Download SSN Histology: The Ear

SSN Histology: The Ear
Anatomy Overview of the Ear
- The middle ear conducts sound
from the air to the fluid-filled inner
ear with acoustic impedance
matching.
- Movement of the stapes in and out
of the oval window causes
mechanical vibrations which are
carried through the perilymph and
inner ear tissues. (auditory system)
- 3 semicircular canals at right angles
to each other detect head rotation.
(vestibular system)
- Tensor tympani and stapedius
muscles are responsible for the
attenuation reflex.
Inner Ear Structures and Functions
Structure
Function
Bony labyrinth
- vestibule
- scala vestibuli
- scala tympani
Membranous labyrinth
- 3 semicircular ducts
contains the membranous labyrinth; filled with perilymph
contains utricle and saccule
essentially one long channel (continuous at the helicotrema at the
cochlear apex) that conducts sound vibrations to the scala media
DFICT, epithelia. Floats in perilymph and contains endolymph
detect angular acceleration (vestibular ear)
- utricle
- saccule
- scala media
(cochlear duct)
Sensory Regions
detect linear acceleration (vestibular ear). The utricle communicates
with the semicircular canals, and the saccule with the cochlea.
detect sound (auditory ear)
3 cristae ampullaris (in
ampulla of each duct)
2 maculae (utriculi is
horiz, sacculi is vertical)
organ of Corti
Cochlea (Auditory Ear)
Note: The cochlea is a conically shaped helix. The
section is through multiple turns of the spiral so you
see multiple sections of the cochlear duct.
Structure
Description
modiolus
spiral ganglia
bony core
sensory ganglia, cells are
bipolar (central process to
brain, peripheral process
to habenula perforata)
site where scala vestibuli
and scala tympani meet
filled w/ endolymph
filled w/ perilymph
filled w/ perilymph
helicotrema
scala media
scala tympani
scala vestibuli
Cochlear Duct and the Organ of Corti
Structure
Function
basilar membrane
fibroelastic membrane; movement due to sound vibrations through the cochlea
causes the phalangeal cells on them to move
2 layers of epithelial cells separating the scala vestibuli and scala media
attaches between modiolus and stereocilia of inner and outer hair cells
DFICT thickening of endostium of temporal bone; covered by stria vascularis
the only vascularized epithelium in the body, these stratified epithelial cells secrete
endolymph and appear highly eosinophilic (due to high [mitochondria])
path of spiral ganglia nerve fibers into and out of organ of Corti
Reissner’s (vestibular) membrane
tectorial membrane
spiral ligament
stria vascularis
inner osseous spiral lamina
habenula perforata
phalangeal cells
pillar cells (inner ie. towards
modiolus, and outer)
hair cells
- external hair cells
*
support hair cells; tight junctions form the reticular lamina (border b/t endolymph
and the true intercellular spaces of the organ of Corti)
microtubules and microfilament bundles give rigidity and support
neuroepithelial cells with stereocilia*; shearing motion of stereocilia from sound
vibrations generates membrane depolarizations that initiate neuronal transduction
- 3 cylindrical cells; for tuning
- white “bubbling” at base of cells are
nerve endings
- internal hair cells
1 flask shaped cell; for sound detection
stereocilia = modified microvilli (Note: NO kinocilium in sound detection)
Hearing: The Big Picture
Movement of the stapes at the oval window causes vibrations to travel through the perilymph of the scala vestibuli (and
continue on to the scala tympani, where they are dissipated through the round window). The pressure changes in the scala
vestibuli are transmitted to the adjacent scala media, and a traveling wave is initiated in the basilar membrane. As the basilar
membrane moves up and down, the stereocilia of the hair cells are sheared back and forth because they are also attached to the
tectorial membrane which vibrates differently. Bending of the stereocilia causes stretching of the hair cell plasma membrane and
generation of transmembrane potential changes. Depolarization of the hair cell causes an action potential in an afferent nerve
process lying beneath the Organ of Corti, and the electrical impulse is transmitted to the spiral ganglion (stretched out within
the modiolus), and along the cochlear nerve (a division of CN VIII) to the brain stem.
Utricle and Saccule (Vestibular Ear)
Crista Ampullaris – Angular Movement
- Look for the crista ampullaris to identify the utricle
- cupula (not fixed in this slide image) floats in
endolymph above the crista ampullaris
- rotational movement of fluid in semicircular ducts
causes shearing motion on hair cells on crista
ampullaris Æ movement of stereocilia towards
kinocilium Æ depolarization Æ stimulation
Maculae – Linear Movement
- 2 maculae: when standing: macula utriculi is
horizontal and macula sacculi is vertical
- an otolithic membrane sits above each macula
- sliding motion of otolithic membrane Æ
movement of stereocilia w.r.t. kinocilium Æ
detection of gravity and linear acceleration (same
mechanism as rotational movement)
Questions
1) Which numbered structure in the is incorrectly paired with its function?
a. #1 sensory receptor
b. #2 vibrates during sounds transmission
c. #3 secrete endolymph
d. #4 seals the endolymphatic compartment
2) The receptor cells in region 1 are involved in _________________ and the receptor cells in
region 2 are involved in _____________.
a. hearing; linear movement
b. angular movement; hearing
c. angular movement; linear movement
d. linear movement; angular movement
3) The receptor cells in this region have:
a. 1 stereocilium and multiple kinocilia
b. 1 stereocilium and 1 kinocilium
c. only stereocilia
d. only 1 kinocilium
e. multiple stereocilia and 1 kinocilium
Answers:
1) C [Organ of Corti]. Endolymph is secreted by the stria vascularis, not the limbus spiralis (#3).
Hair cells (#1) are the sensory receptors for sound; when sound is transmitted from the scala
vestibuli to the scala media, the basilar membrane (#2) vibrates, causing stereocilia on the hair
cell to bend. The apical ends of the phalangeal cells (#4) forms the reticular lamina, which seals
the endolymphatic compartment from the true intracellular spaces of the organ or Corti.
2) C [Utricle]. Region 1 is the crista ampullaris of the semicircular canals, which detects rotational
movement. Region 2 is the macula of the utricle, which detects linear movement.
3) E [Crista ampullaris]. The cells in the crista ampullaris detect movement by the bending of
stereocilia towards or away from a single kinocilium.