Transcript Hair cells
10-26 Receptors are exteroceptors because respond to chemicals in external environment Interoceptors respond to chemicals in internal environment 10-27 Detects sweet, sour, salty, bitter, & amino acids (umami) Taste receptor cells are modified epithelial cells ◦ 50-100 are in each taste bud Each bud can respond to all categories of tastants Fig 10.7 10-28 Salty & sour do not have receptors; act by passing through channels Fig 10.8 10-29 Sweet & bitter have receptors; act thru G-proteins Fig 10.8 10-30 Olfactory apparatus consists of receptor cells, supporting cells, & basal cells Fig 10.9 ◦ Receptor cells are bipolar neurons that send axons to olfactory bulb ◦ Basal cells are stem cells that produce new receptor cells every 1-2 months ◦ Supporting cells contain detoxifying enzymes 10-32 Odor molecules bind to receptors & act through G-proteins Olfactory receptor gene family is huge 10-33 10-34 Sound waves funneled by pinna (auricle) into external auditory meatus External auditory meatus channels sound waves to tympanic membrane Fig 10.17 10-47 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 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 Consists of a tube wound 3 turns & tapered so looks like snail shell Fig 10.19 10-51 Tube is divided into 3 fluid-filled chambers ◦ Scala vestibuli, cochlear duct, scala tympani Fig 10.19 10-52 Oval window attached to scala vestibuli (at base of cochlea) Vibrations at oval window induce pressure waves in perilymph fluid of scala vestibuli Scalas vestibuli & tympani are continuous at apex ◦ So waves in vestibuli pass to tympani & displace round window (at base of cochlea) Necessary because fluids are incompressible & waves would not be possible without round window 10-53 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 High frequencies produce maximum stimulation of Spiral Organ closer to base of cochlea & lower frequencies stimulate closer to apex Fig 10.20 10-55 Is where sound is transduced Sensory hair cells located on the basilar membrane Fig 10.22 ◦ 1 row of inner cells extend length of basilar membrane ◦ Multiple rows of outer hair cells are embedded in tectorial membrane 10-56 Pressure waves moving thru cochlear duct create shearing forces between basilar & tectorial membranes, moving & bending stereocilia ◦ Causing ion channels to open, depolarizing hair cells ◦ The greater the displacement, the greater the amount of NT released & APs produced 10-57 Info from 8th nerve goes to medulla, then to inferior colliculus, then to thalamus, & on to auditory cortex Fig 10.23 10-58 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 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 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 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 Utricle and saccule provide info about linear acceleration Semicircular canals, oriented in 3 planes, give sense of angular acceleration Fig 10.12 10-37 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 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 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 sensitive to horizontal acceleration Fig 10.14 ◦ Hairs pushed backward during forward acceleration Saccule sensitive to vertical acceleration Hairs pushed upward when person descends 10-41 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 Hair cell processes are embedded in cupula of crista ampullaris When endolymph moves cupula moves Fig 10.15 ◦ Sensory processes bend in opposite direction of angular acceleration 10-43 Fig 10.16 10-44 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