This document discusses taste and smell (gustatory and olfactory) pathways. It describes how smell provides awareness of pleasurable sensations and helps identify toxic foods or chemicals. Olfaction is unique in that it reaches the cerebral cortex without relaying through the thalamus. Clinical manifestations of olfactory lesions can include loss or reduction of smell, distortions or illusions of smell, and hallucinations or delusions caused by temporal lobe or psychiatric disorders. Bilateral anosmia is a common complaint that patients believe causes a loss of taste as well.

1. Taste and Smell
Gustatory / Olfactory pathways
Daniel Vela-Duarte, MD
Department of Neurology
Loyola University Medical Center
July 2012

2. Smell.
 It's a warning system to identify
potentially toxic food or noxious
chemicals.
 Contributes to various life
qualities, provides awareness of
many pleasurable
sensations, including
appreciationof certain foods and
beverages and other pleasures.

4. The trigeminal system also participates in chemesthesis through
undifferentiated receptors in the nasal mucosa. These receptors have
little discriminatory ability but a great sensitivity to all irritant stimuli.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

6.  Olfactory impulses reach
the cerebral cortex without
relay through the thalamus.
 Olfaction is unique among
sensory systems. From the
prepiriform cortex fibers
project to the neighboring
entorhinal cortex and the
medial dorsal nucleus of
the thalamus.
 The amygdaloid nuclei
connect with the
hypothalamus and septal
nuclei.

8. Clinical Manifestations of
Olfactory Lesions
 Quantitative abnormalities:
 loss or reduction of the sense of smell
(anosmia, hyposmia) or, rarely, increased olfactory
acuity (hyperosmia)
 Qualitative abnormalities:
 distortions or illusions of smell (dysosmia or
parosmia)
 Olfactory hallucinations and delusions caused by
temporal lobe disorders or psychiatric disease
 Higher-order loss of olfactory discrimination (olfactory
agnosia)

9. Clinical presentation
 Bilateral anosmia is a common complaint, and
the patient is usually convinced that the sense of
taste has been lost as well (ageusia).
 Parosmia may also be a troublesome symptom
in middle-aged and elderly persons with a
depressive illness, who may report that every
article of food has an extremely unpleasant odor
(cacosmia). Sensations of disagreeable taste
are often associated cacogeusia).

10. Differential diagnosis
Adams and Victor's Principles of Neurology. 9th Ed.

11. Taste
 Older notions of a “tongue map,” which implied
the existence of specific areas subserving one or
another taste, are incorrect. Any one taste bud is
capable of responding to a number of sapid
substances, but it is always preferentially
sensitive to one type of stimulus.