Sense of Taste 13 chemical receptors in the taste cells
2 Na Receptors 2 K Receptors 1 Cl Recptor 1 Adenosine Receptor 1 Inosine Receptor 2 Sweet Receptors 2 Bitter Receptors 1 Glutamate Receptor 1 Hydrogen Receptor
Primary Sensation of Taste 1. Sour o o
Caused by acids - Hydrogen ion concentration Intensity of sourness is proportional to the log of the hydrogen ion concentration
2. Salty o
Caused by ionized sales - Na ion Concentration (Na Cations > Na Anions) o Quality varies from one salt to another due to the possibility of a sale eliciting more than 1 primary taste sensation 3. Sweet o Not caused by a single class of chemicals Usually caused by organic chemicals Elicited by sugars, glycols, OH, aldehydes, ketones, amides, esters, some amino acids, some small CHONs, sulfonic acids, halogenated acids and inorganic salts of lead and beryllium 4. Bitter o Not caused by a single class of chemicals Usually organic substances 2 particular classes of substances: Long chain organic substances that contain N Alkaloids Taste and Smell
5. Umami o Dominant taste of food containing L glutamate e.g. Meat extracts and aging cheese
Threshold for Taste Sour (HCl acid)
0.0009 N
Salty (NaCl)
0.01 M
Sweet(Sucrose)
0.01 M
Bitter(Quinine)
0.000008 M
Note: Bitter taste is the most senstive, since it provides an important protective function against many dangerous toxins in food. Taste Blindness Observed mostly for diff types of thiourea compounds o Phenylthiocarbamide: used by psychologist to demonstrate taste blindness Taste Bud and Its function Supporting cells/Sustentacular cells Taste Cells o Continually replaced by mitosis o Mature cells lie at the center of the bud; soon break up and dissolve o Outer tips of the taste cells are arranged around a minute taste pore
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Microvilli/Taste Hair: provide receptor for taste CNS Transmission Number: Children > Adults Taste rcp --> Cerebrum Adults: 3000 - 10,000 o Ant 2/3 of the tongue Lingual Nerve chorda tympani >= 45 yrs old, many taste buds had degenerated Facial Nerve Tractus Solitarius (Brainstem) Location of Taste buds o Circumvallate/Post tongue Glossopharyngeal nerve a. Large number are on the walls of the troughs that Post level of the Tractus solitarius (Brainstem) surround the circumallate papilae o Pharyngeal region Vagus Nerve Tractus Solitarius Circumvallate papillae: form the V line on the surface (Brainstem) of the posterior tongue b. Moderate number of taste buds are on the fungiform papillae Over the flat ant surface of the tongue c. Moderate numberss are on the foliate papillae At the folds along the lateral surfaces of the tongue d. Some are at the palate, tosillar pillars, epiglottis and procimal esophagus Specificity of Taste Buds for Primary taste Stimulus o Taste substance in Low concentration: 1 taste bud reponds mostly to 1 of the 5 primary taste stimuli o Taste substance in High concentration: buds excite >= 2 primary taste stimuli Mechanism of Stimulation of taste Buds o Receptor potential for taste: Change in electrical otential in the taste cell o Saliva gradually washes the taste stimulus o Salty and Sour taste sensations Receptor CHON open specific ion channels in the apical membranes of the taste cells activating the o Nucei of the tractus solitarius Ventral posterior medial receptor nucleus of the thalamus lower tip of the postcentral o Sweet and Bitter taste sensations gyrus in the parietal cerebral cortex deep into the Portions fo the receptor CHON molecules that sylvian fissure opercular insular area protrude thru the apical membranes activatee 2nd Brainstem --> Glands messenger transmitter substances inside the taste o Brainstem Tractus solitarius superior and Inferior cells elicit taste signals saliatory nuclei Submandibular, Sublingual and Parotid glands o Help control the secretion of saliva o
Taste and Smell
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Taste Preference and Control of Diet
Taste Preference o Animal will choose certain types of food in preference to others to automatically help control the type of diet it eats o Changes depending with the body's need for certain specific substances o Give in to your cravings, it's good for you :) Taste Aversion o Negative Experience Negative Taste preference o Won't eat something that made you sick
Taste and Smell
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Sense of Smell Olfactory Membrane
Lies in the superior part of each nostril Medially: folds downward along the surface of the superior septum Laterally: folds over th superior turbinate and even over a sm portion of the upper surface of the middle turbinate Surface Area: 2.4 sq cm Olfactory Cells (Rcp of Smell) o Bipolar nerve cells derived from the CNS 100M intersparsed amoung sustentacular cells o Olfactory hair/Olfactory cilia: project into the mucus that coats the inner surface of the nasal cavity Forms a dense mat in the mucus React to odors in the air stimulate olfactory cells Part of the olfactory cell o Bowman's glands: secrete mucus onto the surface of the oldactory membrane
3. Activation of the Inner Olf Cilia receptor protein by the odorant substance activates the G-protein complex 4. Activates multiple molecules of adenylyl cyclase inside the olfactory cell membrane 5. This causes the formation of many times more molecules of cAMP 6. Finally, the cAMP opens still many times more sodium ion channels. Note: o Intracellular signals amplify signal transduction. Thus, even the weakest odorant substances can stimulate Olfactory Rcp o However, although the threshold concentration of substances that evoke smell are extremely slight, contractions only 10 to 50x above the threshold evoke maximum intensity of smell The difference might be explained by the fact that smell is concerned more with detecting the presence or absence of odors rather than the quantitative detection of their intensities
Physical Factors that Affect the degree of stimulation
Stimulation fo the Olfactory Cells 1. Odorant substance diffuses into the mucus 2. Substance binds to the Outer Olf Cilia rcp CHON Taste and Smell
Only volatile substances that can be sniffed into the nostrils can be smelled The stimulating substance must be at least slightly water soluble o So that it can pass through the mucus to reach the olfactory cilia Substance should be at least slightly lipid soluble o Coz lipid constituents of the cilium itself are a weak barrier to non-lipid-soluble odorants Membrane Potential and Action Potentials in Olfactory Cells Membrane Potential: -55 millivolts Odorants cause depolarization of the olfactory cell membrane from -55 to <= -30 millivolts Adaptation o Olfactory receptors adapt about 50% in 1s or so after stimulation 4
o
However, Extinction occurs due to psychological adaptation Thus, psychological adapatation > physiological adaptation Granule cells: postulated to have inhibitory effects to the olfactory bulb
Transmission of Smell Signals into the CNS Olfactory Rcp Glomeruli CN1/Olfactory Tract Olfactory bulb 1. Very old Olfactory System: Medial Olfactory Area o Consist of a group of nuclei located in the midbasal portions of the brain immediately anterior to the hypothalamus Septal nuclei: feel the hypothalamus and other primitivae portions of the limbic system o Function: Cause primitive emotional drives associated with smeel, such as licking the lips, salivation and other feeding responses Basic olfactory reflex 2. Less Old Olfactory System: Lateral Olfactory Area o Composed mainly of the 1. Prepyriform and pyriform cortex 2. Cortical portion of the amygdaloid nuclei o Passes to almost all portions of the limbic system o Feed to the paleocortex (ant-medial portion of the temporal lobe) Paleocortex: only area of the entire cerebral cortex where sensory signals pass directly to the ortex without passing 1st thru the hypothalamus o Function: Cause a person to develop an absolute aversion to foods that have caused nausea and vomitting Automatic but partially learned control of food intake and aversion to toxic and unhealthy foods
Taste and Smell
3. Newer pathway o Passes thru the thalamus dorsomedial thalamic nucleus lateroposterior quadrant of the orbitofrontale cortex o Function: Helps in the conscious analysis of odor Concious perception and analysis of olfaction Centrifugal control of activity in the olf bulb by the CNS o Small Granule Cells: Located amoung the mitral and tufted cells in the olf bulb Sends inhibitory signals to sharpen one's specific ability to distinguish one odor from another
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