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

Essential IdeasNature of energy transduction, relevant anatomical structures, and specialized pathways in the brain for smell and tasteCommon sensory disorders in relation to smell and tasteThe basic tastesDifferences between sense of taste, smell, and flavor

SMELL

Basics of SmellWhen you smell something, you are really smelling odor particlesSmell signals are NOT relayed through the thalamusThis suggests smell evolved earlier than other sensesOlfaction is the sense of smell- involves a chain of biochemical eventsHumans have around 40 million olfactory receptors that detect up to 10,000 different odors

Basic Steps of OlfactionStep 1: Odors interact with receptor proteins associated with specialized hair (cilia) in the noseStep 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 OdorantsOdor molecules hit the olfactory epithelium- one square inch area of the nasal cavityOdor 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 surfaceBasal 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 receptorSends signal to a microregion (glomerulus) of the olfactory bulbsBrain 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 HumansIn humans, smell connected to memory

Certain scents can evoke past memories

Biologically, a survival skill -- helps us locate and detect foodHuman sense of smell continues to increase and plateaus at around 8, and decreases with old ageSome research suggests humans may use sexual pheromones and pheromones that help identify family members by smell

Smell in AnimalsUsed for communication

For example, some insects secrete odorous signals called pheromones to communicatePheromones can signal sexual receptivity, danger, territorial boundaries, and food sources

Many animals have two separate olfactory systems

Main olfactory system- detects volatile stimuliAccessory olfactory system- detects fluid-phase stimuli and most pheromones

TASTE

Basics of TasteTaste and smell are very closely relatedGustation is your sense of tasteThe 5 Basic Tastes

SweetSaltySourBitterUmani

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

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

Locating the TastesBitter is in the back of tongueSour is on each side of the tongueSweet and Salty are towards the front of the tongueThere are not many taste buds in the middle

The Basic Tastes- BitternessMost sensitive of the tastes

People with more taste buds for bitter flavors are called supertastersSupertasters will have distaste for certain foods like broccoli and diet drinksSurvival advantage since poisons are bitter

The Basic Tastes (Continued)

Saltiness

A taste produced mainly by the presence of sodium ionsOther ions like potassium can also produce a salty taste

Sourness

The taste that detects acidityThe mechanism by which sourness is detected is not fully understoodFruits are the most common group of foods linked to sourness

The Basic Tastes (Continued)

Sweetness

Produced by the presence of sugarsDetected by G Protein coupled receptors

Unami

Described as the taste that comes with monosodium glutamate (MSG)Appetitive and savory tasteCheese and soy sauce are other examples of unami

THE END