Apple #38: The Tongue

TONGUE

I have a sore spot on my tongue, where my teeth have been rubbing against it. This made me think, I know the tongue is a muscle, but is it more complicated than that? And of course, the answer is yes.

• The tongue is the organ of the sense of taste.

• The tongue is also crucial in the activities of chewing and swallowing, breathing, and speaking.

• It is a system of muscles with a mucous membrane on the outside.

• On that mucous membrane, on top of the tongue are lots of follicles, or pores. In each follicle, lots of tiny nodules of tissue are grouped under a sheath of skin. The technical term for this sheath of nodules is "papilla" or, basically, a bump. These bumps essentially contain your taste buds.

• Each of these little nodules has tiny arteries and veins branching into them, as well as numerous nerve cells of different kinds. Some of those nerve cells specifically sense taste. These are called "gustatory cells." Other nerve cells sense pressure and pain, hot and cold.

• The tasting nerve cells sense bitter, sweet, salty, and bitter. People now say that there is also a fifth taste, called umami.

• It's hard for people to describe what umami means, exactly. The Japanese say it means "deliciousness." Others say it is a robust, meaty, or savory taste.

• As table salt activates your salt-sensing nerves, the chemical glutamate activates your umami cells. Mushrooms have a lot of glutamate in them, which accounts for their savory, sometimes meaty flavor. Monosodium glutamate also especially makes you taste the umami. People also say that aged cheese, anchovies, and other foods with complex, rich flavors, are associated with umami.

• In the past, people drew a "taste map," depicting the tongue as especially sensing particular tastes in particular areas of the tongue. For example, people used to say that you sensed sweetness only at the very tip. In fact, the nerve cells that sense different types of taste are scattered all across the tongue, not grouped in special areas. Scientists know this because if you block half the tongue from sensing anything, people still report being able to sense all five tastes.

• By the way, the word flavor refers to the combination of one or more of the five tastes along with smells, the texture, the temperature, and the spiciness of what you're eating.

Sources
My copy of Gray's Anatomy, dated 1977. There's also a Gray's Anatomy online, but I didn't get very good results searching that.
By the way, the TV show is spelled GrEy's Anatomy.

Tongue entry from the Columbia Electronic Encyclopedia, accessed through InfoPlease
"Homing in on a Receptor for the Fifth Taste," press release from the Howard Hughes Medical Institute, February 25, 2002
Umami - the Fifth Taste, MushroomCouncil.org
Taste entry from Wikipedia (Note: the Columbia Encyclopedia's entry on "taste" is outdated and now incorrect)
UConn Taste and Smell Center General Information
Lecture 15 - Organ Systems: Digestive, from Biology 441/541 Histology, Fall 2004 course taught by Dr. David L. Swanson, University of South Dakota
Image of taste cells from pathologyoutlines.com/_oralcavity.html