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The Nervous System Study Guide (page 2)

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Updated on Sep 22, 2011

From One to Many

Although some reflexes involve very few neurons, most of the complex and versatile behavior of vertebrate animals comes from the fact that neurons form many complex connections with other neurons. This complex webbing of many tiny cells reaches its zenith in the vertebrate brain where billions of neurons each make dozens of connections. Collections of individual neurons become what we call nerves. The vertebrate nervous system is the name we give to this complex networking of neurons into nerves. The vertebrate nervous system is divided into two major parts, the central nervous system and the peripheral nervous system.

The central nervous system consists of the brain and spinal cord (contained within the vertebral column or backbone). The brain is a highly specialized organ where neurons have grouped together into many specific areas, each with a specific function. The brain integrates all the signals in the nervous system and thus controls the body. It also acts as a data storage organ by learning and keeping memories. In the higher mammals it is also the seat of the conscious mind.

The peripheral nervous system consists of nerves that connect the central nervous system to the rest of the body. The peripheral nervous system has nerves that connect the brain to each part of the body, including sensory nerves that bring information to the central nervous system and motor nerves that carry signals away from the brain and to the muscles, glands, or organs. The sensory neurons are, in many cases, specialized and have become part of other organs whose function is to sense the internal and external environment. Examples of such organs would be the eyes, ears, touch receptors, and taste buds. The motor portion of the peripheral nervous system is again further divided into the somatic and autonomic nervous systems.

The somatic nervous system is concerned with motor functions. Its nerves make contact with skeletal muscle and are responsible for controlling movement of all kinds, from fine movements to walking and running.

The autonomic nervous system, also part of the peripheral nervous system, works mostly without our conscious control. It is often responsible for critical life functions such as breathing and heart rate. The autonomic nervous system has two divisions. Nerves from each of these divisions usually make contact with the same organs, but they often have opposite effects. The sympathetic division of the autonomic nervous system is responsible for the fight-or-flight response, so it prepares the body for high-energy, stressful situations. The parasympathetic division of the autonomic nervous system is responsible for rest and digest functions, so it tends to slow down the body.

More on Neurotransmitters

The electrical signal produced in the neuron that travels down the axon does not actually cross the tiny synaptic space between neurons (or their target organs). The nervous system relies upon chemical messengers called neurotransmitters to cross the gap. The use of neurotransmitters allows fine-tuning of the signal because different neurotransmitters can be used for different purposes or in different locations.

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