Nervous system

The nervous system is the part of an animal that helps it coordinate its actions and process information. It sends signals to and from different parts of the body, helping animals detect changes in their environment and respond. It works with the endocrine system to keep the body running smoothly. Nervous tissue first appeared in simple wormlike organisms a very long time ago.

In vertebrates, the nervous system has two main parts: the central nervous system, made up of the brain and spinal cord, and the peripheral nervous system. The peripheral system includes nerves that connect the brain and spinal cord to the rest of the body. These nerves carry messages to and from the central system. The peripheral system also helps control movements and automatic body functions.

The nervous system is made of special cells called neurons. These neurons can send electrical and chemical signals quickly through long fibers known as axons. Other supporting cells, called glial cells, help keep the neurons healthy. Nervous systems vary in size and complexity, from simple worms to large African elephants, but they are essential for most animals.

Structure

The nervous system is made of nerves. Nerves are bundles of fibers called axons. They come from the brain and spinal cord. These nerves spread out to every part of the body. People have known about nerves for a long time. We learned about how they work with microscopes.

The nervous system has two main types of cells: neurons and glial cells. Neurons are special cells. They talk to each other using tiny connections called synapses. They help turn things like light and sound into signals the body can understand. Glial cells support and protect neurons. They help neurons work better.

In animals with backbones, like humans, the nervous system has two main parts: the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves outside the brain and spinal cord). These parts work together to help the body react to what it senses.

Function

The nervous system sends signals from one part of the body to another. It helps the body respond to changes around it. It works with the endocrine system to coordinate actions and reactions. Nerve signals travel faster and more precisely than hormonal signals.

The nervous system controls the body by sensing the environment, processing that information, and creating responses. This helps animals develop abilities like vision, social interactions, and coordination. In humans, it supports complex features such as language, abstract thinking, and culture.

Neurons and synapses

Neurons send signals through long arms called axons. These signals are electrochemical waves. Neurons connect at points called synapses, where they release chemicals called neurotransmitters. These chemicals cross a tiny space and bind to receptors on the next neuron, causing it to react. This process happens very quickly.

There are many types of synapses and neurotransmitters, allowing for many effects. Some synapses help form memories by changing strength over time. Networks of connected neurons can process information in many ways, helping animals detect features, generate patterns, and control actions.

Neural circuits and systems

Neurons can work together in circuits to perform various functions. Simple circuits, called reflexes, help the body react quickly to dangers. More complex circuits involve many parts of the brain and allow for detailed processing of signals.

The nervous system can also create rhythms and patterns on its own, without needing outside signals. For example, it controls the sleep-wake cycle through internal clocks. These patterns help coordinate many body functions over different timescales.

Mirror neurons

Main article: Mirror neuron

Mirror neurons are special neurons that activate both when an animal acts and when it observes the same action done by another. They have been found in primates and may help with understanding others' actions and learning new skills by imitation. Scientists are still studying how these neurons work and what roles they play in behavior and cognition.

Development

Main articles: Development of the nervous system and Development of the nervous system in humans

The nervous system starts forming very early in an animal's growth. In vertebrates, it begins with a thin strip of cells along the back called the neural plate. This strip folds and closes to make a tube. This tube becomes the central nervous system (CNS). Other parts become the peripheral nervous system (PNS).

Special signals from other cells help these early cells become part of the nervous system. These signals create the building blocks of nerves, called neurons. Neurons are important for sending messages throughout the body. Similar processes help build nervous systems in many different animals.

Pathology

Main article: Neurology

See also: Psychiatry

The nervous system has special ways to stay safe. The brain and spinal cord are protected by tough layers called meningeal membranes. They are also inside the bones of the skull and vertebral column. A barrier called the blood–brain barrier helps stop harmful chemicals from reaching the brain.

Sometimes nerves can get hurt. This might cause pain or loss of feeling. Nerves can be hurt if they get pressed or damaged, like in carpal tunnel syndrome. Some nerve problems come from other illnesses, such as diabetes or shingles. Doctors have many ways to help treat nervous system problems.