Hearing and Equilibrium Suzanne DAnna 1 Parts of
Hearing and Equilibrium Suzanne D'Anna 1
Parts of the Ear external ear n middle ear n inner ear n Suzanne D'Anna 2
Parts of the Ear inner ear external ear middle ear Eustachian tube Suzanne D'Anna 3
Relationship of Ear to Mouth Suzanne D'Anna 4
External Ear collects sound waves and passes them inward into the external auditory canal n Includes: - auricle - external auditory canal - tympanic membrane n Suzanne D'Anna 5
Auricle flap of elastic cartilage, flared like a funnel n covered with thick skin n helix - top n lobule - bottom, earlobe n attached to head by ligaments and muscles n Suzanne D'Anna 6
External Auditory Canal curved tube about 1 inch long n skin-lined n near exterior opening are ceruminous glands - produce cerumen (wax) which helps to trap foreign material n lies in temporal bone n extends from auricle to tympanic membrane n Suzanne D'Anna 7
Tympanic Membrane thin, semitransparent membrane of fibrous connective tissue n lies between external auditory canal and middle ear n cone-shaped structure with apex directed medially n sound waves in auditory canal cause pressure changes that produce eardrum vibrations Suzanne D'Anna n 8
Middle Ear air-filled cavity in temporal bone n epithelium-lined n contains auditory ossicles n extends from eardrum to thin, bony partition with two membrane covered openings called oval and round window n connected to mouth by Eustachian tube n Suzanne D'Anna 9
Auditory Ossicles transfer vibrations from eardrum to oval window of internal ear n maleus is attached to the internal surface of eardrum at apex n incus is the intermediate bone n stapes is attached by ligaments to the membranous oval window n Suzanne D'Anna 10
Auditory Ossicles (cont. ) malleous vibrates with tympanic membrane; passes vibration to incus n incus causes stapes to vibrate on oval window is pushed in and out, causing motio in fluid within internal ear n action activates receptor cells n impulses travel to temporal lobe of cerebrum an sound sensation results n Suzanne D'Anna 11
Inner Ear complex series of interconnecting chambers n Includes: - bony or osseous labyrinth - membranous labyrinth n Suzanne D'Anna 12
Osseous Labyrinth bony canal within the temporal bone n lined with periosteum n contains the fluid perilymph - chemically similar to cerebrospinal fluid n Divided into three areas: - semicircular canals - vestibule - cochlea Suzanne D'Anna n 13
Membranous Labyrinth surrounded by cerebrospinal fluid n series of sacs following general shape of osseous labyrinth n lined with epithelium n contains endolymph - chemically similar to intracellular fluid n portions within bony canals called semicircular ducts communicate with utricle and vestibule n Suzanne D'Anna 14
Semicircular Canals three canals; anterior, posterior, and lateral n each end enlarges into swelling called ampula n lie at right angles to each other n contain receptors for equilibrium n Suzanne D'Anna 15
Vestibule oval central portion of bony labyrinth n contains two sacs called the utricle and saccule - connect to each other by small duct n contains receptors for equilibrium n Suzanne D'Anna 16
Cochlea (koklea = snail shell) coil-shaped cavity n anterior to vestibule n makes almost three turns n central bony core called modiolus n contains thin, bony shelf which divides cochlea into upper and lower compartments and smaller cochlear duct n contains receptors for hearing n Suzanne D'Anna 17
Three Compartments of Cochlea scala vestibuli n scala tympani n cochlear duct (scala media) n Suzanne D'Anna 18
Scala Vestibuli above bony partition n ends at oval window n filled with perilymph n Scala Tympani below bony partition n ends at round window n contains perilymph n Suzanne D'Anna 19
Cochlear Duct (scala media) portion of membranous labyrinth n separated from scala vestibuli by vestibular membrane n separated from scala tympani by basilar membrane n organ of Corti (spiral organ) located on basilar membrane within cochlear duct n tectoral membrane projects over and in contact with hair cells of spiral organ 20 Suzanne D'Anna n
Organ of Corti spiral organ n lined with epithelial cells - support cells and 16, 000 hair cells contain receptors for auditory sensations n Suzanne D'Anna 21
Hair Cells Two types: - inner - outer n processes at apical end extend into endolymph of cochlear duct n synapse with fibers of the cochlear branch of the vestibulocochlear nerve (VIII) n easily damaged by high intensity sounds n Suzanne D'Anna 22
Sound Waves sound sensations are heard by vibrations transmitted through the air n result from alternate compression and decompression of air molecules n most audible sound vibrations to human ears are frequencies between 1000 and 4000 Hertz n entire audible range is 20 - 20, 000 Hz n Suzanne D'Anna 23
Pitch determined by frequency of vibrations n the higher the frequency of vibrations, the higher the pitch (musical high note) n Loudness determined by amplitude of sound waves n measured in decibels (d. B) n Suzanne D'Anna 24
Decibels of Sounds silence n rustling leaves n normal conversation n crowd noise n vacuum cleaner n pneumatic drill n uncomfortable sound n painful sound Suzanne D'Anna n 0 d. B 15 d. B 45 d. B 60 d. B 75 d. B 90 d. B 120 d. B 140 d. B 25
Physiology of Hearing auricle directs waves into external auditory canal n sound waves strike tympanic membrane n alternate compression and decompression of air cause membrane vibration n movement of membrane depends on intensity and frequency of sound waves n low-frequency = slow membrane vibration n high-frequency = rapid membrane vibration 26 Suzanne D'Anna n
Physiology of Hearing (cont. ) malleus connects in central area of tympanic membrane n malleus vibrates, conducting vibration to incus and then stapes pushes membrane on oval window in and out n movement of oval window causes waves in perilymph of cochlea n Suzanne D'Anna 27
Physiology of Hearing (cont. ) inward movement of oval window pushes on perilymph of scala vestibuli to scala tympani to round window into middle ear n movement of perilymph exerts pressure on vestibular membrane n pressure in endolymph inside cochlea increases and decreases n Suzanne D'Anna 28
Physiology of Hearing (cont. ) pressure fluctuations move basilar membrane causing hair cells of spiral organ to move against tectorial membrane leading to generation of nerve impulses in cochlear nerve fibers n pathway extends into medulla oblongata through midbrain to thalamus and on to temporal lobes of cerebrum for interpretation n Suzanne D'Anna 29
Physiology of Equlibrium when body movement occurs, organs detect motion and aid in maintaining balance n organs provide information on which way is up or down n Organs of equlibrium: - utricle - saccule - semicircular ducts n Suzanne D'Anna 30
Two kinds of Equilibrium static - maintenance of posture in response to changes in body orientation relative to the ground n dynamic - maintenance of body position, mainly the head, in response to sudden movements n Suzanne D'Anna 31
Deafness conduction deafness - impairment of structures that transmit vibrations - punctured eardrum, otitis media, wax buildup n nerve deafness - degeneration of receptors - damage to receptor cells n Suzanne D'Anna 32
Ménière’s Syndrome labyrinth disorder n characterized by fluctuating loss of hearing, vertigo, and tinnitus n caused by an increased volume of endolymph causing enlargement of the labyrinth n disease of cranial nerve VIII n Suzanne D'Anna 33
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