Chapter 32

Pivot

allow one bone to rotate or turn around another, Pivot joints allow you to turn your arm at elbow and shake your head to say no.

Saddle

allow one bone to slide in two directions. Allow a thumb to move across a palm.

Immovable

called fixed joints, allow no movement. The bones at an immovable joint are interlocked and grow together until they are fused. The places where the bones in the skill meet are examples of immovable joints.

Ball-and-socket

found in the shoulders and hips, these joints allow for movement in many directions. The most freely movable.

Bursa

freely movable joints such as the knee, there are small sacs of synovial fluid. Reduce the friction between the bones of a joint and any tissues they come in contact with and also act as tiny shock absorbers.

Axial skeleton

supports central axis of body and consists of the skull, vertebral column, and rib cage.

Bone Remolding and Repair

Bones are remodeled throughout life by osteoblasts, which continue to build bone tissue, and osteoclasts- cells that break down bone minerals. Without the continual breakdown of old bone tissue and build up of new bone tissue, bones would become brittle and weak. Both types of cells work together to repair broken and damaged bones.

Structure

206 bones in adult human skeleton. Some bones are in the axial skeleton and others are in the appendicular skeleton.

Joints

A place where one or more bones meet another bone-joint. Contain connective tissues that hold bones together. Joints permit bones to move without damaging each other.

Bones

A solid network of living cells and protein fibers that are surrounded by deposits of calcium salts. Most of the mass of bone is mineral salts- mainly calcium and phosphorus. Bones are living tissue.

Development

Cartilage is gradually replaced by bone during process of bone formation- ossification, which begins up to seven months before birth. Bone tissues forms as cells called osteoblasts, they secrete mineral deposits that replace cartilage in developing bones. As bone tissue completes its development, most osteoblasts mature into osteocytes which maintain minerals in bone tissue and continue to strengthen growing bone.

Smooth Muscle

Cells don't have striations and therefore look "smooth" under microscope. Spindle-shaped and usually have a single nucleus. Throughout the body, and they form part of walls of hollow structures such as stomach, blood vessels, and intestines. Usually involuntary and perform functions like moving food through digestive tract, controlling the flow of blood through circulatory system, and even decreasing pupil size in bright light. Can function without direct stimulation by nervous system. The cells are connected to one another by gap junctions which allow electrical impulses to travel directly from one muscle cell to a neighboring muscle cell.

Joint Injuries

Common injury in athletes is damaged or anterior cruciate ligament (ACL) of knee. Ligament found in center of knee between femur and tibia It prevents the tibia from shifting too far forward during movements. ACL damage can be caused by rapid pivoting when playing sports like basketball or soccer. Excessive strain on joint may produce inflammation, a response in which excess fluid causes swelling, pain, heat, and redness. Inflammation of a bursa is called bursitis. Wear and tear over the years often leads to osteoarthritis, which develops as the cartilage of often-used joints in the fingers, knees, hips, and spine begins to break down. Joints become painful and stiff as unprotected bones start to rub together.

Muscle fibers

Common referral. Skeletal muscle cells are long and slender.

Growth Plates

Contain dividing cartilage cells that increase the size of a bone until a person reaches his or her adult height. Growth of cartilage at these plates causes bones to lengthen.

White Muscle

Fast twitch muscle contracts more rapidly and generates more force, but its cells contain few mitochondria and tire quickly. Useful for activities that require great strength or quick bursts of speed-sprinting.

Cardiac Muscle

Found in the heart. Striated like skeletal muscle but cells are smaller and usually have one or two nuclei. Usually not under direct control of central nervous system. Cells can contract on their own and are connected to their neighbors by gap junctions.

Joints Structure

Freely movable, cartilage covers surfaces where two bones come together and protects the bones from damage as they move against each other. The joints are also surrounded by fibrous joint capsule that helps hold the bones together while still allowing for movement.

Synovial fluid

Inner layer of joint capsule-synovial cavity, produces a substance called synovial fluid. Enables surfaces of the bones connected at the joint to slide over each other smoothly.

Sliding-Filament Model

Myosin attaches to binding sites of actin, forming cross-bridges. Using ATP, the cross-bridges pull the actin toward the center of sarcomere. Then cross-bridges break, myosin binds to another site, and the cycle begins again until the muscle fiber is contracted. Thick and thin filaments slide past each other, the length of fiber shortens hence name "sliding filament model" of muscle contraction.

Muscle Contraction

Myosin filaments form cross-bridges with actin filaments. The cross-bridges then change shape, pulling actin filaments toward center of sarcomere.

Haversian canals

Nerves and blood vessels that run through compact bone in channels.

Muscular System

One third of the mass of an average person's body is muscle. There are three different types of muscle tissue: skeletal, cardiac, and smooth. Muscle tissue is found everywhere in body. Each tissue is specialized for a specific function in body.

Ligaments

Outer layer of joint capsule forms strips of tough connective. They hold bones together in a joint and are attached to membranes that surround bones.

Freely movable

Permit movement in two or more directions and are grouped according to the shapes of surfaces of adjacent bones.

Neuromuscular junction

Point of contact between a motor neuron and a skeletal muscle is cell is a type of synapse.

Ossification

Process of cartilage being replaced by bone. It is done when someone has "stopped growing." Cartilage remains on tip of nose and other places to keep flexible.

Myofibrils

Skeletal muscle cells, or fibers, are filled with tightly packed filament bundles. Each _______ contains thick filaments of a protein called myosin and thin filaments of a protein called actin. The filaments are arranged in an overlapping pattern that produces striations.

Muscles and Bone

Skeletal muscles are joined to bones by tough connective tissues (tendons). Tendons pull on the bones and make them work like levers. The joint functions as a fulcrum- fixed point around which the lever moves. The muscles provide force to move lever. Most skeletal muscles work in opposing pairs- when one contracts, the other relaxes.

Control of Muscle Contraction

Skeletal muscles are useful only if they contract in a controlled fashion. Impulses from motor neurons control the contraction of muscle fibers. When a motor neuron is stimulated, its axon terminals release a neurotransmitter called acetylcholine (ACh) which diffuses across synapse, producing an impulse in the cell membrane of the muscle fiber. The impulse causes release of calcium ions (Ca2+), which affect regulatory proteins that allow myosin cross-bridges to bind to actin filaments. A muscle cell contracts until release of ACh stops and an enzyme destroys any remaining ACh, Then, the muscle cell pumps calcium ions back into storage, cross-bridges stop forming, and contraction ends.

Muscle and Movement

Skeletal muscles generate force and produce movement by pulling on body parts as they contract. When you lift something light- sheet of paper, your brain stimulates only a few cells to contract. As you exert maximum effort-pole vaulter, almost all muscle cells in arm are stimulated to contract.

Exercise and Health

Skeletal muscles remain in a state of partial contraction-resting muscle tone. Muscle tone is responsible for keeping the back and legs straight and the head upright, even when relaxed. Muscles exercised regularly stay firm and increase in size and strength due to added filaments. Muscles that are not used become weak and can visibly decrease in size. Without gravity, many muscles go unused. An astronaut in space can lose up to 5% of muscle mass a week. Aerobic exercises-running- place strong demands on heart and lungs, helping these systems to become more efficient. Regular exercise also strengthens bones, making them thicker and stronger and less likely to become injured,. Resistance exercises increase muscle size and strength + help you maintain coordination and flexibility over time.

Red Muscle

Slow twitch muscle contains many mitochondria, Color comes from small blood vessels that deliver blood and from an oxygen-storing protein called myoglobin. The abundant mitochondria and oxygen allow fibers to derive energy through aerobic respiration and work for long periods of time. Useful for endurance activities like long-distance running.

Osteoporosis

Some older adults, especially women, develop disorder. osteoclasts break down bone much faster than osteoblasts rebuilds. Leads to weak bones due to excessive decrease in bone density. Research suggest consuming plenty of calcium and performing weight-bearing exercise could help prevent serious problem.

Cartilage

The skeleton of a human embryo is composed almost entirely of a type of connective tissue.

Skeletal System

The skeleton supports body, protects internal organs, assists movement, stores minerals, and site of blood cell formation. To retain shapes, all organisms need structural support, or skeleton. Include external exoskeletons of arthropods and the internal endoskeleton of vertebrates.

Periosteum

Tough layer of connective Tissue

sarcomere

Two Z lines and the filaments between them make up a unit.

Bone Marrow

Within many bones are cavities that contain soft tissue. Yellow marrow consists primarily of cells that store fat. Red marrow consists stem cells that produce most types of blood cells.

Appendicular skeleton

consists of bones of arms and legs, along with the bones of the pelvis and shoulder area.

Hinge

joints permit back and forth motion like opening and closing of door, in elbows, knees, ankles.

Spongy Bone

less dense tissue; outer layer of compact bone, found in the ends of long bones-femur and in the middle of short, flat bones- like those in skull. Latticework structure in spongy bone adds strength without adding excess mass.

Slightly movable

permit small amount of movement, Unlike bones of immovable joints, bones of slightly movable are separated from each other, The joints between the two bones of the lower leg and joints between vertebrae are examples of slightly movable.

Compact Bone

thick layer (dense), beneath periosteum; nerves and blood vessels run through.

Skeletal Muscle

usually attached to bones. Consciously controlled by central nervous system )brain and spinal cord). Under a microscope appears to have alternating light and dark bands called "striations." This reason it is said to be striated. Large, has many nuclei, and varies in length.