Vestibular Perception and Gustation

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Vestibular Perception and Gustation

• Receptor Mechanisms
• Vestibular End Organs
• Vestibular Nuclei
• Motion Sickness
• Tastants
• Taste receptor Cells Transduction
• Gustatory Pathway

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Receptor Mechanisms of Vestibular System

• 3 semicircular canals in inner ear (temporal
  bone) - rotation
• Connected at ends to utricle
• Responds to angular acceleration static
  position
• Saccule small fluid-filled sac below utricle
• respond to linear acceleration static position
• Ampulla
• Hair cells in enlarged region of each canal /
  embedded in gelatinous layer
• Located at right angles to detect rotational
  acceleration
• Otoliths
• Small bony crystals bind cilia above
  gelatinous layer
• Increase sensitivity to movement

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Vestibular End Organs

• Auditory end organ evolved from vestibular system
• Vestibular system evolved from Lateral-line
  system
• Found in fish amphibians
• Array of receptors along side of body
• Tiny hairs emerge
• Embedded in gelatinous columns (cupulae)

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Nerve Fibers of Vestibular System

• Nerve fibers (VS) enter brain stem
• Synapse in vestibular nuclei
• Outputs to motor nuclei of eye muscles, thalamus,
  cerebral cortex, etc.
• Cerebellum (some fibers bypass vestibular nuclei)

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Motion Sickness

• Low frequency movements
• Out of control of individual
• Most common when riding in boat, car, plane or
  roller coaster
• Sensory Conflict Theory
• Discrepancy between visual and vestibular
  information
• Preservation of life to avoid toxicity

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Taste Detection

• 5 basic tastes
• Salty
• Sweet
• Sour
• Bitter
• Umami
• Informed by odor detection
• Ability to detect tastes at birth
• salty develops in first few months

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Specialized Taste Receptors

• Papillae
• Taste buds line sides (1 or more)
• 50-150 cells per taste bud
• Detection of all tastes over the tongue
• 3 kinds of papillae
• Fungiform (most numerous)
• Single-couple taste buds
• Circumvallate
• Multiple taste buds
• Foliate
• Multiple taste buds

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Salty

• Na channels transport sodium
• Block Na inhibits salt taste
• Facilitating Na flux enhances salt taste
• Na depolarizes taste cells
• Release NT translated as salty taste

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Sour

• Organic / Inorganic compounds
• Release H ion
• H ion blocks K channels
• Blockage of passive flux of K
• K Build-up leads to depolarization
• NT release translated as acidic taste

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Sweet

• Involves G protein / 2nd messenger system
• T1R and T2R
• 2 members of T1R family (T1R2 and T1R3
  heterodimerize) combine to function as sweet
  receptor
• ? subunit identified (gustducin)
• Multiple sweet tastes

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Bitter

• Multiple receptors for bitter
• Members of T2R family G-protein-coupled receptors
• Discrimination of different bitter tastes
• Phenylthiocarbamide (PTC), 6-n-propylthiouracil(P
  ROP) not detected by some people
• recessive trait
• fewest taste buds (non-tasters)

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Umami

• Meaty, savory flavor
• Glutamate metabotropic-like receptor
• MSG
• T1R1 and T1R3 receptors
• Respond to 20 amino acids

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Gustatory Pathway

• Taste receptor cells
• Facial
• Glossopharyngeal
• Vagus
• Brainstem nuclei
• Thalamus
• Cerebral cortex

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Take Home Message

• Receptor Mechanisms
• Vestibular End Organs
• Vestibular Nuclei
• Motion Sickness
• Tastants
• Taste receptor Cells Transduction
• Gustatory Pathway