Larger text size Large text size Regular text size. Bones are made up of two types of bone tissues: Compact bone is the solid, hard outside part of the bone.
It looks like ivory and is extremely strong. Holes and channels run through it, carrying blood vessels and nerves. Cancellous pronounced: KAN-suh-lus bone , which looks like a sponge, is inside compact bone. It is made up of a mesh-like network of tiny pieces of bone called trabeculae pronounced: truh-BEH-kyoo-lee. This is where bone marrow is found. How Do Bones Grow? Bone contains three types of cells: osteoblasts pronounced: AHS-tee-uh-blastz , which make new bone and help repair damage osteocytes pronounced: AHS-tee-o-sites , mature bone cells which help continue new born formation osteoclasts pronounced: AHS-tee-o-klasts , which break down bone and help to sculpt and shape it What Are Muscles and What Do They Do?
Humans have three different kinds of muscle: Skeletal muscle is attached by cord-like tendons to bone, such as in the legs, arms, and face. Skeletal muscles are called striated pronounced: STRY-ay-ted because they are made up of fibers that have horizontal stripes when viewed under a microscope. These muscles help hold the skeleton together, give the body shape, and help it with everyday movements known as voluntary muscles because you can control their movement.
They can contract shorten or tighten quickly and powerfully, but they tire easily. Smooth, or involuntary, muscle is also made of fibers, but this type of muscle looks smooth, not striated. We can't consciously control our smooth muscles; rather, they're controlled by the nervous system automatically which is why they're also called involuntary.
Examples of smooth muscles are the walls of the stomach and intestines, which help break up food and move it through the digestive system. Smooth muscle is also found in the walls of blood vessels, where it squeezes the stream of blood flowing through the vessels to help maintain blood pressure.
Smooth muscles take longer to contract than skeletal muscles do, but they can stay contracted for a long time because they don't tire easily. Cardiac muscle is found in the heart. The walls of the heart's chambers are composed almost entirely of muscle fibers. Cardiac muscle is also an involuntary type of muscle.
Its rhythmic, powerful contractions force blood out of the heart as it beats. How Do Muscles Work? Joints are classified by their range of movement: Immovable, or fibrous, joints don't move. The dome of the skull, for example, is made of bony plates, which move slightly during birth and then fuse together as the skull finishes growing.
Between the edges of these plates are links, or joints, of fibrous tissue. Fibrous joints also hold the teeth in the jawbone. Partially movable, or cartilaginous pronounced: kar-tuh-LAH-juh-nus , joints move a little. 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 say: TEN-dunz.
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 the biggest and most powerful muscles are your calf and thigh muscles. They 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. 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 don't all attach directly to bone like 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 your nose. 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. Because there are so many skeletal muscles in your body, we can't list them all here. But here are a few of the major ones:. Reviewed by: KidsHealth Medical Experts. Larger text size Large text size Regular text size. Smooth Muscles Smooth muscles — sometimes also called involuntary muscles — are usually in sheets, or layers, with one layer of muscle behind the other.
Try imagining a bicep curl. As you pull your fist upward to your shoulder, the angle between your forearm and bicep decreases as the flexor muscle tightens and contracts. Extensors serve the opposite purpose -- extending and straightening joints. In a bicep curl, the extensor muscles contract as the fist is let down from the shoulder.
The same occurs with walking or running, as hip extensors contract and pull the thigh back to the anatomical position. By virtue of generating the movement of exercise, flexor and extensor muscles already benefit from your regular routine. You can, however, target specific groups of flexors and extensors. For example, try performing barbell wrist curls and palm press stretches to work out wrist flexors and extensors.
Stretching and strengthening these muscles can relieve the stiffness and soreness that can occur when muscles are weakened or overworked.
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