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CHEMICAL SENSES 1 Define and identify the anatomy of the olfaction receptor cells and epithelium a Localization and structure of olfactory receptors i Olfactory epithelium covers the superior nasal concha on each side of the nasal septum and contains millions of olfactory receptor cells These receptor cells are cushioned by columnar supporting cells which give the olfactory epithelium its yellow hue 1 The olfactory receptor cells are unusual bipolar neurons with a thin apical dendrite that terminates in a knob from which several cilia radiate a Olfactory cilia increase the receptive surface area and are covered by a thin layer of mucus that is produced by the supporting cells i Nonmotile odorants b The mucus is a solvent that captures and dissolves airborne c The unmyelinated axons of the olfactory receptor cells are gathered into small fascicles which form the filaments of the olfactory nerve cranial nerve I Filaments of the nerve run through the cribriform plate d Undergo noticeable turnover throughout adult life due to their superficial location being a risk for damage e Typical life span 30 60 days replaced by basal cells 2 Supporting cells surround the olfactory cells 3 Basal cells base of epithelium stem cells b Specificity of the olfactory receptors i Our olfactory receptor cells can distinguish about 10 000 different odors ii We have smell genes 1 000 that encode a unique receptor protein and each of the receptor proteins respond to one or more different odors Each odor binds to several different receptor types Each receptor cell has only one type of unique receptor protein iii Olfactory neurons are very sensitive some of what we can smell is actually pain 1 There are pain receptors within the nasal cavities that respond to irritants such as the sharpness of ammonia the hotness of chili peppers and the chill of methanol Impulses from these pain receptors reach the CNS via afferent fibers of the trigeminal nerves 2 2 Explain in detail the transduction of smell and its process and adaptation through the somatosensory system a Physiology of smell for us to smell a particular odorant it must be volatile gaseous state as it enters the nasal cavity It must dissolve in the fluid coating the olfactory epithelium i Activation of the olfactory receptors dissolved odorants stimulate the olfactory receptors by binding to receptor proteins in the olfactory cilium membranes opening cation channels and generating a receptor potential An action potential is conducted to the first relay station in the olfactory bulb b The olfactory pathway ii Smell transduction transduction of odorants uses a receptor linked to a G protein 1 Odorant binds to its receptor 2 Receptor activates G protein 3 G protein activates adenylate cyclase 4 Adenylate cyclase converts ATP to cAMP 2nd messenger 5 cAMP opens a cation channel allowing Na and Ca2 influx an causing depolarization and impulse transmission a Ca2 influx allows the transduction process to adapt decreasing its response to a sustained stimulus olfactory adaptation i Axons of the olfactory receptor cells form the olfactory nerves that synapse in the overlying olfactory bulbs the distal ends of the olfactory tracts The filaments of the olfactory nerves synapse with mitral cells in complex structures called glomeruli 1 Each glomerulus represents a single aspect of an odor but each odor activates a unique set of glomeruli Different odors activate different subsets of glomeruli The mitral cells refine the signal amplify it and then relay it a Granule cells in the olfactory bulbs inhibit mitral cells so that only highly excitatory olfactory impulses are transmitted Quiz Question Mitral cells housed inside glomeruli True ii When the mitral cells are activated impulses flow from the bulbs to two main destinations through the olfactory tracts 1 The first pathway travels via the thalamus to the piriform lobe of the olfactory cortex and the part of the frontal lobe just above the orbit where smells are consciously interpreted and identified 2 The second pathway bypasses the thalamus and flows directly via the subcortical route to the hypothalamus amygdale which elicits emotional responses to odors a Smells associated with danger trigger sympathetic flight or flight response emotional response b Appetizing odors cause increased salvation and stimulation of the digestive tract c Unpleasant odors stimulate chocking and sneezing c Adaptation i Olfaction has a low threshold only a few molecules need to be present ii Adaptation occurs rapidly olfactory receptors adapt by 50 in the first second and then more slowly thereafter iii Complete adaptation to certain strong odors occurs in about 1 minute i e peppermint 3 Describe and locate the types of taste buds associated with gestation a Location and structure of the taste buds i The taste buds are located primarily in the oral cavity mostly on the papillae peg like projections of the tongue mucosa that give the tongue surface a slightly abrasive feel 1 Fungiform papillae contain the majority of taste buds scattered over the tongue surface 2 Foliate papillae 3 Vallate papillae largest and the least numerous form an inverted V at the back of the tongue ii Each flask shaped taste bud consists of 50 100 epithelial cells either gustatory cells or basal cells 1 Gustatory cells taste cells 2 Basal cells act as stem cells dividing and differentiating into new 4 Describe the gustatory cells a Gustatory taste cells gustatory cells i Contain long microvilli gustatory hairs that project from the tips of all gustatory cells and extend through a taste pore to the surface of the epithelium where they are bathed with saliva 1 Sensitive portions of the gustatory cells receptor membranes ii Sensory dendrites coil around the gustatory cells representing the initial gustatory pathway to the brain 1 Two kinds emphasized test question a One forms traditional synapses with the sensory dendrites and releases the neurotransmitter serotonin b The other kind lacks synaptic vesicles but instead releases ATP that acts as a neurotransmitter 2 Taste bud cells are subjected to huge amounts of friction and are routinely burned by hot foods replaced every 10 days 5 Name the major types of taste stimuli and where they most commonly occur i Sweet elicited by organic substances including sugars saccharin alcohols lead ii Sour produced by acids specifically their H in solution quiz question salts and some amino acids 1 Tip of the tongue 1 Sides of


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FSU PET 3323C - CHEMICAL SENSES

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