Organ of Corti.pptx

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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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

12. 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 .

13. 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 .

14. 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

15. Function of Organ of Corti Mechanisms of hearing can be broadly divided into: Mechanical conduction of sound(conduction apparatus) Transduction of mechanical energy to elctrical impulses(sensory system of cochlea) 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).

16. 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.

17. 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.

18. 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.

19. 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.

20. Reference Scott_Brown's_Otorhinolaryngology_Head_and_Neck_Surgery , Seven Edition, Vol-1. Dhingra disease of ear, nose, and throat, 7 th Edition. LOGAN TURNER’S, DISEASES OF THE NOSE, THROAT AND EAR HEAD AND NECK SURGERY, Eleven Edition. 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

21. THANK YOU.