The Nervous System: Everything You Need to Know

Medically Reviewed By Heidi Moawad, M.D.
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The nervous system consists of the brain, the spinal cord, and the nerves throughout the body. It works to control all bodily systems and responses, both consciously and unconsciously. This article explains all you need to know about the nervous system, including its divisions, anatomy, and disorders, as well as the symptoms of such disorders. 

What is the nervous system? 

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The nervous system controls the body’s thoughts, movements, and even unconscious responses to stimuli, called reflexes. It contains a complex network of nerve cells called neurons that carry messages to and from the brain to other parts of the body.

It also controls and regulates body processes such as respiration, digestion, and reproduction.

Because the nervous system is the center of all mental activity and the control center for all voluntary actions, damage to any part of the system can cause serious medical complications. These may include:

  • a loss of sensation
  • paralysis
  • seizures
  • poor coordination
  • mental health conditions

The nervous system is made up of three primary parts: the brain, the spinal cord, and the nerves. There are also substructures to each of these.

Divisions of the nervous system

The nervous system is divided into two parts:

  • the central nervous system (CNS), which comprises the brain and spinal cord
  • the peripheral nervous system (PNS), which comprises the nerves

The central nervous system

Similar to a computer’s central processing unit, the CNS is the body’s processing unit. This means that the CNS collects information from all parts of the body through neurons, processes the information, and then uses it to coordinate all the functions of the body.

It is the center that controls muscular movements, thoughts, emotions, body temperature, heart rate, speech, hormone release, and breathing, among other important functions. 

The peripheral nervous system

The PNS is made up of nerves that connect all the different parts of the body to the CNS. More specifically, the PNS consists of:

  • the cranial nerves that emerge from the brain
  • the spinal nerves that leave the CNS through the spinal cord
  • the different roots and branches that conduct information from the peripheral parts of the body to the CNS

Doctors also further divide the PNS into two separate systems: the somatic and autonomic nervous systems.

The somatic nervous system

The somatic nervous system has nerve fibers that receive signals from parts of the body and send out signals that cause movements and muscle contractions.

It is responsible for both voluntary actions, which you control, and reflex actions.

The autonomic nervous system

The autonomic nervous system (ANS) controls involuntary actions, which you cannot consciously control. It consists of nerves that control processes such as digestion, respiration, and blood pressure.

The ANS is further divided into:

  • The sympathetic nervous system: This part of the ANS drives the “fight or flight response.” It plays a primary role when the body is stressed or threatened by preparing the body to respond. For instance, it activates different pathways to increase heart rate, dilate the eye pupils, and increase blood flow to the heart, brain, and muscles.
  • The parasympathetic nervous system: This division of the ANS controls the activities of the soft organs, such as the heart muscles. It is more involved in controlling body functions when the body is at rest or feeding. It also helps conserve the body’s energy when needed.

The sympathetic and parasympathetic nervous systems are intertwined and coordinated nerves that control the same organs. These systems work in balance to keep the organs functioning correctly, and they adjust minute by minute in response to the body’s changing needs.

The brain

The brain weighs about 1,198 grams (g) in adult females and 1,336 g in adult males. It is the major control unit of the nervous system and is divided into four parts:

  • the left and right brain hemispheres, which together make up the cerebrum
  • the brainstem, which is made up of the pons, midbrain, and medulla oblongata
  • the diencephalon, which is located more in the middle of the brain and contains the thalamus and hypothalamus
  • the cerebellum, which is the major feature of the hindbrain

All parts of the brain are important, but some of the key structures involved in the nervous system functioning include the following.

Cerebrum

The cerebrum is the biggest part of the brain. It is primarily located in the outer part of the brain and is made up of gray matter called the cerebral cortex. The inner part is called the white matter. The cerebrum controls higher intellectual functions, voluntary movements, and sensory coordination.

The white matter contains nerve fibers that communicate signals between the nerve fibers of the cerebral cortex and the brainstem.

Epithalamus

This structure is mostly made up of the pineal gland, which is responsible for secreting melatonin. This is a hormone that plays a role in the sleep-wake cycle.

Thalamus

In general, the thalamus is the area where sensory input from the body travels from the brainstem to the cerebral cortex. It both relays and filters messages back and forth.

Hypothalamus

The hypothalamus is an important structure of the nervous system. It secretes hormones that control growth, that help with blood pressure, and that are involved with love and bonding. The hypothalamus also plays a role in biological timing, thermoregulation, and feeding and satiety.

Medulla oblongata

This is the lowest part of the brain that connects to the spinal cord. The medulla is important for sending information between the brain and spinal cord.

Spinal cord

The spinal cord is a long, cylindrical structure that extends from the lowest part of the brain (the medulla) into the second lumbar vertebra of the backbone. It is covered by three layers of protective tissues called the meninges, and it contains many long tracks of nerve fibers that send signals between the brain and body. 

Nerves

The third part of the nervous system is the nerves. There are two main types of nerves:

  • Motor nerves: These send signals that control movement.
  • Sensory nerves: These send signals that help you feel, touch, taste, and see.

There are also two groups of nerves:

  • Spinal nerves: These extend from the spinal cord.
  • Cranial nerves: These come from the brain.

Main functions of the nervous system 

The nervous system works alongside other bodily systems to control all activities in the body. Its major functions include the following.

Reflexes

A reflex is an involuntary action that someone performs in response to a stimulus. You do not control a reflex; it just happens. A knee-jerk is an example of a spinal reflex that occurs when the patellar tendon (a tendon in the front of the thighs) is stretched, causing the quadriceps (the muscles of the thighs) to contract.

Voluntary movements

The nervous system directly controls voluntary movements such as walking, raising an arm, running, and bending by sending messages to the part of the body involved in the movement.

These are actions that you control.

Memory and learning

The nervous system, particularly the brain, is in charge of mental and cognitive health. The nervous system controls emotions and functions such as learning, memory, thinking, and cognition. 

Homeostasis

Homeostasis is the regulation of the body’s internal environment in response to environmental changes, such as temperature.

When you are in a very hot temperature or working out, the body responds to keep your internal organs cool. For instance, to regulate the body temperature, the nervous system sends messages to the blood vessels and sweat glands. This increases blood flow to the skin and causes you to sweat. As the sweat evaporates from your body, it cools your body.

Autonomic (involuntary) actions

The sympathetic division of the ANS prepares the body for emergencies with the “flight or fight” response.

The parasympathetic division does the opposite and works to relax, stop, or slow down certain bodily systems when needed. For example, it reduces respiration rate, reduces blood pressure, and promotes digestion when the body is at rest.

Disorders of the nervous system

Disorders of the nervous system include damage resulting from infections, trauma, structural defects, vascular issues, degeneration, and autoimmune conditions.

There are more than 600 disorders of the nervous system. Some of these include:

Symptoms of a nervous system disorder

Symptoms of a nervous system disorder can be different from person to person. However, some common symptoms that might indicate that a person has a neurological problem include:

  • a sudden headache
  • a loss of memory
  • tingling or a loss of sensation in a part of the body
  • vision problems or a loss of sight
  • impaired cognitive function
  • muscle weakness
  • a lack of coordination
  • seizures and tremors
  • back pain that radiates to other parts of the body
  • slurred speech
  • shrinking muscles
  • muscle rigidity

Contact a doctor right away if you experience any of these symptoms. The cause needs identifying, and treatment is important.

Read about eight reasons you should contact a neurologist.

Tips for general nervous system health

Although factors such as trauma, infections, degeneration, and blood flow issues can cause nervous system disorders, there are some things you can do to support your nervous system health. These include the following:

  • Exercise often, as it can prevent headaches, stroke, and muscle rigidity.
  • Eat well-balanced, nutritious meals that contain healthy fats, fruits and vegetables, and fish.
  • Get enough sleep.
  • Include stretching or a low impact exercise, such as yoga, in your routine.
  • Consider regularly practicing meditation or another quiet mindfulness activity.
  • Avoid activities that could cause trauma or injuries, such as walking on an uneven surface if you are recovering from a fracture or riding a bike without a helmet.
  • Get outside regularly if possible.
  • Manage any other medical conditions you may have, such as high blood pressure or diabetes.
  • Drink plenty of water.
  • Avoid eating meals that contain unhealthy fats, including saturated fats and triglycerides.
  • Limit your consumption of alcohol.
  • Avoid drug misuse and smoking. Seek professional help to stop if needed.
  • Maintain a moderate weight.

Summary

The nervous system is the body’s control center. It consists of the brain, the spinal cord, and the nerves.

The nervous system controls the entire body and guides everything you do, feel, think, and say. It is divided into the central and peripheral nervous systems, which control simple and complex processes such as memory, movements, and thoughts.

There are many types of neurological disorders that can affect the nervous system. In general, symptoms include a loss of sensation in the limbs or in other parts of the body, weakness or difficulty controlling the muscles, and cognitive problems, such as not being able to remember things.

You can help support a healthy nervous system by managing any medical conditions you may have, eating a healthy diet, getting enough sleep, and maintaining a moderate weight.

If you notice any symptoms that are new or worrisome to you, consult with your doctor.

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Medical Reviewer: Heidi Moawad, M.D.
Last Review Date: 2022 Jun 29
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.