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If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. Although terminology seems to indicate otherwise, there is really only one nervous system in the body. Although each subdivision of the system is also called a "nervous system," all of these smaller systems belong to the single, highly integrated nervous system. Each subdivision has structural and functional characteristics that distinguish it from the others. The nervous system as a whole is divided into two subdivisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The Central Nervous SystemThe brain and spinal cord are the organs of the central nervous system. Because they are so vitally important, the brain and spinal cord, located in the dorsal body cavity, are encased in bone for protection. The brain is in the cranial vault, and the spinal cord is in the vertebral canal of the vertebral column. Although considered to be two separate organs, the brain and spinal cord are continuous at the foramen magnum. The Peripheral Nervous SystemThe organs of the peripheral nervous system are the nerves and ganglia. Nerves are bundles of nerve fibers, much like muscles are bundles of muscle fibers. Cranial nerves and spinal nerves extend from the CNS to peripheral organs such as muscles and glands. Ganglia are collections, or small knots, of nerve cell bodies outside the CNS. The peripheral nervous system is further subdivided into an afferent (sensory) division and an efferent (motor) division. The afferent or sensory division transmits impulses from peripheral organs to the CNS. The efferent or motor division transmits impulses from the CNS out to the peripheral organs to cause an effect or action. Finally, the efferent or motor division is again subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system, also called the somatomotor or somatic efferent nervous system, supplies motor impulses to the skeletal muscles. Because these nerves permit conscious control of the skeletal muscles, it is sometimes called the voluntary nervous system. The autonomic nervous system, also called the visceral efferent nervous system, supplies motor impulses to cardiac muscle, to smooth muscle, and to glandular epithelium. It is further subdivided into sympathetic and parasympathetic divisions. Because the autonomic nervous system regulates involuntary or automatic functions, it is called the involuntary nervous system. Your nervous system is your body’s command center. Originating from your brain, it controls your movements, thoughts and automatic responses to the world around you. It also controls other body systems and processes, such as digestion, breathing and sexual development (puberty). Diseases, accidents, toxins and the natural aging process can damage your nervous system.
OverviewWhat is the nervous system?Your nervous system guides almost everything you do, think, say or feel. It controls complicated processes like movement, thought and memory. It also plays an essential role in the things your body does without thinking, such as breathing, blushing and blinking. Your nervous system affects every aspect of your health, including your:
This complex system is the command center for your body. It regulates your body’s systems and allows you to experience your environment. A vast network of nerves sends electrical signals to and from other cells, glands, and muscles all over your body. These nerves receive information from the world around you. Then the nerves interpret the information and control your response. It’s almost like an enormous information highway running throughout your body. FunctionWhat does the nervous system do?Your nervous system uses specialized cells called neurons to send signals, or messages, all over your body. These electrical signals travel between your brain, skin, organs, glands and muscles. The messages help you move your limbs and feel sensations, such as pain. Your eyes, ears, tongue, nose and the nerves all over your body take in information about your environment. Then nerves carry that data to and from your brain. Different kinds of neurons send different signals. Motor neurons tell your muscles to move. Sensory neurons take information from your senses and send signals to your brain. Other types of neurons control the things your body does automatically, like breathing, shivering, having a regular heartbeat and digesting food. AnatomyWhat are the parts of the nervous system?The nervous system has two main parts. Each part contains billions of cells called neurons, or nerve cells. These special cells send and receive electrical signals through your body to tell it what to do. The main parts of the nervous system are: Central nervous system (CNS): Your brain and spinal cord make up your CNS. Your brain uses your nerves to send messages to the rest of your body. Each nerve has a protective outer layer called myelin. Myelin insulates the nerve and helps the messages get through. Peripheral nervous system: Your peripheral nervous system consists of many nerves that branch out from your CNS all over your body. This system relays information from your brain and spinal cord to your organs, arms, legs, fingers and toes. Your peripheral nervous system contains your:
Conditions and DisordersWhat conditions and disorders affect the nervous system?Thousands of disorders and conditions can affect your nerves. An injured nerve has trouble sending a message. Sometimes it’s so damaged that it can’t send or receive a message at all. Nerve injury can cause numbness, a pins-and-needles feeling or pain. It may be difficult or impossible for you to move the area that’s injured. Nerve damage can happen in several ways. Some of the most common causes of nerve damage include:
How common are these conditions?Some causes of nerve damage occur more frequently than others. They include:
CareHow do I keep my nervous system healthy?Your nervous system is the command center for your entire body. It needs care to keep working correctly. See your doctor regularly, eat a healthy diet, avoid drugs, and only drink alcohol in moderation. The best way to avoid nerve damage from disease is to manage conditions that can injure your nerves, such as diabetes. Frequently Asked QuestionsWhen should I call my doctor?Call your doctor right away if you have any sudden changes in your health, such as losing coordination or noticing severe muscle weakness. You should also see your doctor if you have:
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How is information carried through the nervous system?Neurons send and receive electrical signals to communicate with each other in the nervous system and with other types of cells in the body, particularly muscles. At one end, neurons have branch-like projections called dendrites that allow them to receive signals.
How is information carried from the central nervous system to a muscle or gland?Your nervous system uses specialized cells called neurons to send signals, or messages, all over your body. These electrical signals travel between your brain, skin, organs, glands and muscles.
Which neurons are used to carry information to the central nervous system?Afferent neurons carry information from sensory receptors found all over the body towards the central nervous system, whereas efferent neurons carry motor information away from the central nervous system to the muscles and glands of the body in order to initiate an action.
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