SMELL AND TASTE Jeffrey Zhao, Michael Dawkins, Ryan Fischer, Leah Politte, Sarah Mariani, Alexa Stanley

Essential Ideas Nature of energy transduction, relevant anatomical structures, and specialized pathways in the brain for smell and taste Common sensory disorders in relation to smell and taste The basic tastes Differences between sense of taste, smell, and flavor

SMELL

Basics of Smell When you smell something, you are really smelling odor particles Smell signals are NOT relayed through the thalamus This suggests smell evolved earlier than other senses Olfaction is the sense of smell- involves a chain of biochemical events Humans have around 40 million olfactory receptors that detect up to 10,000 different odors

Basic Steps of Olfaction Step 1: Odors interact with receptor proteins associated with specialized hair (cilia) in the nose Step 2: The stimulated nerve cells associated with these hairs covey information to the brain’s olfactory bulbs (underside of the brain between the frontal lobes) Step 3: In the olfactory bulbs, sensations of smell are realized

Detecting the Odorants Odor molecules hit the olfactory epithelium- one square inch area of the nasal cavity Odor molecules stimulate olfactory receptor cells, which are neurons Olfactory hairs cover the dendrites When the molecule binds to the receptor cell, the dendrite fires an electrical impulse to the olfactory bulb

Detecting the Odorants (continued) Supporting cells provide structure to the epithelium, insulate receptor cells, and detoxify chemicals on the epithelium surface Basal stem cells divide and create new olfactory receptors (regenerate monthly) Trigeminal nerve fibers in the olfactory epithelium respond to pain For example, when you breathe in ammonia

Processing the Odorants Richard Axel and Linda Buck discovered each olfactory receptor only has one type of receptor Sends signal to a microregion (glomerulus) of the olfactory bulbs Brain interprets this pattern of signals (called an “odorant pattern”) Luca Turin proposed an alternative theory Olfactory sensors respond to quantum vibrations of odors. Each receptor is not limited to just one type of odorant molecule

Smell in Humans In humans, smell connected to memory Certain scents can evoke past memories Biologically, a survival skill -- helps us locate and detect food Human sense of smell continues to increase and plateaus at around 8, and decreases with old age Some research suggests humans may use sexual pheromones and pheromones that help identify family members by smell

Smell in Animals Used for communication For example, some insects secrete odorous signals called pheromones to communicate Pheromones can signal sexual receptivity, danger, territorial boundaries, and food sources Many animals have two separate olfactory systems Main olfactory system- detects volatile stimuli Accessory olfactory system- detects fluid-phase stimuli and most pheromones

TASTE

Basics of Taste Taste and smell are very closely related Gustation is your sense of taste The 5 Basic Tastes Sweet Salty Sour Bitter Umani

Taste Receptors Taste receptor cells are gathered in taste buds on the top and side of tongue These receptors cluster in small mucous-membrane projections (papillae) Sensitivity to taste sensations is a result of papillae density on the tongue

Pathway of Tasting Specialized nerve “hotline” carries taste messages to brain A specialized region in the somatosensory cortex (in the parietal lobe) realizes taste This area is next to the part of the brain that receives touch stimulation from the face

Locating the Tastes Bitter is in the back of tongue Sour is on each side of the tongue Sweet and Salty are towards the front of the tongue There are not many taste buds in the middle

The Basic Tastes- Bitterness Most sensitive of the tastes People with more taste buds for bitter flavors are called supertasters Supertasters will have distaste for certain foods like broccoli and diet drinks Survival advantage since poisons are bitter

The Basic Tastes (Continued) Saltiness A taste produced mainly by the presence of sodium ions Other ions like potassium can also produce a salty taste Sourness

The Basic Tastes (Continued) Sweetness Produced by the presence of sugars Detected by G Protein coupled receptors Unami

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