1
Integrated Block
MBBS III
Clinical Skills Sessions
ENT - EAR
Physiology of Hearing
Peripheral Auditory System
• Translate physical stimulus of sound
into physiological signal
• Transmit to CNS
• Analysed by cortex
• Sensation of hearing
How do we hear sound?
• Cochlea transmits fluid vibration from
the stapes footplate in the oval window
to the sensory epithelium of the organ
of corti
• Vibrations are then tranduced by
cochlea into nerve impulses
Modiolus
• Cochlea has two
and a quarter turns
• Coils around
modiolus - a bony
& hollow core
• Modiolus contains
VIII cranial nerve
and bipolar cells
bodies – spiral
ganglion
2
Cochlear Partitions
• Three fluid-filled
columns:
Scala vestibuli filled
with perilymph
Scala media
(cochlear duct)
filled with
endolymph
Scala tympani filled
with perilymph
Separation of Cochlear Partitions
• The perilymphatic scalae are
separated from each other by
Reissner’s memebrane
Basilar membrane
Organ of Corti
• Sensory epithelium of
hearing
• Inner and outer hair
cells
• Pillar cells
• Tunnel of Corti (filled
with perilymph)
• Inner and outer
supporting hair cells
Inner Hair Cell (IHC)
• Inner supporting hair cells lies on osseous
spiral lamina
• Supports a IHC
• IHCs are flask-shaped
• Stereocilia arranged in one row
• Rootlets in cuticular plate
• During development, IHC has a kinocilium
but lost during maturation
• No contact with tectorial membrane
(controversial)
Inner and Outer Hair Cells
Outer Hair Cell (OHC)
• Outer supporting cell (Deiters’ cell) has cup-
shaped depression that support base of an
OHC
• OHC are cylindrical-shaped
• OHCs line up in three or four W-shaped
rows
• Kinocilia is at the bottom of the W
• The tip of the kinocilia is embedded in the
tectorial membrane (shearing)
• When stimulated at resonant frequency,
OHC actually vibrates (active process)
3
Excitation and Inhibition of Hair
Cells
Innervation of OHC and IHC
• Cochlear hair cells are innervated by
peripheral processes of spiral ganglion
cells
• Three times a