Muscular and Skeletal Systems

Muscular System

The muscular system controls movement--both the kind of movement that allows you to walk and run, and the kind of movement that you have no control over, such as your heart beating and your stomach churning.

The muscles you CAN control are called skeletal (or voluntary) muscles, and the muscles you cannot control are called smooth (or involuntary) muscles. Your arm and leg muscles are voluntary muscles, and your stomach and heart muscles are involuntary.

Muscles create movement by contracting and relaxing. Your muscles use energy to contract, and they produce mechanical energy (or movement) and thermal energy (or heat). Muscles change size depending on how much you use them.

Kinds of Muscular Tissue

1. Skeletal Muscles: Voluntary muscles that move bones, such as the muscles in your arms or legs. The connective tissues that attach skeletal muscle to bones are called tendons. Skeletal muscles usually work in pairs around a bone--when one muscle contracts, the other relaxes.
2. Smooth Muscles: Involuntary muscles that work in internal organs like your digestive tract.
3. Cardiac Muscles: Involuntary muscles that make your heart pump. Cardiac muscles are found ONLY in your heart.

Skeletal System

The skeletal system has many functions:

1. It supports your body and gives it shape.
2. It protects your internal organs, such as your lungs and brain.
3. It stores calcium and other minerals.
4. It produces red and white blood cells.

The skeletal and muscular systems work together to create

Movement.

Cartilage

1. The skeleton is made of hard bones and a flexible hard tissue called cartilage. Cartilage is a smooth, firm, and flexible tissue that is found on the ends of bones. Cartilage cushions and reduces friction between bones in your joints. Cartilage is also found in your ears and nose.

Bones

1. Though bones seem just like hard sticks in your body, they are actually complex organs made of different kinds of tissue. A hard outer membrane called the periosteum covers the outside of the bone. The periosteum has blood vessels and nerve endings that can signal pain.
2. Compact Bone: Compact bone is beneath the periosteum. Calcium and phosphorus minerals, which are deposited and stored in the compact bone, harden the bones.
3. Spongy Bone: Spongy bone is found beneath the compact bone in long bones, such as your thighbone or arm bone. Spongy bone is sort of like a hard sponge; it has tons of little air pockets, which make the bone lighter.
4. Bone Marrow: Bone marrow fills bone cavities and the spaces in spongy bone. Bone marrow is either yellow or red. The yellow marrow is made of fat, while the red marrow is made of a material that produces blood cells.

Joints

1. Joints are where bones meet, such as your knees or elbows. Ligaments, a type of connective tissue, hold the bones together at the joints. Usually, joints allow movement, although some joints, such as the ones in your skull, are fixed and don’t move. Your body moves around joints. There are four main types of joints.
   1. Pivot Joint: Bones pivot, or rotate around a central point. Like the joints in your wrists, neck, and elbows.
   2. Gliding Joint: Bones glide over each other. Like your wrists, ankles, and vertebrae.
   3. Hinge Joint: Bones hinge at a central point, sort of like the hinge on a door. In your knees, elbows, fingers, and toes.

Ball-and-Socket Joint: The bone is in a socket so it can rotate in a circle. In your shoulders and hips.