Neuroscience is the study of the nervous system. The nervous system includes the brain, spinal cord, and networks of sensory and motor nerve cells, called neurons, throughout the body. Neuroscience aims to understand how the nervous system works to produce and regulate emotion, thought, behavior, and critical bodily functions, including breathing and keeping the heart beating.

Neuroscientists study the nervous system on many different levels. They examine molecules, nerve cells, nerve networks, and brain structure, individually and collectively, and how these components interact to perform different activities. These scientists study how a typical nervous system develops and functions, as well as disorders and diseases that cause problems with how the nervous system grows or works.

For example, when someone reads these words, his or her brain sends signals to the eye muscles to help track along this line of text. At the same time, eyes change the words into signals that travel along neurons to the brain. The brain decodes these signals to “read” the words. Then the brain reaches into its stored information—including memories—to give meaning to the words by themselves, and then to give meaning to what the words are saying together. The entire process happens almost instantly, which is just further proof that the nervous system is amazing.

The nervous system has two main parts:

• The central nervous system is made up of the brain and spinal cord.
• The peripheral nervous system is made up of nerves that branch off from the spinal cord and extend to all parts of the body.

The nervous system transmits signals between the brain and the rest of the body, including internal organs. In this way, the nervous system’s activity controls the ability to move, breathe, see, think, and more.

The basic unit of the nervous system is a nerve cell, or neuron. The human brain contains about 100 billion neurons. A neuron has a cell body, which includes the cell nucleus, and special extensions called axons (pronounced AK-sonz) and dendrites (pronounced DEN-drahytz). Bundles of axons, called nerves, are found throughout the body. Axons and dendrites allow neurons to communicate, even across long distances.

Different types of neurons control or perform different activities. For instance, motor neurons transmit messages from the brain to the muscles to generate movement. Sensory neurons detect light, sound, odor, taste, pressure, and heat and send messages about those things to the brain. Other parts of the nervous system control involuntary processes. These include keeping a regular heartbeat, releasing hormones like adrenaline, opening the pupil in response to light, and regulating the digestive system.

When a neuron sends a message to another neuron, it sends an electrical signal down the length of its axon. At the end of the axon, the electrical signal changes to a chemical signal. The axon then releases the chemical signal with chemical messengers called neurotransmitters (pronounced noor-oh-TRANS-mit-erz) into the synapse (pronounced SIN-aps)—the space between the end of an axon and the tip of a dendrite from another neuron. The neurotransmitters move the signal through the synapse to the neighboring dendrite, which converts the chemical signal back into an electrical signal. The electrical signal then travels through the neuron and goes through the same conversion processes as it moves to neighboring neurons.

The nervous system also includes non-neuron cells, called glia (pronounced GLEE-uh). Glia perform many important functions that keep the nervous system working properly. For example, glia:

• Help support and hold neurons in place
• Protect neurons
• Create insulation called myelin, which helps move nerve impulses
• Repair neurons and help restore neuron function
• Trim out dead neurons
• Regulate neurotransmitters

The brain is made up of many networks of communicating neurons and glia. These networks allow different parts of the brain to “talk” to each other and work together to control body functions, emotions, thinking, behavior, and other activities.

The nervous system plays a role in nearly every aspect of our health and well-being. It guides everyday activities such as waking up; automatic activities such as breathing; and complex processes such as thinking, reading, remembering, and feeling emotions.

The nervous system controls:

• Brain growth and development
• Sensations (such as touch or hearing)
• Perception (the mental process of interpreting sensory information)
• Thought and emotions
• Learning and memory
• Movement, balance, and coordination
• Sleep
• Healing and rehabilitation
• Stress and the body’s responses to stress
• Aging
• Breathing and heartbeat
• Body temperature
• Hunger, thirst, and digestion
• Puberty, reproductive health, and fertility

Neuroscientists study these and other nervous system functions in both healthy and diseased states. Studying and understanding the nervous system is important because it affects so many areas of human health and well-being.

Diagnostic tests and procedures are vital tools that help physicians confirm or rule out the presence of a neurological disorder or other medical condition. A century ago, the only way to make a positive diagnosis for many neurological disorders was by performing an autopsy after a patient had died. But decades of basic research into the characteristics of disease, and the development of techniques that allow scientists to see inside the living brain and monitor nervous system activity as it occurs, have given doctors powerful and accurate tools to diagnose disease and to test how well a particular therapy may be working.

Perhaps the most significant changes in diagnostic imaging over the past 20 years are improvements in spatial resolution (size, intensity, and clarity) of anatomical images and reductions in the time needed to send signals to and receive data from the area being imaged. These advances allow physicians to simultaneously see the structure of the brain and the changes in brain activity as they occur. Scientists continue to improve methods that will provide sharper anatomical images and more detailed functional information.

Researchers and physicians use a variety of diagnostic imaging techniques and chemical and metabolic analyses to detect, manage, and treat neurological disease. Some procedures are performed in specialized settings, conducted to determine the presence of a particular disorder or abnormality. Many tests that were previously conducted in a hospital are now performed in a physician’s office or at an outpatient testing facility, with little if any risk to the patient. Depending on the type of procedure, results are either immediate or may take several hours to process.

The nervous system not only works to produce thoughts, emotions, and behavior, but also controls important body functions, like breathing.

Studying the nervous system advances understanding of our basic biology and body function. Knowing how things typically work can help shed light on what may happen when there are problems. It can help researchers find ways to prevent or treat problems that affect the brain, nervous system, and body.

In addition to examining the normal development and activity of the nervous system, neuroscience studies diseases, disorders, and injuries that affect parts of the nervous system, how it develops, and how well it functions. There are more than 1,000 disorders of the brain and nervous system, including:

• Intellectual and developmental disabilities, such as Down syndrome and Fragile X syndrome
• Behavioral disorders, such as attention deficit/hyperactivity disorder and autism spectrum disorders
• Learning disabilities and reading disorders
• Mental health problems, such as schizophrenia, obsessive-compulsive disorder, and addiction
• Degenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and Niemann-Pick disease
• Musculoskeletal disorders, such as muscular dystrophy and stroke
• Structural defects, such as neural tube defects, which include spina bifida, hydrocephaly, and myelomeningocele
• Injuries, including traumatic brain injury and spinal cord injury, as well as how the body processes pain
• Cancers, including brain tumors such as paragangliomas
• Immune system disorders, such as HIV/AIDS
• Epilepsy, seizures, and stroke

Understanding how to prevent and treat these disorders and diseases is crucial for maintaining the overall health and well-being of all people.

There are many different branches of neuroscience. Each focuses on a specific topic, body system, or function:

• Developmental neuroscience describes how the brain forms, grows, and changes.
• Cognitive neuroscience is about how the brain creates and controls thought, language, problem-solving, and memory.
• Molecular and cellular neuroscience explores the genes, proteins, and other molecules that guide how neurons function.
• Neurogenetics focuses on inherited changes to neurons, including studies of certain genetic diseases, such as Huntington’s disease and Duchenne muscular dystrophy.
• Behavioral neuroscience examines the brain areas and processes underlying how animals and humans act.
• Clinical neuroscience explores how to treat and prevent neurological disorders and how to rehabilitate patients whose nervous system has been injured.
• Neurophysiology describes the study of the nervous system itself and how it functions.
• Sensory neuroscience examines features of the body’s sensory systems and how the nervous system interprets and processes sensory information.