compendium 6

This review will cover
1. The human skeletal system
2. Bone structure and cartilage
3. Bone growth and repair
4. The axial skeleton
5. The appendicular skeleton
6. Movement of the joints
7. Skeletal muscle structure and function
8. Muscle disorders and homeostasis


1. There are 206 bones that make up the human skeletal system. This system serves many functions: support, protection, production of red blood cells, storage of fat and minerals, allows for flexible movement.

2. There are two basic types of bones compact bone which is very organized and spongy bone which looks less organized but serves a very important function. Cartilage is a flexible matter that works in conjunction with many bones and joints. There are three types of cartilage that are arranged differently to serve different purposes. Hyaline cartilage is firm and contains a good amount of collagen, it is found in the nose, ribs, and the end of long bones. Fibrocartilage contains more collagen than hyaline cartilage and is found in the nee and vertebrae. Elastic cartilage is flexible and contains more elastin than collagen, it is found in the ear and the epiglottis.
3. At about six weeks after conception the skeletal system begins to develop, showing how crucial it is to the human form. Bone growth in humans can continue until 25 years of age, but remodeling and repair can happen at any time. The three bone cells involved in the growth, remodel and repair of bones are osteoblasts, which form the bones, osteocytes maintain the bones, and osteoclasts break down the bones whenever necessary. Ossification is the term used to describe the formation of bones. Intramembranous bones are flat bones such as the ones in the skull. Endochondral ossification forms most of the rest of the bones in the skeletal system. Many factors affect the growth of bones and proper growth of bones is vital to a properly functioning skeletal system. These factors include proper hormones including the hormone that is produced in the kidneys from vitamin D. Growth hormone and thyroid hormone are two other hormones fundamental to the growth and formation of bones. Bones are constantly being remodeled; up to 18% of bones in adults are remodeled in a one year period of time! Repair of bones is necessary after an injury to a bone occurs. Injuries to bones are classified as follows; complete fractures are when the bone is broken through, incomplete fractures are when the bone is not completely separated. Simple fractures do not puncture the skin and compound fractures puncture the skin. If the ends of the broken bones are wedged into each other is known as impacted and if the bone twists and becomes ragged, it is known as a spiral fracture.
4. The axial skeleton contains 80 bones and consists of the skull, hyoid bone, vertebral column, and the rib cage. The skull includes the cranium, which has eight bones and protects the brain. The facial bones include the mandible, the maxillae, the zygomatic bones and the bones that make up the nasal cavity.

The hyoid bone is located near the larynx and is suspended by ligaments and muscles; it aids in swallowing and is an anchor for the tongue. The vertebral column is composed of 33 vertebrae and they are classified according to location. There are 7 vertebrae that make up the cervical vertebrae lie in the neck. The 12 thoracic vertebrae lie below the cervical vertebrae and ribs attach to them. Below the thoracic vertebrae are the five sacral vertebrae, and directly below them is the tailbone or coccyx. Between the vertebrae are small disks that protect the discs from grinding against each other and act as a cushion. Also in the axial skeleton is the rib cage which protects the heart and other vital internal organs. Ribs are connected to the thoracic vertebrae and occur in pairs. The true ribs are connected to the sternum by costal cartilage and the three pairs below that are false ribs and are connected by a common cartilage to the sternum. The floating ribs are the last two pairs of ribs and are not connected to the sternum at all. The sternum is the set of three bones that is positioned in the midline of the body. Its main purpose is to protect the heart.
5. The appendicular skeleton consists of the bones of the hip (pelvic) and shoulder (Pectoral) regions and the bones that are attached to them. The body is split into two divisions’ right and left and the regions are classified the same way. These photographs show the included bones in both regions

6. Joints are the meeting place of bones and are classified as fibrous, cartilaginous, or synovial. Fibrous joints are generally not able to move. Cartilaginous joints are typically joined by hyaline cartilage and are somewhat moveable. Synovial joints are easily moveable because they are filled with a synovial fluid which acts as a lubricant to allow for movement. INSERT KNEE JOINT Synovial joint movement means that when a muscle contracts, two bones move in relation to each other the most common types of movements are flexion when the angle of the joint decreases and its opposite extension when the angle increases. Abduction when the body part moves away from the midline and adduction when the body part moves closer to the midline. Rotation means that the body part is rotating around its own axis and circumduction is when the body part moves so that a cone shape is made.
7. Skeletal muscle is made up of fibers that are tubular, multinucleated, and striated. Skeletal muscles line the skeleton and movement of the muscle is voluntary, meaning that we can control its movement. Skeletal muscles are multifunctional and those functions include support of the body, movement of bones, maintenance of body temperature, assists in movement of cardiovascular and lymphatic vessels, and protection of internal organs. Skeletal muscles occur in pairs that work opposite of each other but at the same time in union with one another. The muscle in a particular group that does most of the work is known as the prime mover and the muscle that works opposite of it is the antagonist. When a muscle contracts it shortens in length and a particular muscle can only pull, not push. Skeletal muscles are named according to their size, shape, location, direction of the fibers, where it is attached, number of attachments, and the action that it fulfils. Muscle fibers are cells but some of the parts are named differently, the cytoplasm is the sarcoplasm, the membrane is the sarcloemma, and the endoplasmic reticulum is the sarcoplasmic reticulum. The muscle fibers also have t tubules that come in contact with the sarcoplasmic reticulum where calcium is stored. Microfibrils are enclosed in the sarcoplasmic reticulum and run the length of the muscle fiber. Within a microfibril is what is known as a sarcomere. Sarcomeres are composed of thick filaments that contain myosin and thin filaments that contain actin. When muscles contract the actin slides toward each other past the myosin and shorten the grouping that is altogether the sarcomere. This is known as sliding filament. Due to the fact that axons have several branches, they can stimulate the movement of many muscle fibers at once. A motor unit is the grouping of a nerve fiber and all the muscle fibers it innervates. In addition to cellular respiration and fermentation as methods of ATP production, muscles have the Creatine phosphate pathway as well. This is a quick easy anaerobic method for producing ATP. Muscles have for methods for acquiring the fuel needed for energy, glycogen and fat are stored in the muscles and blood glucose and plasma fatty acids are stored in the blood.

8. Muscular disorders range from those that are not very serious to those that are life threatening. Spasms, cramps tics and strains are non-life threatening muscular conditions that happen to many people on a regular basis. More serious disorders such as myalgia, fibromyalgia, muscular dystrophy, myasthenia gravis and amyotrophic lateral sclerosis( Lou Gehrig’s disease) are more serious disorders of the muscles and can be life threatening. Homeostasis is maintained by both the muscular and skeletal systems working together to allow movement in many areas of our body that without that movement, we would be unable to continue living as we do. These systems together also help protect our body from serious injury. The skeletal system produces calcium and red blood cells which are vital to sustain life. Also the muscles on the body help regulate a constant body temperature, this aids in homeostasis by allowing the outside temperature to drop and rise a considerable amount without detrimental effects to the body.