G protein gustducin in sweet bitter and umami tastes

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G protein gustducin in sweet, bitter, and umami tastes (leads to release of Ca2 from intracellular stores, which causes opening of cation channels in the plasma membrane) The Ear: Hearing and Balance Three parts of the ear: 1. External (outer) ear: hearing 2. Middle ear (tympanic cavity): hearing 3. Internal (inner) ear: hearing and equilibrium
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External Ear Auricle (pinna) is composed of Helix (rim) and Lobule (earlobe) External acoustic meatus (auditory canal): short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands (secret wax) Tympanic membrane (eardrum) 1. Boundary between external and middle ears 2. Connective tissue membrane that vibrates in response to sound 3. Transfers sound energy to the bones of the middle ear Middle Ear A small, air-filled, mucosa-lined cavity in the temporal bone Consists of oval and round windows Consists of three tiny bones (ossicles): Transmit vibratory motion of the eardrum to the oval window 1. Malleus: Hammer, attached to tympanic membrane 2. Incus: Anvil 3. Stapes: Stirrup, attached to oval window Pharyngotympanic (auditory) tube - connects the middle ear to the nasopharynx Equalizes pressure in the middle ear cavity with the external air pressure
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Internal Ear ( Bony Labyrinth) Three parts 1. Vestibule 2. Semicircular canals 3. Cochlea Bony labyrinth is filled with perilymph (similar to CSF) Membranous labyrinth is suspended in the perilymph Filled with potassium-rich endolymph
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Vestibule: Central, egg- shaped cavity of the bony labyrinth Contains two membranous sacs 1. Utricle: continuous with the semicircular canals 2. Saccule: continuous with the cochlea These sacs house equilibrium receptors regions (maculae) and respond to gravity and changes in the position of the head Semicircular Canals Three canals (anterior, lateral, and posterior) that each define two-thirds of a circle Right angles to each other Semicircular ducts line each canal and communicate with the utricle Ampulla of each canal houses equilibrium receptor region called the crista ampullaris Receptors respond to angular (rotational) movements of the head The Cochlea (Snail) A spiral, conical, bony chamber, size of a split pea Extends from the vestibule Contains the cochlear duct, which houses the spiral organ the receptor organ for hearing Cavity of the Cochlea is divided into three chambers 1. Scala vestibuli - superior to cochlear duct, continuous with the vestibule, abuts oval window, contains perilymph 2. Scala media (cochlear duct) - contains endolymph 3. Scala tympani - inferior to cochlear duct, terminates at the round window, contains perilymph The scalae tympani and vestibuli are continuous with each other at the helicotrema
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(apex) The “roof” of the cochlear duct is the vestibular membrane The “floor” of the cochlear duct is composed of: 1. The bony spiral lamina 2. The basilar membrane, which supports the organ or Corti 3. Plays a critical role in sound reception Physiology of Hearing
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