PET3323C Spring 2012 Exam II Study Guide Dr Newlin The Chemical Sense Olfaction and Gustation Smell and Taste General Senses Somatic skeletal and visceral Not localized scattered Simple structures pathways Special Senses Smell taste vision hearing equilibrium Concentrated localized in locations within head Anatomically distinct structures more complex Olfaction the sense of smell Olfactory Epithelium contains receptors that bind to scents 3 types of cells first order neurons 1 Olfactory bipolar increase surface area for binding Are neurons and receptors Cells replaced every 30 60 days Olfactory Cilia project from dendrites axons form Olfactory Nerve filaments 2 Supporting 3 Basal are the bulk of the epithelium nourish cells help in the production of new cells These cells require a generated potential depends on whether scents reach actual threshold 2nd order neurons lead to Olfactory tract Specificity of Olfactory Cells Stimulated by different combinations of olfactory quantities 1000 smell genes active in nose o Unique receptor proteins different combinations of smell o Each protein responds to some odorants smells more than others Nasal cavity contains pain receptors that respond to irritants o Impulses sent via Trigeminal Nerve Smell Transduction G protein mediated 1 Odorant molecule binds to olfactory receptor 2 Receptor activates G protein G protein then activates adenylate cyclase 3 Adenylate cyclase converts ATP to cAMP 4 cAMP opens cation channel allowing Na and Ca2 influx o This causes depolarization o Ca2 influx causes K efflux which is involved in adaptation 5 Generator potential from inflow nerve impulse through olfactory nerves 6 Olfactory nerves lead to olfactory bulbs lead to olfactory tract lead to cerebral cortex olfactory portion hypothalamus and limbic system Olfactory Pathway Epithelium generates action potential to be sent up to 2nd order neurons Olfactory Bulb helps us to sharpen sense of smell based on the structures within Sense of scent through Olfactory Tract o Some smells trigger certain memories via limbic system PET3323C Spring 2012 Exam II Study Guide Dr Newlin Odor Thresholds and Adaptation Very low threshold only few molecules need to be present to trigger Adaptation occurs rapidly within 50 by the first second of smell o Complete adaptation to stronger odors occur 1 minute or so after exposure Smell Interpretation 2 pathways Olfactory Cortex via thalamus Interpretation and identification of smell via Limbic System Emotional response to odors PNS fight or flight activity gag reflexes digestive activity Gustation The Sense of Taste Structures consist of the tongue cheeks soft palate pharynx and epiglottis Taste buds on tongue housed in papillae o Fungiform papillae mushroom shaped most numerous o Foliate papillae lateral portion of tongue o Circumvallate papillae posterior portion of tongue Gustatory Cells taste receptors NOT neurons they are chemoreceptors Basal Cells PET3323C Spring 2012 Exam II Study Guide Dr Newlin Molecule stimulates and binds receptor Gustatory hairs increase surface area Gustation taste 4 major classes of stimuli can be distinguished Sour hydrogen ions causes depolarization Sweet sugar G protein linked Salty sodium ions causes depolarization Bitter alkaloids quinine stimulate the release of a neurotransmitter Umami amino acids primarily glutamate and aspartate savory If no ion is involved G protein mechanism Physiology of Gustation 1 Chemicals dissolved in saliva contact gustatory hairs 2 Binding of chemical to gustatory hair induces a graded potential 3 Graded potential results in release of neurotransmitter from synaptic vesicles 4 Binding of neurotransmitter to associated dendrite neurons triggers an action potential in 1st order neurons gustatory fibers Taste transduction Salty sour direct influx and depolarization of cell Bitter sweet umami G protein activation will also cause depolarization of cell Gustatory Pathway Facial nerve anterior tongue PET3323C Spring 2012 Exam II Study Guide Dr Newlin Glossopharyngeal posterior tongue and orpharynx Vagus throat Taste dissolves in saliva contacts gustatory hairs causes receptor potential nerve impulse Pathway From each nerve to medulla from medulla 2nd order to thalamus from thalamus 3rd order to primary gustatory area in cerebral cortex Are rare Olfactory disorders can be due to head injury upper respiratory infections tumors of anterior Taste is 80 smell o Mechanoreceptors texture of food o Thermoreceptors temperature of food o Nociceptors pain too hot Disorders of Chemical Senses fossa exposure to toxic materials Olfactory Disorders Anosmias absence of smell Hyposmia impaired sense of smell Dysosmia distorted sense of smell Gustation disorders Ageusia absence of taste Hypogeusia decreased sensitivity Hypergeusia increased sensitivity Dysgeusia distorted sense of taste The Ear PET3323C Spring 2012 Exam II Study Guide Dr Newlin External Ear outer Auricle pinna lobule ear lobe and helix harder cartilage External Auditory Canal direct soundwaves towards middle inner ear o Contain sebaceous glands which produce ear wax o Tube for ear cleaning is inserted here Tympanic Membrane ear drum boundary between external and middle ear Middle Ear Bony Ossicles direct soundwaves 1 Malleus articulates with the tympanic membrane 2 3 Stapes covers oval window Stapedius and Tensor Tympani Muscles Incus articulates with malleus and stapes protect us from loud sounds dampen the noise o Protection from sustained loud sounds not sudden ones gun shot Pharyngotympanic auditory tube links middle ear with pharynx o Releases and equalizes pressure o Ear infections otitis media common in children Auditory tube is smaller in children easily infected tube will fill with bacteria fluid etc causing infection o Rupture in ear drum will alleviate ear infection pain Babies yelling screaming alleviates their ear aches Internal Ear also called labyrinth because of complex series of canals Outer bony labyrinth encloses inner membranous labyrinth Membranous labyrinth filled with endolymph contains more potassium Bony Labyrinth filled with perilymph this surrounds membranous labyrinth Bony Labyrinth divided into 3 parts cochlea vestibule semicircular canals 1 Cochlea which are passed on to the brain hearing converts sound pressure impulses from outer ear into electrical impulses Bony chamber and membranous chamber spiral PET3323C Spring 2012 Exam II Study Guide Dr Newlin Cochlear Duct small membranous sac contains
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