Organ of corti

1. Organ of Corti
Capt. Pyae Sone Thu
PG 1, ORL-HNS

2. ORGAN OF CORTI
• The organ of Corti, in between the scala tympani and the scala media, develops after
the formation and growth of the cochlear duct about 9 week of gestation.
• Organ of Corti is the sense organ of hearing and is situated on the basilar membrane
of cochlea duct and extends with a repetitively patterned structure along the spiral
for approximately 35 mm in humans.

3. • The cochlear duct is subdivided by two longitudinally running membranes that
separate three chambers, the scala tympani, scala media and scala vestibuli.
• The organ of Corti runs in a spiral along the floor of the scala media, an acellular layer
called the basilar membrane.

4. • The scala media is triangular in section, the other boundaries represented by
Reissner's membrane,which runs obliquely with respect to the basilar membrane
from a ridge of tissue (the spiral limbus) near the modiolus, to the lateral wall runs
along the inside of the bony wall.
• And the stria vascularis.
Basilar membrane
• stretches across the cochlear duct from a bony shelf spiralling around the central
bony modiolus to a bony promontory, the spiral prominence, on the inside of the
outer wall of the cochlea.

5. • Underneath the basilar membrane is a layer of spindle-shaped cells, the tympanic
cells, whose long axes are orientated in an apical-basal direction along the cochlea.
• A branching spiral vessel lies under the basilar membrane.
• The organ of Corti extends across the upper surface of the basilar membrane from
the spiral limbus situated over the osseous spiral lamina
• to the Claudius' cells that lie between the edge of the sensory region and the outer
anchorage of the basilar membrane.

7. • The longitudinal ridge of the spiral limbus is composed of a layer of epithelial cells,
the interdental cells, forming its upper surface and a main body containing blood
vessels and connective tissue cells embedded in extracellular matrix.
• The side of the limbus facing the organ of Corti is concave.
• The concavity is lined by cells and forms a longitudinal groove, called the inner
sulcus, which borders the region of the organ of Corti containing the sensory cells
and the supporting cells.

9. Reissner's membrane
• consists of two layers of cells separated by a basement membrane.
• The layer facing into the scala tympani is the mesothelial cell layer and consists of
cells with an extremely thin cytoplasm and prominent central nucleus.
• Facing the scala media is the endothelial cell layer, consisting of a greater density of
thicker cells covered by a dense mat of microvilli.
• The cells within each layer are joined by tight junctions which act as an impermeable
barrier to ions and small molecules.

11. The stria vascularis
• The lateral wall consists of the stria vascularis, composed of three layers of cells on
the external side of which is a layer of fibrocytes and connective tissue called the
spiral ligament.
• Both regions are supplied with blood vessels. The three layers of the stria vascularis
are composed of marginal cells facing the scala media, the intermediate cells and the
basal cells.
• The cells of the lateral wall contain a variety of ion pumps, enzymes and transport
proteins associated with homeostatic mechanisms for maintaining the ionic
composition of the fluids of the cochlea.

12. Important components of the organ of Corti are:
1. Tunnel Of Corti
• It is formed by the inner and outer rods. It contains a fluid called cortilymph. The
exact function of the rods and cortilymph is not known.

13. 2. Hair Cells
• They are important receptor cells of hearing and transduce sound energy into
electrical energy.
• Inner hair cells form a single row while outer hair cells are arranged in three or four
rows.
• Inner hair cells are richly supplied by afferent cochlear fibres and are probably more
important in the transmission of auditory impulses.
• Outer hair cells mainly receive efferent innervation from the olivary complex and are
concerned with modulating the function of inner hair cells.

14. • Differences between inner and outer hair cells are given in table.
Inner hair cells Outter hair cells
Total no. 3500 12,000
Rows One row Three or four rows
Shape Flask shaped Cylindrical
Nerve supply Primarily afferent fibres and very few
efferent
Mainly efferent fibres and very few afferent
Development Develop earlier Develop late
Function Transmit auditory stimuli Modulate function of inner hair cells
Vulnerability More resistant Easily damaged by ototoxic drugs and high
intensity noise

16. 3. Supporting Cell. Deiters’ cells
• They are situated between the outer hair cells and provide support to the latter.
• Cells of Hensen lie outside the the pillar cells called Deiters’ cells.
4. Tectorial Membrane
• It consists of gelatinous matrix with delicate fibres. It overlies the organ of Corti.

17. • The shearing force between the hair cells and tectorial membrane produces the
stimulus to hair cells.
• An acellular flap, the tectorial membrane forms a thin layer over the weakly convex
top of the spiral limbus and projects over the inner sulcus and across the organ of
Corti.
• It widens substantially in crosssectional area as it does so, to a maximum, then tapers
again to a thin edge that lies over the outer side of the organ of Corti.

18. NERVE SUPPLY OF HAIR CELLS
• Ninety-five per cent of afferent fibres of spiral ganglion supply the inner hair
cells while only five per cent supply the outer hair cells.
• Efferent fibres to the hair cells come from the olivocochlear bundle.
• Their cell bodies are situated in superior olivary complex.
• Each cochlea sends innervation to both sides of the brain

19. Function of Organ of Corti
Mechanisms of hearing can be broadly divided into:
1. Mechanical conduction of sound(conduction apparatus)
2. Transduction of mechanical energy to elctrical impulses(sensory system of
cochlea)
3. Conduction of electrical impulses to the brain(neural pathway)
Among these three stages, Organ of Corti play crucial role in Transduction of
mechanical energy to elctrical impulses(sensory system of cochlea).

21. • Movements of the stapes footplate transmitted to the cochler fluids,move the basilar
membrane and hair cells
• The distoration of hair cells gives rise to cochler microphonics which trigger the nerve
impulses
• A sound wave depending on its frequency,reaches maximum amplitude and
stimulates that segment.
• Higher frequencies are represented in the basal turn of cochler and the progressively
lower ones towards the apex.

23. • In fact, the composition of the fluid within the scala media, endolymph, is unusual for
an extracellular fluid, containing high potassium but low sodium levels at an
unusually high positive electrical potential (+ 80 m V) called the endolymphatic
potential (EP).
• This contrasts with the scala tympani and scala vestibuli, both of which are filled with
perilymph that has high sodium content and 0 m V electrical potential.
• At the apex of the cochlea, these two outer chambers are joined via an aperture
called the helicotrema. Maintenance of the EP is crucial to hearing.

24. • As with both the stria vascularis and Reissner's membrane, the cells of the organ of
Corti facing the scala media are joined by tight junctions
• Thus the whole of the scala media is chemically and electrically isolated from the
other scalae, the only communication being through ion channels in the sensory cells
of the organ of Corti.
• The EP is involved in driving currents through transduction channels that are
fundamental to hair-cell function and is thus a vital component required for
producing the high sensitivity to the cochlea.

25. • One of the initial pathological changes found in animal models of age-related hearing
loss is damage to and loss of the fibrocytes in the lateral wall, which in turn leads to
reduction in EP.
• Subsequent age-related damage to other structures may then, at least in some cases,
result from failure of lateral wall homeostatic mechanisms.

27. Reference
1. Scott_Brown's_Otorhinolaryngology_Head_and_Neck_Surgery, Seven Edition, Vol-1.
2. Dhingra disease of ear, nose, and throat, 7th Edition.
3. LOGAN TURNER’S, DISEASES OF THE NOSE, THROAT AND EAR HEAD AND NECK
SURGERY, Eleven Edition.
4. YOSHIHARU IGARASHI and TETSUO ISHII (1980), EMBRYONIC DEVELOPMENT OF THE
HUMAN ORGAN OF CORTI: ELECTRON MICROSCOPIC STUDY, International Journal of
Pediatric Otorhinolaryngology, Vol-2, 51-62

28. THANK YOU.