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SPECIAL SENSES II AUDITROY AND VESTIBULAR SYSTEMS November 14, 2011 Chapter 17: 574 – 588 OBJECTIVES: What is the anatomy of the ear? How are the sound vibrations detected How does the brain perceive sound? How does the ear help with balance? WHAT IS THE ANATOMY OF THE EAR? External ear – sound collection Middle Ear – sound amplification (convert air into vibrations of liquid) Inner Ear – sound detection (cochlea) & balance (vestibular apparatus) EXTERNAL EAR Auricle: provides directional sensitivity Tympanic Membrane: “ear drum” separates external ear from middle ear Wax: prevent any damage to tympanic membrane Middle Ear Also called tympanic cavity Auditory Ossicles: 3 smallest bones in the body: -Malleus (hammer), Incus (Anvil), Stapes (stirrup) -Malleus attached to tympanic membrane -Stapes attached to oval window of cochlea --take sound vibrations of large area and amplify to a much smaller area Two smallest muscles in body protect ear from prolonged loud sounds: Tensor Tympani: stiffens tympanic membrane Stapedius: Reduces movement of stapes at oval window Long period of time of loud sounds: these muscles are in constant contraction Eustachian tube: equalizes pressures within middle ear: drains into the pharynx INNER EAR Subdivided into: Vestibule – balance Semicircular canals – balance Cochlea – auditory VIBRATION OF TYMPANIC MEMBRANE Converts sound waves at tympanic membrane into movement of fluids in membranous labyrinth of cochlea AUDITORY RECEPTORS LIKE WITHIN THE ORGAN OF CORTI OF THE COCHLEA Organ corti contains auditory receptor cells ORGAN OF CORTI HAIR CELLS – auditory receptor MECHANORECEPTORS The Organ of COrti rests on the basilar membrane The Auditory receptors, known as hair cells, have cilia that are in contact with the tectorial membrane Movement of the basilar membrane causes movement of the cilia and depolarization Cilia move against tectorial membrane and can detect sound/pitch How does the brain perceive sound? SOUND FREQUENCY IS MAPPED ON THE BASILAR MEMBRANE High frequency receptors are damaged first THE MAP IS MAINTAINED IN THE COCHLEAR NERVE AND COCHLEAR NUCLEUS IN THE BRAINSTEM THE MAP IS MAINTAINED ALL THE WAY TO THE AUDITORY CORTEX IN THE TEMPORAL LOBE Tonotopic map -auditory nerves keeps tonotopic map AUDITORY PATHWAY 1. Synapse in cochlear nuclei in medulla 2. Synapse in inferior colliculus 3. Synapse in medial geniculate nucleus of thalamus (tonotopic map in between) 4. Synapse in auditory cortex of temporal lobe HOW DOES THE EAR HELP WITH BALANCE Vestibular system -The vestibular apparatus in the inner ear consists of two Otolith Organs: --static equilibrium, linear Utricle – responds to tilting and horizontal movement (moving car) Saccule – responds to vertical movement (elevator) Otochonia: “rocks” move hair cells and gives s sense of direction Semicircular Canals detect rotation Fluid in all three planes to detect each type of direction THERE IS ONE SEMICIRCULAR CANAL FOR EACH PLANE OF SPACE VESTIBULAR PATHWAY Axons from semicircular and vestibular will form vestibular branches of cranial nerve 8 They ten go to structures that are responsible for keeping balanced Examples: red nucleus Cerebellum Cranial nerves 3, 4, and 6 GUSTATION AND OLFACTION (TASTE AND SMELL) Humans: omnivores Chapter 17: 549-555 HOW ARE SMELL AND TASTE CLINICALLY IMPORTANT Taste intimately linked to sense of smell The number of taste buds begin declining rapidly by age 50 Sense of smell declines with ageing Elderly aren’t motivated to eat because food has little taste PARKINSON’S ANOSMIA In Parkinson’s disease, the incidence of smell loss is greater than the incidence of tremor! TASTE BUDS GUSTATORY RECEPTORS CHEMORECEPTORS – chemical receptors Clustered in papillae(contain taste buds) of tongue -to detect, must have saliva GUSTATORY RECEPTORS ARE SPECIALIZED EPITHELIAL CELLS NOT NEURONS Survive only 10 days before replacement (just like skin, has a turnover rate) TASTE ZONES Do not correspond to papillae types Primary: -sweet -salty -sour -bitter Additional: -Umani -Characteristic of beef/chicken broths and parmesan cheese -receptors sensitive primarily to amino acids Water Detected by receptors in the pharynx (“dry throat”) Fats GUSTATORY MECHANISM Salt and sour receptors -chemically gated ion channels *salt and sour work directly on ion channel Sweet, bitter and umani receptors -gustducins – g proteins *use a second messenger cascade that will eventually affect ion channel GUSTATORY PATHWAY 3 cranial nerves (3,7,9) go to brainstem to thalamus to primary gustatory complex into parietal lobe EVOLUTION OF OLFACTION Olfactory doesn’t need to go to thalamus --when it’s emotional, goes straight to limbic lobe OLFACTORY ORGANS OLFACTORY EPITHELIUM CHEMORECEPTORS Olfactory receptors: true neurons Olfactory epithelium contains: -olfactory receptors = bipolar neurons -basal (stem) cells -***One of few examples of neurons replaced throughout life*** Nerve foes through cribriform plate -cilia cannot detect unless dissolved in nucleus OLFACTORY PATHWAY Olfactory tract has 3 primary targets: -contralateral olfactory bulb – smell localization -thalamus – smell perception -limbic system – smell emotion Baumann’s gland: make nucleus used to dissolved THE OLFACTORY SYSTEM PROJECTS TO THE LIMBIC SYSTEM WITHOUT A THALAMIC RELAY