Special Senses Olfaction & Gustation

Introduction We know what we know because of sensory receptors Our perceptions governs our interpretation of reality Perception depends on state of nervous system We get this information through 5 special senses Olfaction Gustation Vision Equilibrium Hearing

Olfaction – Sense of Smell Olfactory organs work together to perceive smell Organs are located in nasal cavity Contains olfactory epithelium  olfactory receptors Contains a second layer, “lamina propria”  olfactory glands

Olfactory Receptors Highly modified neurons Only neurons that routinely regenerate!

Olfactory Pathways Olfactory receptors  olfactory bulbs of the cerebum  olfactory tract  olfactory cortex, hypothalamus, and limbic system This is why smells are often able to illicit emotions or memory recall Only type of sensory information that reaches the cerebral cortex directly (does not go to the Thalamus relay center first)

Discriminating Smells Humans can detect over 20,000 kinds of smells The pattern of receptor binding and activity is what causes a particular perception of smell Due to the sensitivity of receptors, some odorants can be detected in tiny concentrations Ex. Mercaptan added to natural gas https://www.youtube.com/watch?v=snJnO6OpjCs

Gustation – Sense of Taste Provides information about the foods and liquids we ingest Gustatory receptors are distributed over the tongue and parts of throat Taste buds = taste receptors + specialized epithelial cells Epithelial projections  lingual papillae Filiform Fungiform Vallate Foliate

Filiform Papillae Provide friction that helps tongue move objects around in the mouth Most common type No taste buds

Fungiform Papillae Involved in the sensation of taste and have taste buds embedded in their surfaces Mostly found on tips and sides of tongues

Vallate Papillae Contain tastebuds Lie near posterior tongue in a V- formation

Foliate Papillae Located on sides and back of tongue

Taste Receptors Humans have about 10,000 taste buds Each taste bud has about 40-100 receptor cells and basal cells Receptors are innervated by sensory neurons

Gustatory Pathways Cranial nerves 8, 9, and 10 innervate the taste buds CN 8 (facial)  taste buds located on anterior 2/3 of the tongue CN 9 (glossopharangyeal)  innervates the vallate papillae and posterior 1/3 of tongue CN 10 (vagus)  innervate tastebuds scattered on the epiglottis Cranial nerves  medulla oblangata Neurons join there to carry sensory information on touch, pressure, and sense of movement The gustatory information is finally relayed to the relay center  thalamus

Gustatory Pathways Brain correlates information received from taste buds with other sensory data Texture of food and taste-related sensations (hot, cold, spicy)  relayed by the trigeminal nerve (CN 5) Olfactory receptors also a play a role in taste perception!

Gustatory Discrimination Primary taste sensations: sweet, salty, sour, and bitter Other sensations found in humans: water and umami

Umami Pleasant, savory taste Ex. Chicken broth, parmesan cheese Presence of free glutamates in food https://www.youtube.com/watch?v=f46cLbftDPI https://www.livescience.com/17684-sixth-basic-taste.html

Water Some vertebrate species contain receptors for water in the pharynx Information is processed by hypothalamus which then regulates water balance and blood volume in the body Ex. Fluctuations in ADH after drinking lots of water!

Gustation Reception Receptors respond more readily to unpleasant stimuli – essential for survival Taste sensitivity also varies among people and can be inherited Ex. Phenylthicarbamide (PTC) – tastes bitter to some people, but tasteless to others. Not found in food. But related compounds found in cauliflower, cabbage, broccoli Taste receptors, just like smell receptors, decline with age

Due Next Week Ch. 28