4. Muscles are bundles of cells and fibers.
Muscles work in a very simple way. All they do is tighten up--that is, contract--and relax.
You have two sets of muscles attached to many of your bones which allow them to move.

5. Muscles are made up of millions of tiny protein filaments which work together to produce motion in the body.
Each of more than 600 muscles is served by nerves which link the muscle to the brain and spinal cord.
Muscle is attached to bone by tendons and other tissues, and exerts force by converting chemical energy into tension and contraction.
Muscles move and make us capable of a variety of actions by simply contracting and becoming shorter.
Muscles pull but they cannot push

6. Muscle Cell Types
skeletal (or voluntary/striated) muscle, the most abundant tissue in the human body, producing movement. Each skeletal-muscle fiber is roughly cylindrical, contains many nuclei, and is crossed by alternating light and dark bands called striations. Fibers bind together, via connective tissue, into bundles; and these bundles, in turn, bind together to form muscles.
smooth muscle, forming the muscle layers in the walls of the digestive tract, bladder, various ducts, arteries and veins, and other internal organs. Smooth- muscle cells are elongated and thin, not striated, have only one nucleus, and interlace to form sheets rather than bundles of muscles.
cardiac (or heart) muscle, a cross between the smooth and striated muscles, comprising the heart tissue

7. Skeletal muscles are also known as voluntary muscles - these are the muscles that you can control. Your leg won't bend to kick the ball unless you want it to, and your dog's dinner won't find its way into the dish unless you tell your muscles to make it happen.
Skeletal muscles are the body's most abundant tissue, comprising about 23% of a woman's body weight and about 40% of a man's body weight.

8. Voluntary muscles, such as your arms and legs can be controlled by your thoughts.
All this muscle action is controlled by your brain, which sends and receives signals through your nervous system.

9. Smooth muscles are sometimes also called involuntary muscles
Smooth muscles are sometimes also called involuntary muscles. You can't control this type of muscle - these muscles work involuntarily, which means that your brain and body tell these muscles what to do without you even thinking about it. You can't use your smooth muscles to make a muscle in your arm or jump into the air.
Smooth muscles are in your stomach, and they work by contracting and relaxing to allow food to pass into your small intestine. If you've ever thrown up, then you've felt the smooth muscles in your stomach at work. The muscles push the food back out of the stomach so it comes up through the esophagus and out of the mouth

10. Muscle actions can be voluntary or involuntary
Muscle actions can be voluntary or involuntary. Involuntary muscles, such as the heart, diaphragm and intestines, are automatically controlled by the brain. You don't have to think about making them work. For example the heart beats between 60 and 80 beats every minute without you having to think about it.
The muscle that makes up the heart is called the myocardium. It is sometimes also called cardiac muscle. The thick muscles of the heart contract (tighten up) to pump blood out and then relax (loosen up) to let blood back in after it's circulated through the body.

11. You have over 30 facial muscles which create looks like surprise, happiness, sadness, and frowning.
Eye muscles are the busiest muscles in the body. Scientists estimate they may move more than 100,000 times a day!
                              

12. Humerus The humerus is the large bone in the arm that connects the shoulder to the elbow.
Radius This is one of the bones found in the forearm.
Ulna This is the other bone found in the forearm.
Biceps The bicep muscles bend the forearm arm at the elbow.
Triceps These muscles allow the forearm to extend to a straightened position.
Deltoid The deltoid is the muscle located at the top part of the arm in the shoulder.

14. Gluteus Maximus This is the main muscle in the hip.
Quadricep Muscles These muscles allow a person to straighten the leg at the knee and bend the thigh at the hips.
Femur The strongest, longest bone in the body, the femur extends from the hip down to the knee.
Patella The patella is also known as the kneecap.
Calf Muscles Located at the back of the lower leg, calf muscles allow a person to stand on their toes.
Fibula The smaller bone found in the lower leg.
Tibia The larger of the two bones found in the lower leg.
Achilles Tendon This muscle is attached to the heel and extends up into the calf muscles.

15. Phalanges These bones are found in the toes -- two in the big toe and three in the rest of the toes.
Metatarsals Metatarsals connect the phalanges with the tarsals at mid-foot.
Tarsals These bones make up the ankle.
Plantar Aponeurosis This strong ligament keeps the bones of the foot in place and protects the nerves, muscles and blood vessels.
Calcaneus This is the heel bone of the foot.

16. Because there are so many skeletal muscles in your body, it would be impossible to name every single one - it would be like calling out 650 names in class! But some of the more important skeletal muscles may be ones that you've heard of already.
In each of your shoulders is a deltoid. Your deltoid muscles help you move your shoulders every which way - from swinging a softball bat to shrugging your shoulders when you're not sure of an answer.
The pectoralis muscles are found on each side of your upper chest. These are usually called pectorals, or pecs for short. When many boys hit puberty, their pectoral muscles become larger. Many athletes and bodybuilders often have large pecs, as well.
Below these pectorals, down under your rib cage, are your rectus abdominus muscles, or abdominals. They are also sometimes called abs for short.

17. Remember before when you made a muscle with your arm
Remember before when you made a muscle with your arm? The muscle in your upper arm is called your bicep. When you contract your bicep, you can actually see it push up under your skin.
And when you pulled your leg down and through to do that pretend kick? The muscle that you contracted in the front of your thigh is called quadriceps or quad, for short. Many people who run, bike, or play certain kinds of sports can develop their quads and make them get large and strong.
And when it's time for you to take a seat? You'll be sitting on your gluteus maximus, the muscles that are under the skin and fat in your behind!