Book T of C
Chap T of C
A single Pacinian corpuscle
The cutaneous sense or sense of touch involves three different types of receptors. One-the basket cell -consists of neural fibers wrapped around the base of a hair cell. You can verify that a single basket cell, when stimulated, produces a detectable sensation. Find a single hair on your arm, carefully bend it without disturbing other hairs or pressing on your skin, and note the sensation. When the hair is bent by pressure, the neuron sends impulses to the brain.
What are basket cells? How can you stimulate one? What is a Pacinian corpuscle? What is a free nerve ending?
On hairless skin such as fingertips, a receptor called the Pacinian corpuscle senses physical pressure to the skin. It consists of a multi-layered bag surrounding a sensitive nerve ending. Pressure to the bag triggers a nerve impulse.
A third type of touch receptor is the free nerve ending. It is simply a nerve fiber in the skin. Free nerve endings are sensitive to any sort of distortion, from pressure to tissue damage. Free nerve endings are the most numerous of the cutaneous receptors.
Basket cells and Pacinian corpuscles are pressure receptors. Free nerve endings are pressure receptors and also temperature receptors. Pressure and temperature are the basic ingredients of the cutaneous sense.
What can a free nerve ending do that the other receptors cannot?
Your sense of touch operates over time. Your brain is sensitive to overall patterns of cutaneous input that may be quite complex. When you rub your fingertips (which are particularly rich in cutaneous receptors) over a surface like cloth, plastic, or wood, the distinct texture of the surface depends on activity from thousands of touch receptors firing in sequence and in combination. This is called active touch and is used, for example, in reading Braille.
How can the cutaneous sense become "educated"?
Braille is the system of writing for blind people invented by Louis Braille in 1824. Letters are represented by patterns of raised dots. Expert readers of Braille report that they interpret the touch sensations automatically (without any conscious effort) the same way expert readers of written words convert them into sounds without any conscious effort. The motor cortex of the brain changes in response to Braille reading, with areas devoted to touch sensations from fingertips growing larger.
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Copyright © 2007 Russ Dewey