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Chapter 11. Smell & Taste

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A young boy was diagnosed with congenital anosmia, a rare disorder in which an individual is born without the ability to smell. Which parts of the nervous system might be defective in an individual with congenital anosmia to account for the inability to detect odors?

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A. Glossopharyngeal nerve, ventral posterior medial nucleus of the thalamus, and anterior insula-frontal operculum

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B. Nodose ganglion, nucleus of the tractus solitarius, and ventral posterior lateral nucleus of the thalamus

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C. Olfactory nerve, olfactory bulb, and anterior insula-frontal operculum

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D. Olfactory nerve, piriform cortex, and frontal cortex

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E. Trigeminal nerve, olfactory tubercle, and entorhinal cortex

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The correct answer is D. The olfactory nerve innervates mitral and tufted cells in the olfactory bulb; the axons of mitral and tufted cells pass through the lateral olfactory stria to terminate in five regions of the olfactory cortex (anterior olfactory nucleus, olfactory tubercle, piriform cortex, amygdala, and entorhinal cortex). From these regions, information travels directly to the frontal cortex or via the thalamus to the orbitofrontal cortex. The glossopharyngeal nerve, nodose ganglion, nucleus of the tractus solitarius, ventral posterior medial nucleus of the thalamus, and anterior insula-frontal operculum are components of the pathway mediating the sensation of taste (rules out A, B, and C). The trigeminal nerve terminals in the olfactory epithelium are activated by irritant stimulants (eg, peppermint) that initiates sneezing and other reflexes (rules out E).

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A 37-year-old female was diagnosed with multiple sclerosis. One of the potential consequences of this disorder is diminished taste sensitivity. Which three cranial nerves might be defective in an individual with diminished taste sensitivity?

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A. Trigeminal, facial, and vagal nerves

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B. Abducens, trigeminal, and glossopharyngeal nerves

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C. Trigeminal, trochlear, and facial

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D. Trochlear, glossopharyngeal, and vagal nerves

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E. Facial, glossopharyngeal, and vagal nerves

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The correct answer is E. Taste buds on the anterior two-thirds of the tongue relay information via the facial nerve, those on the posterior third of the tongue relay information via the glossopharyngeal nerve, and taste buds located elsewhere (eg, pharynx) relay information via the vagus nerve. Options A–D are ruled out because the trigeminal nerve mediates information about facial pain, and the trochlear nerves contains motor fibers controlling eye movement.

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A medical student was doing research in a laboratory that studied olfaction. She is intrigued by the fact that a simple sense ...

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