C12- Smell
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Questions and Answers

Odorants interact with photoreceptors located within the olfactory mucosa.

False (B)

The olfactory cells are modified epithelial cells that are not derived from the central nervous system.

False (B)

Each olfactory cell possesses between 4 to 25 olfactory hairs that are approximately 0.3 micrometers in diameter and up to 200 nanometers in length.

False (B)

Bowman glands are located in the submucosa and produce a viscous substance that facilitates the removal of waste products.

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

The axons of olfactory neurons pass through the foramina of the sphenoid bone before terminating in the olfactory bulb.

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

Mitral cells transmit the output of the olfactory bulb via the optic tract.

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

The primary function of air turbulence in the nasal cavity is to reduce the contact between odorants and the olfactory mucosa.

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

The mucus secreted in the nasal cavity is produced exclusively by the goblet cells located in the olfactory epithelium.

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

The watery mucus layer is positioned under the viscous mucus layer, close to the surface of the olfactory epithelium.

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

Mucus has a primary role in transporting olfactory signals to the brain via direct neural pathways.

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

Ageusia is the diminished ability to detect gustatory stimulants.

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

Hyposmia indicates an increased sensitivity to olfactory stimulants.

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

During pregnancy, all odorants are perceived as disgusting.

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

Olfactory receptor neurons are unipolar cells, leading to a single axon carrying sensory data.

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

The dendrites of olfactory receptor neurons have a knoblike protrusion from which several microfibrils extend into the mucus.

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

Dysosmia refers to the complete absence of olfactory sensory experiences.

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

Agnosia is the inability to recognize a visual object.

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

Olfactory receptor neurons are protected from damage by a robust myelin sheath around their axons.

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

Tumors in the insular lobe can sometimes manifest with visual disturbances.

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

Gap junctions in the olfactory mucosa organize receptor proteins in four rings.

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

Hypergeusia means a decreased sensitivity to gustatory stimulants.

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

The active portion of olfactory receptors where odorants bind is located on the main body of the neuron.

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

If someone has Dysgeusia, they will have complete absence of the affected taste sensory experience.

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

Olfactory receptors are highly specific, with each receptor interacting with only one type of odorant molecule.

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

The nose's turbinate bones reduce airflow turbulence and enhance odorant delivery to receptors.

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

An indication of a potential seizure, related to an insular lobe tumor, is the recognition of sounds that are not present.

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

Headache is not a sign of insular lobe tumors.

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

Odorant binding to olfactory receptors directly opens ion channels, initiating an action potential.

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

Mitral cells in the olfactory bulb transmit signals directly to the thalamus, bypassing the olfactory tract.

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

Olfactory perception improves with aging due to an increase in receptor sensitivity.

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

Flashcards

Olfactory mucosa

The lining of the nasal cavity containing olfactory receptor cells.

Odorants

Chemical compounds that stimulate olfactory receptors, causing the sensation of smell.

Olfactory receptors

Nerve cells in the olfactory mucosa that detect odorants.

Olfactory cilia

Hair-like projections of olfactory cells that increase the surface area for odorant detection.

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Olfactory mucus

Mucus secreted by Bowman's glands in the olfactory mucosa, aiding in the detection of odorants.

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Bowman's glands

Glands located in the olfactory mucosa that produce mucus.

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Cribriform plate

The path taken by the axons of olfactory receptor cells, passing through a bone to reach the olfactory bulb.

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Olfactory bulb

A structure in the brain that processes olfactory information.

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Mitral cells

Neurons within the olfactory bulb that receive input from olfactory receptors.

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Turbulence in the nasal cavity

The flow of air carrying odorants into the nasal cavity, increasing the probability of odorant detection.

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Ageusia

Complete inability to taste.

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What are olfactory receptor neurons (ORNs)?

The main cells responsible for detecting odors. These neurons are found in the nasal epithelium, which is the lining of the nasal cavity. They have hair-like projections called cilia that extend into the mucus layer, where they come in contact with odorant molecules.

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Anosmia

Complete inability to smell.

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How do ORNs regenerate?

ORNs are constantly damaged due to exposure to potential harmful substances like pollutants, allergens, and microbes. To combat this, they undergo regular regeneration. This process relies on a population of neural stem cells located in the olfactory epithelium.

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Hypogeusia

Reduced sense of taste.

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How do odorants activate ORNs?

Odorants, or scent molecules, bind to specific receptors on the cilia of ORNs. This binding triggers a series of events involving G-proteins and second messengers, leading to the generation of a signal that travels to the brain.

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How do odorants generate an electrical signal?

Odorant molecules encounter the cilia of ORNs. This interaction leads to the creation of an inward current, which is a flow of electrically charged particles. This current signifies the initiation of the smell signal.

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Hyposmia

Reduced sense of smell.

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Hypergeusia

Increased sensitivity to taste.

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How do ORNs contribute to smell discrimination?

Each ORN expresses a single olfactory receptor protein, making it sensitive only to a specific set of molecules. This specificity contributes to the ability to distinguish between a wide range of smells.

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How do turbinate bones contribute to smell?

The nasal cavity contains turbinate bones, which are curved structures that increase the turbulence of air as it enters the nose. This turbulence helps to create a swirling motion that brings odorants into contact with the olfactory epithelium.

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Hyperosmia

Increased sensitivity to smell.

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Dysgeusia

Distorted perception of taste.

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How do mitral cells contribute to smell processing?

The mitral cells in the olfactory bulb receive signals from the ORNs. These cells then transmit the olfactory information to various brain regions involved in processing and interpreting smells.

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Dysosmia

Distorted perception of smell.

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What is the olfactory bulb and its role?

The olfactory bulb, located in the brain, is a structure that plays a crucial role in processing odor information. The olfactory bulb is organized into different zones, each sensitive to a specific family of odorants. This organization helps in identifying and differentiating various smells.

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How does aging affect the sense of smell?

The perception of flavors, including those related to smell, tends to decline with age. This loss of olfactory sensitivity can affect the enjoyment of food and beverages.

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Agnosia

Inability to identify a taste or smell.

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How does COVID-19 affect smell and taste?

COVID-19 can lead to loss of smell and taste, referred to as anosmia and ageusia, respectively. These losses result from the virus's ability to affect the olfactory epithelium and the pathways involved in smell and taste.

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Olfactory Aura

A phantom smell associated with seizures originating in the insular lobe.

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Study Notes

Olfactory Mucosa and Odorants

  • Odorants, the molecules responsible for smells, interact with chemoreceptors, extensions of the brain.
  • Olfactory cells, bipolar nerve cells originally from the CNS, number approximately 100 million in the olfactory epithelium.
  • Olfactory cilia (hairs) project into mucus lining the nasal cavity, crucial for odor detection.
  • Bowman glands secrete mucus, aiding odor molecule binding.
  • Dendrites are present in olfactory cells, as receptors for odorants are neurons.
  • Axons of olfactory neurons pass through the cribriform plate to glomeruli in the olfactory bulb.
  • Mitral cells, output of the glomeruli, transmit signals in the olfactory tract.
  • Air turbulence, created by nasal conchae, increases odorant contact with the olfactory mucosa.
  • Mucus, secreted by submucosal and goblet cells, increases odorant binding and protects the lower airways.
  • Two types of mucus exist: watery (superficial) and viscous (covering cilia).

Olfactory Receptor Neurons (ORNs)

  • ORNs, bipolar cells defining the neural portion of the olfactory epithelium, have a single dendritic process.
  • Microvilli, also known as olfactory cilia on the apical surface, extend into mucus, containing odorant receptors.
  • ORNs are directly exposed to inhaled air, putting them at risk from pollutants, allergens, and microorganisms.
  • Regeneration of ORNs is crucial, supported by neural stem cells in the basal cells of the olfactory epithelium.
  • Odorant receptors are structured in four rings linked by gap junctions.
  • Multiple neurons responding to stimulation are needed for a relevant signal transmission.
  • Receptor action occurs at the cilia level, when odorants bind, generating an inward current.

Olfactory Sense

  • Olfaction relies on lock-and-key interactions between odorants and receptor molecules.
  • Unlike taste, olfaction receptors lack channels; they react based on the shape of odorant molecules.
  • Receptors show selectivity for different odorants, depending on their structure.
  • The shape of the nose plays a role in olfaction through its impact on air turbulence.
  • Odorants bind to receptor molecules in cilia membranes, activating G-protein coupled receptors.
  • This activation amplifies the signal by increasing cAMP production, which modulates ion channels.
  • Receptor proteins have 7 transmembrane domains, a variable cell surface region, and a cytoplasmic tail for G-protein interaction.
  • Over 1000 genes code for odorant receptors, each detecting a unique set of odorants.
  • Stimulation intensity of receptors, varies from strong to mild to no response.
  • Each receptor is selective to a particular set of substrates.
  • Receptors are distributed throughout the nasal mucosa.
  • Axons of receptors project to olfactory bulbs.
  • In the olfactory bulb, receptor families cluster, forming a matrix.
  • Mitral cells transmit the stimuli to the olfactory tract to different brain regions.
  • Olfactory bulb activity can be measured optically.
  • Receptor sensitivity shifts with increasing odorant concentrations.

Olfactory Bulb Organization and Brain Regions

  • The olfactory bulb is organized into zones sensitive to different odorant families.
  • Mitral cells project to various brain areas, including the contralateral olfactory bulb, olfactory tubercle, thalamus, orbito-frontal cortex, frontal cortex, enthorinal and pyriform cortex, amygdala, and hypothalamus.

Olfactory Exploration and Memory

  • Animals use olfaction for environmental exploration, food searching, and danger detection.
  • The frontal cortex is linked to decision-making in primates and humans.
  • Olfactory memory, including recalling scents, is connected to the hippocampus.
  • Sensitivity to smell can decline with age.

Smell and Taste Deficits

  • Covid-19 can cause taste and smell loss (ageusia and anosmia).
  • Diminished abilities are termed hypogeusia and hyposmia.
  • Increased sensitivity is termed hypergeusia and hyperosmia.
  • Pregnancy can alter perceptions of some smells.
  • Distorted sensory perceptions are called dysgeusia and dysosmia.
  • Difficulty recognizing smells or tastes is called agnosia.
  • Tumors in the insular lobe can cause seizures, preceded by unusual smell perception and headache.

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Description

This quiz covers the anatomy and functions of the olfactory system, including the role of olfactory cells, the interaction with photoreceptors, and the significance of mucous secretions. Test your knowledge about the structure and function of the olfactory mucosa and its associated components.

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