Chapter 28-Special Senses II-Ear & Mouth (1).pptx

Special Senses

1. Chapter 28 Special Senses II-Ear Textbook of Human Histology Author: Dr Yogesh Sontakke JIPMER, Pondicherry ©CBS Publishers & Distributors Pvt Ltd, New Delhi Created by Dr Ujwala Bhanarkar AIIMS, Kalyani

2. Ear Sensory organ of hearing and equilibrium Consists of three parts: External ear, middle ear, and internal ear INTRODUCTION

3. Ear External ear consists of auricle and external acoustic meatus Auricle − Consists of elastic cartilage that is covered on both sides by tightly adherent layers of thin skin Skin of auricle shows presence of hair follicles, sweat glands, and sebaceous glands Helps to gather sound waves INTRODUCTION

4. External auditory meatus Extends from concha to the tympanic membrane Has two parts : Outer one-third – cartilaginous I nner two-thirds – bony part Covered by thin skin Has ceruminous glands (modified apocrine sweat glands) that secrete earwax INTRODUCTION

5. Lined by ciliated columnar or cuboidal epithelium Contains three ossicles (incus, malleus and stapes) that are composed of compact bone Contains two skeletal muscles (tensor tympani and stapedius muscles) Auditory tube /Eustachian tube connects middle ear cavity with nasopharynx Middle Ear

6. Oval and 9 mm × 10 mm Has two surfaces: Outer and inner Histologically, 3 layers : Outer cuticular layer of skin Middle fibrous layer Inner mucous layer Fibrous layer has superficial radiating fibers and deep circular collagen fibers Inner mucous layer is lined by ciliated simple columnar epithelium Tympanic membrane

7. Lies in the petrous part of temporal bone Consists of two parts : Bony labyrinth : Cochlea V estibule S emicircular canals Membranous labyrinth D uct of cochlea S emicircular ducts D uctus reuniens U tricle S accule E ndolymphatic duct and sac Filled with a fluid called endolymph Separated from the bony labyrinth by perilymph (fluid) INTERNAL EAR

8. Consists of three parts : Cochlea anteriorly V estibule in the middle S emicircular canals posteriorly Bony Labyrinth Fig. 28.2: Left bony labyrinth.

9. Resembles the shell of a common snail Cone-shaped, spirally arranged bony canal Has a conical central axis/ modiolus around which cochlea makes two and three-quarter (2¾) turns Cochlea Fig. 28.2: Left bony labyrinth.

10. A spiral ridge of bone ( spiral lamina ) projects from modiolus and divide the bony cochlear canal into scala vestibuli above and scala tympani below Scala vestibuli and scala tympani are filled with perilymph Basilar membrane completes the division of bony cochlear canal Cochlea

11. Scala vestibule communicates with the scala tympani at the apex of cochlea by a small opening called helicotrema Cochlear nerve emerges from the base of cochlea Cochlea

12. Central part of bony labyrinth Opens into the middle ear by two openings: Oval window (Fenestra vestibuli) that is closed by foot plate of stapes Round window (Fenestra cochleae) that is closed by a membrane called secondary tympanic membrane Vestibule Fig. 28.2: Left bony labyrinth.

13. Three bony semicircular canals open into the vestibule through five openings Has opening for aqueduct of vestibule and it is closed by endolymphatic duct Vestibule

14. Three bony semicircular canals: Superior, posterior, and lateral Dilated end of each canal is called ampulla These canals lie perpendicular to each other Semicircular Canals

15. Membrane-bound cavity filled with endolymph Has three receptors— Organ of Corti (for sound) M aculae (for static balance) C ristae (for kinetic balance) Membranous Labyrinth Fig. 28.3: Membranous labyrinth

16. Consists of following parts : Spiral duct of cochlea or organ of Corti (lies within cochlea) Utricle and saccule with maculae (lie within vestibule) Semicircular ducts with cristae (lie within bony semicircular canals) Membranous Labyrinth Fig. 28.3: Membranous labyrinth

17. Spiral duct Occupies the middle part of cochlear canal between scala vestibuli and scala tympani Triangular in cross-section Has three walls − Floor – basilar membrane − Roof – vestibular/ Reissner’s membrane − Outer wall – bony wall of cochlea Contains endolymph Basilar membrane supports the organ of Corti Duct of Cochlea/Scala Media

18. Organ of Corti − innervated by peripheral processes Central processes of bipolar cells form cochlear nerve Vestibular/ Reissner’s membrane extends from spiral lamina to the lateral wall of cochlear canal Vestibular membrane separates cochlear duct from scala vestibuli Duct of Cochlea/Scala Media

19. Basilar membrane is a fibrous sheet that extends from free edge of spiral lamina to the spiral ligament Stria vascularis is highly vascular zone in the lateral wall of cochlear duct Duct of Cochlea/Scala Media Fig. 28.5: Section of cochlea.

20. These are parts of membranous labyrinth Saccule lies within vestibule and is connected to cochlear duct by ductus reuniens Utricle – also lies within vestibule and c ommunicates ampulla of semicircular ducts Maculae of saccule and utricle are supplied by vestibular ganglion Saccule and Utricle Fig. 28.3: Membranous labyrinth

21. Three semicircular ducts lie within the bony semicircular canals (superior, posterior, and lateral) Each semicircular duct has dilated terminal parts called ampulla that open into the utricle Each ampulla has ampullary crest/crista/cupola Ducts are arranged perpendicular to each other Hence, they help to sense angular acceleration of head Saccule and Utricle Fig. 28.3: Membranous labyrinth

22. Q. Write a short note on organ of Corti Q. List the names of cells of organ of Corti End organ of hearing Situated on the basilar membrane and extends in a spiral manner along with turns of cochlea ORGAN OF CORTI

23. Consists of supporting cells, receptor hair cells Cells are covered by gelatinous membrane called membrana tectoria Tips of stereocilia of hair cells are embedded in the membrana tectoria ORGAN OF CORTI

24. Supporting cells : inner and outer pillar cells, phalangeal cells of Dieters, cells of Hensen , and cells of Claudius Pillar/ Rod cells : Have broad base/footplate/crus that rests on basilar membrane and elongated middle part/rod Arranged in two rows as inner and outer Pillar/rod cells Supporting Cells

25. Pillar/Rod cells : Heads of these cells have expanded horizontal processes/pharyngeal processes These processes join to form reticular lamina Tunnel of Corti : Rod cells enclose a cavity called tunnel of Corti . It contains cortilymph fluid Supporting Cells

26. Phalangeal cells of Deiters : rest on basilar membrane and support outer hair cells Hensen cells : support phalangeal and outer hair cells Cells of Claudius : Cuboidal cells that lie lateral to the Hensen cells Boettcher cells : P olygonal cells that lie deep the cells of Claudius and rest on basilar membrane Supporting Cells

27. Hair Cells – Receptor cells of hearing Columnar/pyriform cells Rest on phalangeal cells Their apical surface has thickened cuticular plate and bundle of stereocilia (hairs) Hair Cells

28. Hair Cells – Each hair cell has 30–100 stereocilia Few stereocilia are embedded within the membrana tectoria Arranged into two groups: Inner hair cells (a single row) and outer hair cells (3–4 rows) Peripheral processes of bipolar neurons end in hair cells Hair Cells

29. Fig. 28.7: Photomicrograph. Section of cochlea (high magnification, H & E stain).

30. Maculae − thickened zone in the utricle and saccule (otolith organs) Utricular macula h as ~33,000 hair cells S accular macula has ~18,000 hair cells Macula Fig. 28.8: Macula of utricle and saccule.

31. Structure Has two parts : Sensory neuroepithelium and otolithic membrane Sensory neuroepithelium Has hair cells and supporting cells Supporting cells are tall columnar cells with basal nuclei – produce gelatinous otolith membrane Hair cell has numerous stereocilia at its free surface and one long cilium called kinocilium Macula Fig. 28.8: Macula of utricle and saccule.

32. Both kinocilia and stereocilia are embeded in the otolith membrane There are type I and type II hair cells Type I hair cells are flask-shaped T ype II cells are columnar Otolithic membrane Consists of a gelatinous membrane Consists of gelatinous mass and otoliths Otoliths are crystals of calcium carbonate with organic protein matrix They lie on the top of the gelatinous mass Macula Fig. 28.8: Macula of utricle and saccule.

33. Macula are the organs of static balance It appreciates position of head in response to gravity and linear acceleration Macula of saccule sense low frequencies of sound Functional Correlation of Macula

34. Ampulla of each semicircular ducts has elongated projection called ampullary crest Long axis lies at right angles to that of the semicircular duct Lined by a columnar epithelium with hair and supporting cells Function: Ampullary crests are stimulated by the movements of head Ampullary crests Fig. 28.9: Structure of ampullary crest.

35. Hair cells Apical surface of hair cells has two types of hairs: Single large kinocilium and numerous stereocilia Cupula : conical gelatinous mass that covers hair cells Hairs extend into cupula Type I hair cells (inner hair cell) are flask-shaped, whereas type II hair cells are columnar Each hair cell is innervated by terminals of afferent fibers of the vestibular nerve Ampullary crests Fig. 28.9: Structure of ampullary crest.

36. Supporting/sustentacular cells Cells are elongated Support the hair cells and provide them with nutrition Ampullary crests Fig. 28.9: Structure of ampullary crest.

37. Thank you…