Histology of ear

1. Ear Histology
Assoc. Prof. Dr. Karim Al-Jashamy
IMS/MSU2010

2. AudioreceptorSystem
•The Ear (VestibulocochlearApparatus)
•The functions of the vestibulocochlearapparatus are
related to equilibrium and hearing.
•The organ consists of three parts: the external ear,which
receives sound waves; the middle earin which sound
waves are transmitted from air to bone and by bone to the
internal ear; and the internal earin which these vibrations
are transducedto specific nerve impulses that pass via the
acoustic nerve to the central nervous system.
•The internal ear also contains the vestibular organ, which
maintains equilibrium.

4. External Ear
•The auricle(pinna) consists of an irregularly shaped plate of
elastic cartilage covered by tightly adherent skin on all sides.
•The external auditory meatusis flattened canal extending
from the surface into the temporal bone.
•Its internal limit is the tympanic membrane. A stratified
squamousepithelium continuous with the skin lines the
canal.
•Hair follicles, sebaceous glands, and the ceruminous
glands(a type of modified sweat gland) are found in the
submucosa.
•Ceruminousglands are coiled tubular glands that produce
the cerumenor earwax a brownish, semisolid mixture of fats
and waxes.

5. •Hairs and cerumenprobably have a protective function.
The wall of the external auditory meatusis supported by
elastic cartilage in its outer third, whereas the temporal
bone provides support for the inner part of the canal.
•Across the deep end of the external auditory meatuslies
an oval membrane, the tympanic membrane(eardrum).
•Its external surface is covered with a thin layer of
epidermis, and its inner surface is covered with simple
cuboidalepithelium continuous with the lining of the
tympanic cavity. Between the two epithelial coverings is a
tough connective tissue layer composed of collagen and
elastic fibers and fibroblasts.

6. Middle Ear
•Themiddleearislinedwithsimplesquamousepitheliumrestingonathin
laminapropriathatisstronglyadherenttothesubjacentperiosteum.
•Thesimpleepitheliumthatlinesthemiddleearisgraduallytransformed
intociliatedpseudostratifiedcolumnarepithelium.
•Inthemedialbonywallofthemiddleeararetwomembrane-covered
oblongregionsdevoidofbone;thesearetheovalandroundwindows.
•Thetympanicmembraneisconnectedtotheovalwindowbyaseriesof
threesmallbones,theauditoryossiclesthemalleus,incus,and
stapesthattransmitthemechanicalvibrationsgeneratedinthetympanic
membranetotheinternalear.
•Thesebonesarearticulatedbysynovialjointsandcoveredwithsimple
squamousepithelium.Inthemiddleeararetwosmallmusclesthatinsert
themselvesintothemalleusandstapes.Theyhaveafunctionin
regulatingsoundconduction.

7. Internal Ear
•The internal ear is composed of two
labyrinths.
•The membranous labyrinth is a continuous
epithelium-lined series of cavities of
ectodermalorigin.
•The bony labyrinthconsists of spaces in the
temporal bone.
•There is an irregular central cavity, the
vestibule,
•The cochlea, about 35 mm in total length,
makes two-and-one-half turns around a bony
core known as the modiolus.
•The modiolushas spaces containing blood
vessels and the cell bodies and processes of
the acoustic branch of the eighth cranial nerve
(spiral ganglion).
•The membranous labyrinth contains
endolymph,which is characterized by its low
sodium and high potassium content.

8. -The utricle and sacculeare filled with
endolymph, while the surrounding
vestibule with loose connective tissue
contains perilymph.
-Both the utricle and sacculecontain a
neurosensoryarea known as the
macula. This consists of hair and
supporting cells overlaid by a
gelatinous otolithicmembrane
covered with otolithsor otoconia.

9. -The three semicircular ductsare oriented in 3
perpendicular planes.
-At the origin of each semicircular duct near the utricle,
there are ampullae. Each one of these dilations has a
cristaampullarisprojecting into the lumen.
-The thickened sensory epithelium at the tip of the crista
contain many neurosensorycells with stereocilia
-The hair cells insert into the cupula, which is a gelatinous
material similar to the otolithmembrane but lacking any
otoliths.
-Like other parts of the inner ear, the membranous part of
the semicircular duct contains endolymphwhile the bony
part contains perilymph.