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Answer:
Neurons (also called neurones or nerve cells) are the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between.
Explanation:
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Answer:
When you stub your toe, how do you know it hurts? Thousands of tiny nerve cells send a message up to your brain. The brain interprets the incoming message as pain, and you become aware that your toe is hurting. The nerve cells are called neurons. Each neuron has a cell body with a nucleus. chromosomes, and DNA. However, neurons have the unique ability to communicate with each other. The neurons located outside the brain and spinal cord make up the peripheral nervous system.
The shape and size of a neuron depend on its function and location in the body. Some neurons are sensory neurons. They carry messages to the brain. Others are motor neurons, sending messages from the brain and spinal cord to the muscles. Neurons can live for a long time, longer than most cells. However, most neurons that die are not replaced.
The dendrite receives the electrical impulse, or message, from another neuron. The dendrite passes that message to the cell body. The cell body passes the message to the axon, which sends the impulse on the next neuron. Although a neuron usually has only one axon, it can have many dendrites. Some nerve cells have as many as 10,000 dendrites. The nerve fibers in your body are actually bundles of axons and dendrites from many neurons.
Between each neuron is a little gap called a synapse. As the electrical impulse arrives at the synapse, the electricity causes chemicals called neurotransmitters to be released. These chemicals cross the synapse and carry the message on to the next sensory neuron, sometimes as fast as 120 m per second. This impulse could travel the length of a football field in less than one second. When the sensation reaches your brain, the brain interprets it and lets your finger know that it is experiencing pressure. By the time you feel the pressure, the message has already traveled to the brain, been interpreted, and traveled back through the motor neurons to tell your finger to move. The amount of electricity involved in sending the nerve message to the brain is about one-tenth of a volt.
Some axons have a protective covering called a myelin sheath. This extra insulation helps the neurons send messages faster. Because myelin sheaths are white, areas of the nervous system with myelin sheaths called white matter. Areas of the central nervous system where the neurons do not have myelin sheaths are sometimes called gray matter.
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