posted by cynthia rygalski .
are they found in central nervous system
are they found in peripheral nervous system
do they form a myelin sheath
do they increase the speed of propagation of nervous impulses
Thank you for using the Jiskha Homework Help Forum. Here is a site with the definition and yes, they are found iin the peripheral nervous system.
The basic structural unit of the nervous system, wheather central, motor or sensory is the neuron.....
most neurons are unable to survive for long; they require the nutritional support provided by companion Neurogleal cells. More than half the volume of the human nervous system is composed of supporting neurogleal cells. Two of the most important kinds of supporting neurons are the Schwann cells and Ogleodendrocytes which envelop the axon of many neurons with a sheath of fatty material called Mylen, which acts as an electrical insulator. Schwann cells produce mylin in the P.N.S. while ogleodendrocytes produce mylin in the C.N.S. during development these cells wrap themselves aroung each axon several times to form a Mylin Sheath....
the mylin sheath is interupted at intervals leaving un insulated gaps called nodes of Ranvier where the axon is in direct contact with the surounding fluid. The nerve impulse jumps from node to node, speeding its travel down the axon.
Excerpted from; The Living World by George B. Johnson, 3rd edition, 2003, McGraw Hill.
In my oppinion the most poorly writen bioligy text I have read. Luckely the parts on Schwann cells et.al. was ok.
Why is schwann cells important?