Chapter 9 Majority of illustra3ons in this presenta3on are from Biological Psychology 4 th edi3on ( Sinuer Publica3ons) Taste and Smell Taste Differences Smell Taste is a proximal sense Number of chemicals producing the sensa3on of taste are few. Parietal cortex (S2) Smell is a distal sense Number of chemicals producing the sensa3on of smell are large. Temporal cortex (Entorhinal cortex) 2 Taste and Smell Taste Similari3es Smell 1. Both are chemical senses, i.e., both senses are sensi3ve to chemicals that are delivered through fluids or air. 2. In marine animals the taste and smell sense are the same. Some rep3les (snakes) use tongues (flicking them) as an accessory smelling organ. 3. Both senses are involved in making us aware of flavor. More on flavor later in the lecture. 3 1
4 Func3ons of Taste Taste provides informa3on about foods and toxins 1. Sweet tastants are usually high calorie foods, and the individual enjoys ea3ng them. 2. Salty tastants are food elements for regula3ng internal milieu or homeostasis. 3. BiRer tastants mostly toxic (poisonous) need to be recognized early so that individuals can discharge them out. High threshold (mm) for salt, sweet, and sour tastants. Low threshold (μm) for birer tastants. 5 Ontology of Taste Ekman and colleagues carried out experiments to observe expressions of newborn babies to different tastes and found: Taste Water Sour Sweet Bitter Salt Expression No expression Pucker Smile Disgust No expression 6 2
History [Sensa3on of taste] lies between sweet and the birer on the side of the sweet, the succulent on the side of the birer, the saline [and] between these come the pungent, the harsh, the astringent, and the acid[ic]. Succulent Sweet BiRer Pungent Harsh Astringent Sour Salty Aristotle outlined a one- dimensional arrangement of tastants. 7 Henning s Tetrahedron Henning (1916) proposed four primary tastes on a hollow tetrahedron, to propose that any par3cular taste could lie between two primaries on an edge, or three primaries on the surface of the solid. No taste could be a combina3on of all four primaries, thus the hollow tetrahedron. Sour Salty Sweet BiRer 8 Henning s Tetrahedron Henning s ideas proved not very useful either in theore3cal or prac3cal domains. Addi3on of a new primary taste like Umami changed our basic understanding of taste. Sweet Sour Umami Salty BiRer 9 3
Supertasters & Taste Blindness 1. About 25% of people (because of two recessive alleles) have no taste for a compound propylthiouracil, (PROP) thus taste blind. Figy percent taste it as mildly birer, and 25% as extremely birer, having two dominant alleles. 2. Women more than men are supertasters. And supertasters tend to have more taste buds than regular tasters. 10 Taste Regions: Oral Cavity Taste regions in oral cavity comprise of tongue, palate, pharynx, epiglois, larynx and esophagus. Palate Pharynx Epiglottis Larynx Esophagus Tongue http://www.mythos.com 11 Taste Map 1. Many people con3nue to think that different tastes are represented on different areas of the tongue, thus there was a dis3nct taste map on the tongue. 2. Now it is believed that different taste sensa3ons are present in all loca3ons of the tongue, however some of them are dominant in one place than the others (Bartoshuk, 1993; Collins, 1974; Yanagisawa, 1994). BiRer Sour Salty Sweet Salty Sweet Sour Bi.er 12 4
Papillae and Taste Buds Circumvallate Taste buds 1000 taste buds Foliate 1000 taste buds Fungiform Filiform (Non- gustatory) 1-5 taste buds 10,000 taste buds total 13 Taste Bud Taste buds Saliva Pour Taste cell Epithelial cells 50-100 Taste cells in each taste bud. Recycle in 7-10 days from basal cells. Gustatory afferent nerve Basal cell 14 Single Taste Cell Hypothesis Single taste cell hypothesis suggested that there was only one type of cell in the taste bud, thus a bud responded to sweet or salty or sour. However recent data suggests different taste cells in a single bud. Cells sensi3ve to many tastes Cells sensi3ve to single taste 15 5
Taste Cell Physiology Salty and sour taste use ion channels to to depolarize the taste cell causing release of neurotransmirer (NT). Sweet, birer and umami ac3vate metabotropic receptors for NT release. 16 Gustatory Nerves Pharynx, Epiglois, Esophagus 1/3 of anterior tongue innervated by glossophryngeal nerve Vagus Nerve (X) Glossophryngeal Nerve (IX) 2/3 of anterior tongue innervated by tympanic nerve Facial Nerve (VII) 17 Gustatory Pathway Ventral Posterior Medial Thalamus Gustatory Cortex (S2) Nucleus of the Solitary Tract Nerves VII, IX and X 18 6
19 Olfac3on and Smell 1. Olfac3on is specific term reserved for the ac3va3on of specific class of chemoreceptors (olfactory receptors) in the nasal cavity. 2. Smell on the other hand refers to a general term describing a general perceptual experience resul3ng from ac3va3on of these chemoreceptors. 20 Olfac3on & Smell: Aspects 1. Humans are less sensi3ve to odors than animals. Rats are 8-50 3mes and dogs are 300-10,000 3mes more sensi3ve than humans (Lang, Doty, & Breihpohl, 1991). 2. Recogni3on to odor declines with age due to the reduc3on of receptors cells or receptors on cilia of the olfactory epithelium. 3. Smell works as gatekeeper sense providing informa3on about irrita3ng and noxious smells, predators, prey and mates. 21 7
Olfac3on & Smell: Aspects 4. Smell is in3mately linked with memory. Mothers can recognize their infant s clothing by smell. And one can recognize gender by smelling breath. 5. There are 5,000 odors or so. About 20% are pleasant. Since many different smells, model for olfac3on is difficult to form. Though people have tried to develop such a model (see below). 6. Need vola3le chemicals for olfac3on. 22 Flavor 1. Flavor (retronasal) is the result of sensory interac3on of smell and taste, along with other sensory cues such as texture, temperature, appearance etc of the s3mulus. 2. Sight and smell have a strong effect on flavor when tas3ng s3muli. 3. To test the significance of flavor eat something (like starburst) with eyes closed and nose plugged, and then eyes open and nose unplugged. 4. Taste is borom- up while flavor is top- down processing. 23 History Like taste Aristotle came up with the idea of separa3ng smells. He divided all odors into four basic kinds. Essen3ally the way he described taste on a single dimension. Succulent Pungent Acidic Astringent 24 8
Henning s Pyramid Just like his tetrahedron, Henning (1916) proposed six basic odors, where a single odor could be a combina3on of one, two, three or four primary smells. Putrid (Hydrogen Sulfide) Flowery (Violet) Burnt Fruity (Lemon) Spicy (Nutmeg) Resinous (Balsam) 25 Amoore s Model Amoore (1970) proposed seven odor receptors (later 30) based on his study of anosmia (smell blindness). He proposed seven different kinds of molecules bound to seven receptors. However, Schiffman (1974) found no correla3on between molecular shape and similarity of odor. Smell Example Molecule Camphoraceous Mothballs Football shaped Musky Cinnamon Necklace shaped Mint Peppermint Wedged shaped Flowery Violets Tadpole shaped Ethereal Ether Long- chain Alkanes Putrid Peanut Large Nega3ve Charge Pungent Coffee Large Posi3ve Charge 26 Nasal Cavity & Olfactory Epithelium Copyright 2005 Pearson Education, Inc., 27 9
Olfactory Receptors Olfactory epithelium consist of: 1. Olfactory receptor cells (Cilia, dendrites, and axons). 2. Sustentacular cells. 3. Basal cell. Olfactory Receptor Cell Dendrite Axon Basal Cell Cilia Sustentacular Cell 28 Olfactory Receptor Facts 1. Finite life span of receptor cells, thus con3nuously replaced. 2. Develop from basal cells. 3. The number of olfactory receptors in humans equal 25 million, with about 350 different types of receptors. To smell 5000 odors, receptors must be working in combina3on. 4. Unmyelinated axons form the olfactory nerve (cranial nerve I). 29 Molecular Mechanisms 1. Odorant must be vola3le and soluble in mucus (filter and capture site). 2. Odors bind to metabotropic receptors to transduce signals and communicate them to the brain. Odorant Cilia Ca3on (+) 30 10
Olfactory Pathways 1. Mitral cells from the olfactory bulb project to Anterior Olfactory Nucleus (AON) and olfactory tubercle. 2. From here projec3ons go separately to amygdaloid complex, piriform and entorhinal cortex, and to orbitofrontal cortex. 3. From olfactory tubercle to thalamus (odor discrimina3on) and from amygdala to hypothalamus (odor emo3on). Olfactory Bulb Olfactory Nerve Olfactory Receptor Neurons Olfactory Tract Piriform Cortex Olfactory Tubercle Amygdala Entorhinal Cortex Frontal Cortex Thalamus (Odor Discrimination) Hypothalamus (Odor Emotions) Hippocampus 31 11