Ears & Hearing 10-34

Ears & Hearing - Outer Ear Sound waves funneled by pinna (auricle) into external auditory meatus External auditory meatus channels sound waves to tympanic membrane Fig 10.17 10-47

Ears & Hearing - Middle Ear continued Malleus (hammer) is attached to tympanic membrane Carries vibrations to incus (anvil) Stapes (stirrup) receives vibrations from incus, transmits to oval window Fig 10.18 10-49

Ears & Hearing - Middle Ear continued Stapedius muscle, attached to stapes, provides protection from loud noises Can contract & dampen large vibrations Prevents nerve damage in cochlea Fig 10.18 10-50

Ears & Hearing - Cochlea Consists of a tube wound 3 turns & tapered so looks like snail shell Fig 10.19 10-51

Ears & Hearing - Cochlea continued Low frequencies can travel all way thru vestibuli & back in tympani As frequencies increase they travel less before passing directly thru vestibular & basilar membranes to tympani Fig 10.20 10-54

Ears & Hearing - Cochlea continued High frequencies produce maximum stimulation of Spiral Organ closer to base of cochlea & lower frequencies stimulate closer to apex Fig 10.20 10-55

Spiral Organ (Organ of Corti) Fig 10.22 Is where sound is transduced Sensory hair cells located on the basilar membrane 1 row of inner cells extend length of basilar membrane Multiple rows of outer hair cells are embedded in tectorial membrane 10-56

Neural Pathway for Hearing Info from 8th nerve goes to medulla, then to inferior colliculus, then to thalamus, & on to auditory cortex Fig 10.23 10-58

Neural Pathways for Hearing Neurons in different regions of cochlea stimulate neurons in corresponding areas of auditory cortex Each area of cortex represents different part of cochlea & thus a different pitch Fig 10.24 10-59

Hearing Impairments Conduction deafness occurs when transmission of sound waves to oval window is impaired Impacts all frequencies Helped by hearing aids Sensorineural (perceptive) deafness is impaired transmission of nerve impulses Often impacts some pitches more than others Helped by cochlear implants Which stimulate fibers of 8th in response to sounds 10-60

Vestibular Apparatus Provides sense of equilibrium =orientation to gravity Vestibular apparatus & cochlea form inner ear V. apparatus consists of otolith organs (utricle & saccule) & semicircular canals Fig 10.11 10-35

Semicircular Canals Provide information about rotational acceleration Project in 3 different planes Each contains a semicircular duct At base is crista ampullaris where sensory hair cells are located Fig 10.12 10-42

Vestibular Apparatus continued Utricle and saccule provide info about linear acceleration Semicircular canals, oriented in 3 planes, give sense of angular acceleration Fig 10.12 10-37

Vestibular Apparatus continued Hair cells are receptors for equilibrium Each contains 20-50 hair-like extensions called stereocilia 1 of these is a kinocilium Fig 10.13 10-38

Vestibular Apparatus continued When stereocilia are bent toward kinocilium, hair cell depolarizes & releases NT that stimulates 8th nerve When bent away from kinocilium, hair cell hyperpolarizes In this way, frequency of APs in hair cells carries information about movement Fig 10.13 10-39

Utricle & Saccule Have a macula containing hair cells Hair cells embedded in gelatinous otolithic membrane Which contains calcium carbonate crystals (=otoliths) that resist change in movement Fig 10.14 10-40

Utricle & Saccule continued Fig 10.14 Utricle sensitive to horizontal acceleration Hairs pushed backward during forward acceleration Saccule sensitive to vertical acceleration Hairs pushed upward when person descends 10-41

Semicircular Canals Provide information about rotational acceleration Project in 3 different planes Each contains a semicircular duct At base is crista ampullaris where sensory hair cells are located Fig 10.12 10-42

Semicircular Canals continued Hair cell processes are embedded in cupula of crista ampullaris When endolymph moves cupula moves Sensory processes bend in opposite direction of angular acceleration Fig 10.15 10-43

Neural Pathways for Equilibrium & Balance Fig 10.16 10-44

Nystagmus & Vertigo Vestibular nystagmus is involuntary oscillations of eyes that occurs when spinning person stops Eyes continue to move in direction opposite to spin, then jerk rapidly back to midline Vertigo is loss of equilibrium Natural response of vestibular apparatus Pathologically, may be caused by anything that alters firing rate of 8th nerve Often caused by viral infection 10-45