When the action potential occurs in the first segment of the axon, it quickly creates a similar change in the next segment, which then stimulates the next segment, and so forth as the positive electrical impulse continues all the way down to the end of the axon. The electrical charge moves down the axon from segment to segment, in a set of small jumps, moving from node to node. Each of these gaps is a node of Ranvier The break in the myelin sheath of a nerve fiber. Once the action potential occurs, the number of positive ions exceeds the number of negative ions in this segment, and the segment temporarily becomes positively charged.Īs you can see in Figure 3.4 "The Myelin Sheath and the Nodes of Ranvier", the axon is segmented by a series of breaks between the sausage-like segments of the myelin sheath. This change in electrical charge that occurs in a neuron when a nerve impulse is transmitted is known as the action potential A change in electrical charge that occurs in a neuron when a nerve impulse is transmitted. When the segment of the axon that is closest to the cell body is stimulated by an electrical signal from the dendrites, and if this electrical signal is strong enough that it passes a certain level or threshold, the cell membrane in this first segment opens its gates, allowing positively charged sodium ions that were previously kept out to enter. Normally, the axon remains in the resting potential A state in which the interior of the neuron contains a greater number of negatively charged ions than does the area outside the cell., a state in which the interior of the neuron contains a greater number of negatively charged ions than does the area outside the cell. The electrical signal moves through the neuron as a result of changes in the electrical charge of the axon. This video clip shows a model of the electrochemical action of the neuron and neurotransmitters. Video Clip: The Electrochemical Action of the Neuron (click to see video) Axons branch out toward their ends, and at the tip of each branch is a terminal button. is a layer of fatty tissue surrounding the axon of a neuron that both acts as an insulator and allows faster transmission of the electrical signal. The myelin sheath A layer of fatty tissue surrounding the axon of a neuron that acts as an insulator and allows faster transmission of the electrical signal. To improve the speed of their communication, and to keep their electrical charges from shorting out with other neurons, axons are often surrounded by a myelin sheath. The axons are also specialized, and some, such as those that send messages from the spinal cord to the muscles in the hands or feet, may be very long-even up to several feet in length. Some neurons have hundreds or even thousands of dendrites, and these dendrites may themselves be branched to allow the cell to receive information from thousands of other cells. As you can see in Figure 3.2 "Components of the Neuron", neurons are made up of three major parts: a cell body, or soma The part of the neuron that contains the nucleus of the cell and that keeps the cell alive., which contains the nucleus of the cell and keeps the cell alive a branching treelike fiber known as the dendrite The part of the neuron that collects information from other cells and sends the information to the soma., which collects information from other cells and sends the information to the soma and a long, segmented fiber known as the axon The part of the neuron that transmits information away from the cell body toward other neurons., which transmits information away from the cell body toward other neurons or to the muscles and glands. is a cell in the nervous system whose function it is to receive and transmit information. A neuron One of the more than 100 billion cells in the nervous system. The nervous system is composed of more than 100 billion cells known as neurons. List three of the major neurotransmitters and describe their functions.Draw a diagram of the pathways of communication within and between neurons. Describe the structure and functions of the neuron.
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