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Internal ear 1 by P.R.Desai Prof & HOD Physiology, DYPMCKOP

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Structure of Internal Ear
Structure of Organ of Corti and Basillar membrane.
Functions of hair cells

Veröffentlicht in: Gesundheit & Medizin
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Internal ear 1 by P.R.Desai Prof & HOD Physiology, DYPMCKOP

  1. 1. Internal Ear Dr Mrs Padmaja R Desai Professor & Head Department of Physiology D Y Patil Medical College Kolhapur
  2. 2. Specific Learning Objectives • Structure of Internal Ear • Structure of Organ of Corti and Basillar membrane. • Functions of hair cells
  3. 3. • Internal Ear:-Internal ear contains two organs • Cochlea meant for audition or hearing. • Vestibular apparatus meant for maintainence of equilibrium and posture.
  4. 4. • The cochlea is so named because of its appearance (Cochlea= a snail).It consists of 2,3/4 turns. • There is a central bony pillar called modiolus which has internal auditory canal containing auditory nerve. • Bony canal of cochlea winds round the modiolus for 2 and ¾ turns from base to the apex.
  5. 5. • The membranes are →Reissners membrane. → Basilar membrane. • Cavities are • →Scala vestibuli. → Scala media. → Scala tympani.
  6. 6. • On the top of the Reissners membrane lies the Scala vestibuli containing a fluid called perilymph which is like ECF rich in Na+.
  7. 7. • Between Reissners membrane and basilar membrane lies Scala media containing endolymph which is like ICF rich in K+.
  8. 8. • Below the basilar membrane is the perilymph filled cavity called as Scala tympani.
  9. 9. • On the basilar membrane rests the organ of corti. • Scala vestibule and Scala tympani are connected at the apex through helicotrema. • At the base Scala vestibuli opens at oval window where foot plate of stapes lies. • Scala tympani open at round window at the base of the cochlea. Round window is covered by a thin membrane called as secondary tympanic membrane.
  10. 10. Organ of corti
  11. 11. • It is the structure located on the basilar membrane. • It contains the hair cells, which are the auditory receptors. • It extends from the base to the apex of the cochlea.
  12. 12. • lamina reticularis • It is a tough membrane like structure supported by the rods of corti .The processes of the hair cells pierce it . • There is inner rod of corti and outer rod of corti. • Tunnel of corti is present between these rods.
  13. 13. • The inner hair cells form a single row on the inner side of the inner rod of corti. • They are 3500 in numbers. • 90 to 95% of the cochlear nerve ending innervate the inner hair cells
  14. 14. • The outer hair cell form 3 to 4 rows on outer side of the outer rod of corti. • They are 12,000 in number. • 5-10 % innervate the outer hair cells.
  15. 15. • Hair cells are stimulated by the fluid moving between the tectorial membrane and hair cells. • The minute hair or Stereocilia project from the hair cells and they are embedded in the tectorial membrane. • The shorter Stereocilia are attached to the backside of the longer Stereocilia by thin filament called as tip links.
  16. 16. In tectorial membrane the tips of the hairs of outer hair cells only are embedded. The bases of the hair cells are resting on the basilar membrane.
  17. 17. The axons of the neurons of the spiral ganglion form the cochlear Nerve which is a division of Vestibulocochlear nerve. This nerve then terminates in the dorsal and ventral cochlear nuclei of the medulla.
  18. 18. Functions of the hair cells:- • The inner hair cells are primary sensory cells that generate action potential in the auditory nerves. • These cells are responsible for fine auditory discrimination.
  19. 19. • The outer hair cells control the sensitivity of the inner hair cells for different sound pitches. • They are responsible for detecting the presence of sound.
  20. 20. Basillar membrane
  21. 21. • Basilar membrane is a fibrous plate containing about 20000 –30000 basilar fibres. • These fibres they project from the bony centre of the cochlea the modiolus toward the outer wall. These fibres are stiff, elastic and hair like. • Distal ends are embedded in the loose basilar membrane
  22. 22. These fibres vibrate like the reeds of harmonica. The length of the basilar fibres increases progressively from the base to apex of cochlea. Diameter of the fibres decrease from the base to the apex of cochlea.
  23. 23. As a result the stiff short fibers at the base vibrate at a high frequency and long linear fibres near the tip of the cochlea vibrate at a low frequency.
  24. 24. References 1. Text book of Medical Physiology -Guyton & Hall, 12th edition. 2. Ganong’s review of Medical Physiology - 23rd edition. 3. Text book of Medical Physiology - 2nd edition 4. Net sources ( Acknowledge for all online source) 5. Text book of Medical Physiology - Prof. A.K.Jain