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Questions and Answers
What is the primary function of the mitral cells in the olfactory bulb?
What is the primary function of the mitral cells in the olfactory bulb?
Which area is the main target of the projections from the mitral cells in the olfactory bulb?
Which area is the main target of the projections from the mitral cells in the olfactory bulb?
What proportion of taste buds is found in circumvallate papillae?
What proportion of taste buds is found in circumvallate papillae?
Which type of papillae are primarily located at the tip of the tongue?
Which type of papillae are primarily located at the tip of the tongue?
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What is the role of olfactory receptors in olfactory sensory neurons (OSNs)?
What is the role of olfactory receptors in olfactory sensory neurons (OSNs)?
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What happens when taste chemicals stimulate receptors in taste buds?
What happens when taste chemicals stimulate receptors in taste buds?
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Where is the olfactory cortex primarily located?
Where is the olfactory cortex primarily located?
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What factors influence the detection threshold of tastants?
What factors influence the detection threshold of tastants?
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Which cranial nerve primarily innervates the taste buds located on the anterior two-thirds of the tongue?
Which cranial nerve primarily innervates the taste buds located on the anterior two-thirds of the tongue?
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What is the role of the gustatory nucleus in the central taste pathways?
What is the role of the gustatory nucleus in the central taste pathways?
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Which type of papillae is primarily associated with the perception of bitter taste?
Which type of papillae is primarily associated with the perception of bitter taste?
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Which of the following areas is part of the gustatory cortex?
Which of the following areas is part of the gustatory cortex?
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Which of the following chemicals is known to activate the trigeminal chemosensory system?
Which of the following chemicals is known to activate the trigeminal chemosensory system?
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The ventral posterior medial (VPM) nucleus is primarily involved in which aspect of taste processing?
The ventral posterior medial (VPM) nucleus is primarily involved in which aspect of taste processing?
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How does the orbitofrontal cortex contribute to the processing of taste?
How does the orbitofrontal cortex contribute to the processing of taste?
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The vagus nerve primarily innervates taste buds located where?
The vagus nerve primarily innervates taste buds located where?
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What role do odorant-binding proteins play in the olfactory epithelium?
What role do odorant-binding proteins play in the olfactory epithelium?
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How are olfactory receptor neurons (ORNs) activated by odorant molecules?
How are olfactory receptor neurons (ORNs) activated by odorant molecules?
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What is unique about the first synapse in the olfactory system compared to other sensory systems?
What is unique about the first synapse in the olfactory system compared to other sensory systems?
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What is a significant characteristic of the olfactory receptor neurons (ORNs)?
What is a significant characteristic of the olfactory receptor neurons (ORNs)?
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What initiates the action potential in an olfactory receptor neuron?
What initiates the action potential in an olfactory receptor neuron?
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Which structure primarily serves as the entry point for odor molecules in the olfactory system?
Which structure primarily serves as the entry point for odor molecules in the olfactory system?
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What defines the unique response pattern to an individual odorant in the olfactory system?
What defines the unique response pattern to an individual odorant in the olfactory system?
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What type of molecules can directly diffuse to the receptors on the microvilli of ORNs?
What type of molecules can directly diffuse to the receptors on the microvilli of ORNs?
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Study Notes
Chemical Senses
- The olfactory system is the only sensory system where the first synapse is in the telencephalon (olfactory bulb).
- Olfactory receptor neurons (ORNs) are replaced every two months.
- The olfactory epithelium in the nasal cavity consists of ORNs.
- ORNs have a peripheral and a central process:
- Peripheral process: Extension from the cell body to the surface of the epithelium, consisting of microvilli.
- Central process: Makes up the olfactory nerve fascicles that penetrate the cribriform plate to terminate at the olfactory bulb.
- Microvilli are bathed in mucus where odor molecules are dissolved.
- Hydrophilic odor molecules dissolve and diffuse to the receptors on the microvilli.
- Hydrophobic molecules are transported to the microvilli by odorant-binding proteins.
- Odorant molecules bind with ORN receptors, producing electric potentials.
- Each ORN expresses one or very few of about 400 genes.
- Each olfactory receptor can be activated by multiple odorant molecules within one or very few families of odorants.
- Potentials generated by G protein-coupled receptors propagate passively to the ORN soma where action potentials are generated.
- ORNs send their axons to the olfactory bulb neurons through the cribriform plate.
- Axons of ORNs constitute the olfactory nerve (cranial nerve I) which projects to the olfactory bulb.
- Each olfactory bulb principal neuron (mitral cell) receives inputs from thousands of ORNs that express the same single olfactory receptor gene.
- Mitral cells of the olfactory bulb project to other brain regions via the olfactory tract.
- The olfactory tract projects to the olfactory cortex, which includes the olfactory tubercle, pyriform cortex, entorhinal cortex, and the amygdala.
- Conscious discrimination of odors occurs in the orbitofrontal cortex, which receives input from the pyriform cortex.
Taste
- The taste system detects and assesses the chemical composition of ingested substances.
- Tastants are dissolved in saliva, and the perceived intensity of taste is proportional to the concentration of the tastant.
- Detection thresholds vary over a large range depending on the value or toxicity of the tastant.
- Taste cells are found in specialized structures called taste buds, distributed on the dorsal surface of the tongue, soft palate, pharynx, and upper esophagus.
- Each taste bud contains 30 to 100 taste cells.
- Taste buds are located in structures called papillae:
- Fungiform papillae (25% of all taste buds): Located on the anterior two-thirds of the tongue, with the highest density at the tip.
- Circumvallate papillae (50%): Located at the rear of the tongue.
- Foliate papillae (25%): Located on the posterolateral tongue.
- Taste cells in individual taste buds synapse with axons from branches of three cranial nerves (VII, IX, and X).
- Taste cells on the anterior two-thirds of the tongue (fungiform and foliate papillae) are innervated by the facial nerve (linked to salts, umami, and sugar).
- The circumvallate papillae at the rear of the tongue are innervated by the glossopharyngeal nerve (linked to bitter).
- Taste buds of the epiglottis and esophagus are innervated by the vagus nerve.
- The rostral part of the solitary nucleus (nucleus solitarius), often called the gustatory nucleus, is where taste fibers (CN X, IX, VII) terminate.
- The gustatory nucleus projects to the thalamus (ventral posterior medial (VPM) nucleus) through the central tegmental tract.
- Direct projections from the gustatory nucleus to the amygdala and hypothalamus influence appetite and other behavioral responses.
- The VPM projects to several neocortical areas collectively referred to as the gustatory cortex including the anterior insula (insular taste cortex).
- The gustatory cortex projects to the amygdala, influencing emotional responses to food.
- The orbitofrontal cortex receives taste information from the gustatory cortex, integrating it with olfactory, visual, and somatosensory inputs to give rise to the appreciation of flavor and food reward.
Trigeminal Chemosensory System
- The trigeminal system includes nociceptive receptor neurons activated by high concentrations of irritating chemicals in direct contact with the mucous membranes of the head (mouth, nose, eyes).
- Important activators of this system include ammonia, ethanol, acetic acid, CO2, and capsaicin.
- This "pain" information is relayed to the cerebral cortex along with other trigeminal pain and temperature information.
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Description
This quiz delves into the intricacies of the olfactory system, exploring how olfactory receptor neurons function and their role in our chemical senses. It covers the anatomical features, receptor mechanisms, and the unique processes involved in odor detection. Test your knowledge on the fascinating world of smell!
