Biopsychology Taste/Olfaction Chemical Senses
taste buds/receptors
- Certain taste buds are better at detecting different taste buds due to varying distributions of taste receptors. EX. There can be bitter, sweet, and sour taste buds on the tip of the tongue, but you can have more of one taste bud.
metabotropic effects in Olfactory receptors
- An ordorant molecule triggers changes in a G protein inside the cell, G protein then provokes chemical activites (the second messenger system) that will lead to an open or closed ion channel or alter gene expression. - Proteins in olfactory receptors respond to chemicals outside the cell triggering changes in G protein inside the cell. - G protein triggers chemical activites that lead to action potentials.
Taste variations in people
- Genetic factors and hormones play a role fo differences in taste sensitivity. - Related to the number of fungiform papillae near the tip of the tongue, having three times as many taste buds.
Dangers in Olfaction
- Olfactory receptors are vulnerable to damage because they're exposed to the air. - Olfactory receptors are usually replaced every month but can be subject to massive damage if you inhale toxic fumes causing the system to replace all the receptors, which may not fully recover.
Olfactory Cortex
- Receives sensory information from the glomeruli which receives its information from the olfactory receptor cells. - Projects into the amygdala to provide an immediate emotional reaction to an odorant. (disgust)
Mechanisms of Taste Receptors
- Salt taste (ion channel PCKD): Taste cells that detect salty flavors will depolarize in the presence of Na+ ions. Taste cell will permit Na+ ions on the tongue to cross the membrane. - Sour taste (ion channel ENaC): Taste cells that detect sour flavors will depolarize in the presence of H+ ions. H+ ions block potassium channels, which will build up. - Sweet taste (metabotropic receptors T1R2+T1R3): This is a G protein-coupled receptor. - Umami Taste (metabotropic receptors T1R1+T1R3): Taste of red meat and mushrooms, similar to sweet receptors. - Responds to sugar or glutamate. - Bitter taste (metabotropic receptors T2Rs): There are 30 different bitter taste cells and they will respond to different types of bitter molecules. (A way of detecting dangerous chemicals).
Taste Aversion
- associated with the insular cortex, amygdala and PVN responds strongly to taste. - powerful enough to be learned in one trial.
Everyday use of taste
- toothpaste contains sodium lauryl sulfate, that intensifies bitter and weakens sweet receptor cells. - Mircaculin binds to sweet taste receptors causing sour foods to be sweet. - Gymnema sylvestre causes sweet tasting foods to become tasteless.
Cribiform Plate
-Olfactory receptor cells leading up to the glomerulus are moving through hole in the skull (Cribiform Plate).
Process of tasting in the brain
1. Taste receptors on the tongue will detect tastants (taste molecules) through the membrane receptors. 2. When tastants interact with the cell, it depolarizes the taste cell. 3. Causing neurotransmitter release to the taste neurons. 4. The neurons will send the taste signal to the brain through cranial nerves. 5. The nucleus of the tractus solitarius (NTS) receives the information and projects it to the gustatory portion of the thalamus. 6. Thalamus projects information to the insula (primary gustatory cortex). - NOTE: Each hemisphere of the cortex is also responsive to the ipsilateral side of the tongue.
Facial Nerve (VII)
Carries taste information to the anterior two-thirds (chords tympani nerve). - Projects to the nucleus of the tractus solitarius (NTS).
Glossopharyngeal nerve (IX)
Carries taste information to the back the tongue and throat. - Projects to the nucleus of the tractus solitarius (NTS).
phremones
Chemicals released by an animal that affects the behavior of other members of the same species. - Mainly animals respond to this, but humans unconsciously respond to some pheromones (physiologically, not physically) through receptors in the olfactory mucosa. EX. The smell of women's sweat near ovulation increased testosterone production in males.
Trigeminal Nerve (CN V)
Detects burning sensations in the nose and mouth, including foods that contain Capsaicin or abrasive odors like ammonia. - Distinct from the normal taste and smell.
Taste
Each part of the tongue is capable of detecting all the taste sensations. There are no specific areas of the tongue that detect specific flavors. - Currently we experience taste as: BITTER, SALTY, SWEET, SOUR, and UMAMI. - studies argue the additon for Fat, starch, water, and calcium taste.
Three main tasks from chemical cues
Humans and animals: Feed, Fight, and Reproduce.
retronasal olfaction
Important for perceiving odors through your mouth while breathing and chewing. This occurs when we are smelling something that is inside our mouth and is what gives us the experience of flavor. - This occurs as a result of taste and smell axons converging in on the endopiriform cortex. - Important for our food selection linked to taste. - 90% of our flavor is based on our sense of smell.
Synthesthesia
Is the experience of one sense in response to stimulation of a different sense. - The mixing of our senses that build on our perception of the world. - Axons of one cortical area branching into another. EX. People see numbers in colors, hear certain types of color, hearing a sound a person can see a color.
taste buds/receptors
Modified sensory skin cell in the mouth that contain the receptors for taste. - Have excitable membranes and release neurotransmitters to excite neighboring neurons, transmitting that information to the brain. - are NOT TRUE neurons. - Are located inside papillae which is a structure on the surface of the tongue. - each taste bud contains about 50 receptors. - The majority of taste buds are located on the outside edge of the tongue. - some are located in your stomach and brain used to detect chemicals.
Olfactory Receptors
Neurons responsible for smell that line the nasal air passages. Each olfactory cell has and is located on cilia (threadlike dendrites) that extend from the cell body into the muscous surface of the nasal passage. - Some can be responsive to certain chemicals and unresponsive to others.
nontasters
Not so sensitive to taste, seek out relatively sweeter or fattier foods to maximize taste.Lower desity of papillae, weaker reaction to flavors.
vomernasal organ (VNO)
Set of receptors located near the olfactory bulb, where the VNO receptors only respond to pheromones, only. - Each VNO receptor responds to only one pheromone.
Glomeruli
Sites in the brain's olfactory bulb where signals from the smell receptors converge. - is a synapse between an olfactory cell and a cell in the olfactory bulb called the mitral cell. - Each glomerulus reacts to multiple different odors and each activation of the glomerulus is unique for each odor. - Glomeruli takes smell to the olfactory cortex. EX. Lemon scent can activate blue, purple, and red mitral cells. Lime scent can activate purple, red, and green mitral cells.
Generalist taste buds
Taste buds that responds more to other types of taste.
Olfaction (smell)
The sense of smell in response to chemicals making contact with membranes inside the nose. - Certain animals (dogs) are able to smell changes in human body chemistry, specifically, detect oncoming seizures. - Does NOT make a stop in the thalamus.
Papillae of the tongue
These are the small projections on the tongue. Inside are the taste buds. - each could contain 10 or more taste buds.
Olfactory Bulb
a brain structure located above the nasal cavity beneath the frontal lobes - Sends axons to the olfactory area of the cerebral cortex.
Supertasters
people with heightened sensitivity to all tastes and mouth sensations, have more density of papillae, thus stronger reaction to flavors.
nucleus of the tractus solitarius (NTS)
structure in the medulla that receives input from taste receptors and projects the information to various parts of the brain (thalamus).
Specialist taste buds
taste buds that exclusively respond to a single taste.