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. motor neurones - which collectively make up efferent nerves - causing muscles to contract, or innervating glandsĪ sensory neurone typically has its cell body off to one side of the main tubular process that carries nerve impulses.interneurones which pass on impulses from sensory neurones, up the spinal cord to the brain, or directly on to :.sensory neurones - which collectively make up afferent nerves - inputs to the nervous system, and.Within the peripheral nervous system there are 3 main types of neurone: Schwann cells and oligodendrocytes ( see below) are examples of neuroglial cells. The more numerous neuroglial cells perform a support function. There are many types/shapes of neurone, and it is helpful to consider sensory, relay/intermediate and motor neurones, especially in the context of a reflex action. Others pass on impulses to other neurones and then to muscles or glands. Some neurones generate impulses as a result of detecting a stimulus. Dendrites bring impulses in, and the axon takes impulses away from the cell body. Neurones have thin extensions - also known as nerve fibres - bringing impulses into and away from the cell. axon also contains 10nm diameter neurofilaments composed of polypeptide chains related to keratin (structural support).microtubules along axon (transport of proteins etc from cell body).prominent Nissl granules/bodies - endoplasmic reticulum with rosettes of free ribosomes - in cell body only (protein synthesis).mitochondria in cell body and terminal bulbs (aerobic respiration).Structures not shown on the diagram above (and functions) : They provide a pathway for the flow of information from one part of the body to another, as well as the processing of that information, possibly preventing information from proceeding. Some neurones can be quite long - the length of a limb. Nerve cells - neurones or neurons - have all the normal features of body cells: a cell membrane enclosing the cytoplasm and a nucleus, but there are some modifications related to their specific function - the passage of nervous impulses.
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