Muscles enable your heart to beat, your chest to rise and fall as you breathe, and your blood vessels to help regulate the pressure and flow of blood through your body.
When we smile and talk, muscles are helping us communicate, and when we exercise, they help us stay physically fit and healthy. The movements your muscles make are coordinated and controlled by the brain and nervous system. The involuntary muscles are controlled by structures deep within the brain and the upper part of the spinal cord called the brain stem.
The voluntary muscles are regulated by the parts of the brain known as the cerebral motor cortex and the cerebellum. When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract.
The motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa. The cerebellum pronounced: ser-uh-BEL-um coordinates the muscle movements ordered by the motor cortex. This feedback results in smooth, coordinated motion. If you want to lift your arm, your brain sends a message to the muscles in your arm and you move it.
When you run, the messages to the brain are more involved, because many muscles have to work in rhythm. Muscles move body parts by contracting and then relaxing. So they work in pairs of flexors and extensors.
The flexor contracts to bend a limb at a joint. Joints allow our bodies to move in many ways. Some joints open and close like a hinge such as knees and elbows , whereas others allow for more complicated movement — a shoulder or hip joint, for example, allows for backward, forward, sideways, and rotating movement.
Joints are classified by their range of movement. The dome of the skull, for example, is made of bony plates, which must be immovable to protect the brain. 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. They are linked by cartilage, as in the spine. Each of the vertebrae in the spine moves in relation to the one above and below it, and together these movements give the spine its flexibility.
Freely movable , or synovial pronounced: sih-NO-vee-ul , joints move in many directions. The main joints of the body — found at the hip, shoulders, elbows, knees, wrists, and ankles — are freely movable. They are filled with synovial fluid, which acts as a lubricant to help the joints move easily. There are three kinds of freely movable joints that play a big part in voluntary movement:.
As strong as bones are, they can break. Muscles can weaken, and joints as well as tendons, ligaments, and cartilage can be damaged by injury or disease. The following are problems that can affect the bones, muscles, and joints in teens:. Arthritis is the inflammation of a joint, and people who have it experience swelling, warmth, pain, and often have trouble moving. Although we often think of arthritis as a condition that affects only older people, arthritis also can affect children and teens.
Health problems that involve arthritis in kids and teens include juvenile idiopathic arthritis JIA, also know as juvenile rheumatoid arthritis, or JRA , lupus , Lyme disease , and septic arthritis a bacterial infection of a joint. A fracture is when a bone breaks; it may crack, snap, or shatter. After a bone fracture, new bone cells fill the gap and repair the break. Applying a strong plaster cast, which keeps the bone in the correct position until it heals, is the usual treatment.
If the fracture is complicated, metal pins and plates can be placed to better stabilize the fracture while the bone heals.
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Types of joints Joints are described by how much movement they allow. The three broad classes of joints include: Immovable — the two or more bones are in close contact, but no movement can occur — for example, the bones of the skull.
The joints of the skull are called sutures. Slightly movable — two or more bones are held together so tightly that only limited movement is permitted — for example, the vertebrae of the spine.
Freely movable — most joints within the human body are this type. Motion is the purpose of the joint. Freely moving joints The six types of freely movable joint include: Ball and socket joint — the rounded head of one bone sits within the cup of another, such as the hip joint or shoulder joint.
Movement in all directions is allowed. Saddle joint — this permits movement back and forth and from side to side, but does not allow rotation, such as the joint at the base of the thumb.
Hinge joint — the two bones open and close in one direction only along one plane like a door, such as the knee and elbow joints. Condyloid joint — this permits movement without rotation, such as in the jaw or finger joints. Pivot joint — one bone swivels around the ring formed by another bone, such as the joint between the first and second vertebrae in the neck. Gliding joint — or plane joint. Smooth surfaces slip over one another, allowing limited movement, such as the wrist joints.
Types of movement To achieve movement, the joint may: Slide one broad and flat surface across another — examples include the bones in the wrist or ankle. Synovial Joints. Synovial joints are characterized by the presence of an articular capsule between the two joined bones. Bone surfaces at synovial joints are protected by a coating of articular cartilage. Synovial joints are often supported and reinforced by surrounding ligaments, which limit movement to prevent injury.
There are six types of synovial joints:. Major gliding joints include the intervertebral joints and the bones of the wrists and ankles. These joints allow for flexion and extension. Major hinge joints include the elbow and finger joints. At the top of the spine, the atlas and axis form a pivot joint that allows for rotation of the head.
The wrist joint between the radius and the carpal bones is an example of a condyloid joint. The hip and shoulder joints are examples of ball and socket joints. See more from our free eBook library. Human Anatomy Atlas offers thousands of models to help understand and communicate how the human body looks and works.
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