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Vestibular system


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Vestibular system

  2. 2. INTRODUCTION • Two important functions of the ear • Enables us to hear • Sensory organ of balance or equilibrium • Location of one ear on each side of head produces binaural hearing • Hearing from both sides
  3. 3. • External ear • Visible portion, not contained within the head • Auricle or pinna • Cartilaginous flap or ear lobe • External auditory canal • Tube leading from auricle to the middle ear • Lined with tiny hairs called cilia to aid in transmitting sound waves inward • Tympanic membrane (eardrum) • Separates external ear from middle ear Structures of the Ear
  4. 4. • Middle ear • Three tiny bones known as auditory ossicles • Malleus • Resembles shape of a hammer • Connected to tympanic membrane and transmits sound vibrations to second auditory ossicle • Incus • Resembles shape of an anvil • Transmits sound vibrations from malleus to third auditory ossicle Structures of the Ear
  5. 5. • Middle ear • Stapes • Shaped like a tiny stirrup • Transmits sound vibrations from incus to inner ear • Eustachian tube • Connects middle ear to pharynx • Auditory tube • Oval window • Separates middle ear from inner ear • Base of stapes fits into oval window Structures of the Ear
  6. 6. • Inner ear • Vestibule • Central portion of inner ear • Located next to stapes and between cochlea and semicircular canals • Contains utricle and saccule-membranous pouches or sacs that aid in maintaining balance • Cochlea • Snail-shaped bony structure • Contains endolymph and perilymph • Auditory fluids that aid in transmission of sound vibrations Structures of the Ear
  7. 7. Structures of the Ear
  8. 8. Introduction to vestibular appratus  It is part of inner ear or labyrinth  It is a sensory organ that detects sensation of equilibrium  Vestibular apparatus plays an important role in maintaining posture and equilibrium  The other part of labyrinth is the cochlea, which is concerned with sensation of hearing
  9. 9. LABYRINTH Labyrinth or inner ear consists of two structure:  BONY LABYRINTH MEMBRANOUS LABYRINTH
  10. 10. BONY LABRINGTH  It is composed of a system of bony tubes and chambers located in the petrous portion of the temporal bone, called the bony labyrinth,  And within this, is a system of membranous tubes and chambers called the membranous labyrinth.  The space between bony and membranous labyrinth filled with a fluid called perilymph or periotic fluid. This fluid is similar ECF in composition with large amount of sodium ions.
  11. 11. MEMBRANEOUS LABYRINTH  It is formed by membraneous tubules and sacs.  Tubules are semicicular canals & sacs are vestibular and cochlear duct.  The vestibular duct consists of otolith organ.  Otolith organ is formed is formed by utricle and saccule. The membranous labyrinth is filled with a fluid called endolymph or otic fluid. The endolymph is similar to ICF in composition.This has more quantity of potassium ions.
  12. 12. STRUCTURE OF SEMICIRCULAR CANAL  Vestibular apparatus is formed by three semicircular ducts and otolith organ SEMICIRCULAR CANALS  The three semi-circular canals in each vestibular apparatus, are placed at right angles to each other.  Because of this type of arrangement, the semicircular canals represent the three axes of rotation: vertical, anteroposterior and transverse axes
  13. 13. The semicircular canals are named according to the situation as follows: 1.Anterior or superior canal 2.Posterior canal 3.Lateral or horizontal or external canal The anterior and posterior canals are situated vertically and the lateral canal is situated in horizontal plane. The lateral canal of vestibular apparatus on both sides are placed horizontally in the same plane with the convexities directed outwards and a little backward
  14. 14. The vestibular organ Horizontal canal Anterior vertical canal Posterior vertical canal Vestibular Nerve Facial Nerve Vestibulocochlear (VIII) Nerve Cochlea Cochlear NerveCochlear Nerve UtricleSaccule
  15. 15.  When the head is bent forward about 30 degrees, the lateral semicircular canals are then approximately horizontal with respect to the surface of the earth  The anterior canals are in vertical planes that project forward and 45 degrees outward, whereas the posterior canals are also in vertical planes but project backward and 45 degrees outward.
  16. 16. AMPULLA  Among the two ends of semicircular canal , one and is narrow and other end is enlarged.  The enlarged end is called ampulla.  The ampulla contains the receptor organ known as crista ampullaries.  The ampulla of all the 3 canals & narrow end of horizontal canal open directly into the utricle .  The narrow end of anterior & posterior canals open into the utricle jointly , by forming a common crus .  Thus, semicircular canals open into the utricle by means of five openings.
  17. 17. AMPULLA
  18. 18. The vestibular organ Horizontal canal Anterior vertical canal Posterior vertical canal Vestibular Nerve Facial Nerve Vestibulocochlear (VIII) Nerve Cochlea Cochlear NerveCochlear Nerve UtricleSaccule
  19. 19. OTOLITH ORGAN OR VESTIBULE  Otolith organ or vestibule is formed by utricle and saccule.  Often utricle and saccule are together called otoliths.  Utricle communicates with saccule through utriculo-saccular duct.  Saccule communicates with cochlear duct through ductus reuniens.  Another duct called endolymphatic duct arises from utriculosaccular duct.  It ends in a bag like structure called endolymphatic sac, which lies on the cranial surface of petrous bone.
  20. 20. RECEPTOR ORGAN IN SEMICIRCULAR CANAL CRISTA AMPULLARIS It is a crest like structure situated inside the ampulla of semicircular canals The crest is formed by a receptor epithelium (neuroepithelium) which consists if hair cells, supporting cells and secreting epithelial cells The secreting cells secrete the ground substance, proteoglycan These cells are arranged in planum semilunatum (group of epithelial cells) around hair cells
  21. 21. HAIR CELLS • Hair cells are the receptor cells of crista ampullaris. There are 2 types of hair cells, type I and type II hair cells. Hair cells of semicircular canals, utricle and saccule receive both afferent and efferent nerve terminals.  TYPE I HAIR CELLS Type I hair cells are flask shaped. The afferent nerve terminates in the form of calyx that surrounds the cell body. The efferent nerve terminal ends on the surface of the calyx.  TYPE II HAIR CELLS These cells have a cylindrical or test tube shape. Both afferent and efferent nerve fibres terminate on the surface cell without forming calyx.
  22. 22. CUPULA From crista ampullaris, a dome-shaped gelatinous structure extends up to the roof of the ampulla. It is known as cupula. The cupula encloses the cilia of hair cells. The cilia of hair cells are projected in the cupula.
  23. 23. Semicircular canals UtricleAmpulla Crista hair cells Cupula
  24. 24. MACULA  The receptor organs in utricle and saccule are called maculae.  Like crista ampullaris it is also formed by neuroepithelium and supporting cells  The neuroepithelial of this also has two types of hair cells, the type 1 and 2 hair cells.  Situation of macula is different in utricle and saccule .  In utricle , the macula is situated in horizontal plane, so that the cilia from hair cells are in verticle plane .  In saccule , the macula is in verticle plane and the cilia are in horizontal.
  25. 25. BLOOD SUPPLY TO THE VESTIBULAR END ORGAN  The main blood supply is through the internal auditory (labyrinthine artery), which usually arises from the anterior cerebellar artery, superior cerebellar artery, or basilar artery  The labyrinthine artery divides into two branches- anterior vestibular artery and the common cochlear artery  Anterior vestibular artery provides the blood supply to most of the utricle, to superior and horizontal ampullae’ and to small portion of the saccule  The common carotid artery supply posterior ampulla, the major part of the saccule, parts of the body of the utricle and the horizontal and superior ampullae
  26. 26. NERVE SUPPLY TO VESTIBULAR APPARATUS  The impulses from the hair cells of crista ampullaris and maculae are transmitted to medulla oblongata and other parts of CNS through the fibres of vestibular division of vestibulocochlear (VIII cranial) nerve. FIRST ORDER NEURON  The first order neurons of the sensory pathway are bipolar in nature. The soma of the bipolar cells is situated in vestibular or Scarpa’s ganglion ( situated in internal auditory meatus) .  The dendrites of the bipolar cells reach the receptor organs, i.e. crista ampullaris and maculae in vestibular apparatus.
  27. 27.  The axon form the vestibular division of vestibulo cochlear nerve.  The fibres from bipolar reach medulla oblongata and terminate in the vestibular nuclei.The nerve fibres are called primary vestibular fibres.
  28. 28. VESTIBULAR NUCLEI  There are four vestibular nuclei in the medulla oblongata, viz. superior, inferior, lateral and medial nuclei.  Most of the primary vestibular fibres reaching superior and medial nuclei come from crista ampullaris of semicircular canals.  Lateral vestibular nucleus receives the fibres mostly from maculae of otolith organ, and, the inferior vestibular nucleus receives fibres from both crista ampullaris and maculae.  It is believed that the efferent fibres to hair cells provide tonic inhibition of hair cells.  The fibres from some bipolar cells reach cerebellum directly and terminate in the flocculonodular lobe or the fastigial nucleus in the cerebellum.
  29. 29. Connections to the vestibular nucleus from the canals
  30. 30. Nuclear Connections of the Otolith Organs
  31. 31. The Process of Hearing Pathway of sound vibrations
  32. 32. SECOND ORDER NEURON  The second order neurons of this pathway are located in the four vestibular nuclei which forms secondary vestibular fibres which further forms four tracts : 1. Vestibulo-ocular tract This tract is concerned with movements of eyeballs in relation to the position of the head. 2. Vestibulo-spinal tract The fibres of this tract are involved in reflex movements of head and body during postural changes. 3. Vestibulo-recticular tract These fibres are concerned with facilitation of muscle tone. 4. Vestibulo-cerebellar tract Involved in coordination of movement acc. to body position.
  33. 33. FUNCTIONS OF VESTIBULAR APPRATUS It is responsible for dectecting the position of head during different movements. It causes the reflex adjustments in the position of eyeball, head and body during postural changes. FUNCTION OF SEMICIRCULAR CANALS Semicircular canals sense angular acceleration
  34. 34. FUNCTION OF OTOLITH ORGAN  The otolith organs sense linear acceleration  The saccule senses acceleration in the sagittal vertical plane: up and down (so it senses gravity) and forward and backward.  The utricle senses acceleration in the horizontal plane
  35. 35. APPLIED PHYSIOLOGY – EFFECT OF LABYRINTHECTOMY  BILATERAL LABYRINTHECTOMY- Removal of labyrinthine apparatus on both sides leads to complete loss of equilibrium The equilibrium could be maintained only by visual sensation. The postural reflexes are severely affected. There is loss of hearing sensation .
  36. 36. UNILATERAL LABYRINTHECTOMY • Removal of labyrinthine apparatus on one side causes less effects on postural reflexes. • Severe autonomic symtoms occur like nausea , vomiting and diarrhea.
  37. 37. MOTION SICKNESS o It is defined as syndrome of physiological response during movement to which the person is not adapted . o Motion sickness is due to excessive and repeated stimulation of vestibular apparatus.  Symtoms o Nausea Discomfort o Vomiting Headache o Sweating Disorientation o Diarrhoea o Pallor o Salivation
  38. 38. PREVENTION o It can be done by avioding greasy and bulky food before travel and by taking antiemic drugs
  39. 39. THANK YOU