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Central Nervous System
The central nervous system is responsible for processing all the information within the body. This information includes motor, sensory and cognitive data. In order to accomplish this mission, the system consists of two kinds of specialized cells: glia and neurons. Glia cells provide support and structure functions. Neurons, like a computer's central processing unit (CPU), represent the processing unit of the central nervous system.
Neurons
Neurons are tasked with processing information. They receive information from other neurons as input, process that information and then send the new information to other neurons as output. Each neuron is connected to between 5,000 and 200,000 other neurons, creating a neural network. While there are as many as 10,000 specific types of neurons in the brain, there are three general kinds: motor neurons, sensory neurons and interneurons. Interneurons act like a middle-man, conveying information between different types of neurons.
Structure of Neurons
Most neurons have four primary parts. The cell body, or soma, serves as the processor. Dendrites extend from the soma like tree branches. Information flows into the soma through these dentrites. Each neuron has one axon, through which information flows out of the soma. Finally, there is an axon terminal at the end of the cell's axon. This terminal contains a neurotransmitter.
Synapses
Synapses represent the connections between individual neurons. These structures function like an information bridge between neurons. Signals generated in a neuron's soma are transmitted across these connections, enabling neurons to communicate with each other in a highly efficient manner. There are two types of synapses: electrical and chemical.
Electrical Synapses
Electrical synapses form a physical connection between the dendrites of neurons. The electrical signal is able to flow through these connections, called gap junctions. The speed of these electrical signals is very fast, as much as 500 feet per second. This speed allows the neurons of a neural network to synchronize their actions. For example, it allows a group of neurons to release hormones in a coordinated burst.
Chemical Synapses
Chemical synapses occur between axons and dendrites. In this case, the two neurons are separated by a synoptic cleft, which is filled with extracellular fluid. Though the gap is small, it creates a physical barrier that the electric signal cannot cross. Here, the neurotransmitter completes the circuit by sending a chemical signal across the synapse to a receptor on the other neuron's dendrite. Hence, the neurotransmitter converts the electrical signal that flowed down the axon to a chemical signal. The receptor converts the chemical signal back into an electrical signal that then flows up the dendrite of the receiving neuron.