Nervous system

Your body uses messages to work.

These messages travel through tiny parts. They help you move your muscles. They also help you feel things.

Small cells send these messages fast. Some cells help the brain. Other cells help the body stay calm. This system helps you react to the world. It is a very busy system!

The nervous system helps animals act and feel.

It sends signals between different body parts. This system started in wormlike animals long ago.

In vertebrates, there are two main parts. The first is the central nervous system. This includes the brain and the spinal cord. The second is the peripheral nervous system. This part is made of nerves. These nerves connect the brain to the rest of the body.

Some nerves carry sense information to the brain. Other nerves carry orders to your muscles.

Special cells called neurons make up this system.

Neurons send signals using electrical and chemical pulses. They use long fibers called axons to send messages. Another type of cell is called glial cells. These cells act like glue. They support and feed the neurons. They also help signals move faster by making a fatty layer called myelin.

Nervous systems vary in size. A simple worm may have only a few hundred cells. An African elephant has about 300 billion cells. Scientists who study this system are called neuroscientists.

The nervous system is a very complex part of an animal. It helps an animal coordinate its actions and its senses. It does this by sending signals to and from different body parts. This system can detect changes in the environment that affect the body. It works together with the endocrine system to help the body respond.

Most animals have a nervous system, but they vary in size. A simple worm might have only a few hundred cells. An African elephant has about 300 billion cells.

In vertebrates, the system has two main parts. The first part is the central nervous system, or CNS. This includes the brain and the spinal cord. The second part is the peripheral nervous system, or PNS. The PNS is made of nerves that connect the CNS to the rest of the body.

Some nerves are sensory nerves that send information to the CNS. Other nerves are motor nerves that send signals from the brain to the body. The PNS also has two subsystems called the somatic and autonomic systems. The autonomic system helps control things like your internal organs.

Special cells called neurons make the nervous system work.

Neurons send signals using electrochemical impulses. These signals travel along long, thin fibers called axons. When a signal reaches the end of an axon, it can pass the message to a neighbor. This happens at a junction called a synapse. At a chemical synapse, the neuron releases chemicals called neurotransmitters.

Other cells called glial cells provide support. Glial cells act like glue to hold neurons in place. They also provide nutrients and help insulate axons with a fatty layer called myelin. This myelin helps signals move much faster.

Nervous tissue first appeared in wormlike organisms a long time ago. These early organisms lived about 550 to 600 million years ago.

Ancient Egyptians, Greeks, and Romans knew about nerves. However, they did not understand how they worked inside. Scientists did not know neurons were the basic units of the brain until around 1900. It was not known how chemicals helped the brain communicate until about 1930. In the 1950s, researchers learned how the electrical signals move. By the 1990s, we understood how these parts work at a molecular level.

Understanding the nervous system helps us learn about ourselves. Many different animals have different types of nervous systems. Sponges, placozoans, and mesozoans are animals that have no nervous system at all. Some animals, like jellyfish, have a simple nerve net.

Most other animals have a brain and a central cord. If the nervous system does not work right, it can cause problems. Doctors who study these problems are called neurologists. Scientists who study the whole system are called neuroscientists. They work hard to understand how we perceive the world.

The nervous system is a highly complex biological network. It coordinates an animal's actions and sensory information. It works by transmitting signals to and from different body parts. This system detects environmental changes that impact the body. It then works with the endocrine system to respond to these events.

Most multicellular animals possess a nervous system. However, the complexity varies greatly between different species. Sponges, placozoans, and mesozoans are the only multicellular animals without one. The size of these systems can range from a few hundred cells in simple worms to 300 billion cells in African elephants.

In vertebrates, the system is divided into two main parts. The first is the central nervous system (CNS). The CNS consists of the brain and the spinal cord. The brain sits in the cranial cavity. The spinal cord is located within the spinal canal. Both are protected by the meninges, which are three layers of membranes. The outer layer is called the dura mater. The brain is also protected by the skull. The spinal cord is protected by the vertebrae. This structure allows the CNS to manage signals and receive feedback.

The second main part is the peripheral nervous system (PNS). This includes all nervous structures outside the CNS. Most nerves belong to the PNS. These nerves are bundles of long fibers called axons. The PNS is divided into the somatic and autonomic nervous systems. The somatic system innervates the skin, joints, and muscles. The autonomic system, or visceral part, controls internal organs and glands.

The autonomic system has three subdivisions. These are the sympathetic, parasympathetic, and enteric nervous systems. The sympathetic system mobilizes energy during emergencies. The parasympathetic system activates during relaxation. The enteric system controls the gastrointestinal system.

Nervous tissue is defined by specialized cells called neurons. Neurons communicate via synapses, which are junctions between membranes. They send signals as electrochemical impulses. These impulses travel along thin fibers called axons.

A signal can reach a neighbor through an electrical synapse. It can also trigger the release of chemicals called neurotransmitters at a chemical synapse.

Once a signal is received, the next cell may be excited or inhibited. These connections form neural pathways and circuits. These networks generate an organism's perception and behavior.

Other specialized cells called glial cells support the neurons. The name comes from the Greek word for "glue." Glial cells provide structural and metabolic support. They supply nutrients and maintain homeostasis. Some glia, like microglia and astrocytes, act as immune cells. Certain glia, such as oligodendrocytes and Schwann cells, create myelin. Myelin is a fatty substance that wraps around axons. This provides electrical insulation. It allows action potentials to travel much more rapidly.

In the human brain, the number of glia roughly equals the number of neurons.

History shows how our understanding of this system has grown. Ancient Egyptians, Greeks, and Romans recognized nerves. However, they did not understand their internal structure. It was not known that neurons were the basic units of the brain until about 1900. The concept of chemical transmission was not known until around 1930. In the 1950s, scientists understood the electrical action potential. By the 1960s, researchers saw how networks code stimuli. Finally, the 1990s brought knowledge of molecular mechanisms in behavior.

Different animals show different evolutionary paths for these systems. Radially symmetric animals like jellyfish have a diffuse nerve net. Most other species have a brain and a central cord. This common structure originated over 550 million years ago.

Malfunctions can occur due to genetic defects, trauma, or infection. Problems like multiple sclerosis involve the failure of nerve conduction. Neurology is the medical specialty that studies these disorders. Neuroscience is the broader scientific field that studies the entire system.