It is made up of a mesh-like network of tiny pieces of bone called trabeculae pronounced: truh-BEH-kyoo-lee. This is where red and white blood cells are formed in the marrow. Bones are fastened to other bones by long, fibrous straps called ligaments pronounced: LIG-uh-mentz. Cartilage pronounced: KAR-tul-ij , a flexible, rubbery substance in our joints, supports bones and protects them where they rub against each other.
Muscles pull on the joints, allowing us to move. They also help the body perform other functions so we can grow and remain strong, such as chewing food and then moving it through the digestive system. The human body has more than muscles. They are connected to bones by tough, cord-like tissues called tendons , which allow the muscles to pull on bones.
If you wiggle your fingers, you can see the tendons on the back of your hand move as they do their work. 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. Cardiac pronounced: KAR-dee-ak muscle is found in the heart.
Cardiac muscle is also an involuntary type of muscle. Its rhythmic, powerful contractions force blood out of the heart as it beats. Muscles and Movement Even when you sit perfectly still, there are muscles throughout your body that are constantly moving. 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.
Tendons another type of tough connective tissue on each side of a joint attach to muscles that control movement of the joint. Tendons connect muscles to bones. Fluid-filled sacs, called bursas, between bones, ligaments, or other nearby structures. They help cushion the friction in a joint. Synovial fluid. A clear, sticky fluid secreted by the synovial membrane. This is a curved part of cartilage in the knees and other joints. This space is referred to as the synovial or joint cavity and is filled with synovial fluid.
Synovial fluid lubricates the joint, reducing friction between the bones and allowing for greater movement. The ends of the bones are covered with articular cartilage, a hyaline cartilage, and the entire joint is surrounded by an articular capsule composed of connective tissue that allows movement of the joint while resisting dislocation.
Articular capsules may also possess ligaments that hold the bones together. Synovial joints are capable of the greatest movement of the three structural joint types; however, the more mobile a joint, the weaker the joint.
Knees, elbows, and shoulders are examples of synovial joints. The functional classification divides joints into three categories: synarthroses, amphiarthroses, and diarthroses. A synarthrosis is a joint that is immovable.
This includes sutures, gomphoses, and synchondroses. Amphiarthroses are joints that allow slight movement, including syndesmoses and symphyses. Diarthroses are joints that allow for free movement of the joint, as in synovial joints. The wide range of movement allowed by synovial joints produces different types of movements. The movement of synovial joints can be classified as one of four different types: gliding, angular, rotational, or special movement.
Gliding movements occur as relatively flat bone surfaces move past each other. Gliding movements produce very little rotation or angular movement of the bones. The joints of the carpal and tarsal bones are examples of joints that produce gliding movements. Angular movements are produced when the angle between the bones of a joint changes.
There are several different types of angular movements, including flexion, extension, hyperextension, abduction, adduction, and circumduction. Flexion , or bending, occurs when the angle between the bones decreases.
Moving the forearm upward at the elbow or moving the wrist to move the hand toward the forearm are examples of flexion. Extension is the opposite of flexion in that the angle between the bones of a joint increases. Straightening a limb after flexion is an example of extension.
Extension past the regular anatomical position is referred to as hyperextension. This includes moving the neck back to look upward, or bending the wrist so that the hand moves away from the forearm. Abduction occurs when a bone moves away from the midline of the body. Examples of abduction are moving the arms or legs laterally to lift them straight out to the side.
Adduction is the movement of a bone toward the midline of the body. Movement of the limbs inward after abduction is an example of adduction. Circumduction is the movement of a limb in a circular motion, as in moving the arm in a circular motion. Rotational movement is the movement of a bone as it rotates around its longitudinal axis.
Rotation can be toward the midline of the body, which is referred to as medial rotation , or away from the midline of the body, which is referred to as lateral rotation.
Movement of the head from side to side is an example of rotation. Some movements that cannot be classified as gliding, angular, or rotational are called special movements.
Inversion involves the soles of the feet moving inward, toward the midline of the body. Eversion is the opposite of inversion, movement of the sole of the foot outward, away from the midline of the body. The articular capsule prevents wear and tear on the bones. The bones in a synovial joint are connected by ligaments. The movement at a synovial joint is caused by the muscles attached across the joint.
Muscles are attached to bone by tendons. Tendons are very strong, inelastic connective tissues that allow a muscle to pull on a bone to move it. Different types of synovial joints allow varying degrees of movement.
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