru external auditory canal

3. Strikes the tympanic membrane, causing it to vibrate

4. Middle ear ossicles vibrate at oval window, moving inner ear fluid

5. Inner ear fluid movement causes vibration of vestibular membrane which causes vibration of cochlear fluid

6. Fluid movement stimulates hair cells on the cochlea membrane

7. The bending stimulation generates a receptor potential and is sent to brain stem via auditory nerve.