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 ◦ are in each taste bud  Each bud can respond to all categories of tastants Fig

 Salty & sour do not have receptors; act by passing through channels Fig

 Sweet & bitter have receptors; act thru G-proteins Fig

 Olfactory apparatus consists of receptor cells, supporting cells, & basal cells ◦ 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 Fig

 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

 Malleus (hammer) is attached to tympanic membrane ◦ Carries vibrations to incus (anvil) ◦ Stapes (stirrup) receives vibrations from incus, transmits to oval window Fig

 Stapedius muscle, attached to stapes, provides protection from loud noises ◦ Can contract & dampen large vibrations ◦ Prevents nerve damage in cochlea Fig 10.18

 Consists of a tube wound 3 turns & tapered so looks like snail shell Fig

 Tube is divided into 3 fluid-filled chambers ◦ Scala vestibuli, cochlear duct, scala tympani Fig

 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

 High frequencies produce maximum stimulation of Spiral Organ closer to base of cochlea & lower frequencies stimulate closer to apex Fig

 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 Fig

 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

 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

 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

 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

 Utricle and saccule provide info about linear acceleration  Semicircular canals, oriented in 3 planes, give sense of angular acceleration Fig

 Hair cells are receptors for equilibrium ◦ Each contains hair-like extensions called stereocilia  1 of these is a kinocilium Fig

 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

 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

 Utricle sensitive to horizontal acceleration ◦ Hairs pushed backward during forward acceleration  Saccule sensitive to vertical acceleration  Hairs pushed upward when person descends Fig

 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

 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

Fig

 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