WHAT IS CALLED NEURONS?
Neurons are cells specialized for communicating information, the basic building blocks of the nervous system. They consist of three basic parts,
1. A cell body
2. An axon
3. One or more dendrites
Dendrites carry information toward the cell body. Axon carries information away from it. Neurons are one way channels of communication. Information usually moves from dendrites or the cell body toward the axon and then outward along its structure.
In many neurons, the axon is covered by a sheath of fatty material known as myelin. The myelin sheath is interrupted by small gaps. Both the sheath and gaps in it play an important role in the neuron's ability to transmit information. The myelin sheath is produced by another basic set of building blocks within the nervous system called, glial cells (cells in the nervous system that surrounded, supported, and protect neurons). Glial cells form the myelin sheath around the axons and perform basic housekeeping chores, such as cleaning up cellular debris. The axons divide into several small branches, which are round structures known as axon terminals (structures at the end of axons that contain transmitter substances). Axon terminals do not touch other cells (other neurons, muscle cells, or gland cells). The region at which the axon terminals of a neuron closely approach other cells is known as the synapse.
FUNCTIONS OF NEURONS
1. Graded potential : A basic type of signal within neurons that results from external physical stimulation of the dendrite or cells in the body. An important feature of graded potentials is that their magnitude varies in proportion to the size of the stimulus that produced it, thus a loud sound or bright light produces graded potentials of greater magnitude than a softer sound or dim light. Because graded potentials tend to weaken quickly, they typically convey incoming information over short distances, usually along the dendrite toward the neuron's cell body.
2. Action potential : A rapidly moving wave of depolarization (shift in electrical potential) that travels along the cell membrane of a neuron. This disturbance along the membrane communicates information within the neuron. The action potential is the most basic signal in the nervous system. Axon terminals are many structures known as synaptic vesicles (structure in the axon terminals that contain various neurotransmitters). The arrival of the action potential causes these vesicles to approach the cell membrane, where they fuse with the membrane and then empty their contents into the synapse, the chemical thus released known as neurotransmitters. Neurotransmitters travel across the tiny synaptic gap until they reach specialized receptor sites in the membrane of the other cell. These receptors are complex protein molecules. Specific neurotransmitters can deliver signals only at certain locations on cell membranes, thereby introducing precision into the nervous system's complex communication system. Neurotransmitters either produce their effects directly, or function indirectly through the interaction of the neurotransmitter and its receptor with other substances. Neurotransmitters produce one of two effects. If their effects are excitatory in nature, they make it more likely for the neuron they reach to fire. If, instead, their effects are inhibitory, they make it less likely that the neuron will fire.
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