A&P Exam 7: Lecture 3
Receptors for taste are distributed over the tongue, but sensitivity for ____, ____, ____, and ____ is acute at various positions on the tongue
Sweet, Sour, Bitter, and Salty
Receptor potentials for taste: ____, ____, and ____ tastes (recapitulation): -These do not themselves enter gustatory receptor cells. Instead they bind to receptors on the plasma membrane that are linked to G proteins -The G-proteins then activate second messengers inside the gustatory receptor cell -Second messengers then initiate depolarization, and neurotransmitter is released
Sweet, bitter, and umami
Gustatory pathway: Gustatory receptor cells synapse with dendrites of the ____ ____ neurons that comprise the initial portion of the gustatory pathway. Each first-order neuron synapses with many gustatory receptor cells in several taste buds.
First order neurons
Physiology of gustation: After being dissolved (in saliva) the tastant contacts the plasma membrane of the gustatory ____. The gustatory ____ are the sites of taste transduction.
Hairs
Concentration differences of the same substance can result in different odorants What is a substance found in both coal tar and perfumes? Concentrated _____ just plain stinks. When sufficiently diluted, _____ gives off a fragrance like jasmine.
Indole
Olfactory pathway: The axons subsequently project into what area? Which is probably the primary olfactory area where conscious awareness of smells begins, as well as to other parts of the brain
Lateral olfactory area
From the taste buds, impulses propagate along the appropriate cranial nerve to the *gustatory nucleus* in what? Free: From the medulla some axons project to the limbic system and hypothalamus, others project to the thalamus and on to the primary gustatory area in the parietal lobe of the cerebral cortex to give rise to the conscious perception of taste
Medulla Oblongata
Most taste buds are on the tongue, but some are also on what three locations?
Soft palate (posterior portion of the roof of the mouth) Pharynx (throat) Epiglottis (cartilaginous flap over the voice box)
Taste transduction -Protons either flow into the cell via *H+ channels* or they block K+ channels, inhibiting them -Depolarization occurs -Ca2+ enters the cell through depolarization-activated Ca2+ channels -Transmitter is released, firing the primary afferent nerve
Sour
What tastes are associated with spoiled foods: many foods become bitter or acidic when they spoil?
Sour
Receptor potentials for taste: What tastants (recapitulation): -The ____ taste is due to hydrogen ions -Hydrogen ions of sour tastants probably flow into gustatory receptor cells through H+ channels, where they influence opening and closing of other types of ion channels -The result is depolarization that leads to release of neurotransmitter
Sour Tastants
Millions of olfactory receptors are present in a little less than 1 in2 of olfactory epithelium, which located where?
Superior part of the nasal cavity
Cell progression: Basal cells produce ________ cells. Supporting cells then differentiate into _____________ cells. Gustatory receptor cells have a life span of about ___ days
Supporting cells Gustatory receptor cells Ten days
What cells are columnar epithelial cells of the mucous membrane lining the nose? They provide support, nourishment and electrical insulation for the olfactory receptors.
Supporting cells of the olfactory epithelium
Taste transduction -Membrane receptors bind glucose, activating adenylyl cyclase, thereby increasing cAMP (second messenger) -This causes phosphorylation of K+ channels, inhibiting them -Depolarization occurs -Ca2+ enters the cell through depolarization-activated Ca2+ channels -Transmitter is released, firing the primary afferent nerve
Sweet
What tastes are associated with safe foods: we have an absolute requirement for carbohydrates?
Sweet
Locations on the tongue for acute sensitivity: Tip of tongue: Back sides of tongue: Back middle of tongue: Front sides of tongue:
Sweet Sour Bitter Salty
Physiology of gustation: What is a chemical that stimulates gustatory receptor cells. ______ must be dissolved before they can be tasted (a substance that is not water-soluble can not be tasted)
Tastants
The receptors for taste sensations are located in the ____ ___. The number of these decline with age.
Taste buds
Taste transduction: may be similar to cAMP mediated depolarization of sweet tastes. Receptor location: diffuse (there is no conventional location)
Umami
What is a Japanese word for the taste imparted by glutamate in foods, and though there is no direct English translation it is often described as meaty, savory, or broth-like?
Umami
What is the taste of certain amino acids, which are the building blocks of protein?
Umami
In some specific instances the odorant binds to membrane receptors linked to G proteins in the plasma membrane, setting up actions whereby the odorant is ultimately perceived: PUT IN ORDER: -Generation of nerve impulse. -Conversion of ATP into cAMP. -Activation of adenylate cyclase -Inflow of Na+ -Depolarizing generator -Opening of Na+
-Activation of adenylate cyclase -Conversion of ATP into cAMP -Opening of Na+ channels -Inflow of Na+ -Depolarizing generator potential -Generation of nerve impulse
Each olfactory receptor has what three things?
-Axon ending in the olfactory bulb -Knob-shaped dendrite -Cilia projecting from the dendrite
Three cranial nerves include axons of first-order gustatory neurons from taste buds. What are the three nerves?
-Facial nerve (cranial nerve VII), anterior two-thirds of the tongue -Glossopharyngeal nerve (cranial nerve IX), posterior one-third of the tongue -Vagus nerve (cranial nerve X), throat and epiglottis
Each taste bud is an oval body consisting of an aggregation of three kinds of neuroepithelial cells. What are they?
-Gustatory receptor cells -Supporting cells (AKA sustentacular cells) -Basal cells
The olfactory epithelium is a *pseudostratified ciliated columnar epithelium* consisting of three kinds of cells. What are those cells?
-Olfactory receptors -Supporting cells (AKA sustentacular cells) -Basal stem cells
What are the five modern-day primary tastes are?
-Sweet -Sour -Bitter -Salty -Umami (only with modern-day primary tastes)
There are three types of papillae that contain taste buds. What are they?
-Vallate papillae -Fungiform papillae (mushroom-shaped) -Foliate papillae (mostly lost during childhood)
________ to odors initially occurs rapidly—about 50% in the first few seconds after stimulation. After the first few seconds ________ continues, but at a slower rate. Virtually complete insensitivity to some odors can occur in about a minute, even if the odors are strong
Adaptation
Gustatory pathway: Taste receptor cells do not have an ____ (the graded potentials they produce are called receptor potentials, rather than generator potentials)
Axon
What cells are interspersed among the supporting cells. They undergo continuous cell division producing new olfactory receptors, which live only about a month?
Basal stem cells of olfactory epithelium
Olfactory receptors are ______ neurons that are the first-order neurons of the olfactory pathway
Bipolar
Taste transduction -_____ substances cause release of Ca2+ from internal stores (external Ca2+ is not required) -Transmitter is released, firing the primary afferent nerve
Bitter
What tastes are associated with poisonous foods (many natural poisons and spoiled foods are bitter)?
Bitter
Taste threshold: Each primary taste has a different threshold -The threshold for _____ substances is the lowest -The threshold for ____ substances is somewhat higher than for bitter substances -The threshold for the remaining primary tastes are higher than for sour substances.
Bitter Sour
From posterior to anterior what are the tastes of the tongue?
Bitter Sour, Sour Salt, Salt Sweet
What cranial nerve innervates olfactory glands of the olfactory epithelium?
Facial nerve CN VII
Olfactory pathway: Bundles of slender, *unmyelinated axons* of olfactory receptors extend through olfactory foramina in what location? All the bundles taken together comprise the ______ nerves forming what cranial nerve?
Cribriform plate of the ethmoid bone Olfactory nerve (cranial nerve I)
What cells are a subtype of stem cell. When dividing, the __________ cell undergoes a proliferative division producing two identical cells. After this division, the daughter cells produce another identical daughter cell as well as a non-stem-cell progenitor or a neuron by asymmetric divisions
Neuroepithelial cells
Only slight molecular alterations may distinguish different odorants What is an ingredient of petroleum and natural gas which exudes an orange and rose-like bouquet. Change one atom in the molecule's structure, and it becomes octanoic acid, which is characterized by a rancid, sweaty smell.
Octanol
What chemicals that can stimulate the olfactory hairs, which means that _____ are chemicals that have an odor? When olfactory receptors are stimulated they create a generator potential initiating the olfactory response.
Odorants
What is more sensitive to taste, Olfaction or Gustation?
Olfaction
What are two chemical senses since they are stimulated by chemicals, the molecules of which interact with receptors to produce a generator potential (______) or receptor potential (_______)?
Olfaction & Gustation
++++Olfactory pathway: What sensations are the only sensations that reach the cerebral cortex without first synapsing in the thalamus? Other axons of the olfactory tract project to what system of the hypothalamus which accounts for emotional and memory-evoked responses to odors?
Olfactory Limbic system
What are within the supporting connective tissue produce mucus? These ducted glands are also called Bowman's glands. The mucus moistens the olfactory epithelium surface, and dissolves odorants
Olfactory Glands
Olfactory pathway: The olfactory nerves terminate in the _______ _____ (paired masses of gray matter in the brain) within which the axon terminals of the first-order neurons (olfactory receptors) form synapses with dendrites and cell bodies of second-order neurons.
Olfactory bulbs
The cilia projecting from the dendrites of the olfactory receptor cells are termed what?
Olfactory hairs
What are the sites of olfactory transduction (conversion of stimulus energy into a graded potential in a sensory receptor)?
Olfactory hairs
________ receptors are neurons, so their replacement is unusual since mature neurons are not generally replaced
Olfactory receptors
Olfactory pathway: Axons of olfactory bulb neurons extend posteriorly to form the ______ _____.
Olfactory tract
Taste buds occur in elevations on the tongue called ______. Filiform ______ contain tactile receptors, but not taste buds.
Papillae
Taste transduction -*Na+ ions enter the receptor cells via Na+ channels* (a type of Na+ channel that is different from voltage-gated Na+ channels) -Entry of Na+ causes depolarization Ca2+ enters the cell through depolarization-activated Ca2+ channels -Transmitter is released, firing the primary afferent nerve
Salty
What tastes are associated with sodium chloride, something we need in our diet?
Salty
Receptor potentials for taste: _____ foods (recapitulation): -Their ______ is due to sodium ions -The sodium ions enter gustatory receptor cells via Na+ channels in the plasma membrane -The accumulation of Na+ within the cell causes depolarization, which in turn opens Ca2+ channels -Inflow of Ca2+ triggers exocytosis of synaptic vesicles and liberation of neurotransmitter
Salty foods
Physiology of gustation: The result of ________ is a receptor potential that stimulates exocytosis of synaptic vesicles from the gustatory receptor cell. The neurotransmitter molecules trigger nerve impulses in the first-order sensory neurons that synapse with the gustatory receptor cell
Transduction