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Nervous System

An organ system that coordinates the activities of muscles, monitors organs, constructs and processes data received from the senses and initiates actions.

PubMed Health Glossary
(Source: Wiktionary)

Drawing of the outline of a body showing the nervous system with descriptions of each of the four types of nerves. Cranial nerves go from your brain to your eyes, mouth, ears, and other parts of your head. Central nerves are in your brain and spinal cord. Peripheral nerves go from your spinal cord to your arms, hands, legs, and feet. Autonomic nerves go from your spinal cord to your lungs, heart, stomach, intestines, bladder, and sex organs. Click to enlarge

The 4 main parts of the nervous system National Institutes of Health

About the Nervous System

The nervous system is made up of all the nerve cells in your body. It is through the nervous system that we communicate with the outside world and, at the same time, many mechanisms inside our body are controlled. The nervous system takes in information through our senses, processes the information and triggers reactions, such as making your muscles move or causing you to feel pain. For example, if you touch a hot plate, you reflexively pull back your hand and your nerves simultaneously send pain signals to your brain. Metabolic processes are also controlled by the nervous system.

There are many billions of nerve cells, also called neurons, in the nervous system. The brain alone has about 100 billion neurons in it. Each neuron has a cell body and various extensions. The shorter extensions (called dendrites) act like antennae: they receive signals from, for example, other neurons and pass them on to the cell body. The signals are then passed on via a long extension (the axon), which can be up to a meter long... Read more about the Nervous System

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Terms to know

Autonomic Nervous System (Involuntary Nervous System)
The part of the nervous system that controls muscles of internal organs (such as the heart) and glands. One part of the autonomic nervous system helps the body rest, relax, and digest food and another part helps a person fight or take flight in an emergency.
Brain
The part of the central nervous system that is contained within the skull (cranium).
Central Nervous System
The brain and spinal cord. Also called CNS.
Cranial Nerves
Cranial nerves are nerves emerging directly from the brain, in contrast to spinal nerves (which emerge from various segments of the spinal cord). Cranial nerves exchange information between the brain and parts of the body, primarily to and from regions of the head and neck.
Enteric Nervous System (Intrinsic Nervous System)
A mesh-like system of neurons that governs the function of the gastrointestinal system.
Nerves
A bundle of fibers that receives and sends messages between the body and the brain. The messages are sent by chemical and electrical changes in the cells that make up the nerves.
Neurons (Nerve Cells)
A type of cell that receives and sends messages from the body to the brain and back to the body. The messages are sent by a weak electrical current. Also called nerve cell.
Parasympathetic Nervous System
The part of the nervous system that slows the heart, dilates blood vessels, decreases pupil size, increases digestive juices, and relaxes muscles in the gastrointestinal tract.
Peripheral Nervous System
The nervous system outside of the brain and spinal cord.
Somatic Nervous System (Voluntary Nervous System)
The part of the peripheral nervous system that transmits signals from central nervous system to skeletal muscles, and from external stimuli thereby mediating sight, hearing and touch.
Spinal Cord
A column of nerve tissue that runs from the base of the skull down the back. It is surrounded by three protective membranes, and is enclosed within the vertebrae (back bones). The spinal cord and the brain make up the central nervous system, and spinal cord nerves carry most messages between the brain and the rest of the body.
Spinal Nerves
A spinal nerve carries signals between the spinal cord and the body. There are 31 pairs of spinal nerves, one on each side of the vertebral column.
Sympathetic Nervous System
The part of the nervous system that increases heart rate, blood pressure, breathing rate, and pupil size. It also causes blood vessels to narrow and decreases digestive juices.

Terms to know

Autonomic Nervous System (Involuntary Nervous System)
The part of the nervous system that controls muscles of internal organs (such as the heart) and glands. One p...
Brain
The part of the central nervous system that is contained within the skull (cranium)....
Central Nervous System
The brain and spinal cord. Also called CNS....
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