Suzanne D'Anna1 Hearing and Equilibrium

Suzanne D'Anna2 Parts of the Ear n external ear n middle ear n inner ear

Suzanne D'Anna3 Parts of the Ear external ear middle ear inner ear Eustachian tube

Suzanne D'Anna4 Relationship of Ear to Mouth

Suzanne D'Anna5 External Ear n collects sound waves and passes them inward into the external auditory canal n Includes: - auricle - external auditory canal - tympanic membrane

Suzanne D'Anna6 Auricle n 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

Suzanne D'Anna7 External Auditory Canal n 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

Suzanne D'Anna8 Tympanic Membrane n 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'Anna9 Middle Ear n 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

Suzanne D'Anna10 Auditory Ossicles n 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

Suzanne D'Anna11 Auditory Ossicles (cont.) n malleous vibrates with tympanic membrane; passes vibration to incus n incus causes stapes to vibrate on oval window n oval window is pushed in and out, causing motion in fluid within internal ear n action activates receptor cells n impulses travel to temporal lobe of cerebrum and sound sensation results

Suzanne D'Anna12 Inner Ear n complex series of interconnecting chambers n Includes: - bony or osseous labyrinth - membranous labyrinth

Suzanne D'Anna13 Osseous Labyrinth n 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'Anna14 Membranous Labyrinth n 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

Suzanne D'Anna15 Semicircular Canals n 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

Suzanne D'Anna16 Vestibule n 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

Suzanne D'Anna17 Cochlea (koklea = snail shell) n 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

Suzanne D'Anna18 Three Compartments of Cochlea n scala vestibuli n scala tympani n cochlear duct (scala media)

Suzanne D'Anna19 Scala Vestibuli n above bony partition n ends at oval window n filled with perilymph Scala Tympani n below bony partition n ends at round window n contains perilymph

Suzanne D'Anna20 Cochlear Duct (scala media) n 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

Suzanne D'Anna21 Organ of Corti n spiral organ n lined with epithelial cells - support cells and 16,000 hair cells contain receptors for auditory sensations

Suzanne D'Anna22 Hair Cells n 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

Suzanne D'Anna23 Sound Waves n 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 ,000 Hz

Suzanne D'Anna24 Pitch n determined by frequency of vibrations n the higher the frequency of vibrations, the higher the pitch (musical high note) Loudness n determined by amplitude of sound waves n measured in decibels (dB)

Suzanne D'Anna25 Decibels of Sounds n silence n rustling leaves n normal conversation n crowd noise n vacuum cleaner n pneumatic drill n uncomfortable sound n painful sound 0 dB 15 dB 45 dB 60 dB 75 dB 90 dB 120 dB 140 dB

Suzanne D'Anna26 Physiology of Hearing n 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

Suzanne D'Anna27 Physiology of Hearing (cont.) n malleus connects in central area of tympanic membrane n malleus vibrates, conducting vibration to incus and then stapes n stapes pushes membrane on oval window in and out n movement of oval window causes waves in perilymph of cochlea

Suzanne D'Anna28 Physiology of Hearing (cont.) n 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

Suzanne D'Anna29 Physiology of Hearing (cont.) n 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

Suzanne D'Anna30 Physiology of Equlibrium n 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

Suzanne D'Anna31 Two kinds of Equilibrium n 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

Suzanne D'Anna32 Deafness n conduction deafness - impairment of structures that transmit vibrations - punctured eardrum, otitis media, wax buildup n nerve deafness - degeneration of receptors - damage to receptor cells

Suzanne D'Anna33 Ménière’s Syndrome n 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