Guyton and Hall Physiology Chapter 54 - The Chemical Senses—Taste and Smell
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Questions and Answers

What is the primary role of olfactory cilia in the olfactory membrane?

  • To amplify sound waves in the nasal cavity
  • To filter out unwanted particles from inhaled air
  • To react to odors in the air and stimulate olfactory cells (correct)
  • To provide structural support to the olfactory membrane
  • How does the sense of smell in humans compare to that of many other mammals?

  • It is better developed than in most mammals
  • It is poorly developed compared to many mammals (correct)
  • It is completely absent in humans
  • It has the same level of sensitivity as in most mammals
  • What is the estimated total surface area of the olfactory membrane in humans?

  • 15 square centimeters
  • 10 square centimeters
  • 5 square centimeters (correct)
  • 2 square centimeters
  • What type of cells are the olfactory cells within the olfactory epithelium?

    <p>Bipolar nerve cells derived from the central nervous system</p> Signup and view all the answers

    What is the approximate length range of the olfactory hairs that project from the olfactory cells?

    <p>150 to 200 micrometers</p> Signup and view all the answers

    What brain structure is primarily associated with the transmission of olfactory signals?

    <p>Olfactory bulb</p> Signup and view all the answers

    Which part of the brain developed around the primitive sense of smell?

    <p>Limbic system</p> Signup and view all the answers

    Which cranial nerve is responsible for olfactory function?

    <p>Cranial nerve I</p> Signup and view all the answers

    What is the primary function of the medial olfactory area?

    <p>Modulating emotional responses</p> Signup and view all the answers

    Where is the olfactory bulb located?

    <p>Over the cribriform plate</p> Signup and view all the answers

    What is the primary role of the olfactory tract?

    <p>Conveying olfactory signals to the central nervous system</p> Signup and view all the answers

    How do the septal nuclei contribute to the sense of smell?

    <p>They transmit olfactory signals to the hypothalamus.</p> Signup and view all the answers

    What is a significant evolutionary aspect of the olfactory system?

    <p>It evolved into systems controlling emotions and basic behaviors.</p> Signup and view all the answers

    Which area of the brain is primarily activated by olfactory signals?

    <p>Medial olfactory area</p> Signup and view all the answers

    Which structure acts as an anterior outgrowth of brain tissue responsible for smell?

    <p>Olfactory bulb</p> Signup and view all the answers

    What role does the hippocampus play in relation to dietary preferences?

    <p>It is crucial for learning to like or dislike foods based on experiences.</p> Signup and view all the answers

    Which area receives sensory signals in the cerebral cortex without going through the thalamus?

    <p>Paleocortex</p> Signup and view all the answers

    Which process leads to an aversion to certain foods due to nausea?

    <p>Signal pathways from the lateral olfactory area into the limbic system</p> Signup and view all the answers

    What is a characteristic of the newer olfactory pathway?

    <p>It passes through the thalamus to the dorsomedial thalamic nucleus.</p> Signup and view all the answers

    How does the lateral olfactory area influence the limbic system?

    <p>By establishing pathways that shape emotional responses to different odors.</p> Signup and view all the answers

    What is the primary function of the paleocortex mentioned in the content?

    <p>To handle sensory signals directly from the olfactory area.</p> Signup and view all the answers

    What implication does the connection between olfactory signals and the limbic system have on human behavior?

    <p>They can trigger complex emotional reactions.</p> Signup and view all the answers

    What determines a person's threshold for detecting smells?

    <p>The olfactory receptor density in the nasal cavity.</p> Signup and view all the answers

    What is the primary function of the cribriform plate?

    <p>To facilitate the passage of nerves from the olfactory membrane</p> Signup and view all the answers

    Which area of the brain, when removed, minimally affects basic olfactory responses like lip licking?

    <p>Lateral olfactory areas</p> Signup and view all the answers

    What happens to olfactory conditioned reflexes when the lateral olfactory areas are removed?

    <p>They are abolished entirely</p> Signup and view all the answers

    Which cells in the olfactory bulb receive inhibitory signals from granule cells?

    <p>Mitral and tufted cells</p> Signup and view all the answers

    What role do centrifugal nerve fibers play in the olfactory system?

    <p>They send signals from the brain to the olfactory tract</p> Signup and view all the answers

    Which of the following is primarily associated with the lateral olfactory area?

    <p>Prepyriform and pyriform cortex</p> Signup and view all the answers

    In the context of olfactory processing, what is the likely effect of granule cells on mitral and tufted cells?

    <p>They suppress activity</p> Signup and view all the answers

    How does the olfactory system impact feeding behavior?

    <p>Via basic emotional drives associated with smell</p> Signup and view all the answers

    What type of reflexes are most affected by the removal of the lateral olfactory area?

    <p>Olfactory conditioned reflexes</p> Signup and view all the answers

    What is the significance of the relationships between olfactory cells and the olfactory bulb as depicted in the content?

    <p>They indicate a direct sensory pathway from the nose to the brain.</p> Signup and view all the answers

    What is the primary function of the substance mixed with natural gas?

    <p>To provide a detectable odor for gas leaks</p> Signup and view all the answers

    At what concentration range does maximum intensity of smell occur for most odorants?

    <p>10 to 50 times above the threshold</p> Signup and view all the answers

    Which statement best describes the medial olfactory area?

    <p>It is the oldest olfactory system pathway</p> Signup and view all the answers

    How do the olfactory pathways enter the brain?

    <p>At the anterior junction of the mesencephalon and cerebrum</p> Signup and view all the answers

    What might explain the different intensity discrimination ranges between olfactory and other sensory systems?

    <p>Smell emphasizes presence or absence of odors</p> Signup and view all the answers

    What are the two pathways the olfactory tract divides into?

    <p>Medial and lateral olfactory areas</p> Signup and view all the answers

    What is a significant characteristic of the lateral olfactory area?

    <p>It represents a newer, more advanced olfactory system</p> Signup and view all the answers

    Which of the following best describes the olfactory sensory systems compared to other sensory systems?

    <p>Olfactory systems have a narrower range of intensity discrimination</p> Signup and view all the answers

    Which sensory system has a higher range of intensity discrimination than olfactory pathways?

    <p>Auditory system</p> Signup and view all the answers

    What is a potential function of the medial olfactory area in response to odors?

    <p>Detection of emotional responses to smells</p> Signup and view all the answers

    What primarily elicits the salty taste sensation?

    <p>Sodium ions</p> Signup and view all the answers

    Which of the following substances is NOT typically associated with a sweet taste?

    <p>Alkaline earth metals</p> Signup and view all the answers

    How does the quality of salty taste vary?

    <p>It can change based on the specific salt used.</p> Signup and view all the answers

    What role does smell play in the recognition of other animals?

    <p>It allows recognition of the proximity of other animals.</p> Signup and view all the answers

    Which statement accurately reflects the relationship between taste and smell?

    <p>The sense of smell enhances the perception of taste.</p> Signup and view all the answers

    Which substance has the highest taste index for sweetness according to the taste indices?

    <p>Saccharin</p> Signup and view all the answers

    Which of the following sour substances has the lowest taste index?

    <p>Potassium H tartrate</p> Signup and view all the answers

    What is the taste index of quinine, classified as a bitter substance?

    <p>11</p> Signup and view all the answers

    Which substance is listed as having a taste index value of 0.02?

    <p>Morphine</p> Signup and view all the answers

    Which of the following substances is NOT categorized as a salty substance?

    <p>Chloroacetic acid</p> Signup and view all the answers

    How does aging affect taste bud sensitivity?

    <p>Degeneration of taste buds leading to decreased sensitivity</p> Signup and view all the answers

    What is the receptor potential in taste cells?

    <p>The change in electrical potential in response to taste stimuli</p> Signup and view all the answers

    Which of the following statements about the specificity of taste buds is true?

    <p>Most taste buds respond predominantly to one primary taste at low concentrations</p> Signup and view all the answers

    What initiates the receptor potential in taste receptor cells?

    <p>Binding of taste chemicals to specific proteins on the cell surface</p> Signup and view all the answers

    What effect does high concentration of taste substances have on taste buds?

    <p>They can be excited by multiple primary taste stimuli</p> Signup and view all the answers

    What primarily contributes to the depolarization of taste cells?

    <p>Entry of positively charged sodium or hydrogen ions</p> Signup and view all the answers

    Which cranial nerves are involved in the taste transmission process?

    <p>Chorda tympani (VII) and glossopharyngeal (IX)</p> Signup and view all the answers

    What is a consequence of taste bud degeneration in older adults?

    <p>Decreased sensitivity to taste</p> Signup and view all the answers

    Which of the following characteristics applies to the membrane of taste cells?

    <p>It is negatively charged on the inside at rest</p> Signup and view all the answers

    Which ion's entry is crucial for inducing receptor potential in taste cells?

    <p>Sodium or hydrogen ions</p> Signup and view all the answers

    The bitter taste can be caused by long-chain organic substances that contain nitrogen and alkaloids.

    <p>True</p> Signup and view all the answers

    All types of bitter taste sensations are caused by the same chemical agents.

    <p>False</p> Signup and view all the answers

    The presence of certain substances in food can enhance the sweetness detected by taste receptors.

    <p>False</p> Signup and view all the answers

    A high intensity of bitter taste typically leads to the rejection of food by a person or animal.

    <p>True</p> Signup and view all the answers

    Saccharin is an example of a substance that can taste sweet initially but has a bitter aftertaste.

    <p>True</p> Signup and view all the answers

    Adults typically have 3000 to 10,000 taste buds, whereas children have significantly fewer.

    <p>False</p> Signup and view all the answers

    Most taste buds respond to multiple primary taste stimuli at low concentrations.

    <p>False</p> Signup and view all the answers

    Beyond the age of 45, many taste buds begin to degenerate, leading to an increase in taste sensitivity.

    <p>False</p> Signup and view all the answers

    The receptor potential for taste is generated when positively charged ions enter the taste cell, leading to depolarization.

    <p>True</p> Signup and view all the answers

    High concentrations of taste substances stimulate only one specific type of taste bud.

    <p>False</p> Signup and view all the answers

    T1R3 serves as a co-receptor for both sweet and umami tastes.

    <p>True</p> Signup and view all the answers

    Bitter taste is sensed by a single type of G-protein coupled receptor family.

    <p>False</p> Signup and view all the answers

    Each bitter-sensing taste receptor cell expresses multiple T1Rs.

    <p>False</p> Signup and view all the answers

    Sour taste perception is linked to the detection of hydrogen ions.

    <p>True</p> Signup and view all the answers

    The KIR2.1 channel is believed to mediate responses in taste receptor cells for bitter taste.

    <p>False</p> Signup and view all the answers

    Taste receptor cells have a single-type ion channel that opens when detecting sour taste.

    <p>False</p> Signup and view all the answers

    An individual taste receptor can recognize more than one type of bitter compound.

    <p>True</p> Signup and view all the answers

    The generation of nerve impulses by taste buds occurs immediately upon first application of a taste stimulus.

    <p>False</p> Signup and view all the answers

    The precise mechanism of how sour taste is sensed is fully understood.

    <p>False</p> Signup and view all the answers

    Taste hairs (microvilli) are involved in the sensing of sweet and umami tastes.

    <p>True</p> Signup and view all the answers

    Match the following taste sensations with their descriptions:

    <p>Sour = Caused by hydrogen ion concentration Salty = Primarily stimulated by sodium chloride Sweet = Primarily stimulated by sucrose Bitter = Caused by quinine</p> Signup and view all the answers

    Match the following taste cells with their lifespan:

    <p>Taste cells = Approximately 10 days average lifespan Young taste cells = Continually replaced by mitotic division Mature taste cells = Located towards the center of the bud Eliminated taste cells = Some survive over 3 weeks</p> Signup and view all the answers

    Match the following food sources to their primary taste sensation:

    <p>Meat extracts = Umami Aging cheese = Umami Hydrochloric acid = Sour Sucrose = Sweet</p> Signup and view all the answers

    Match the following taste sensations with their molar thresholds:

    <p>Sour = 0.0009 M Salty = 0.01 M Sweet = 0.01 M Bitter = 0.000008 M</p> Signup and view all the answers

    Match the following tastes with their tasting characteristics:

    <p>Umami = Pleasant taste sensation Sour = Intensely acidic Bitter = Intensely bitter taste Salty = Common table salt taste</p> Signup and view all the answers

    Match the following primary sensations of smell with their corresponding descriptors:

    <p>Camphoraceous = Strong, medicinal scent Musky = Earthy and animalistic aroma Floral = Sweet and fragrant Pepperminty = Fresh and minty scent</p> Signup and view all the answers

    Match the stages of olfactory signal processing with their descriptions:

    <p>Activation = Onset of olfactory stimulus G-protein complex activation = Initiates signal transduction cAMP formation = Amplifies the signal Sodium ion channel opening = Leads to nerve impulse generation</p> Signup and view all the answers

    Match the factors that affect olfactory stimulation with their requirements:

    <p>Volatile substances = Must be sniffed into the nasal cavity Concentration of odorant = Must be at significant levels Feedback inhibition = Suppresses signal relay Sodium channels = Open in response to cAMP</p> Signup and view all the answers

    Match the process in the olfactory system with its effects:

    <p>Cascading effect = Opens large numbers of sodium channels Sensitivity of olfactory neurons = Responds to minute concentrations of odorant Activation of adenylyl cyclase = Produces many cAMP molecules Feedback inhibition = Suppresses strong stimuli</p> Signup and view all the answers

    Match the chemical mechanisms in the olfactory system with their actions:

    <p>Odorant substance = Activates receptor proteins G-protein complex = Transmits the signal inside the cell cAMP = Prepares channels for sodium influx Sodium ion channels = Triggers olfactory nerve response</p> Signup and view all the answers

    Study Notes

    Olfactory System

    • Lateral Olfactory Area
      • The lateral olfactory area connects to the hippocampus, which is responsible for learning and memory.
      • This area appears to play a significant role in developing preferences and aversions to foods based on prior experiences.
      • It receives signals from the lateral olfactory area that contribute to the development of strong aversions to foods associated with nausea or vomiting.
      • This area also has direct connections to the paleocortex which is part of the cerebral cortex.
      • It is the only area of the cerebral cortex where sensory signals bypass the thalamus before reaching the cortex.
    • Newer Olfactory Pathway
      • This newer pathway also helps to transmit smell information.
      • The signal travels from the thalamus to the dorsomedial thalamic nucleus and then to the lateroposterior quadrant of the orbitofrontal cortex.
    • Concentration
      • The olfactory system has a very low threshold for detecting odors making it highly sensitive.
    • Odor Intensity
      • The range of odor intensity that can be perceived is far smaller than other sensory systems like vision or hearing.
      • The olfactory system primarily detects the presence or absence of odors, rather than precisely quantifying their intensity.

    ### Olfactory Transmission

    • Olfactory Nerve Fibers
      • Olfactory nerve fibers originate from the olfactory bulb and transmit information to the brain.
      • These fibers form cranial nerve I, also known as the olfactory tract.
    • Olfactory Bulb
      • The olfactory bulb is an anterior outgrowth of brain tissue from the base of the brain.
      • It sits atop the cribriform plate, separating the brain cavity from the nasal cavity.
      • The cribriform plate contains small perforations through which olfactory nerve fibers pass from the olfactory membrane into the bulb contained within the cranial cavity.
      • The olfactory bulb receives signals from the olfactory cells through the olfactory nerve fibers.

    Primitive Olfactory System

    • Medial Olfactory Area
      • It is a primitive olfactory system located in the midbasal portions of the brain, anterior to the hypothalamus.
      • It includes the septal nuclei which are located in the midline of the brain and project to the hypothalamus and other primitive parts of the limbic system.
      • This area plays a crucial role in regulating basic behaviors such as feeding and responding to smells.
    • Influence of Damage
      • Damage to the lateral olfactory area does not significantly affect basic olfactory responses such as licking and salivation caused by food scents or basic emotional drives.
      • However, it disrupts more complex olfactory conditioned reflexes.
      • The removal of the lateral olfactory area leaves intact the more basic olfactory responses regulated by the medial olfactory system.

    Less Old Olfactory System

    • Lateral Olfactory Area
      • This system is less primitive than the medial olfactory area.
      • It is made up of the prepyriform and pyriform cortex, and includes the cortical portion of the amygdala.
      • It is more complex than the medial olfactory area, reflecting a higher level of olfactory processing.

    Olfactory Membrane

    • Cells in the Olfactory Membrane
      • The olfactory membrane is located in the superior portion of the nasal cavity.
      • It contains olfactory cells, which are bipolar nerve cells derived from the CNS.
      • These cells have 4 to 25 olfactory cilia or hairs that project into the mucous layer lining the nasal cavity.
    • Olfactory Cells
      • These cells are responsible for detecting odors.
      • They are bipolar nerve cells derived from the central nervous system.
      • They are interspersed among sustenticular cells.
      • The olfactory cells contain cilia which detect odor molecules in the air.
    • Function of Olfactory Cilia
      • These cilia are microscopic projections extending from the olfactory cells.
      • They are covered in a mucus layer.
      • They are highly sensitive and detect odor molecules in the air.
      • They transmit these odors to the olfactory cells, triggering the sensation of smell.

    Central Nervous System Regulation of Smell

    • Control of the Olfactory Bulb
      • The olfactory bulb is regulated by the central nervous system through centrifugal control.
      • Nerve fibers from the brain travel centrifugally to the olfactory bulb.
      • These fibers connect to granule cells within the bulb.
      • Granule cells release inhibitory signals to the mitral and tufted cells, helping to refine odor discrimination.
      • This control is necessary for sharpening a person’s ability to distinguish between different odors.

    Taste

    • Taste buds are mainly responsible for the sense of taste, but smell also contributes strongly
    • There are 3,000 to 10,000 taste buds in adults, with a higher amount in children
    • Taste bud sensitivity decreases with age as many degenerate after the age of 45
    • Taste buds are specific to one of the five primary tastes at low concentrations: salty, sour, sweet, bitter, and umami
    • Taste buds can detect multiple tastes at higher concentrations
    • The salty taste is caused by ionized salts, mainly by sodium ions
    • Sweet taste is not caused by any single chemical, but rather a range of substances like: sugars, glycols, alcohols, aldehydes, ketones, amides, esters, amino acids, small proteins, sulfonic acids, halogenated acids, and inorganic salts
    • The mechanism of stimulation starts with activation of the taste cells, which causes a depolarization, leading to the receptor potential of taste
    • The receptor potential is initiated by the binding of the taste chemical to a protein receptor molecule on the taste receptor cell, opening ion channels, allowing positively charged sodium or hydrogen ions to enter and depolarize the cell
    • Taste sensations adapt quickly, usually within a minute, occurring mostly in the central nervous system, rather than at the taste bud receptors

    Taste Preference and Diet Control

    • Taste preference plays an important role in diet selection, allowing animals to choose foods that are desirable and nutritious
    • Taste preferences can change based on the body's needs for specific substances
    • The septal nuclei, located in the midline of the brain, are involved in taste preference and dietary control
    • The septal nuclei feed into the hypothalamus and other areas of the limbic system, which are responsible for basic behavior

    Smell

    • The olfactory system is one of the earliest developed brain structures in primitive animals
    • Olfactory signals are transmitted through the olfactory bulb, which is an outgrowth of brain tissue
    • Olfactory nerve fibers travel back from the bulb as cranial nerve I, or the olfactory tract
    • The olfactory bulb lies over the cribriform plate, separating the brain cavity from the nasal cavity
    • The medial olfactory area is important for basic behavior and connects to the hypothalamus and other areas of the limbic system

    Taste

    • The five primary taste sensations are: sour, salty, sweet, bitter, and umami.
    • Taste buds are located on the tongue and palate.
    • Each taste bud is usually most sensitive to one of the five primary taste stimuli.
    • Taste receptor cells are located within taste buds and are depolarized by taste stimuli.
    • The receptor potential is triggered by the binding of taste chemicals to protein receptor molecules on the surface of taste receptor cells, which opens ion channels.
    • The intensity of the taste sensation is proportional to the concentration of the stimulating substance.

    Smell

    • Smell is detected by olfactory receptor cells in the olfactory epithelium in the nasal cavity.
    • Olfactory receptor cells are bipolar neurons with cilia that project into the nasal cavity.
    • Odorant molecules bind to receptor proteins on the cilia of olfactory receptor cells, triggering a signal transduction cascade that leads to the generation of nerve impulses.
    • Each olfactory receptor cell expresses only one type of receptor protein, which binds to a specific odorant or a small group of related odorants.
    • The olfactory nerve is composed of axons from olfactory receptor cells and carries signals to the olfactory bulb.
    • The olfactory bulb is located in the brain and processes olfactory information.
    • The olfactory bulb projects to the olfactory cortex, which is responsible for conscious perception of smell.
    • The olfactory bulb also projects to the amygdala and hippocampus, which are involved in emotional responses and memory associated with smell.
    • The medial olfactory area is a primitive olfactory system located in the midbasal portions of the brain.
    • The lateral olfactory area is a newer olfactory system that projects to the prefrontal cortex and other brain areas.
    • The medial olfactory area is involved in basic behavioral responses to odors, while the lateral olfactory area is involved in conscious perception and complex olfactory processing.

    Sour Taste

    • Caused by the concentration of hydrogen ions
    • Sour taste intensity increases proportionally to the logarithm of the hydrogen ion concentration

    Umami Taste

    • Japanese for "delicious"
    • Perceived as a pleasant taste qualitatively different from sour, salty, sweet, or bitter
    • Dominant flavor in food containing L-glutamate
    • Thought to promote ingestion of proteins

    Taste Thresholds

    • Sour taste: 0.0009 M hydrochloric acid
    • Salty taste: 0.01 M sodium chloride
    • Sweet taste: 0.01 M sucrose
    • Bitter taste: 0.000008 M quinine

    Smell: The Olfactory System

    • Mechanism: Odorant molecules bind to olfactory receptors, activating a G-protein complex
    • The G-protein activates adenylyl cyclase, producing cAMP
    • cAMP opens sodium channels, causing depolarization
    • This triggers action potentials in olfactory nerve fibers
    • Physical factors influencing smell:
      • Odorant must be volatile
      • Odorant must be slightly water-soluble
      • Odorant must be slightly lipid-soluble

    Olfactory Cell Membrane Potentials

    • Unstimulated olfactory cells have a membrane potential of about -55 millivolts
    • Unstimulated cells generate action potentials at a slow rate
    • Odorants cause depolarization, decreasing the membrane potential to -30 millivolts or less
    • Depolarization triggers rapid action potential firing

    Primary Sensations of Smell

    • At least 100 primary sensations of smell
    • Some studies suggest there may be as many as 1000 different types of odorant receptors
    • Odor blindness, the inability to smell a specific substance, has been identified for over 50 different substances

    Affective Nature of Smell

    • Smell, more than taste, has the affective quality of pleasantness or unpleasantness
    • Can trigger strong emotional responses
    • Plays a role in food selection

    Olfactory System Structure

    • Olfactory neurons: Located in the olfactory epithelium
    • Olfactory bulb: Contains glomeruli, where olfactory neurons synapse with mitral and tufted cells
    • Mitral and tufted cells: Send axons to higher brain structures

    Neural Connections

    • Olfactory bulb projects to the brain, including:
      • Lateral olfactory area (prepyriform and pyriform cortex, amygdaloid nuclei)
      • Medial olfactory area (hippocampus, temporal cortex)
      • Orbitofrontal cortex

    Centrifugal Control of Olfactory Bulb

    • Nerve fibers from the brain project to the olfactory bulb, terminating on granule cells
    • Granule cells send inhibitory signals to mitral and tufted cells
    • This feedback mechanism may sharpen odor discrimination

    The Less Old Olfactory System - The Lateral Olfactory Area

    • Involved in complex olfactory functions like conditioned reflexes
    • Removal of this area impairs these complex functions but doesn't affect basic olfactory responses

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