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Physical
Nervous System
The nervous system is the network of neurons and nerves that carries signals around an animal's body to sense changes and coordinate its actions.
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The idea
The nervous system is the part of an animal's body that coordinates its actions and senses by sending signals to and from different body parts. It detects changes in the environment that affect the body and works together with the endocrine system, which uses hormones, to respond to them.
In vertebrates, which are animals with backbones, the nervous system has two main parts. The central nervous system (CNS) is made up of the brain and spinal cord. The peripheral nervous system (PNS) consists mainly of nerves, bundles of long fibers called axons that connect the CNS to every other part of the body. Motor nerves carry signals from the brain outward, and sensory nerves carry information from the body back to the CNS. The PNS has a somatic part and an autonomic part. In the autonomic part, the sympathetic system mobilizes energy in emergencies. The parasympathetic system is active when the body is relaxed, and the enteric system controls the gut.
The basic cell of the nervous system is the neuron. Neurons send fast electrochemical impulses along their axons and pass signals to other cells at junctions called synapses, often by releasing chemicals called neurotransmitters. Connected neurons form circuits and networks that shape how an animal perceives the world and behaves. Glial cells give the neurons structural and metabolic support. Nervous systems range from a few hundred cells in the simplest worms to around 300 billion cells in African elephants.
Check yourself
Question 1 of 2
Which cells give neurons structural and metabolic support?
Composition
what it's made of
- Central nervous system — The brain and spinal cord.
- Peripheral nervous system — The nerves that connect the central nervous system to the rest of the body.
- Neurons — Cells that send rapid electrochemical signals to other cells.
- Synapses — Junctions where a neuron passes its signal to another cell, often through neurotransmitters.
- Glial cells — Cells that give neurons structural and metabolic support.
Connection
how it relates
Under Human Body
Change
how and why it evolves
- Past
- Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. Later, animal nervous systems ranged from the simple nerve nets of jellyfish to systems with a brain and a central cord.
- Now
- Neuroscience studies how the nervous system works, and the medical specialty of neurology looks for ways to prevent or treat its disorders, such as multiple sclerosis.
- Next
- Research on neurons and neural circuits will likely lead to better treatments for nerve damage and disease. How networks of neurons produce perception is still only partly understood.