The Human Muscular System
Types of muscle
Smooth muscles are sometimes also called involuntary muscles and they are usually in sheets, or layers,
with one layer of muscle behind the other. You cannot control this type of muscle. Your brain and body tell these muscles
what to do without you even thinking about it. You cannot use your smooth muscles to make a muscle in your arm or jump into
However, smooth muscles are at work all over your body. In your
stomach and digestive system, they contract (tighten up) and relax to allow food to make its
journey through the body. Your smooth muscles come in handy if you're sick and you need to throw up. The muscles push the
food back out of the stomach so it comes up through the esophagus and out of the mouth.
Smooth muscles are also found in your bladder. When they are relaxed, they allow you to hold in urine (pee)
until you can get to the bathroom. Then they contract so that you can push the urine out. These muscles are also in a woman's
uterus, which is where a baby develops. There they help to push the baby out of his or her mother's body when it is time to
You will find smooth muscles at work behind the scenes in your eyes, too. These muscles keep the eyes focused.
The muscle that makes up the heart is called cardiac muscle. It is also known as the myocardium. The thick muscles of the
heart contract to pump blood out and then relax to let blood back in after it is circulated through the body.
Just like smooth muscle, cardiac muscle works all by itself with no help from you. A special group of cells
within the heart is known as the pacemaker of the heart because it controls the heartbeat.
They are also sometimes called striated muscle because the light and dark parts of the muscle
fibers make them look striped.
Skeletal muscles are voluntary muscles, which means you can control what they do. Your leg will not
bend to kick the soccer ball unless you want it to.
These muscles help to make up the musculoskeletal system - the combination of your muscles and your
skeleton, or bones. Together, the skeletal muscles work with your bones to give your body power
and strength. In most cases, a skeletal muscle is attached to one end of a bone. It stretches all the way across a joint (the
place where two bones meet) and then attaches again to another bone.
Skeletal muscles are held to the bones with the help of tendons. Tendons are cords made of tough tissue,
and they work as special connector pieces between bone and muscle. The tendons are attached so well that when you contract
one of your muscles, the tendon and bone move along with it.
Skeletal muscles come in many different sizes and shapes to allow them to do many types of jobs. Some of
your biggest and most powerful muscles are in your back, near your spine. These muscles help keep you upright and standing
tall. They also give your body the power it needs to lift and push things.
Muscles in your neck and the top part of your back aren't as large, but they are capable of some pretty amazing
things: Try rotating your head around, back and forth, and up and down to feel the power of the muscles in your neck. These
muscles also hold your head high.
Muscle Contraction / Movement
Nerve impulses bring about muscle contraction and contraction causes fiber shortening so light and dark fibers
become closer together. As contraction of muscle ends, fibers relax and muscle length is once again attained due to increased
length of muscle fiber.
The smallest muscle of the skeleton is the stapedius, which measures 1/20th of an inch. It is the activator
of the stirrup that sends vibrations from the eardrum to the inner ear.
The largest muscle is the latissimus dorsi. This is the flat muscle of the back that operates during arm
There are over 650 muscles in your body. A smile uses 17 muscles, a frown uses 43.
The eye muscle is the fastest reacting muscle of the whole body. It contracts in less than 1/100th of a second.
The longest muscle in your body is the sartorius.
You may not think of it as a muscular body part, but your face has plenty of muscles. You can check
them out next time you look in the mirror.
Facial muscles do not all attach directly to bone as if they do in the rest of the body. Instead, many of
them attach under the skin. This allows you to contract your facial muscles just a tiny bit and make dozens of different kinds
of faces. Even the smallest movement can turn a smile into a frown. You can raise your eyebrow to look surprised or wiggle
And while you're looking at your face, don't pass over your tongue - a muscle that's attached only at one end! Your tongue is actually made of a group
of muscles that work together to allow you to talk and help you chew food. Stick out your tongue and wiggle it around to see
those muscles at work.
In each of your shoulders is a deltoid muscle. Your deltoid muscles help you move your shoulders in many directions
- from swinging a softball bat to shrugging your shoulders when you are 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
have large pecs, too.
Below these pectorals, down under your rib cage, are your rectus abdominus muscles, or abdominals.
They are also sometimes called abs for short.
When you make a muscle in your arm, you tense your biceps muscle. When you contract your biceps muscle,
you can actually see it push up under your skin.
Your quadriceps or quads, are the muscles on the front of your thighs. Many people who run,
bike, or play sports develop large, strong quads. Moreover, when it is time for you to take a seat? You will be sitting on
your gluteus maximus the muscle that is under the skin and fat in your behind.