Olfactory Organs

The olfactory organs, which contain the olfactory receptors, also include epithelial supporting cells. These organs appear as yellowish brown masses surrounded by pinkish mucous membrane. They cover the upper parts ears

— Nerve fibers within the olfactory bulb

Olfactory tract

— Nerve fibers within the olfactory bulb

Olfactory tract

Figure

Blood Vessels Figures

Olfactory area of nasal cavity

Superior nasal concha

Nasal cavity

Olfactory area of nasal cavity

Superior nasal concha

Nasal cavity

Figure

(a) Columnar epithelial cells support olfactory receptor cells, which have cilia at their distal ends. (b) The olfactory area is associated with the superior nasal concha.

The Olfactory Area

of the nasal cavity, the superior nasal conchae, and a portion of the nasal septum (fig. 12.6).

The olfactory receptor cells are bipolar neurons surrounded by columnar epithelial cells. These neurons have knobs at the distal ends of their dendrites covered with hairlike cilia. The cilia project into the nasal cavity and are the sensitive portions of the receptors (fig. 12.7). A person's 12 million olfactory receptor cells each have ten to twenty cilia.

Chemicals that stimulate olfactory receptors, called odorant molecules, enter the nasal cavity as gases, but they must dissolve at least partially in the watery fluids that surround the cilia before they can be detected. Odorant molecules bind to about 500 different types of olfactory receptors that are part of the cell membranes on the olfactory receptor cells, depolarizing them and thereby generating nerve impulses.

The expert nose of the bloodhound is due to its 4 billion olfactory cells. A bloodhound's olfactory epithelium spread out covers 59 square inches, compared to 1 1/2 square inches in a human. Still, the human sense of smell is nothing to sneeze at—people can detect one molecule of green pepper smell in a gaseous sea of 3 trillion other molecules. Our 12 million olfactory receptor cells and their 500 receptor types allow us to discern some 10,000 scents. But, without air, we cannot smell, as early astronauts could attest; eating through tubes, early astronauts could not smell their food. Currently, astronauts eat in pressurized cabins, unaffected by the vacuum in which they travel.

Sensory receptors are not the same as membrane receptors. Sensory receptors may be as small as individual cells or as large as complex organs such as the eye or ear. They respond to sensory stimuli. Membrane receptors are molecules such as proteins and glycoproteins located on the cell membranes. They allow cells, such as neurons and olfactory receptor cells, to respond to specific molecules. Thus, the olfactory receptors are cells that respond to chemical stimuli, but they depend on cell membrane receptors to do so.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment