![]() They can be measured using sensitive electrical apparatus, and can be generated using electrical stimulation, but they move at a different (much slower) speed. Nervous impulses are electrochemical in nature, and the electical potential (voltage) concerned is generally quite low - generally (tens of) millivolts. Nervous impulses are different from electrical signals carried along wires, such as from a microphone or to a loudspeaker. ![]() In fact within the brain there are distinct areas of so-called grey matter: mostly cell bodies of neurones, and white matter: myelinated neurones.ĭon't use the term "messages" or "signals" when referring to nerve impulses This sort of neurone is much more efficient than an unmyelinated one and it transmits impulses at a greater speed - see below.Īccessory cells called oligodendrocytes perform a similar function in neurones of the central nervous system. These cells - Schwann cells - present several layers of membrane, containing a white fatty material called myelin on the outside of the axon membrane. Some neurones (especially longer ones in the peripheral nervous system of vertebrates) have an outer coating consisting of a number of cells wound around their axons. The cytoplasm inside the axon (axoplasm) usually differs chemically from the liquid outside (extracellular fluid). Some of these may function as pumps for the active transport of ions across the membrane, or as ion channels, permitting the passage of specific ions by diffusion. It has a cylindrical membrane consisting of a phospholipid bilayer, with a number of proteins embedded in it. In some cases the axon can be quite long. They generally do not have myelin sheaths. They are smaller, as the axon is quite short. Interneurones - also known as relay neurones - are cells that pass on impulses within the central nervous system. See below for more information about the myelin sheath and nodes of Ranvier. The (usually much longer) section carrying impulses from the receptor (sometimes known as a nerve ending) is called the dendron, and the (usually much shorter) section leading away is called the axon.
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