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Questions and Answers
What is the conscious or subconscious awareness of changes in the external or internal environment?
Which type of sensory neuron carries information for only one modality?
What is the term for the conscious interpretation of sensations?
Which type of sensory receptor is sensitive to mechanical stimuli such as touch and pressure?
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What is the term for the decrease in receptor potential during a maintained, constant stimulus?
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Which type of sensory receptor is responsible for detecting changes in temperature?
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What is the term for the sensory receptors that monitor conditions in the internal environment?
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Which type of sensory receptor is responsible for detecting painful stimuli?
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What is the term for the sensory receptors that provide information about equilibrium, body position, and muscle length?
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Which type of sensory receptor is responsible for detecting chemicals in the mouth?
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What is the shape of fungiform papillae on the tongue?
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Where are foliate papillae located on the tongue?
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What type of receptors are found in filiform papillae?
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How many taste buds are found in each circumvallate papilla?
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What is the lifespan of gustatory epithelial cells?
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What is the function of gustatory microvilli?
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What type of sensations arise from stimulation of sensory receptors embedded in the skin or subcutaneous tissue?
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Which type of receptors are responsible for detecting sensations of itch and tickle?
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What is the primary function of proprioceptors in the body?
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What is the name of the receptors that detect changes in skeletal muscle length?
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Which type of sensations result from stimulation of lamellar and bulbous corpuscles?
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What is the name of the glands that produce mucus that helps to dissolve odorants in the olfactory epithelium?
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What is the primary function of the olfactory epithelium in the nose?
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What is the name of the type of receptor that detects sweet tastes?
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Which type of sensations arise from stimulation of free nerve endings in the skin?
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What is the name of the type of receptor that detects amino acids and is responsible for the umami taste?
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What is the function of gustatory epithelial cells?
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What is the role of Na+ channels in the physiology of gustation?
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What is the result of sour tastants entering gustatory epithelial cells?
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What is the purpose of IP3 in the physiology of gustation?
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How do tastants interact with gustatory epithelial cells?
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What is the characteristic of each gustatory epithelial cell?
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What is the result of continuous stimulation of gustatory epithelial cells?
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What is the purpose of the threshold for bitter substances?
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What is the function of G proteins in the physiology of gustation?
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What is the result of the interaction between tastants and gustatory epithelial cells?
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Study Notes
Sensory Physiology - Touch, Taste, and Smell
Process of Sensation
- Sensation: the conscious or subconscious awareness of changes in the external or internal environment
- Perception: the conscious interpretation of sensations, primarily a function of the cerebral cortex
- Each unique type of sensation (e.g., touch, pain, vision, or hearing) is called a sensory modality
- Two types of sensory modalities: general senses (somatic and visceral) and special senses (smell, taste, vision, hearing, and equilibrium)
Sensory Receptors
- Classified based on microscopic structure, location, and type of stimulus detected
- Types of sensory receptors:
- Free nerve endings (detect pain, temperature, touch, and itch sensations)
- Encapsulated nerve endings (detect pressure, vibration, and some touch sensations)
- Separate cells (specialized cells that synapse with sensory neurons, e.g., olfactory sensory neurons)
Location of Receptors
- Exteroceptors: detect external stimuli, providing information about the external environment (e.g., hearing, vision, smell, taste, touch, pressure, vibration, temperature, and pain)
- Interoceptors or visceroceptors: detect internal stimuli, monitoring conditions within the body (e.g., blood pressure, stretch, chemicals, nausea, hunger, and temperature)
- Proprioceptors: detect changes in muscle length, tension, and joint position
Type of Stimulus Detected
- Mechanical energy (sound waves, pressure, vibration, and proprioception)
- Electromagnetic energy (light and heat)
- Chemical energy (taste, smell, and chemoreceptors)
Adaptation
- A characteristic of most sensory receptors, where the receptor potential decreases in amplitude during a maintained stimulus
- Causes the frequency of nerve impulses in the sensory neuron to decrease
- Perception of a sensation may fade or disappear even though the stimulus persists
Somatic Sensations
- Arise from stimulation of sensory receptors embedded in the skin or subcutaneous tissue
- Include tactile sensations (touch, pressure, vibration, itch, and tickle) and proprioceptive sensations (position, movement, and tension)
Tactile Sensations
- Include touch, pressure, vibration, itch, and tickle
- Mediated by different types of encapsulated mechanoreceptors (e.g., Meissner corpuscles, Pacinian corpuscles, and Merkel discs) and free nerve endings
- Adaptation rates vary among receptors (rapidly adapting, slowly adapting, and non-adapting)
Proprioception
- Allows recognition of body parts and their position in space
- Includes kinesthesia (perception of body movements) and weight discrimination
- Mediated by proprioceptors embedded in muscles, tendons, and joints
Olfactory System (Smell)
- Detects chemical molecules in the air
- Olfactory epithelium contains olfactory sensory neurons (OSNs) with olfactory receptors
- Each OSN expresses only one type of olfactory receptor
- Binding of an odorant molecule to an olfactory receptor protein activates a G-protein signaling pathway, leading to a graded potential in the OSN
Gustatory System (Taste)
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Detects chemical molecules in food and drinks
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Taste buds contain gustatory epithelial cells with gustatory microvilli (gustatory hairs) that project to the external surface through the taste pore
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Five primary tastes: salty, sour, sweet, bitter, and umami
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Complex flavors are combinations of the five primary tastes### Gustatory System
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Dendrites contact many gustatory epithelial cells in several taste buds.
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Basal epithelial cells, which are stem cells, are found at the periphery of the taste bud near the connective tissue layer and produce new cells.
Physiology of Gustation
- Chemicals that stimulate gustatory epithelial cells are known as tastants.
- Na+ enters gustatory epithelial cells via Na+ channels, causing depolarization and release of neurotransmitter.
- G proteins activate enzymes that produce the second messenger inositol trisphosphate (IP3).
- IP3 causes depolarization of the gustatory epithelial cell and release of neurotransmitter.
- H+ in sour tastants flow into gustatory epithelial cells via H+ channels, causing depolarization and release of neurotransmitter.
- Tastants dissolve in saliva and contact the plasma membranes of the gustatory microvilli, which are the sites of taste transduction.
- This results in a depolarizing receptor potential, stimulating exocytosis of neurotransmitter, and triggers graded potentials and nerve impulses in the first-order sensory neurons that synapse with gustatory receptor cells.
Gustatory Epithelial Cells
- Individual gustatory epithelial cells respond to only one type of tastant.
- Each gustatory epithelial cell is “tuned” to detect a specific primary taste.
- Each taste bud contains gustatory epithelial cells for each type of tastant, allowing all primary tastes to be detected in all parts of the tongue.
- Different tastes arise from activation of different combinations of gustatory epithelial cells.
- The threshold for bitter substances, such as quinine, is lowest (high sensitivity) and may have a protective function.
- Complete adaptation to a specific taste can occur in 1–5 minutes of continuous stimulation.
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