Olfaction
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Questions and Answers

What are cilia on olfactory receptor neurons (ORNs) responsible for?

  • Transmitting signals to the olfactory cortex
  • Regulating olfactory adaptation
  • Binding odourant molecules (correct)
  • Protecting the dendrites from external stimuli

    • Which statement about olfactory receptors is correct?

  • Humans have about 300-400 types of functioning olfactory receptors. (correct)
  • Dogs possess a higher percentage of pseudogenes in comparison to humans.
  • Each olfactory receptor gene codes for multiple types of ORNs.
  • Olfactory receptors have a protective barrier similar to other sensory receptors.

    • What is cross-adaptation in olfaction?

  • Increased sensitivity to distinct odours after continuous exposure.
  • Reduced sensitivity to similar odourants after repeating exposure. (correct)
  • The ability to identify different odours without context.
  • A mechanism that blocks strong odours from being perceived.

    • Which region is considered the primary olfactory cortex?

    <p>Piriform cortex</p> Signup and view all the answers

    How does sex impact olfactory detection thresholds?

    <p>Women have lower thresholds, especially during the ovulatory period.</p> Signup and view all the answers

    At what age does approximately 50% of the population experience effective anosmia?

    <p>85 years</p> Signup and view all the answers

    What unique relationship do odours have concerning emotional and memory contexts?

    <p>Identification of odours generally benefits from contextual clues.</p> Signup and view all the answers

    How many olfactory receptor genes do mammals typically have?

    <p>About 1000</p> Signup and view all the answers

    What is the primary function of olfactory receptor neurons (ORNs)?

    <p>Detect odourants in the inspired air</p> Signup and view all the answers

    Which statement correctly describes the role of the cribriform plate in olfaction?

    <p>It allows axons from olfactory receptor neurons to enter the brain.</p> Signup and view all the answers

    What are glomeruli in the context of olfactory function?

    <p>Conglomerates of incoming axons from olfactory receptor neurons</p> Signup and view all the answers

    What occurs in the posterior piriform cortex (PPC) concerning odour recognition?

    <p>It produces representations of the quality of an odour.</p> Signup and view all the answers

    What is the role of supporting cells in the olfactory epithelium?

    <p>Provide metabolic and physical support to olfactory receptor neurons</p> Signup and view all the answers

    Anosmia is caused by which of the following conditions?

    <p>Damage to the cribriform plate or olfactory neurons</p> Signup and view all the answers

    Which type of cell acts as precursor cells to olfactory receptor neurons?

    <p>Basal cells</p> Signup and view all the answers

    What role does the limbic system play in olfaction?

    <p>It is involved in many aspects of emotion and memory.</p> Signup and view all the answers

    What is receptor adaptation in the context of olfaction?

    <p>The process by which olfactory receptors stop responding to an odourant after continuous exposure.</p> Signup and view all the answers

    Which of the following characteristics is required for a molecule to be considered an odourant?

    <p>It must be volatile, small, and hydrophobic.</p> Signup and view all the answers

    Cognitive habituation affects our sense of smell by causing what?

    <p>Decreased perception of an odourant after long-term exposure.</p> Signup and view all the answers

    Which mechanism contributes to cross-adaptation in olfactory perception?

    <p>Shared olfactory receptors between different odours.</p> Signup and view all the answers

    How does the sense of smell primarily function as a detector?

    <p>As a change detector rather than a constant detector.</p> Signup and view all the answers

    What can be a consequence of olfactory receptor internalization during odour adaptation?

    <p>Prolonged recovery time for receptors to be recycled.</p> Signup and view all the answers

    Which aspect of the olfactory process is most influenced by genetics?

    <p>Sensitivity to specific odourants.</p> Signup and view all the answers

    What is the tip-of-the-nose phenomenon?

    <p>The familiar sensation of an odour without the ability to name it.</p> Signup and view all the answers

    What phenomenon describes the reduced sensitivity to odourants that are chemically similar to those a person has repeatedly encountered?

    <p>Cross-adaptation</p> Signup and view all the answers

    Humans have a higher percentage of functional olfactory receptor genes compared to dogs and mice.

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

    What percentage of the population is effectively anosmic by age 85?

    <p>50</p> Signup and view all the answers

    The __________ cortex is regarded as the main area for olfactory processing in the brain.

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

    Match the following odour-related professions with their associated skills:

    <p>Professional perfumers = Distinguishing up to 100,000 odours Wine tasters = Evaluating smell and taste properties Olfactory researcher = Studying olfactory perception General population = Varied capacity for odour detection</p> Signup and view all the answers

    Which factor does NOT significantly affect olfactory detection thresholds?

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

    Women typically have lower olfactory detection thresholds than men.

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

    What role does the amygdala–hippocampal complex play in olfactory cognition?

    <p>Emotional and associative properties</p> Signup and view all the answers

    Which of the following is NOT a requirement for a molecule to be classified as an odourant?

    <p>It must be aromatic</p> Signup and view all the answers

    Anosmia can result from a fractured cribriform plate due to head trauma.

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

    What is the primary purpose of the nose?

    <p>To filter, warm, and humidify air.</p> Signup and view all the answers

    The __________ is a bony structure that separates the nose from the brain.

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

    Match the following types of cells with their function in the olfactory epithelium:

    <p>Supporting cells = Metabolic and physical support for ORNs Basal cells = Precursor cells to olfactory receptor neurons Olfactory receptor neurons (ORNs) = Main sensory neurons in the olfactory epithelium</p> Signup and view all the answers

    Which structure contains spherical conglomerates of incoming axons from olfactory receptor neurons?

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

    The posterior piriform cortex is responsible for identifying the specific quality of an odour.

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

    What is the role of olfactory receptor neurons (ORNs) in the olfactory system?

    <p>They detect odourants in the inspired air.</p> Signup and view all the answers

    What effect does receptor adaptation have on odor detection?

    <p>Detection of the odorant ceases after continuous exposure</p> Signup and view all the answers

    Cognitive habituation can lead to an inability to detect familiar smells.

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

    What primary brain region is involved in olfactory processing?

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

    Continuous exposure to an odorant leads to __________, where receptors stop responding to that odorant.

    <p>receptor adaptation</p> Signup and view all the answers

    Match the following concepts with their descriptions:

    <p>Receptor adaptation = Reduction in detection after continuous exposure Cross-adaptation = Reduction in detection following exposure to another odorant Cognitive habituation = Diminished ability to detect smells after prolonged exposure Tip-of-the-nose phenomenon = Inability to name a familiar odorant</p> Signup and view all the answers

    Which statement best describes the role of olfaction?

    <p>It serves as a change detector in the environment.</p> Signup and view all the answers

    The amygdala is part of the olfactory system but does not play a role in emotional responses.

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

    What is the term for the inability to name an odourant despite familiarity?

    <p>Tip-of-the-nose phenomenon</p> Signup and view all the answers

    Study Notes

    Odour and Odourants

    • Odour: A general smell sensation of a particular quality
    • Odourant: Molecules that olfactory receptors recognize and respond to, producing neural signals that the brain interprets as different odours
    • Chemical compounds, not all chemicals are odourants
    • To be smelled, molecules must be volatile, small, and hydrophobic
    • Detection threshold: The concentration of an odourant needed for detection

    Identifying and Discriminating Odours

    • Smell's primary purpose: Filtering, warming, and humidifying inhaled air
    • Nose structures: Ridges, olfactory cleft, and olfactory epithelium
    • Olfactory cleft: Area of the nose where the main olfactory epithelium is located
    • Olfactory epithelium: Secretory mucosa detecting odourants in inhaled air
    • Cribriform plate: Bony structure with tiny holes, separating the nose from the brain. Axons from olfactory receptor neurons (ORNs) pass through these holes into the brain.
    • Anosmia: Complete inability to smell, often caused by sinus illness or head trauma. Cribriform plate damage can sever olfactory neurons
    • Posterior piriform cortex (PPC): Area of the brain that processes the overall quality of an odour.
    • Retina of the nose: Three types of cells
      • Supporting cells: Provide metabolic and structural support for ORNs
      • Basal cells: Precursor cells to ORNs
      • Olfactory receptor neurons (ORNs): Main cells in the olfactory epithelium under a layer of mucus
      • Supporting structures
        • Mitral cells: Projecting output neurons in olfactory bulbs
        • Tufted cells: Secondary output neurons in olfactory bulbs
        • Glomeruli: Spherical collections of ORN axons
        • Turbinates: Nasal cavity bones that help distribute air

    Olfactory Receptors and Adaptations

    • Cilia: Hair-like protrusions on ORN dendrites; contain receptor sites for odourant molecules
    • Olfactory Receptor (OR): Region on cilia where odourant molecules bind; ~8 molecules bind to one receptor to trigger an action potential
    • Difference from other sensory cells: No protective barrier between ORNs and the brain, unlike visual or auditory receptors.
    • Adaptation to Odours
      • Cross-adaptation: Reduced sensitivity to odourants with similar chemical structures or perceived qualities after continuous exposure.
    • Neural Code for Odour
      • Genome contains ~1000 olfactory receptor genes, each coding for a single type of ORN
      • All mammals have a nearly identical set of ~1000 OR genes. Variations in pseudogene frequency exist between species
      • Humans have ~300-400 functional OR genes. Significant variation due to different numbers of pseudogenes.

    Smell and the Brain

    • Pathway from Nose to Brain: Olfactory receptors to olfactory bulbs to the olfactory tract, then the olfactory cortex, amygdala, hypothalamus, and other brain regions
    • Olfactory bulbs contain glomeruli where ORN axons synapse with mitral and tufted cells
    • Representing Odours in the Brain
      • Piriform cortex: Primary olfactory cortex
      • Amygdala-hippocampal complex: Processes emotional and associative aspects of smell
      • Entorhinal: sensory association projections to hippocampus

    Odours, Emotion, Memory, and Environmental Factors

    • People vary in their ability to identify odours, even with context
    • Detection, discrimination, and recognition rely on many factors like sex, age, general health
    • Olfactory detection thresholds vary by sex, are typically lower in women
    • Odours influence the limbic system, a region of the brain involved in emotion and memory, strongly
    • Tip-of-the-nose phenomenon: Inability to name a familiar odour
    • Mechanisms of Odour Adaptation:
      • Internalization of olfactory receptors into cell bodies
      • Absorption of odourants into the bloodstream
      • Cognitive/emotional factors
    • Odour habituation: The psychological process of reduced ability to detect an odour after prolonged exposure
    • Three mechanisms for habituation
    • Attention influences odour detection
    • Importance of attention; cannot smell while asleep
    • Effects of Odours on Social Behavior
      • Pheromones: Chemicals that trigger behavioral or physiological responses in other members of the same species.
      • Vomeronasal olfactory system: Detects pheromones; distinct from the main olfactory system
      • Humans use HLA detection (differences in immune system genes) in odours as cues to attract mates

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    Related Documents

    Olfaction PDF

    Description

    Test your knowledge on the basics of odours and odourants. This quiz covers the structures involved in olfactory perception, the definition of odourants, and the mechanisms by which we detect smells. Ideal for students studying biology or sensory perception.

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