Power Point 1 The Chemical Senses Objective 1 Define and identify the anatomy of the olfaction receptor cells and epithelium Olfaction smell Smell receptors excited by air chemicals which dissolve in the nasal membrane detects chemicals in a solution Olfactory epithelium on top of the nasal canal holes through the cribiform plate that allows passage to olfactory bulbs Olfactory epithelium Pseudostratified epithelium 1 layer of cells giving the false impression of multi layer o Known as olfactory epithelium located on the roof of the nasal cavity Three types of cells serve to increase receptive surface area these lie flat on epithelium and are covered by mucous Olfactory receptor millions on each side of nasal septum it is a bipolar cell cell body in middle spreads in 2 different directions Supporting Basal surround olfactory cells secretes mucous base of epithelium acts like stem cell for olfactory receptors catch different air chemicals when breath afferent electric signal goes to brain Olfactory cilia Olfactory receptor cells o Bipolar neurons o Olfactory cilia thin dendrite that ends with a knob giving way to olfactory cilia that is produced by the supporting cells The mucous captures airborne chemicals Filaments of the olfactory nerve run superior to inferior through the cribiform plate o o Replaced ever 30 60 days by differentiation of the basal cells Specificity of Olfactory Receptor Cells These cells can distinguish about 10 000 different odors o o Receptors are stimulated by at least 1 000 smell genes active in the nose Unique receptor protein Each cell has only ONE TYPE of receptor protein Each protein responds to some odorants more than others sensitivity might be different depending on receptors o Nasal cavity contains pain receptors that responds to irritants if smell is too strong and irritates it is because of pain receptor o Receptor replacements in concurrence with expression of smell genes from nuclei Objective 2 Explain in detail the transduction of smell and its process and adaptation through the somatosenstory system 1 Odor binds to a receptor 2 G protein signaling molecule is activated which activates the enzyme adenylate cyclase to synthesize cAMP cAMP is a secondary messenger if G protein is bound to GTP activation occurs if G protein is bound to GDP activation turned off 3 cAMP allows cation membrane channel to open from the extracellular to intracellular space Facilitates AP depolarization nerve is activated and sending afferent signals to the brain 4 Na and Ca2 flow in causing depolarization Cyclic AMP the key to open cation channel depolarization mechanism for smell o Adynelate cyclase breaks down ATO to make cyclic AMP o o Receptors with specific binding sites for different odors odors captured by cilia o Odor specificity activates nerve o o Signals relayed in glomeruli Signals brain Circuit Level of Olfaction o Olfactory receptors send AP to the second order neurons Mitral Cells which are inside glomeruli Receptors are 1st order neurons o Different glomeruli responds to different odors o Mitral cells send information up olfactory tract to either the thalamus or pas the thalamus to the hypothalamus amygdala or limbic system sympathetic emotional responses to odor Odor Thresholds and Adaptations o Olfaction has a low threshold sensitive only a few molecules need to be present to detect o o o o o o Adaptation to odors occurs rapidly olfactory receptors adapt by 50 in the first second or so and more slowly thereafter Complete adaptation to certain strong odors occurs in about 1 minute after exposure Objective 3 Describe and locate the types of taste buds associated with gustation Gustation taste Taste receptors excited by food chemicals receptors are spread all over tongue Taste buds our sensory receptors for taste Tongue cheek soft palate pharynx epiglottis Taste buds are PRIMARILY on the tongue housed in papillae abrasive feel o o o o o o o o Fungiform papillae Foliate papillae Circumvallate papillae top lateral back Largest and the least only about 8 12 of them Objective 4 Describe the gustatory cells Each bud has 50 100 cells of where there are 2 types o Gustatory cells and basal cells replaced every 7 10 days Basal cell most dynamic cell in the body stem cells for taste Gustatory cells gustatory hairs Project through at taste pore into saliva Like olfactory cilia and mucous Dendrites in each cell take signal from receptor cell to the brain o 2 types of gustatory cells one release its neurotransmitter serotonin the other uses ATP o ATP acts like neurotransmitter these do not have synaptic vesicles Serotonin in brain lack of serotonin related to depression Objective 5 Name the major types of taste stimuli and where they most commonly occur Taste four major classes of stimuli that can be distinguished o Sour o Sweet o Salty o Bitter o Umami acids acidic H elicited by organics sugars salts inorganic salts metal ions NaCl alkaloids caffeine nicotine amino acids glutamate aspartate Discovered by Japanese means delicious meat savory beef taste All other tastes such as chocolate coffee pepper are combinations of these five plus accompanying olfactory sensations Taste Type Location Sweet receptors tip of tongue Salty and sour sides of tongue o o o Bitter back of tongue o Umami pharynx o However all taste can come from all areas these are just primary regions Objective 6 Describe the physiology and transduction of gustation including the afferent fibers that are involved Chemicals dissolved in saliva contact gustatory hairs Binding of chemical to gustatory cell induces depolarization At highest change in membrane voltage neurotransmitter serotonin ATP released from synapse Binding of NT to the associated afferent fiber dendrite moves information to the 1st order neurons Chemical stimulus changing to electrical voltage to transmit signal to CNS Cations come into cell to change membrane potential Chemical Depolarization o Salty Na influx through Na channels causes depolarization Lose K from cell at same time Sour H blockage of K channels don t let K out of cell allows cations to enter o o Bitter Sweet Umami receptor coupled with gustducin G protein o o o o o o o o o o Gustducin causes the release of intracellular Ca2 which opens cation channels allowing for depolarization Release of Ca2 stored in SR causes Na channels to open Gustatory Pathway Afferent Fibers Origination o Facial Nerve VII Anterior 2 3 of tongue o Glossopharyngeal Nerve IX Posterior 1 3 of
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