Pain, muscle movement, the sensitive touch of a spouse, cold sensations, tickling and just about any essential organ function all depend on the nervous system. Two major divisions make up the complex nervous system that keeps our bodies functioning like finely tooled machines: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS is composed of the brain and spinal cord and the PNS includes nerves and concentrations of nerve cells called ganglia, along with virtually everything nerve-related except the brain and spinal cord.
The brain -- the "nerve center" of the nervous system and indeed the body -- has billions of cells that control basic functions such as hunger and consciousness in the brainstem to judgment and problem solving in the cerebrum. Areas of the brain also control vision, speech, memory and even recognition of smells [source: OSU Medical Center].
The brain can't control a sense like vision alone, however, and a nerve in your finger can't feel pain without your brain. The CNS and PNS work together to send signals back and forth so rapidly that you are not even aware that your nervous system is running in the background. For example, when you touch a hot burner, a pain signal runs through your nervous system to your brain, and a nerve signal runs back to the muscles of your hand telling you to remove it from the burner. This happens even more rapidly than you can say, "ouch," or any other expressive word. Your body is busy multitasking, too. Your nervous system can handle up to 1,000 nerve impulses each second [source: Stanford].
The PNS breaks down further into somatic nerves and autonomic nerves. Somatic nerves control muscles and gather information from sensory receptors, while the autonomic nerve system regulates internal organs. Even more specifically, autonomic nerves consist of parasympathetic nerves that are related to relaxation and sympathetic nerves, which regulate the "fight or flight response" [source: Farabee]. Within the brain, neurotransmitters are released from axons and move across synapses, or tiny gaps. These neurotransmitters might shut down or simulate certain nerve cells.
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