Ototoxicity

1
(No Transcript)
2
Review of Cochlear Anatomy

• Bony Capsule
• Semicircular Canals
• Vestibule
• Scala Tympani
• Scala Vestibuli
• Cochlear Aqueduct
• Vestibule Aqueduct

• Membranous Labyrinth
• Semicircular Canals
• Membranous Ampullae
• Utricle
• Saccule
• Utricular Duct
• Saccular Duct
• Endolympatic Duct
• Endolympatic Sac
• Cochlear Duct
• Canal Reunions

3
Winding of the Cochlea
4
(No Transcript)
5
The Cochlea

• The Snails Shell

6
The Cochlea
This figure shows the location of the cochlea
with respect to the external ear canal. The
cochlea is shown here as the blue spiral
structure, which resembles a snail. (The word
cochlea is derived from the Latin word for a
snail shell) The cochlea is responsible for
converting sounds which enter the ear canal, from
mechanical vibrations into electrical signals.
This process, known as transduction, is performed
by specialized sensory cells within the cochlea.
The electrical signals, which code the sound's
characteristics, are carried to the brain by the
auditory nerve.
7
The Cochlea
The cochlea is partially divided into an upper
duct called the scala vestibuli and a lower duct,
the scala tympani, by a thin bony shelf called
the osseous spiral lamina. It is a narrow shelf
of bone arising from the modiolar side of the
cochlea.
This division is completed by the membranous
cochlear duct or scala media. Its floor is
formed by the basilar membrane. The vestibular
membrane, or Reissners membrane, forms the roof
of the scala media.
8
Stria Vascularis

The stria vascularis is a very important
structure. It secretes endolymph.
9
The Organ of Corti

• 1. Inner Hair Cell
• 2. Outer Hair Cells
• 3. Inner tunnel of Corti
• 4. Basilar membrane
• 5. Reticular Membrane
• 6. Tectorial membrane
• 7. Deiters cells (outer
  
  
  phalangeal cells)
• Space of Nuel
• Cells of Hensen
• Inner Sulcus

10
Sensory Receptor Organ

• Sensory Receptor Cells
• Special neurons that are capable of interacting
  with the environment
• (i.e. responsive to specific factors in the
  environment such as light, vibration, heat, etc.)
• Accessory Structures
• Framework for the sensory cells. They act as a
  FUNNEL for the stimulus to the receptor cells.
• (i.e. for the eye lens cornea funnel to
  rods.
• for the ear ossicular chain TM
  funnel to hair cells.)

11
The Typical Neuron

• Three parts
• Receptive pole or dendritic zone
• Transmission apparatus or axon
• Distribution apparatus or presynaptic zone

12
Hair Cells
Inner Hair Cells
Outer Hair Cells
13
Inner Hair Cells (IHC)
There is one row of approx. 3,500 inner hair
cells. These cells receive about 95 of the
innervation from the afferent nerve fibers from
the acoustic portion of the VIII nerve.
FYI--The cuticle capped apex of an IHC is
slightly concave and bears about 48 stereocilia,
oriented parallel to the longitudinal axis of the
cochlea. The cell body height of the IHC is
fairly constant over the extent of the entire
cochlea. Stereocilia vary in length and diameter
within an individual hair cell and also among the
individual turns of the cochlea. The number of
cells also varies along the length of the basilar
membrane. Bredberg (1968) found about 80 inner
hair cells per mm at the basal end and 155 cells
per millimeter at the apical end.
14
Outer Hair Cells (OHC)
There are three rows of approx. 13,500 outer hair
cells. Although they are much greater in number
than the inner hair cells, they receive only
about 5 of the innervation of the afferent nerve
fibers from the acoustic portion of the VIII
nerve. These cells contain muscle-like filaments
that contract upon stimulation and fine tune the
response of the basilar membrane to the movement
of the traveling wave. The OHC cilia are in a W
shape.
15
VIII Nerve
The VIII nerve has two branches, the cochlear
nerve and the vestibular nerve. These nerves
form a common trunk when exiting the internal
auditory meatus. The cochlear nerve arises from
the spiral ganglion of the cochlea. The
peripheral fibers pass to the hair cells of the
cochlea through the canal of the modiolus and
continue into the internal auditory meatus. The
vestibular nerve conveys the impression of
equilibrium and orientation in three dimensional
space. It arises from cells in the vestibular
ganglion. Three peripheral branches supply the
utricle, ampullae and the saccule.
16
The End.Hope that you enjoyed this show.More to
come.