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Taste and Smell. Comparison of General and Special Senses. General Senses. Special Senses. Include smell , taste , vision , hearing and equilibrium . Concentrated in specific locations in the head. Anatomically distinct structures. Complex neural pathway.
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Comparison of General and Special Senses General Senses Special Senses Include smell, taste, vision, hearing and equilibrium. Concentrated in specific locations in the head. Anatomically distinct structures. Complex neural pathway. Include somatic sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations. Scattered throughout the body. Simple structures.
Functions of Smell • Gatekeepers (good in, bad reject) • Orient in space • Mark territory • Guide to find other animals • Guide to find food • Sex • Humans, perfumes indicate still important • Detect spoiled food • Fire • Anosmia • Sex?
Features of Smell Bloodhounds can pick up a 24hr old trail. Dogs have 1,000,000,000,000 olfactory receptors and we have about 10,000,000-100.000.000 Animals have greater numbers of receptors thus better sense of smell. Usually 10,000 times greater. We can smell happiness and fear. Everyone has an unique smell .. except identical twins! Sniffer rats have been used to detect explosives!!!
Olfaction (Smell) • Least understood of all senses and poorly developed in humans. • Olfactory membrane located on the superior part of nasal cavity. • Contains olfactory cells which contain cilia that contain odorant-binding proteins. • Olfactory receptors are actual neurons (Bipolar) but they can regenerate every around 30-45 days.
To Be Smelled To Be Smelled • Substance must be volatile so that it can be sniffed into the nostrils. • Substance must be at least slightly water soluble to penetrate the mucus to reach the olfactory cells. • Substance must be at least slightly lipid soluble to interact with the membrane. • Olfactory receptors adapt very slowly. • Olfactory sensation itself adapts rather rapidly. • Must involve a central mechanism.
Olfaction • Olfactory pathways • No synapse in the thalamus for arriving information. • Olfactory discrimination • Can distinguish thousands of chemical stimuli. • CNS interprets smells by pattern of receptor activity. • Olfactory receptor population shows considerable turnover. • Number of receptors declines with age.
Camphoraceous Musky Floral Pepperminty Ethereal Pungent Putrid Primary Sensations of Smell
Olfaction: Sense of Smell Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air
Olfaction: Sense of Smell Olfactory epithelium contains 10-100 million receptors. Olfactory receptor- a bipolar neuron with cilia called olfactory hairs. Respond to chemical stimulation of an odorant molecule. Supporting cells- provide support and nourishment. Basal cells- replace olfactory receptors.
Specialized neurons present in the olfactory epithelium in the nose. They project cilia into a mucus layer. The cilia are able to bind to odorant molecules the binding triggers an AP which is transmitted to the olfactory area of the olfactory bulb olfactory cortex (lower frontal area and limbic system of the brain Each olfactory receptor is specialized for 1 odorant molecule Olfaction
Olfactory Epithelium and Olfactory Receptors Mitral cell (output cell) Olfactory tract Glomeruli Olfactory bulb Cribriform plate of ethmoid bone Filaments of olfactory nerve Lamina propria connective tissue Olfactory gland Axon Basal cell Olfactory receptor cell Olfactory epithelium Supporting cell Dendrite Olfactory cilia Mucus Route of inhaled air containing odor molecules (b)
Orbitofrontal Cortex • The orbitofrontal cortex (OFC) is aprefrontal cortex region in the frontal lobes in the brainwhich is involved in thecognitive processing of decision-making. • Orbitofrontal cortex is involved in critical human functions, such as social adjustment and the control of mood, drive and responsibility, traits that are crucial in defining the ‘personality’ of an individual. • In humans it consists of Brodmann area 10, 11 and 47.
Neural Pathways for Olfaction Conscious discrimination Emotional response Mitral cells in the olfactory bulb Piriform cortex Amygdala Olfactory receptor neurones Thalamus Orbitofrontal cortex
Emotional response Conscious discrimination Neural Pathways for Olfaction Figure 15.10 Flow diagram of the pathways for olfaction. (From Wilson and Stevenson, 2006) thalamus
Smell and Memory • A smell can bring on a flood of memories, influence people's moods and even affect their work performance. • Because the olfactory bulb is part of the brain's limbic system and smell can call up memories and powerful responses almost instantaneously. • When you first smell a new scent, you link it to an event, a person, a thing or even a moment. • Your brain forges a link between the smell and a memory-- associating the smell of chlorinewith summers at the pool or lilies with a funeral.
Smell and Memory • When you encounter the smell again, the link is already there, ready to elicit a memory or a mood. • Chlorine might call up a specific pool-related memory or simply make you feel content. Lilies might agitate you without your knowing why. This is part of the reason why not everyone likes the same smells. • Because we encounter most new odors in our youth, smells often call up childhood memories. But we actually begin making associations between smell and emotion before we're even born. Infants who were exposed to alcohol, cigarette smoke or garlic in the womb show a preference for the smells. To them, the smells that might upset other babies seem normal or even comforting.
Taste and Smell • Allows one to separate undesirable or lethal foods from those that are nutritious. • Recognize the proximity of other individuals or animals. • Tied to primitive emotional and behavioral functions of the nervous system.
Sense of Taste • Receptor organs are taste buds. • Found on the tongue. • On the tops of fungiform papillae • On the side walls of foliate papillae and circumvallate (vallate) papillae
Location of Taste Buds • Found on three types of papillae of the tongue. • Circumvallate • Form a V on the posterior surface of the tongue. • Foliate • Located along the lateral surfaces of the tongue • Fungiform • located over the flat surface of the tongue. • Extraglossal taste buds • On the tonsillar pillars, palate, epiglottis, and proximal esophagus.
Taste Bud Epiglottis Palatine tonsil Lingual tonsil Foliate papillae Fungiform papillae (a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae.
Taste Bud Circumvallate papilla Taste bud (b) Enlarged section of a circumvallate papilla.
Structure of a Taste Bud • Flask shaped • 50–100 epithelial cells: • Basal cells: Dynamic stem cells • Gustatory cells: Taste cells • Microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium.
Taste Bud Connective tissue Gustatory hair Taste fibers of cranial nerve Stratified squamous epithelium of tongue Basal cells Gustatory (taste) cells Taste pore
Receptors for taste are modified epithelial cell present in taste buds located on the tongue, roof of the mouth and pharynx. Anatomy of Taste Buds
Anatomy of Taste Buds Taste bud- made of three types of epithelial cells: supporting cells, gustatory receptor cells and basal cells. About 50 gustatory cells per taste bud. Each one has a gustatory hair that projects through the taste pore. Taste buds are found in the papillae. Three types of papillae: vallate (circumvallate), fungiform and foliate.
Taste Bud Facts • Adults have 3-10,000 buds. • Children have more. • Taste receptors are epithelial cells able to regenerate every 10-15 days. • Beyond age 45 taste buds start to degenerate, taste becomes less critical.
Gustatory Discrimination • Primary taste sensations • Sweet, sour, salty, bitter • Receptors also exist for umami and water. • Taste sensitivity shows significant individual differences, some of which are inherited. • The number of taste buds declines with age.
Taste (Gustation) • Gustatory Discrimination • Primary taste sensations • Sweet (sugars) • Salty • Sour (acids) • Bitter (alkali) • Umami (savory (fat)
Distribution of Taste Sensations on the Tongue • Sweet and salty buds located on the tip of the tongue. • Sour on the lateral sides of the tongue. • Bitter on the posterior tongue and soft palate.
Taste Sensations - chemical triggers • There are five basic taste sensations: • Sweet:sugars, saccharin, alcohol, and some amino acids • Sour: Hydrogen ions • Salt:Metal ions • Bitter:Alkaloids such as quinine and nicotine • Umami:Amino acids glutamate and aspartate
Influence of Other Sensations on Taste • Taste is 80% smell. • Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastes. • Temperature and texture enhance or detract from taste.
Transmission of Taste Sensations • Activation of taste buds excite taste fibers. • Anterior 2/3 of tongue through facial nerve • Posterior 1/3 of tongue through glossopharyngeal nerve • Posterior aspects of the mouth through vagus nerve • Transmitted to solitary nucleus • From solitary nucleus to thalamus • From thalamus to cortex
Gustatory pathways • Taste buds are monitored by cranial nerves. • Synapse within the solitary nucleus of the medulla oblongata. • Then on to the thalamus and the primary sensory cortex.
Neural Pathway • Taste impulses travel through nerves VII, IX and X to a gustatory nucleus in the medulla oblongata (cross over) thalamus gustatory cortex located in the parietal lobe in the mouth area.
