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 (D)</p> Signup and view all the answers

How does sex impact olfactory detection thresholds?

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

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

<p>85 years (A)</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. (A)</p> Signup and view all the answers

How many olfactory receptor genes do mammals typically have?

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

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

<p>Detect odourants in the inspired air (B)</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. (A)</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 (C)</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. (A)</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 (C)</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 (C)</p> Signup and view all the answers

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

<p>Basal cells (D)</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. (C)</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. (A)</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. (B)</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. (A)</p> Signup and view all the answers

Which mechanism contributes to cross-adaptation in olfactory perception?

<p>Shared olfactory receptors between different odours. (D)</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. (A)</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. (B)</p> Signup and view all the answers

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

<p>Sensitivity to specific odourants. (D)</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. (C)</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 (B)</p> Signup and view all the answers

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

<p>False (B)</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 (C)</p> Signup and view all the answers

Women typically have lower olfactory detection thresholds than men.

<p>True (A)</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 (A)</p> Signup and view all the answers

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

<p>True (A)</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 (A)</p> Signup and view all the answers

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

<p>False (B)</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 (B)</p> Signup and view all the answers

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

<p>True (A)</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. (C)</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 (B)</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

Flashcards

Odourant

Molecule detected by olfactory receptors, triggering a neural signal for smell perception.

Detection Threshold

The lowest concentration of an odourant needed for a person to detect it.

Olfactory Epithelium

Secretory lining in the nose detecting odourants.

Cribriform Plate

Bony structure separating nose from brain, allowing olfactory nerve passage.

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Olfactory Receptor Neurons (ORNs)

Sensory neurons within the olfactory epithelium that detect odourants.

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Anosmia

Complete loss of smell, often due to head trauma or sinus problems.

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Glomeruli

Cluster of incoming olfactory neuron axons in the olfactory bulb.

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Mitral Cells

Principal output neurons in the olfactory bulb.

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Olfactory Receptors (ORNs)

Sensory neurons in the nose that detect odors.

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Cilia

Hair-like structures on olfactory receptor neurons (ORNs) that contain odorant receptor sites.

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Cross-Adaptation (Olfaction)

Decreased sensitivity to similar odors after continuous exposure.

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Piriform Cortex

The primary olfactory cortex, the part of the brain that processes smells.

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Olfactory Detection Thresholds

Amount of stimulus needed to perceive an odor.

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Pseudogenes (Olfactory Receptors)

Non-functional olfactory receptor genes.

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Amygdala-Hippocampal Complex

Brain region crucial for emotional and associative aspects of smell.

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Olfactory Receptors (ORs)

Protein structures where odorant molecules bind to initiate signals.

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Durability of smell

Smell memories can last for a long time without fading.

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Limbic System's Role in Smell

The limbic system, a group of brain areas, directly processes odors, leading to strong emotional connections.

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Tip-of-the-nose phenomenon

Difficulty naming a smell, even when familiar.

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Smell and Language Difference

Fewer words for smells compared to other senses, showing a disconnect in how we describe odors.

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Receptor Adaptation

Smell receptors stop responding after continuous exposure to a scent.

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Cross-Adaptation

Exposure to one smell reduces the detection of a different smell.

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Cognitive Habituation

Unable to detect a smell after long-term exposure.

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Smell Detection

Smell is basically a change detector, which responds to different stimulus.

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What's the function of cilia in ORNs?

Cilia are hair-like protrusions on olfactory receptor neurons (ORNs). They act as the binding sites for odorant molecules, initiating the process of smell detection.

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How many odorant molecules trigger a signal?

Approximately 8 odorant molecules binding to a receptor on a single ORN are needed to initiate an action potential, triggering the perception of smell.

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How does smell differ from other senses?

Unlike vision, hearing, or taste, olfactory receptors don't need a protective barrier. They directly contact the brain, making olfaction more susceptible to external influences.

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What is cross-adaptation in olfaction?

Cross-adaptation occurs when continuous exposure to one odorant reduces sensitivity to similar odors. For example, after smelling coffee, you may not be able to detect the faint smell of cinnamon.

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How many olfactory receptor genes do mammals have?

Mammals typically have around 1000 different olfactory receptor genes, each coding for a specific type of ORN.

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Why are some ORNs non-functional?

Some olfactory receptor genes are inactive pseudogenes. Humans have a higher percentage of pseudogenes compared to dogs and mice, impacting individual smell sensitivity.

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What's the role of the piriform cortex?

The piriform cortex is considered the primary olfactory cortex, responsible for processing and identifying smells.

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What does the Amygdala-hippocampal complex do?

This brain area is crucial for associating smells with emotions and memories, shaping our emotional responses to different scents.

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What makes a molecule an odourant?

To be smelled, a molecule needs to be volatile (easily evaporates), small enough to enter the nose, and hydrophobic (doesn't dissolve in water).

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What is the olfactory epithelium?

The olfactory epithelium is a mucous membrane located in the back of the nose. It contains olfactory receptor neurons (ORNs), which are responsible for detecting odorants.

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What is the cribriform plate?

The cribriform plate is a bony structure that separates the nose from the brain. It has tiny holes that allow axons from ORNs to pass through and reach the brain.

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What is anosmia?

Anosmia is the complete loss of smell. It often occurs due to a sinus illness or head trauma.

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What is the posterior piriform cortex (PPC)?

The posterior piriform cortex (PPC) is a part of the brain that processes the quality of an odor, regardless of its complexity.

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What are the types of cells in the olfactory epithelium?

There are three types: supporting cells provide support for ORNs, basal cells are precursors to ORNs, and ORNs are the main sensory cells that detect odors.

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What are mitral cells and tufted cells?

Mitral cells are the main output neurons in the olfactory bulb. Tufted cells are a secondary type of output neuron.

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What are glomeruli?

Glomeruli are spherical structures in the olfactory bulb. Incoming axons from ORNs converge on them.

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Limbic system

A group of brain structures involved in emotions and memory, directly connected to smell, which explains why scents evoke strong emotions.

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Why are there fewer words for smells?

Olfactory information is processed differently than other senses, making it harder to describe smells with words.

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What makes smell a change detector?

Olfactory receptors are designed to detect differences in smells, responding best to changes in the environment.

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Three mechanisms of olfactory adaptation

Receptors internalized into cell bodies, odourant molecules absorbed into bloodstream, and ongoing research to understand the third.

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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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