Hearing and Equilibrium

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Hearing and Equilibrium

  1. 1. HEARING AND EQUILIBRIUMHEARING AND EQUILIBRIUMThe ear is the sense organ for both hearing and equilibrium
  2. 2. * The outer ear includes an outer projection and a canal ending at amembrane.* The middle ear is an air space containing three small bones.* The inner ear is the most complex and contains the sensory receptorsfor hearing and equilibrium.The ear isdivided intothree mainsections:
  3. 3. THE EAR CONVERTS AIR PRESSURE WAVESINTO ELECTRICAL SIGNALS THAT BRAINPERCEIVES AS SOUND1.- OUTER EAR  collectssoundwaves to eardrumPINNA  “ear”; flap-likestructureAUDITORY CANAL2.- EARDRUM  sheet oftissue that separates outer earfrom middle ear3.- MIDDLE EAREardrum; HAMMER, ANVIL,STIRRUP, OVAL WINDOW4.- INNER EAR. ContainsCOCHLEA  the actualhearing organTHE SENSE OFTHE SENSE OFHEARINGHEARING
  4. 4. Cochlea (= snail ) and organ of CortiCochlea (= snail ) and organ of CortiVibrations of the stapes against the ovalwindow produce pressure waves in theperilymph of the cochlea.Waves inside the cochlea cause thebasilar membrane to vibrate and thehair cells in the organ of Corti hit thetectorial membrane.The hair cells that make up the organ ofCorti produce electrical signals andthese nervous impulses travel down theauditory nerve to the temporal lobe of thecerebrum.Basilar membraneBasilar membranewith the organwith the organof Cortiof CortiTectorial membrane
  5. 5. Sound waves enter the outer ear via the pinna and cause the tympanicmembrane (eardrum) to vibrate.The bones of the middle ear (malleus, incus, stapes) transmit thevibrations to the oval window on the cochlea ("snail") of the inner ear.
  6. 6. Lower frequency wavesmake the distal basilarmembrane vibrateHigher frequency wavesmake the proximal basilarmembrane vibrateHow can we distinguish between different sounds?
  7. 7. http://encyclopedia.lubopitko-bg.com/The_Ear.htmlhttp://encyclopedia.lubopitko-bg.com/The_Ear.htmlThe Middle Ear (extra notes)The middle ear cavity is a small space that contains three small bones, or ossicles. Thethree ossicles are joined in such a way that they amplify the sound waves received bythe tympanic membrane as they transmit the sounds to the inner ear. The first bone isshaped like a hammer and is called the malleus. The handlelike part of the malleus isattached to the tympanic membrane, whereas the headlike part is connected to thesecond bone, the incus. The incus is shaped like an anvil, an iron block used inshaping metal, as is used by a blacksmith. The innermost ossicle is shaped somewhatlike the stirrup of a saddle and is called the stapes. The base of the stapes is in contactwith the inner ear.The eustachian tube (auditory tube) connects the middle ear cavity with the throat,or pharynx. This tube opens to allow pressure to equalize on the two sides of thetympanic membrane. A valve that closes the tube can be forced open by swallowinghard, yawning, or blowing with the nose and mouth sealed, as one often does whenexperiencing pain from pressure changes in an airplane.
  8. 8. THE INNER EAR HOUSES OUR ORGANS OFBALANCE– Ampullae at the bases of SEMICIRCULAR CANALS•HAIR CELLS THAT DETECT MOVEMENT– UTRICLE AND SACCULE (vestibule) •HAIR CELLS THAT DETECT THE POSITION OF THE HEADWITH RESPECT TO GRAVITYEQUILIBRIUM (BALANCE)EQUILIBRIUM (BALANCE)
  9. 9. Balance receptors (ciliated cells) in the inner earvestibule (utricle + saccule): these receptors are called maculaampullae at the bases of semicircular canals: these receptors arecalled cristaeReceptors for positionReceptors formovements
  10. 10. As the headAs the headmovesmoves, a shift inthe position of thecilia within the thickfluid around themgenerates a nerveimpulseThe fluid above theciliated cellscontains smallcrystals ofcalciumcarbonate, calledotoliths, which adddrag to the fluidaround the receptorcells and increasethe effect ofgravity’s pullSTATIC EQUILIBRIUMSTATIC EQUILIBRIUM
  11. 11. Receptors are located atthe bases of thesemicircular canals.It’s easy to rememberwhat these receptors do,because the semicircularcanals go off in differentdirections.Nerve fibers from thevestibule and from thesemicircular canals formthe vestibular nerve,which joins the cochlearnerve to form thevestibulocochlearnerve, the eighth cranialnerve.DYNAMIC EQUILIBRIUMDYNAMIC EQUILIBRIUM
  12. 12. As the body moves towards one direction..… the fluid inside the canals moves towards theopposite direction.This is due to INERTIAInertia is the tendency of an object to resist anychange in its motion.
  13. 13. The mechanism of balance receptors
  14. 14. WHAT CAUSES MOTION SICKNESS?– CONFLICTING SIGNALS FROM THE EYES ANDINNER EAR’S BALANCE MECHANISM– SPIN AROUND OVER AND OVER, THEN SUDDENLYSTOP…WHAT HAPPENS?!?!?!?

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