CHAPTER 36 SKELETAL, MUSCULAR, AND INTEGUMENTARY SYSTEMS

There are 206 bones in a human adult 36-1 The Skeletal System What are the functions of the skeletal system? The skeleton supports the body, protects internal organs, provides for movement, stores mineral reserves, and provides a site for blood cell formation. There are 206 bones in a human adult

Axial skeleton – supports the central axis of the body; skull, vertebral column, and rib cage   Appendicular skeleton – bones of arms and legs What do you think is a better model of a bone, a stick of chalk or a sponge? The chalk may look more like a bone but the sponge shows what the structure actually looks like inside.

What passes through the tubes and spaces inside bone? Blood vessels and nerves PERIOSTEUM Bone is surrounded by a tough layer of connective tissue Haversian canals Network of tubes that contain blood vessels and nerves.

Bone marrow Cavities that contain a soft tissue There are two types of bone marrow: yellow and red. Yellow marrow is made up primarily of fat cells. Red marrow produces red blood cells, some kinds of white blood cells, and cell fragments called platelets.

Cartilage -Cells are scattered in a network of protein fibers—tough collagen and flexible elastin. -Cartilage does not contain blood vessels -Cartilage cells must rely on nutrients from the tiny blood vessels in surrounding tissues -Cartilage is dense and fibrous, it can support weight, despite its extreme flexibility

Ossification -Cartilage is replaced by bone during the process of bone formation -Osteoblasts create bone -Osteocytes maintain the cellular activities of bone -Osteoclasts break down bone   Force must be placed on bone for ossification to occur, because it is force that stimulates the osteoblasts to secrete the minerals that replace cartilage

What effect do you think an exercise such as walking would have on the bones of the legs? It would stimulate ossification, so the bones would contain more minerals and be stronger What do you think might happen to the bones that are not exposed to force, such as the bones of astronauts in zero gravity? The bones would lose minerals because of lack of force exerted on them, so they become weaker

Bone formation occurs in babies and children Seven months before birth cartilage is gradually replaced by bone When a person grows, the growth plates are lengthening in the long bones When you stop growing, those growth plates are then filled in with bone Adults do retain some cartilage Tip of nose, ears, where ribs attach to the sternum

Bone formation also occurs when a bone is broken Osteoclasts remove damaged bone tissue Osteoblasts produce new bone tissue The repair of a broken bone can take months because the process is slow and gradual

What are the three kinds of joints? Depending on its type of movement, a joint is classified as immovable, slightly movable, or freely movable Immovable Joints Where the bones in the skull meet Slightly Movable Joints The joints between the two bones of the lower leg and the joints between adjacent vertebrae are examples of slightly movable joints.

Freely Movable Joints - Ball-and-socket joints permit circular movement—the widest range of movement - Hinge joints permit back-and-forth motion, like the opening and closing of a door - Pivot joints allow one bone to rotate around another - Saddle joints permit one bone to slide in two directions

Structure of joints. -Ends of bones are covered with a Structure of joints -Ends of bones are covered with a smooth layer of cartilage -Joints are surrounded by a fibrous joint capsule that helps hold bones together LIGAMENTS – strip of tough connective tissue that hold bones together Synovial fluid – lubricates the ends so bones can slide past each other smoothly

36-2 The Muscular System What are the functions of muscles? To provide movement What are the three types of muscle? Skeletal, smooth and cardiac

Skeletal -Skeletal muscles are usually attached to bones -Skeletal muscles are responsible for such voluntary movements as typing on a computer keyboard, dancing, or winking an eye -When viewed under a microscope at high magnification, skeletal muscle appears to have alternating light and dark bands or stripes called striations. For this reason, skeletal muscle is sometimes called striated muscle -Most skeletal muscles are controlled by the central nervous system.

Smooth Muscles. -Smooth muscles are usually not under Smooth Muscles  -Smooth muscles are usually not under voluntary control -A smooth muscle cell is spindle-shaped, has one nucleus, and is not striated -Smooth muscles are found in hollow structures such as the stomach, blood vessels, and the small and large intestines -Smooth muscles move food through your digestive tract, control the way blood flows through your circulatory system, and decrease the size of the pupils of your eyes in bright light.

Cardiac Muscle. -Cardiac muscle is found in just one place in the Cardiac Muscle  -Cardiac muscle is found in just one place in the body—the heart -The prefix cardio- comes from a Greek word meaning “heart.” -Cardiac muscle is striated like skeletal muscle, although its cells are smaller. -Cardiac muscle cells usually have one nucleus, but they may have two. -Cardiac muscle is similar to smooth muscle because it is usually not under the direct control of the central nervous system

Muscle Contraction. -A muscle contracts when the thin Muscle Contraction -A muscle contracts when the thin filaments in the muscle fiber slide over the thick filaments -The energy for muscle contraction is supplied by ATP Neuromuscular junction The point of contact between a motor neuron and a skeletal muscle cell

Acetylcholine Vesicles, or pockets, in the axon terminals of the motor neuron release this neurotransmitter -  Acetylcholine molecules diffuse across the synapse, producing an impulse in the cell membrane of the muscle fiber - The impulse causes the release of calcium ions (Ca2+) within the fiber -  From the time a nerve impulse reaches a muscle cell, it is only a few milliseconds before these events occur and the muscle cell contracts -  A muscle cell remains contracted until the release of acetylcholine stops and an enzyme produced at the axon terminal destroys any remaining acetylcholine The contraction of a single muscle fiber is an all-or-none process. A stimulated fiber will contract to its full extent.

So how can there be strong and weak contractions? Each muscle contains hundreds of cells. A single motor neuron may form synapses with more than one muscle fiber How does a spinal cord injury cause paralysis of the legs? The injury interrupts the pathway of impulses from the brain to the nerves that control muscles in the legs.

How do muscles and bones interact? Skeletal muscles are joined to bones by tough connective tissues called tendons - Tendons are attached in such a way that they pull on the bones and make them work like levers -  Most skeletal muscles work in opposing pairs. When one muscle contracts, the other relaxes. The muscles of the upper arm shown in the figure below are a good example of this dual action.

How do body builders get muscles that increase in size? Muscles that are exercised regularly stay firm and increase in size by adding more material to the inside of the muscle cells

36-3 Integumentary System What are the functions of the integumentary system? The integumentary system serves as a barrier against infection and injury, helps to regulate body temperature, removes waste products from the body, and provides protection against ultraviolet radiation from the sun

The skin is the largest organ of the body EPIDERMIS The outer layer of the skin -        keratin, a tough, fibrous protein -        melanin, a dark brown pigment

Dermis The inner layer of the skin Hair and Nails In humans it is made of keratin Hair follicles are tubelike pockets of epidermal cells that extend into the derm