Unit Three: Compendium II

I. Skeletal System

A. Overview

B. Bone: Growth and Repair

C. Axial Skeleton

D. Appendicular Skeleton

E. Articulations.

II. Muscular System

A. Overview

B. Skeletal Muscle Fiber Contraction

C. Whole Muscle Contraction

D. Muscular Disotrophy

E. Homeostasis

I. Skeletal System

A. Overview

The skeletal system consists of bone, cartilage and connective tissue in the ligaments and joints. Its functions are body support, protection, blood cell production, mineral and fat storage and assists in flexible movement. The shaft of a long bone is the diaphysis. The medullary cavity of the diaphysis is filled with yellow bone marrow. This marrow stores fat. The bone fans on the end into the epiphysis. This bone is spongy and contains red bone marrow, which makes blood cells. The bone is covered in periosteum, which contains blood vessels, lymphatic vessels and nerves. This continues right into ligaments and tendons. Compact bone is made of tube-like sections called osteons. Osteocytes are bone cells of the osteon the lie in lacunae (circular chambers around a canal, for vessels and nerves.)Osteocytes nearest the center of the osteon exchange nutrients and wastes with blood vcssels. Spongy bone lies within and looks less organized than compact bone, but its brace-like structure is for strength. Its spaces are filled with red bone marrow. Cartilage is a flexible tissue, not as strong as bone. It has many collagenous and elastic fibers. Cartilage contains no nerves which is ideal for the stress placed on it from flexible movement. It heals slowly, though, as it has no blood vessels. The three types of cartilage are: hyaline (firm fairly flexible), fibrocartilage (stronger than hyaline, found in disks between vertabrae.), elastic cartilage is the most flexible. Ligaments and tendons are made up of fibrous connective tissue. They connect bone to bone and muscle to bone.

B. Bone: growth and repair

Boes first appear at six weeks in an embryo . They continue to grow until as late as age 25. They change shape and size and strength to deal with stress. Bones can repair when fractured. Some different types of bone cells are: osteoblasts (bone forming cells), osteocytes (maintain structure), osteoclasts (breakdown bone.) Ossification is the formation of cone. The two types of ossification are: intramembranous and endochondral. Flat bones, like the skull, are results of intramembranous ossification which develops bone between sheets of fibrous connective tissue. Endochondral ossification happens in most bones of the body where cartilag models are replaced by bone construction. THe cartilage model literally becomes the bone!. The epiphyseal plates close at about age 20 which ends bone legth growth. Vitamin D is vital to bone growth and strength in that it plays a great role in calcuim absorbtion. As much as 18% of bone is recycled each year and renewed in bone remodeling. This helps keep bones strong. Bones are the storage sight for calcium and regulates the amount of calcium in the blood. Two hormones are integral to this process: parathyroid and calcitonin. Osteoperosis is a condition in which osteoclasts are more active than osteoblasts causing bone mass decrease. Bone repair is very important to functioning structure. If a break occurs bood will clot in the break. Thn fibrocartilage will form in the break.Then osteoblasts convert the fibrocartilaginous callus into a bony callus. It is lastly filled in with compact bone and repair is complete.

Normally, a fracture like this will heal through

bone remodeling.

C. Axial skeleton

The axial skeleton refers to the skull, hyoid, vetebral column and rib cage. The skull is the cranium and facial bones. The cranium protects the brain. It is actually eight bones fused together. The sphenoid bone extends across the floor of the cranium. It completes the sides of the cranium and formsthe eye sockets. The ethmoid bone forms the nasal septum. The facial bones are: the mandible, maxillae, zygomatic and nasal. The Hyoid bone is the only bone that does not articulate with other bones. It is attatched to the larynx and anchors the tongue. The vertebral column contains 33 vertebrae (the spine.)There are five types of vertebrae (from the top down): cervical, thoracic, lumbar, sacrum and coccyx. There are fibrocartilagous disks called intervertebral disks that absorb shock and protect the vertebrae. The rib cage is protective and flexible. It is made up of the ribs and the sternum.

skeleton 1 shows the axial skeleton

while skeleton 2 shows the appendicular

skeleton.

D. Appendicular skeleton

The appendicular skeleton makes up every other bone of the body. There are the pectoral girdles on either side that make up the shoulder. They contain the scapulas and the clavicle. The muscles of the arm and chest attach to the scapula. The rotator cup is made of tendons connecting the scapula to the humerus. It is the single long bone of the upper arm. This connects at the elbow to the radius and the ulna. The hand has many bones for increased flexibility. There are the carpal bones, the metacarpal bones and the phalanges. At the waste is the pelvic girdle. The pelvis is made up of two heavy coxal bones, the ilium, the pubis, and the ischium. This connects at a joint, to the femur: the single long bone of the upper leg. This is connected to the tibia and fibula by the patella (kneecap) and ligaments and tendons. There are many bones in the feet, like the hands, for flexibility. The ankle area is made of tarsals then there are five metatarsals and then phpalanges in the toes.

E. Articulations

Bones join at the joints. There are three types of joints: fibrous, cartilaginous and synovial. Fibrous joints are virtually immovable. Cartilaginous joints are slightly movable. Synovial joints are freely movable. The synovial joints are joint cavities that are filled with synovial fluid. Bursae are sacs of this fluid that lubricate bones and overlapping muscle and ease friction. Then areas of hyaline cartilage fill in a C-shaped area for shock absorbtion. The synovial joints in the shoulders and hips are ball joints and permit movement in any direction. Th elbows and knees are hinge joints and only allow single-directional movement.

The joints are capable of impressive articulations.

II. Muscular System

A. Overview

All muscles contract and this causes movement. There are three types of muscle tissue: smoothe, cardiac and skeletal. These are made of muscle fibers. Smooth muscle fibers have a spindle shape. Smooth muscle is found in the walls of hollow organs which causes the contractions in them. These tend to contract without conscious control. Cardiac muscle has inuncleated fibers that are striated and is found in the heart wall. It's formation facillitates quick contractions throughout the heart wall. Cardiac muscle contracts involuntarily. Skeletal muscles have many functions. It supports the body. It makes the skeleton move. They maintain body temperature. The contractions of skeletal muscles help move blood and lymph through their respective vessels. Skeletal muscles also help protect internal organs. Skeletal muscles are made of fascicles. Fascicles are covered with fascia which connects muscles to tendons. When a skeletal muscle contracts its tendons pull on the bone to move it. It takes groups of muscles to move a particular area, but one muscle will take the bulk of the movement. Since muscles work in pairs one must reflex as one contracts in order for the bone to move. Skeletal muscles are named according to one of these seven factors: size, shape, location, direction of fibers, attachment, number of attachments and/or action.

B. Skeletal muscle fiber contractions

The striations in skeletal muscles is dues to the arrangement of myofilaments in the muscle fiber. There are different names for kthe cellular components of muscle fiber. THe plasma membrane is called the sarcolemma, the sarcoplasm is the cytoplasm. Muscle fiber contains sarcoplasmic reticulum. The sarcolemma forms transvers (T) tubules that dip into that make contact with the sarcoplamic reticulum. These sights of contact store calcium which is vital to muscle contraction. The myofibrils are the contracting parts of the muscle fibers. Other organelles are found between the myofibrils. Glycogen in the sarcoplasmacts as stored energy for contraction. Myofibrils are cylindrical. Units that make up the are sarcomeres. There are two types of protein in the myofibrils called myosin and actin. There are thick and thin myofilaments. The thick filaments are made of hundreds of myosin molecules. Thin filaments are made mostly of actin and there are also tropomyosin and troponin proteins in them. As an impulse travels down a T tubules, calcium is released. This causes the myofilaments to shorten, thereby contracting the muscle. The sliding of thin filaments past the thick filament is called the sliding filament model. Motor neurons attached to one or a few muscle fibers stimulate contractions by releasing ACh into the synaptic vesicles. Botox blocks the release of ACh into the symaptic cleft. This can be used to stop wrinkling. Rigor mortis probably sets in because ACh is not inhibited from flowing into the muscles.

C. Whole Muscle Contraction

A motor unit is the combination of the nerve axon as well as all the muscle fibers it stimulates. A muscle twitch is caused by infrequent electrical impulses. The three periods of this are the latent (between relaxation and contraction), contraction and relaxation. When this occurs rapidly without relaxation, the energy is dpleted in a state called tetanus, not to be confused with the infection, tetanus. THe four possible energy sources of contraction are: muscle triglycerides, plasma fatty acids, blood glucose and muscle glyfogen. Which one is used depends of the type of exercise and its intensity. Muscle fibers metabolize aerobically and anaerobically. Fast twitch muscle fibers use the anaerobic methods of producing ATP. They can fatigue very quicly because they dpend on lactate. Slow twitch fibers have more endurance. They are good for running, biking, jogging and swimming. They do not fatigue easilly because they have a more abundant fuel supply.

Cycling uses slow-twitch fibers.

D. Muscular disorders

There are many different muscular conditions. Spasms are involuntary muscle contraction. When this happens in multiple muscles it is called a convulsion. Cramps are strong spasms. Facial tics are spasms in the face that can be controlled with great effort. Strain is a stretching or tearing of the muscle. Sprains are twisting of joints that swell the muscle and the ligaments, tendons, nerves and blood vessels. Tendinitis is an inflamed tendon that does not glide properly. Myalgia is a condition of achy muscles. Fibromyalgia refers to a chronic condition where muscles are sore, stiff and tender. It may be due to an infection. Muscular dystrophy refers to a number of disorders in which the muscles weaken and degenerate. A lack of the protein dystrophin causes the Duchenne muscular dystrophy, a common type. Myasthenia gravis is a disease in which muscle contraction is impared because the body produces antibodies that mistakenly destroy ACh receptors. Lou Gehrig's disease is characterized by the loss of all muscle related abilities, though mental function stays intact.

Mike Neufeldt suffers from Muscular Dystrophy.

E. Homeostasis

Movements is integral to homeostasis. The skeletal and muscular systems work together for movement. Movement helps us respond to changes in the environment. Muscle contraction at the mouth allows us to mechanically breakdown food. Peristasis moves food through the digestive system. Muscle movement is important to breathing and venous return for blood circulation. Bones and muscles work together. They both protect organs. Bones release calcium which is used by muscles. Blood cells are made in the bone marrow, while muscles aid in body temperature homeostasis.