BIO 205 Chapter 17 Lecture Notes

CHAPTER 17

LECTURE OUTLINE

I. INTRODUCTION
A. Receptors for the special senses—smell, taste, vision, hearing, and equilibrium—are housed
in complex sensory organs.
B. Ophthalmology is the science that deals with the eye and its disorders.
C. Otorhinolaryngology is the science that deals with disorders of the ear, nose and throat.


II. OLFACTION: SENSE OF SMELL
A. Both smell and taste are chemical senses.
B. Anatomy of olfactory receptors
1. The receptors for olfaction, which are bipolar neurons, are in the nasal epithelium in
the superior portion of the nasal cavity (Figure 17.1a,b).
a. They are first-order neurons of the olfactory pathway.
b. olfactory hairs are the parts that respond to the olfactory stimulus
2. Supporting cells are epithelial cells of the mucous membrane lining the nose.
3. Basal stem cells produce new olfactory receptors.
C. Physiology of Olfaction
1. Genetic evidence suggests there are hundreds of primary scents.
2. In olfactory reception, a generator potential develops and, through a transduction
process, triggers one or more nerve impulses (Figure 17.2)
D. Odor Thresholds and Adaptation
1. Adaptation to odors occurs quickly, and the threshold of smell is low: only a few
molecules of certain substances need be present in air to be smelled.
E. The Olfactory Pathway
1. Olfactory receptors convey nerve impulses to olfactory nerves, olfactory bulbs,
olfactory tracts, and the cerebral cortex and limbic system (17.1d).
2. Primary olfactory area (17.1d)
3. Orbitofrontal cortex (Figure 14.15)
4. Clinical Connection: Hyposmia, a reduced ability to smell, affects half of those over
age 65 and 75% of those over 80. It can be caused by neurological changes, drugs, or
the effects of smoking

, III. GUSTATION: SENSE OF TASTE
A. Taste is a chemical sense.
1. To be detected, molecules must be dissolved.
2. Taste stimuli classes include sour, sweet, bitter, meaty, and salty.
3. Other “tastes” are a combination of the five primary taste sensations plus olfaction.
B. Anatomy of Taste Buds and Papillae
1. The receptors for gustation—the gustatory receptor cells—are located in taste buds
(Figure 17.3).
2. Taste buds consist of supporting cells, gustatory receptor cells, and basal cells (Figure
17.3c).
3. Taste buds are found on the margins of papillae.
4. The papillae include circumvallate, fungiform, and foliate papillae.
a. Filiform papilla cover the tongue but act as tactile receptors instead of taste
receptors
C. Physiology of Gustation
1. When a tastant is dissolved in saliva it can make contact with the plasma membrane
of gustatory receptor cells.
2. Receptor potentials developed in gustatory hairs cause the release of neurotransmitter
that gives rise to nerve impulses.
a. Receptor potentials develop in response to chemicals in the food (i.e. sodium
or hydrogen)
D. Taste Thresholds and Adaptation
1. Taste thresholds vary for each of the primary tastes. The lowest threshold is bitter,
followed by sour, and then the other primary tastes.
2. Adaptation to taste occurs quickly.
E. The Gustatory Pathway
1. Gustatory receptor cells convey nerve impulses to cranial nerves V, VII, IX, and S,
the medulla, the thalamus, and the parietal lobe of the cerebral cortex (Figure 17.3e).
2. Clinical Connection: Taste aversion causes individuals to avoid foods that upset
their digestive system. Because cancer treatments cause nausea, cancer patients may
lose their appetites because they develop taste aversion for most food.


IV. VISION
A. Introduction