Download Chapter 36 The skeletal system supports the body, protects internal

Chapter 36
The skeletal system supports the body, protects internal organs, provides for movement, stores mineral reserves, and
provides a site for blood cell formation. The human body has 206 bones and is divided into 2 parts:
-Axial Skeleton: Skull, vertebral column, and rib cage. Supports central axis of the body.
-Appendicular Skeleton: Bones of arms, legs, pelvis, and shoulders. (Know bones of skeletal system on p. 922)
Bones are living tissue- a solid network of living cells and protein fibers that are surrounded by deposits of calcium salts.
The bone is surrounded by a tough layer of connective tissue called periosteum. Blood vessels pass through this to carry
oxygen and nutrients to the bone.
Below the periosteum is a layer of dense compact bone, filled with a network of tubes called Haversian canals that contain
blood vessels and nerves.
Spongy bone is under the compact bone- it tends to be near the ends of long bones and is very strong. It adds strength
without adding mass. Within the bone are three types of bone cells.
-Osteocytes: mature bone cells
-Osteoclasts: cells that break down bone
-Osteoblasts: cells that produce bone
Cavities within the bone contain a soft tissue called bone marrow. Yellow marrow is made up of fat cells. Red marrow
produces red blood cells, some white blood cells, and platelets.
The skeleton of an embryo is made up of cartilage, which does not contain blood vessels. About 7 months before birth,
ossification (bone formation) occurs as osteoblasts secrete mineral deposits that replace the cartilage and then mature
into osteocytes. Bones grow through early adulthood. Once ossification is complete, growth stops.
A place where one bone meets another is called a joint. They permit bones to move without damaging each other. There
are 3 types:
1. Immovable: Allow no movement. Like where the bones in the skull meet.
2. Slightly Moveable: Allow a small amount of restricted movement. Like the joints between vertebrae.
3. Freely Moveable: 4 common types:
-Ball and socket: Like shoulder/arm joint. Large range of motion.
-Hinge: Like knee joint. Open and close motion
-Pivot: Like vertebrae under skull that allow head to move back and forth.
-Saddle Joint: Like thumb. Allows movement in two directions.
In freely movable joints, cartilage covers the surfaces where two bones come together to protect the bones as they move
against each other. The joints are surrounded by a joint capsule that is made up of two parts:
1. Ligaments: Tough strips of connective tissue that hold bones together at a joint.
2. Synovial Fluid: Enables the surfaces of the joint to slide over each other smoothly.
There are 3 different types of muscle:
1. Skeletal: Attached to bone and responsible for voluntary movement.
2. Smooth: Responsible for involuntary movement, like in digestive tract and blood vessels.
3. Cardiac: Only found in the heart.
Muscle Contraction
Skeletal muscles are made of filaments. Thick filaments contain a protein called myosin. Thin filaments are made of of a
protein called actin. The filaments are arranged in units called sarcomeres and separated by Z lines.
These filaments cause a muscle to contract when the thin filaments slide over the thick filaments. The myosin attaches to
a binding site on the actin, forming a crossbridge. Powered by ATP, the myosin pulls the actin toward the center of the
sarcomere. The bridge breaks, and the myosin attaches to a new binding site and the process starts again. Let's see!
Skeletal muscles are joined to bones by tough connective tissue called tendons. Most skeletal muscles work in opposing
pairs- one set will flex (bend) a joint and one set will straighten a joint. A good example are biceps that flex your elbow
joint and triceps that straighten it. Regular exercise is important to maintain muscle strength and flexibility.
The integumentary system is your skin. It serves as a barrier against infection and injury, helps to regulate body
temperature, removes waste products from the body, and provides protection against UV radiation from the sun.
The skin is made up of two main layers:
1. Epidermis: Outer layer of skin. The outermost layer is made up of dead skin cells. Under that are living cells. Cells in
the inner layer undergo rapid division and push older cells to the surface. The older cells start producing keratin- a tough,
fibrous protein. When these cells die, the keratin forms a tough, flexible, waterproof outer skin layer. This layer is replaced
every 4-5 weeks!
The epidermis also contains melanin- a dark brown pigment that helps protect the skin from ultraviolet sun rays. Different
skin color is caused by different amounts of melanin.
The inner layer of skin that lies beneath the epidermis is called the dermis. It has collagen, fibers, blood vessels, nerve
endings, glands, sensory receptors, smooth muscles, and hair follicles. This layer plays a large role in homeostasis. On
cold days, blood vessels narrow to prevent heat loss. On hot days, they widen to allow heat loss.
Hair and nails are made of keratin. Hair follicles are located in the dermis and extend through the epidermis. Rapid cell
growth at the base of the hair shaft causes growth. Sebaceous glands maintain the condition of each hair.
Nails grow in a similar way as hair. Fingernails grow about 4 times as fast as toenails.