The Nervous System

What Does The Nervous System Do?

The nervous system is the control system and the network of communication for your body.

Think of your brain as a central computer that controls all voluntary and involuntary bodily functions.

Your “computer” acts through a network that relays messages back and forth from the brain to different parts of the body.

When a message comes into the brain from anywhere in the body, the brain tells the body how to react. For example, if you accidentally touch a hot stove, the nerves in your skin shoot a message of pain to your brain. The brain then sends a message back telling the muscles in your hand to pull away. Fortunately, all of this occurs lightning fast.

Nervous System

What Makes Up The Nervous System?

The nervous system consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS).

Central Nervous System

The CNS is made up of the brain and spinal cord.

  • The Brain

    The brain is made up of three main sections: the forebrain, the midbrain, and the hindbrain.

      The Forebrain

      The forebrain is the largest and most complex part of the brain. It consists of the cerebrum — the area with all the folds and grooves typically seen in pictures of the brain — as well as some other structures beneath it.

      The cerebrum contains the information that essentially makes us who we are: our intelligence, memory, personality, emotion, speech, and ability to feel and move. Specific areas of the cerebrum are in charge of processing these different types of information. These are called lobes, and there are four of them: the frontal, parietal, temporal, and occipital.

      The cerebrum has right and left halves, called hemispheres, which are connected in the middle by a band of nerve fibers (the corpus collosum) that enables the two sides to communicate. Though these halves may look like mirror images of each other, many scientists believe they have different functions. The left side is considered the logical, analytical, objective side. The right side is thought to be more intuitive, creative, and subjective. So when you’re balancing the checkbook, you’re using the left side; when you’re listening to music, you’re using the right side. It’s believed that some people are more “right-brained” or “left-brained” while others are more “whole-brained,” meaning they use both halves of their brain to the same degree.

      The outer layer of the cerebrum is called the cortex (also known as “gray matter”). Information collected by the five senses comes into the brain from the spinal cord to the cortex. This information is then directed to other parts of the nervous system for further processing. For example, when you touch the hot stove, not only does a message go out to move your hand but one also goes to another part of the brain to help you remember not to do that again.

      In the inner part of the forebrain sits the thalamus, hypothalamus, and pituitary gland. The thalamus carries messages from the sensory organs like the eyes, ears, nose, and fingers to the cortex. The hypothalamus controls the pulse, thirst, appetite, sleep patterns, and other processes in our bodies that happen automatically. It also controls the pituitary gland, which makes the hormones that control our growth, metabolism, digestion, sexual maturity, and response to stress.

      The Midbrain

      The midbrain, located underneath the middle of the forebrain, acts as a master coordinator for all the messages going into the brain and out of the brain to the spinal cord.

      The Hindbrain

      The hindbrain sits underneath the back end of the cerebrum, and it consists of the cerebellum, pons, and medulla. The cerebellum — also called the “little brain” because it looks like a small version of the cerebrum — is responsible for balance, movement, and coordination.

      The pons and the medulla, along with the midbrain, are often called the brainstem. The brainstem takes in, sends out, and coordinates all of the brain’s messages. It also controls many of the body’s automatic functions, like breathing, heart rate, blood pressure, swallowing, digestion, and blinking.

  • The Spinal Cord

    The spinal cord is a bundle of nerve tissue about 18 inches long and ¾ inch thick. It extends from the lower part of the brain down through your spine. Along the way, various nerves branch out to the entire body.

    Both the brain and the spinal cord are protected by bone, the brain by the bones of the skull and the spinal cord by a set of ring-shaped bones called vertebrae. They’re both cushioned by layers of membranes called meninges as well as a special fluid called cerebrospinal fluid. This fluid helps protect the nerve tissue, keep it healthy, and remove waste products.

Peripheral Nervous System

The PNS includes all the parts of the nervous system outside of the brain and spinal cord. It has several parts.

5 Interesting Facts About The Nervous System

  1. Your adult brain weighs about 3 pounds.

  2. There are millions of nerve cells in your body. In fact, the number exceeds the number of stars in the Milky Way Galaxy.

  3. The right side of your brain controls the left side of your body, while the left side of your brain controls the right side.

  4. As you grow older, your brain shrinks by a gram each year.

  5. At a given point of time, only four percent of the cells in your brain are active, the rest are kept in reserve.
  • Somatic Nervous System
    The somatic nervous system (SNS) is a division of the PNS that controls your voluntary actions. The SNS is the only consciously controlled part of the PNS and is responsible for stimulating skeletal muscles in the body. So, when I wanted my fingers to type these words, my SNS did the job.

  • Autonomic Nervous System
    The autonomic nervous system (ANS) is a division of the PNS that controls all of your involuntary actions.

    There are 3 divisions of the autonomic nervous system: the sympathetic and parasympathetic divisions, and the enteric nervous system.

      Sympathetic. The sympathetic division forms the body’s “fight or flight” response to stress, danger, excitement, exercise, emotions, and embarrassment. The sympathetic division increases respiration and heart rate, releases adrenaline and other stress hormones, and decreases digestion to cope with these situations.

      Parasympathetic. The parasympathetic division forms the body’s “rest and digest” response when the body is relaxed, resting, or feeding. The parasympathetic works to undo the work of the sympathetic division after a stressful situation. Among other functions, the parasympathetic division works to decrease respiration and heart rate, increase digestion, and permit the elimination of wastes.

      Enteric Nervous System. The enteric nervous system (ENS) is the division of the ANS that is responsible for regulating digestion and the function of the digestive organs. The ENS receives signals from the central nervous system through both the sympathetic and parasympathetic divisions of the autonomic nervous system to help regulate its functions. However, the ENS mostly works independently of the CNS and continues to function without any outside input. For this reason, the ENS is often called the “brain of the gut” or the body’s “second brain.” The ENS is an immense system—almost as many neurons exist in the ENS as in the spinal cord.

  • How Does The Nervous System Work?

    The basic functioning of the nervous system depends mostly on tiny cells called neurons. The brain has billions of them, and they have many specialized jobs. For example, sensory neurons take information from the eyes, ears, nose, tongue, and skin to the brain. Motor neurons carry messages away from the brain and back to the rest of the body.

    All neurons, however, relay information to each other through a complex electrochemical process, making connections that affect the way we think, learn, move, and behave.

    Intelligence, Learning, and Memory

    At birth, the nervous system contains all the neurons you will ever have, but many of them are not connected to each other. As you grow and learn, messages travel from one neuron to another over and over, creating connections, or pathways, in the brain. It’s why driving seemed to take so much concentration when you first learned but now is second nature: The pathway became established.

    As we age, the brain has to work harder to make new neural pathways, making it more difficult to master new tasks or change established behavior patterns. That’s why many scientists believe it’s important to keep challenging your brain to learn new things and make new connections— it helps keeps the brain active over the course of a lifetime.

    Memory is another complex function of the brain. The things we’ve done, learned, and seen are first processed in the cortex, and then, if we sense that this information is important enough to remember permanently, it’s passed inward to other regions of the brain (such as the hippocampus and amygdala) for long-term storage and retrieval. As these messages travel through the brain, they too create pathways that serve as the basis of our memory.

    Movement

    Different parts of the cerebrum are responsible for moving different body parts. The left side of the brain controls the movements of the right side of the body, and the right side of the brain controls the movements of the left side of the body.

    Basic Body Functions

    A part of the peripheral nervous system called the autonomic nervous system is responsible for controlling many of the body processes we almost never need to think about, like breathing, digestion, sweating, and shivering. The autonomic nervous system has two parts: the sympathetic and the parasympathetic nervous systems.

    The Senses

    Your spouse may be a sight for sore eyes at the end of a long day — but without the brain, you wouldn’t even recognize him or her. Pizza sure is delicious — but without the brain, your taste buds wouldn’t be able to tell if you were eating pizza or the box it came in. None of your senses would be useful without the processing that occurs in the brain.

    • Sight. Sight probably tells us more about the world than any other sense. Light entering the eye forms an upside-down image on the retina. The retina transforms the light into nerve signals for the brain. The brain then turns the image right-side up and tells us what we are seeing.

    • Hearing. Every sound we hear is the result of sound waves entering our ears and causing our eardrums to vibrate. These vibrations are then transferred along the tiny bones of the middle ear and converted into nerve signals. The cortex then processes these signals, telling us what we are hearing.

    • Taste. The tongue contains small groups of sensory cells called taste buds that react to chemicals in foods. Taste buds react to sweet, sour, salty, and bitter. Messages are sent from the taste buds to the areas in the cortex responsible for processing taste.

    • Smell. Olfactory cells in the mucous membranes lining each nostril react to chemicals we breathe in and send messages along specific nerves to the brain— which, according to experts, can distinguish between more than 10,000 different smells. With that kind of sensitivity, it’s no wonder research suggests that smells are very closely linked to our memories.

    • Touch. The skin contains more than 4 million sensory receptors — mostly concentrated in the fingers, tongue, and lips — that gather information related to touch, pressure, temperature, and pain and send it to the brain for processing and reaction.

    Cellular Level

    NeuronThe neuron is the basic unit in the nervous system. It is a specialized conductor cell that receives and transmits electrochemical nerve impulses. A typical neuron has a cell body and long arms that conduct impulses from one body part to another body part.

    There are three different parts of the neuron: the cell body, dendrites and axon.

    • Cell body of a neuron. The cell body is like any other cell with a nucleus or control center.

    • Dendrites. The cell body has several highly branched, thick extensions that appear like cables and are called dendrites. The exception is a sensory neuron that has a single, long dendrite instead of many dendrites. Motor neurons have multiple thick dendrites. The dendrite’s function is to carry a nerve impulse into the cell body.

    • Axon. An axon is a long, thin process that carries impulses away from the cell body to another neuron or tissue. There is usually only one axon per neuron.

    The neuron is covered with the Myelin Sheath or Schwann Cells. These are white segmented covering around axons and dendrites of many peripheral neurons. The covering is continuous along the axons or dendrites except at the point of termination and at the nodes of Ranvier.

    The neurilemma is the layer of Schwann cells with a nucleus. Its function is to allow damaged nerves to regenerate. Nerves in the brain and spinal cord do not have a neurilemma and, therefore cannot recover when damaged.

What Can Go Wrong With Your Nervous System?

Because the brain controls just about everything, when something goes wrong with it, it’s often serious and can affect many different parts of the body. Inherited diseases, brain disorders associated with mental illness, and head injuries can all affect the way the brain works and upset the daily activities of the rest of the body.

These are some of the more common nervous system abnormalities.

Brain tumors

A brain tumor is an abnormal tissue growth in the brain. A tumor in the brain may grow slowly and produce few symptoms until it becomes large, or it can grow and spread rapidly, causing severe and quickly worsening symptoms. Brain tumors can be benign or malignant. Benign tumors usually grow in one place and may be curable through surgery if they’re located in a place where they can be removed without damaging the normal tissue near the tumor. A malignant tumor is cancerous and more likely to grow rapidly and spread.

Cerebral palsy

Cerebral palsy is the result of a developmental defect or damage to the brain before or during a child’s birth, or during the first few years of life. It affects the motor areas of the brain. A person with cerebral palsy may have average intelligence or can have severe developmental delays or mental retardation. Cerebral palsy can affect body movement in many different ways. In mild cases of cerebral palsy, there may be minor muscle weakness of the arms and legs. In other cases, there may be more severe motor impairment.

Epilepsy

This condition is made up of a wide variety of seizure disorders. Partial seizures involve specific areas of the brain, and symptoms vary depending on the location of the seizure activity. Other seizures, called generalized seizures, involve a larger portion of the brain and usually cause uncontrolled movements of the entire body and loss of consciousness when they occur. Although the specific cause is unknown in many cases, epilepsy can be related to brain injury, tumors, or infections. The tendency to develop epilepsy may be inherited in families.

Headaches

Of the many different types of headaches, the most frequently occurring include tension headache (the most common type), caused by muscle tension in the head, neck, and shoulders; migraine, an intense, recurring headache with an unclear cause; and cluster headache, considered by some to be a form of migraine. Migraines occur with or without warning and may last for several hours or days. There seems to be an inherited predisposition to migraines as well as certain triggers that can lead to them. People with migraines may experience dizziness, numbness, sensitivity to light, and nausea, and may see flashing zigzag lines before their eyes.

Meningitis and encephalitis

These are infections of the brain and spinal cord that are usually caused by bacteria or viruses. Meningitis is an inflammation of the coverings of the brain and spinal cord, and encephalitis is an inflammation of the brain tissue. Both conditions may result in permanent injury to the brain.

Mental illness

Mental illnesses are psychological and behavioral in nature and involve a wide range of problems in thought and function. Certain mental illnesses are now known to be linked to structural abnormalities or chemical dysfunction of the brain. Some mental illnesses are inherited, but often the cause is unknown. Injuries to the brain and chronic drug or alcohol abuse also can trigger some mental illnesses.

Head injuries

Head injuries fit into two categories: external (usually scalp) injuries and internal head injuries. Internal injuries may involve the skull, the blood vessels within the skull, or the brain..

Concussions

Concussions are also a type of internal head injury. A concussion is the temporary loss of normal brain function as a result of an injury. Repeated concussions can result in permanent injury to the brain.

How Do Your Keep Your Nervous System Healthy?

In addition to doing all the things you normally do to maintain good overall health, follow these tips to keep your nervous system healthy:

  1. Drink plenty of water. Your brain is eighty-five percent water. If you don’t drink enough water, your brain won’t work as well as it could

  2. Give your brain the nutrition it needs. Lack of B vitamins can cause anxiety, depression, headaches, pain in your arms or legs, dizziness, confusion, memory problems, mania and fatigue. You can boost your B vitamin consumption by eating eggs, milk, yogurt, beef, liver, fish, poultry, beans, peas, enriched cereals. and green, leafy vegetables.

    Potassium and calcium are also important nutrients for your brain to function well. Calcium helps your nervous system respond to and heal from injuries. You can get calcium from dairy products such as yogurt, milk and cheese, as well as from tofu, oranges, beans, salmon and leafy, green vegetables. Potassium is necessary for basic neuron functioning. Potassium-rich foods include bananas, squash, sweet potatoes, yogurt, potatoes and broccoli.

    A variety of other vitamins and nutrients can keep your nervous system running strong. Vitamin A boosts eye health, helping your retinas function well. A lack of vitamin A can lead to night blindness and vision problems. Vitamin A is abundant in sweet potatoes, beef liver and carrots. Vitamin C helps your body produce the neurotransmitters serotonin and dopamine, which can prevent depression. Vitamin C-rich foods include oranges, berries, lemons and grapefruit. Vitamin D also helps your nervous system because it allows your body to absorb calcium. Vitamin D is found in tuna, salmon and fortified milk.

  3. Exercise your nervous system every day. A good way to do this is to write on paper as neatly as you can for 10 or 15 minutes a day. The simple act of writing requires that you use all major components of your conscious motor and sensory pathways; a number of different sensory receptors, peripheral nerves, synaptic connections within your spinal cord, major tracts within your spinal cord, and nerve tissue throughout your brain need to be utilized with great precision and coordination to produce neatly written words.

    Writing with pen on paper is far more effective at exercising your nervous system than writing with a keyboard on a computer, as typing on a keyboard doesn’t require as much fine motor control as writing on paper.

This article is part of a series called “Your Body: An Owner’s Manual” which explains how your body systems work and how to maintain them. The first article in the series included a picture of my wife, fitness coach Kathie Lamir, who exemplifies a healthy body. Pictures of Kathie were so well received that I have included one with each article in the series

Fitness Expert Kathie Lamir

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