Psychology 304:
Brain and Behaviour
Lecture 28
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The Vestibular System and the Chemical Senses
1. What are the biological mechanisms associated with
vestibular perception?
2. What are the biological mechanisms associated with
taste?
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By the end of today’s class, you should be able to:
1. describe the structural and functional features of the
receptor organs of the vestibular and gustatory
systems.
2. review the pathways by which vestibular and gustatory
information is transmitted from receptors to the brain.
3. describe the vestibulo-ocular reflex.
4. identify the locations of the primary cortex and
secondary cortex for the gustatory system.
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What are the biological mechanisms associated with
vestibular perception?
• The functions of the vestibular system include the
detection of head movement and, thus, the maintenance
of balance.
• The vestibular system has two components: the
semicircular canals and the vestibular sacs.
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Semicircular Canals and Vestibular Sacs
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• Vestibular receptors are found in enlargements on the
semicircular canals called ampullae. These receptors
respond to angular (i.e., rotational) acceleration of the
head.
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Receptor Cells in the Semicircular Canals
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• Vestibular receptors are also found in the vestibular
sacs. These receptors respond to linear acceleration of
the head and tilting of the head.
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Otoconia
(otoliths):
Crystals of
calcium
carbonate
Receptor Cells in the Vestibular Sacs
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• When hair cells in the semicircular canals and vestibular
sacs are stimulated, action potentials are triggered that
pass down axons of the vestibular nerve—a branch of
cranial nerve VIII.
• Vestibular information is relayed from the vestibular
nerve to the vestibular nuclei in the medulla and the
cerebellum. The vestibular nuclei relay the information to
the pons, the thalamus, the motor nuclei of the eye
muscles, and the temporal cortex.
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TVOR Loop: Vestibulo-Ocular
Reflex Loop
VN: Vestibular nuclei
MN: Motor neurons associated
with the oculomotor, trochlear,
and abducens cranial nerves.
Vestibulo-Ocular Reflex
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What are the biological mechanisms associated with
taste?
• The function of taste (i.e., the gustatory system) is to
monitor the chemical content of the environment. The
gustatory system detects chemicals that dissolve in
saliva in the oral cavity.
• The receptors for taste are found on the tongue and in
parts of the oral cavity.
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• The surface of the tongue is characterized by papillae,
each of which contains numerous taste buds.
• Each taste bud contains 50-150 receptor cells which
extend cilia through a taste pore on the surface of the
taste bud.
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Cilia
Papillae, Taste Buds, Taste Receptor Cells, and Cilia
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Papillae and Taste Buds
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• Tastants stimulate receptor molecules on the surface of
the cilia.
• Each receptor cell detects 1 of 5 tastes: sweet, salty,
sour, bitter, and umami.
• When the receptor cells are stimulated by tastants,
action potentials are triggered that pass down axons of
the facial (front of tongue), glossopharyngeal (back of
tongue) and vagus (back of oral cavity) nerves—cranial
nerves VII, IX, and X, respectively.
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• Taste information is relayed from the cranial nerves to
the solitary nuclei of the medulla and the ventral posterior
(medial) nuclei of the thalamus.
• The majority of thalamic neurons that receive taste
information subsequently project the information to
the primary gustatory cortex in the somatosensory
cortex. Thereafter, information is projected to the
secondary gustatory cortex in the lateral fissure.
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Pathway of the Gustatory System
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The Vestibular System and the Chemical Senses
1. What are the biological mechanisms associated with
vestibular perception?
2. What are the biological mechanisms associated with
taste?
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