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Special sense of hearing

  2. What is Sound ?  (Perception of) pressure waves generated by vibrating air molecules.  Sound is perceived when longitudinal vibrations of the molecules in the external environment, i.e. alternate phases of condensation & rarefaction of the molecules, strikes the tympanic membrane.
  4.  Generally loudness of sound is correlated with the amplitude of sound wave (subjective interpretation of the intensity of a sound)  Decibel - logarithmic scale to measure the intensity of sound waves  Human amplitude range - 0 dB - 120 dB (avg sound intensity of human speech is 65 dB)  Greater than 100 dB can damage to auditory apparatus & greater than 120 dB can cause pain  The pitch is correlated with the frequency ( no of waves or cycles per second )  The sound frequencies audible in humans - 20 Hz to 20000 Hz  Normal pitch of male – 120 Hz female - 250 HZ
  5. THE EAR  Houses two senses  Hearing  Equilibrium (balance)  Receptors are mechanoreceptors
  6. ANATOMY OF THE EAR  The ear is divided into three areas  External (outer) ear  Middle ear (tympanic cavity)  Inner ear (labyrinth)
  8. THE EXTERNAL EAR  Involved in hearing only  Structures of the external ear: Auricle (pinna), lobule, external auditory canal; elastic cartilage  External acoustic meatus (External auditory canal) Narrow chamber in the temporal bone Lined with skin and ceruminous (wax) glands Ends at the tympanic membrane  Tympanic membrane- membrane that vibrates in response to sound waves  Ceruminous glands- wax secreting glands- protects delicate lining of meatus and helps prevent microorganisms from entering the ear
  9. THE MIDDLE EAR (TYMPANIC CAVITY)  Air-filled cavity within the temporal bone  Only involved in the sense of hearing  Oval window- found on cochlea  Round window- pressure window on cochlea  Otitis media- inflammation of the middle ear; due to bacteria or allergies, common in children whose auditory tubes are short and horizontal
  10. THE MIDDLE EAR  There are several openings into the middle ear: The opening from the auditory canal is covered by the tympanic membrane The Pharyngeotympanic auditory tube (Eustachian tube) connects middle ear to pharynx Allows for equalizing pressure Two into the internal ear, the oval window and the round window  Clinical importance of these openings is that they provide routes for infection to travel
  11. BONES OF THE MIDDLE EAR  Three small bones (ossicles) span the cavity  Malleus (hammer)  Incus (anvil)  Stapes (stirrip)  Function help amplify sound  Vibrations from eardrum move the malleus  anvil  stirrup  inner ear
  12. external auditory canal tympanic membrane Auditoy tube malleus incus stapes round window oval window
  13. INNER EAR  Also termed labyrinth  Consist of two main parts: Bony labyrinth consisting of three parts:  vestibule, cochlea, and semicircular canals Membranous labyrinth • Cochlea--Functions in hearing • Semicircular canals--Functions in equilibrium • Vestibule--Functions in equilibrium
  14. INNER EAR  Bony labyrinth is filled with Perilymph fluid, similar to CSF  Endolymph is the clear potassium-rich fluid that fills the membranous labyrinth  These fluids conduct sound vibrations
  15. COCHLEA AND COCHLEAR DUCT  Cochlea means snail  In the center is a cone-shaped core termed modiolus  The modiolus houses the spiral ganglion that has cell bodies of the first sensory neurons in the auditory relay  Cochlear ducts are the only part of the internal ear concerned with hearing
  16. ORGAN OF CORTI  Contains hearing receptor cells (hair cells)  Above the hair cells is a tectorial membrane  On upper surface of basilar membrane  Different vibration frequencies move different regions of the basilar membrane and cause hair cells to shear against the tectorial membrane  Depolarization of hair cells transmits impulse along the cochlear branch of the vestibulo-cochlear sensory nerve
  17. Note the hair cells and cochlear nerve.
  18. How to discriminate the frequency of the sound?
  19. Vibration of Basilar Membrane and the Traveling Wave Theory • Sound wave entering at the oval window is to cause the basilar membrane at the base of the cochlea to vibrate • Different frequencies cause vibrations at different locations (places) along basilar membrane • Higher frequencies at base, lower frequencies at top
  20. 25 MECHANICS OF HEARING  sounds set up vibrations in air  beat against the eardrum  push a chain of tiny bones  press fluid in inner ear against membranes  set up forces that pull on hair cells  stimulate neurons that send impulses to brain  interpretation impulses  hearing
  21. THE PROCESS OF HEARING Pathway of Sound Vibrations
  22. Transmission of sound: Airborne sound → external auditory canal → tympanic membrane →hammer, anvil, stirrup → oval window → vestubularcochlear nerve → cochlear nuclei in medulla → superior olivary nucleus → up the lateral leminiscus → inferior colliculus → primary auditory cortex in the temporal lobe
  23.   A. Perceiving Pitch (Frequency) location of vibration on the basilar membrane   B. Perceiving Differences in Loudness (Intensity) amplitude increases, more hair cells of the basilar membrane (with same pitch) are activated   C. localizing Source of Sound 1. superior olivary nucleus - first point where sound from both ears come together 2. relative intensity - the amplitude of sound waves hitting the different ears 3. relative timing - the difference in timing in which a sound reaches both ears Processing of Auditory Information
  24. Deafness  Hearing loss- due to disease (ex. meningitus), damage, or age related  Conduction deafness- prevention or blocking sounds from entering inner ear.  Ear wax, ruptured ear drum, middle ear inflammation (otitis media), and otosclerosis (hardening of the ossicles of the ear)  Sensoneural deafness- damage to the neural structures from any point from the cochlear hair cells to and including the auditory cortical cells  Nerve deafness
  25. TYPES OF DEAFNESS Conductive Deafness Sensorineural Deafness  due to impaired sound transmission in external and middle ear  impacts all sound frequencies  Causes  plugging of the EAC with cerumen of foreign bodies  otitis externa and otitis media  perforation of eardrum  otosclerosis  due to loss of cochlear hair cells (common), problems with the nerves or within central auditory pathways (nerve deafness)  impairs the ability to hear certain pitches (permanent)  causes  aminoglycoside antibiotics (streptomycin and gentamycin)  prolonged exposure to noise  tumors and vascular damage
  26. Deafness  Tinnitus- ringing or clicking sound in the absence of auditory stimuli  1st symptom of cochlear nerve degeneration  May result from inflammation of the inner or middle ear  Side effect from medicine  Symptoms- vertigo, nausea, hearing loss
  27. DIAGNOSTIC TECHNIQUES AND PROCEDURES  Audiometry  The process of measuring how well an individual hears various frequencies of sound waves  Otoscopy  The use of an otoscope to view and examine the tympanic membrane and various parts of the outer ear

Notas do Editor

  1. Speed in water is 1450 m/s in fresh water