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BCS 110 - Lecture #12 Chemosensory Systems

Perception of Olfaction (smell) + Gustation (taste)
What is Flavor?
Taste is the stimulation of receptor cells in taste buds
What is Gustation (taste)?
Taste buds are receptive organs found on the tongue and parts of the throat, taste buds are found mostly on folds of skin called papillae, taste buds consist of 50-100 cells, each taste bud has capsule cells which form an outer protective layer, at the surface there is a taste pore through which tastants (chemical that can be tasted) enter, in each taste bud there are sensory receptors cell and basal-stem cells, the basal-stem cells give rise to new receptor cells, stem cells can differentiate, sensory-receptor cells have microvilli at their surface to increase surface area for detecting tastants, taste transduction occurs in the microvilli, taste receptors are not neurons (they are specialized epithelial cells) innervated by cranial nerves, if taste buds lose innervation they can disappear but can regenerate with new innervation and stem cell differentiation
What are Taste Buds?
Taste buds are found mostly on folds of skin called papillae, Fungiform, Vallate (Circumvallate), Foliate, Filiform (no taste buds on these)
What are the types of Papillae?
What are Capsule Cells?
At the surface of the taste buds, there is a taste pore though which tastants enter
What is a Taste Pore?
Chemicals that can be tasted, enter through taste pores
What are Tastants?
Sensory, receptor cells have microvilli at their surface to increase surface area for detecting tastants, taste transduction occurs in the microvilli
What are Microvilli?
Occurs in the microvilli
What is Taste Transduction?
They are no neurons, they are specialized epithelial cells) innervated by cranial nerves
What are Taste Receptor Cells?
The tongue is innervated by cranial nerves VII (the facial nerve innervates the anterior tongue), IX (the glossopharyngeal nerve innervates the posterior tongue), & X (the cranial nerve innervates the epiglottis-throat), approximately 50 fibers innervate each taste bud
How are the Taste Buds Innervated?
Labelled Line Theory & Across-Fiber Pattern Theory, the meaning of a response by a particular receptor depends on the context of responses by other receptors
What are the Sensory System Theories?
Each receptor responds to a limited range of stimuli with a direct line to the brain, doesn't apply to vision
What is the Labelled Line Theory?
Each receptor responds to a range of stimuli and contributes to the perception of each of them, it is what happens in the visual system, most sensory systems appear to use across fiber patterns for encoding information
What is the Across-Fiber Pattern Theory?
Sweet (sugars), Sour (acids), Salty (salts), Bitter (quinine), Umani (taste of some amino acids & their derivatives e.g., MSG); different parts of the tongue respond to all taste qualities
What are the 5 Taste Qualities?
By tasting one type of taste quality (e.g. sour, unsweetened lemon juice), you find that tasting the same taste quality (e.g. dilute vineger) right after isn't as strong, this adaptation reflects the fatigue of receptors sensitive to that taste quality
How can we show that there is a Labelled Line Component to taste?
Fibers that innervate taste buds can respond to more than one taste quality, however, each fiber usually responds best to one taste quality
What are the Taste Fiber responses?
After tasting one type of taste quality (e.g., sour, unsweetened lemon juice), you find that tasting the same taste quality right after isn't as strong
What is Adaptation?
Reduced response to a different taste quality
What is Cross-Adaptation?
Some chemicals modify taste qualities (ex: Miracle Fruit-african berry, temporarily modifies sweet receptors so that they can be stimulated by acidic (sour) substances--> lemons taste sweet, toothepaste contains a chemical that intensifies bitter tastes and weakens sweet tastes, different transduction methods for each
What about Modifying Taste Qualities?
Each taste quality affects ion channels in a different way, taste G-protein is called Gustducin, cAMP=second messenger?
How does Taste Transduction work?
Each taste quality can be thought of as a signal that conveys information for ingestion: salty stimuli can signal he availability of salts, essential to life (sodium), sour stimuli can signal acidic substances, which is characteristic of spoiled foods, Sweet stimuli can signal substances that are safe to eat and provide energy, Bitter stimuli can signal poisons (like alkaloids in plants). Pure chocolate is very bitter-the chocolate in stores has a ton of sugar added to it, we can learn to associate specific tastes with certain experiences
What are various Taste Interpretations?
Cranial nerves VII, IX, & X join to form Solitary Tract-nucleus of the Solitary Tract in Medulla: Discrimination Path & Motivational Emotional Path
What are the Taste Pathways?
Goes through a thalamic relay nucleus before reaching cortex, Ventral Posterior Medial (VPM) Limbic System Structures-Nucleus of the Thalamus, Lateral Hypothalamus; Primary Gustatory Cortex (adjacent to somatosensory cortex); Secondary Gustatory Cortex (Insular Cortex)
What is the Discrimination Path?
Central nucleus of the amygdala, involved with emotional associations
What is the Motivational & Emotional Path?
Smell, olfaction refers to detecting odorants (volatile chemicals) through a specialized epithelium in the nose, detection of some noxious chemicals in the nose (like ammonia) is through the trigeminal nerve (not olfaction), humans can detect up to 10,000 different kinds of odorants
What is Olfaction?
What is the Olfactory Epithelium?
The nose is the only place we can develop new neurons?
Can the nose develop new neurons?
Supporting cells, bipolar neurons, basal-stem cells
What are the Cells of the Olfactory Epithelium?
Provide nourishment of receptor cells, produce some mucus
What is a Supporting Cell in the nose?
Receptor cell with cilia protruding from olfactory knobs. Cilia contain receptor proteins for detecting odorants
What is a bipolar neuron?
Capable of continuously generating new neurons
What are Basal, Stem Cells?
Epithelium will degenerate, new neurons can be regenerated by stem cells
What happens in Olfactory Axons are cut?
As opposed to the visual and gustatory systems, there are thought to be 1,000 or more different olfactory receptors, each capable of recognizing many odorants
How many Olfactory Receptors are there?
Odorants are carried to receptor proteins by odorant binding proteins, when odorants bind to their receptors, a specific G protein (Golf) causes second messenger systems to open ion channels
What is Olfactory Transduction?
The olfactory system also has spatial organization but not based on the location of smells in the environment, Olfactory receptors have a rough spatial organization within the nasal cavity
How is the Olfactory System organized?
Axons of the olfactory receptor cells form the diffuse olfactory nerve (Cranial Nerve I), these axons synapse in the olfactory bulb, axons synapse in specialized structures called glomeruli, each glomerulus contains the axon terminals of olfactory receptor cells, the dendrites of periglomerular cells, and the dendrites of mitral cells (the output cells of the olfactory bulb), granule cells in the olfactory bulb modulate olfactory processing and are another type of neuron that can be generated throughout life
What is the Olfactory Bulb?
What are Gloeruli?
The output cells of the olfactory bulb
What are Mitral Cells?
The Discrimination Path & the Endocrine & Emotional Path (and then back to the hypothalamus)
What are the pathways of the Olfactory Bulb?
Does the sense of smell stop in the Thalamus first?
Only sensory system that gets to its primary sensory cortex without going through the thalamus first, discrimination info then goes to thalamus in order to be associated with other information in orbitofrontal cortex, Primary Olfactory Cortex Limbic System Structures 9Ventral surface of Frontal Lobe), Dorsal Medial Thalamus, Orbitofrontal Cortex (Olfactory associations) & then back to the hypothalamus
What is the Olfactory Discrimination Path?
Amygdala involved with the feeling & expression of emotions, Limbic System Structures/Amygdala & then back to the hypothalamus
What is the Endocrine & Emotional Path?
Chemicals that are released by one member of a species that affect another member of the same species (communication between the same species), affect the behavior or physiology of another member of the same species, connections to the hypothalamus mediate endocrine effects produced by pheromone stimulation, in most terrestrial vertebrates pheromones are chemicals that are detected by the olfactory system and a separate system called the vomeronasal system
What are Pheromones?
The vomeronasal system is found in most terrestrial vertebrates, except birds and old-world primates (including humans), Specialized behaviors bring chemicals into the mouth (flehman in horses, tongue flicking in snakes), receptor neurons are found in the vomeronasal organ found in the roof of the mouth, chemicals are brought into the vomeronasal organ by suction
What is the Vomeronasal System?
The vomeronasal receptor neurons can be generated throughout life like olfactory receptor neurons, the vomeronasal system is completely separate from the olfactory system, these separate pathways mediate different behaviors, has no primary sensory cortex & no conscious percpetion is thought to occur
What is the Vomeronasal System?
Lee-Boot Effect, Whitten Effect, Vandenbergh Effect, & Bruce Effect
What are the four Vomeronasal Behaviors in rats?
Groups of female rodents housed together cause the estrous (reproductive) cycles of females to slow down and eventually stop
What is the Lee-Boot Effect?
Groups of non-cycling females exposed to a male odor begin to cycle again and become synchronized
What is the Whitten Effect?
Male odors accelerate the onset of puberty in female rodents
What is the Vandenbergh Effect?
If a pregnant female encounters a male (or his odor) that is different from her mate, she will spontaneously abort
What is the Bruce Effect?