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The Muscular System

What Does The Muscular System Do?

The muscular system has three major functions: producing movement, generating heat and maintaining balance.

Every movement of your body occurs because of muscles. You are aware of, and control, much of your movement, such as when you move your arms or legs. However, there is other muscular movement that you do not control, such as the movement of food down your throat or the beating of your heart.

Muscles also generate heat. When muscles contract, they release heat, and this helps the body maintain its normal temperature.

And muscles maintain posture. Most muscles in your body are always a little contracted. This tension, or muscle tone, which is present even when you are sleeping, maintains your posture.

Muscular System

What Makes Up The Muscular System?

You have more than 600 muscles divided among three types of muscle tissue: skeletal, smooth and cardiac. Muscles make up roughly half of your body weight.

Skeletal Muscle

Skeletal muscles help the body move. Skeletal muscles are the only voluntary muscle tissue in the human body and control every action that a person consciously performs. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other.

Smooth Muscle

Smooth muscles, which are also called visceral muscles, are located inside organs, such as the stomach, intestines and blood vessels. These muscles are called smooth muscles because they do not have the banded appearance of skeletal or cardiac muscle. The weakest of all muscle tissues, visceral muscles contract to move substances through the organ. Because visceral muscle is controlled by the unconscious part of the brain, it is known as involuntary muscle.

Cardiac Muscle

Found only in the heart, cardiac muscle is responsible for pumping blood throughout the body. The heart’s natural pacemaker is made of cardiac muscle that signals other cardiac muscles to contract. Like visceral muscles, cardiac muscle tissue is controlled involuntarily. While hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates itself to contract.

How Does The Muscular System Work?

Muscles function by contracting. In fact, muscles are the only tissue in the body that has the ability to contract.

    5 Interesting Facts About The Muscular System

  1. You sit on the largest muscle in your body, the Gluteus Maximus.

  2. The hardest working muscles are in the eye. Scientists estimate they may move more than 100,000 times a day!

  3. It takes 17 muscles to smile and 42 muscles to frown.

  4. There are muscles in the root of your hair that give you goose bumps.

  5. Muscles account for about 40% your body weight.

Nerve cells called motor neurons control the skeletal muscles. Each motor neuron controls several muscle cells in a group known as a motor unit. When a motor neuron receives a signal from the brain, it stimulates all of the muscles cells in its motor unit at the same time.

The size of motor units varies throughout the body, depending on the function of a muscle. Muscles that perform fine movements — like those of the eyes or fingers — have very few muscle fibers in each motor unit to improve the precision of the brain’s control over these structures. Muscles that need a lot of strength to perform their function — like leg or arm muscles — have many muscle cells in each motor unit. One of the ways that the body can control the strength of each muscle is by determining how many motor units to activate for a given function. This explains why the same muscles that are used to pick up a pencil are also used to pick up a bowling ball.

Because muscles function by contracting, not extending, many muscles work in pairs to allow movement in opposing directions.

Most skeletal muscles are attached to two bones through tendons. Tendons are tough bands of dense connective tissue that firmly attach muscles to bones.

Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other. One of the bones is pulled towards the other bone, which remains stationary. The place on the stationary bone that is connected via tendons to the muscle is called the origin. The place on the moving bone that is connected to the muscle via tendons is called the insertion. The belly of the muscle is the fleshy part of the muscle in between the tendons that does the actual contraction.

Your arm muscles are a good example. When you contract your biceps muscle, it shortens and pulls the ulna bone in your forearm closer to your upper arm bone, the humerus. When you lower your arm, you relax your biceps and contract the opposing muscle, your triceps.

Although the process is not exactly the same, smooth muscle and cardiac muscle also function by contracting.

What Can Go Wrong With Your Muscular System?

These are some of the problems that can affect your muscular system:

Muscle Sprains

Ligaments are bands of fibrous tissue that connect bones together and help to stabilize joints. When those ligaments are stretched or torn, the result is a muscle sprain, which can cause pain and stiffness.

Muscle Strain

When muscles are stretched or torn, a muscle strain results. Sometimes, these are called “pulled muscles.” They often occur when the muscles are suddenly and powerfully contracted or when they stretch unusually far.


Myopathies are muscle diseases that affect skeletal muscles and are caused by genetic problems or metabolic disorders. Most types of myopathies result in weak skeletal muscles and often develop at a young age.

Chronic Fatigue Syndrome

Chronic fatigue syndrome is a syndrome that’s still being researched by physicians and results in extreme fatigue that doesn’t go away with rest. Symptoms of chronic fatigue syndrome include loss of memory, difficulty concentrating, fatigue, random muscle pain, headaches, unrefreshing sleep and sore throats.


Fibromyalgia is a chronic disorder characterized by widespread muscle pain, stiffness, fatigue, and tenderness in localized areas. While this is a difficult disease to pinpoint and diagnose and can mimic many other medical problems, it has gained acceptance as a recognized health issue over the past decade. Approximately 2% of the entire US population is affected by fibromyalgia.

Muscular Dystrophy

Muscular dystrophy is a genetic disease that damages muscle fibers. The symptoms of muscular dystrophy disease include weakness, loss of mobility and lack of coordination. More than 50,000 Americans suffer with one of the nine forms of the disease, which can occur at any time in a person’s life and has no cure. Most types of muscular dystrophy are caused by the deficiency of a protein known as dystrophin.

Compartment Syndrome

Compartment syndrome is an uncommon exercised induced syndrome and causes pain, swelling and sometimes disability in a person’s legs or arms. Compartment syndrome is more common among athletes but can affect anyone.

Cerebral Palsy

Cerebral palsy impacts posture, balance and motor functions. Brain damage during or before childbirth causes a loss of muscle tone, making it difficult to perform everyday tasks. It is one of the most common congenital disorders.

Myasthenia gravis

Myasthenia gravis is a chronic autoimmune disease that results in muscle weakness and fatigue. A breakdown of the neuromuscular junction causes the brain to lose control over these muscles, which can result in difficulty breathing and swallowing.

Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), often referred to as “Lou Gehrig’s disease,” is a progressive neurodegenerative disease that affects nerve cells in the brain. It is a fatal disease that affects 30,000 Americans at any one time and leads to a loss of control over voluntary muscle movement, making it increasingly difficult to swallow, breath and speak. The disease ultimately causes paralysis and death.

How Do Your Keep Your Muscular System Healthy?

To keep your muscular system healthy, follow these three tips:

  1. Eat a balanced diet. Your muscles need vitamins, minerals, water, protein, carbohydrates and healthy fats so that they can function at their best. Eat a diet rich in natural whole foods such as fruit, vegetables and grains to ensure you are getting adequate nutrients to keep your muscles in good shape. Your muscles are made up of around 70 percent water so make sure you drink at least eight tall glasses of water a day to stay well hydrated.

  2. Do strength training. Strength training, sometimes called weight training or resistance training, will improve your muscular strength and endurance. Perform two to three whole-body workouts per week on non-consecutive days to get the most from your training. You can work out by using resistance machines, dumbbells, barbells, resistance bands or body weight exercises–all of which are effective for improving the condition of your muscular system.

  3. Stretch. Your muscles need to be stretched regularly to keep them in good shape. Stretch all of your major muscles at least after each workout and preferably every day. Muscles often tighten between or after exercises, as a result of sitting for long periods and as part of the aging process. Stretching will lengthen your muscles and prevent exercise-related and age-related shortening. Stretch your muscles gently, holding each stretch for 30 seconds or more. You might also consider a yoga class, which involves a lot of stretching.

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 Coach Kathie Lamir

Your Body: An Owner’s Manual

There was a time when I didn’t know much more about the human body than that my wife’s was beautiful!

Fitness Guru Kathie LamirSee what I mean?

How strange, I thought. We only get one body. It has to last a lifetime. And the better it works, the better we feel. Why wouldn’t we want to know everything about how it works and how to maintain it?

Yet most of us don’t. We know more about the insides of our car than how our body functions.

Maybe that’s because cars come with owner’s manuals, but your body doesn’t.

Well, problem solved.

This article introduces a 12-part series that will explain how your body works. This series is the instruction manual for your body that you never got.

This initial article will briefly describe the 11 human body systems.

Articles about each of the body systems will follow, one a day. Each article will answer these questions . . .

  1. What Does The System Do?

  2. What Makes Up The System?

  3. How Does The System Work?

  4. What Can Go Wrong With The System?

  5. How Do You Keep The System Healthy?

And each article will include “5 Interesting Facts About The System.”

Before starting this discussion of our body systems, however, you must understand that dividing your body into 11 systems for the purpose of studying them does not mean that they are independent systems. Far from it, they are interconnected and dependent on each other.

In fact, some body parts are part of multiple systems. For example, the long bones (like the femur) are not only part of the skeletal system, but they are also part of the circulatory system because they manufacture blood cells. And the ovaries are part of the endocrine system as well as the reproductive system. More about all of this later . . .

These are the 11 main human body systems, presented in alphabetical order.

Circulatory System

The circulatory system is made up of your heart, blood vessels and blood. Your heart pumps oxygen-rich blood from your left ventricle into your biggest artery, the aorta. From there, the aorta branches into smaller arteries, which then branch into even-smaller arteries that travel all over the body. When blood reaches the smallest blood vessels, called capillaries, an exchange occurs. Oxygen, nutrients and hormones are deposited into the cells and waste material from the cells, such as carbon dioxide, is collected for the return trip to the heart.

Veins carry the blood back to the heart where it enters the right atria, passes through the right ventricle and is sent to your lungs where, in capillaries in the lungs, the waste carbon dioxide is deposited and oxygen is picked up. The newly oxygenated blood returns to the heart and, this time, it enters the left atria. From there it goes to the left ventricle and, from there, it is pumped again .

Click here to learn more about your circulatory system.

Digestive System

Your digestive system consists of organs that break down food into the protein, vitamins, minerals, carbohydrates and fats that your body uses for energy and for building and repairing cells and tissues.

Food passes from your mouth down through a muscular tube called the esophagus, and into the stomach, where food continues to be broken down. The partially digested food passes into the small intestines where it is broken down into nutrients which enter the bloodstream through tiny hair-like projections called villi. The liver, the gallbladder and the pancreas produce enzymes and substances that help with digestion in the small intestine.

The last section of the digestive tract is the large intestine, which includes the cecum, colon, and rectum. Indigestible remains of food are eliminated through the anus.

Click here to learn more about your digestive system.

Endocrine System

The endocrine system is made up of a group of glands that produce the body’s long-distance messengers, or hormones. Hormones are chemicals that control body functions such as metabolism, growth, and sexual development. The glands, which include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pineal body, pancreas, ovaries, and testes, release hormones directly into the bloodstream, which transports the hormones to organs and tissues throughout the body.

Click here to learn more about your endocrine system.

Immune System

The immune system is our body’s defense system against infections and diseases. Organs, tissues, cells, and cell products work together to respond to dangerous organisms (like viruses or bacteria) and substances that may enter the body from the environment.

An anatomic response physically prevents threatening substances from entering your body. Examples of the anatomic system include the mucous membranes and the skin. If substances do get by, the inflammatory response goes on attack.

The inflammatory system works by excreting the invaders from your body. Sneezing, runny noses, and fever are examples of the inflammatory system at work.

When the inflammatory response fails, the immune response goes to work. This is the central part of the immune system and it is made up of white blood cells, which fight infection by gobbling up antigens. About a quarter of white blood cells, called the lymphocytes, migrate to the lymph nodes and produce antibodies which fight disease.

Click here to learn more about your immune system.

Lymphatic System

The lymphatic system has three main purposes. It removes excess fluid and waste products from the spaces between the cells and returns them to the blood stream. It aids the immune system in destroying and removing waste, debris, dead blood cells, pathogens, toxins, and cancer cells. And it also absorbs fats and fat-soluble vitamins from the digestive system and delivers these nutrients to be used by the cells of the body.

Click here to learn more about your lymphatic system.

Muscular System

The muscular system is made up of tissues that work with the skeletal system to control movement of the body. Some muscles—like the ones in your arms and legs—are voluntary, meaning that you decide when to move them. Other muscles, like the ones in your stomach, heart, intestines and other organs, are involuntary. This means that they are controlled automatically by the nervous system and hormones—you often don’t even realize they’re at work.

Muscles also generate heat to help regulate your body’s temperature and maintain your posture.

Click here to learn more about your muscular system.

Nervous System

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.

This “network” consists of the spinal cord and nerves. The spinal cord runs from the brain down through the back to nerves which branch out to every organ and part of your 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.

Click here to learn more about your nervous system.

Reproductive System

The reproductive system allows humans to produce children. Sperm from the male, which is produced in the testes, fertilizes the female’s egg, or ovum, in the fallopian tube. The fertilized egg travels from the fallopian tube to the uterus, where the fetus develops over a period of nine months.

Click here to learn more about your reproductive system.

Respiratory System

The respiratory system brings air into the body and removes carbon dioxide. It includes the nose, trachea, and lungs.

When you breathe in, air enters your nose or mouth and goes down a long tube called the trachea. The trachea branches into two bronchial tubes, or primary bronchi, which go to the lungs. The primary bronchi branch off into even smaller bronchial tubes, or bronchioles. The bronchioles end in the alveoli, or air sacs. Oxygen follows this path and passes through the walls of the air sacs and blood vessels and enters the blood stream. At the same time, carbon dioxide passes into the lungs and is exhaled.

Click here to learn more about your respiratory system.

Skeletal System

The skeletal system has a number of functions, some obvious and some less so. Of course, it supports your body and gives it structure.

However, in addition, your skeletal system works with the bones to allow movement, protects your internal organs, produces blood (in the bone marrow) and stores minerals such as calcium and phosphorous which it releases into the blood when necessary.

Click here to learn more about your skeletal system.

Urinary System

The urinary system eliminates waste from the body, as urine. The kidneys remove waste from the blood. The waste combines with water to form urine. From the kidneys, urine travels down two thin tubes called ureters to the bladder. When the bladder is full, urine is discharged through the urethra.

Click here to learn more about your urinary system.

Oh . . . if you want to learn more from the world’s greatest personal trainer, my wife Kathie Lamir, this is her website.