• Skeletal System
• Bones Characteristics
• Muscles
**SKELETAL SYSTEM**
The skeletal system has many jobs. It supports and protects the body all the while it makes blood cells. It also stores mineral salts and fat. The skeletal system is made up of the bones in our body. These bones are made of bone tissues and cartilage. There are ligaments, as well. These are made of fibrous connective tissue which serves to connet the bones at points called joints. There are three different kinds of joints. There are fibrous joints, cartilaginous joints, and synovial joints.
The fibrous joints are immovable and include the sutures of the cranium. The cartilaginous joints are barely movable and they are between the pubic symphysis, the sternum and the ribs. Lastly, the synovial joints are readily movable. These joints have a synovial membrane, making this possible. The human body has over 230 moveable and semi-moveable joints.
There is also an axial skeleton. In this skeleton, there is the skull, the hyoid bone, the vertebral column, and the rib cage. The skull is made from the cranium which protects the brain and the bones in the face. The hyoid bone holds the tongue and is where the muscles for swallowing are located, too. The vertebral column is made from shock absorbing disks (vertebrae). The vertebral column owes its flexibility to this characteristic. It holds together the body's top half. It also protects the spinal cord which contains most of the nerves, in other words, it protects a very easily hurt area of the body.
Finally there is the appendicular skeleton.
This skeleton includes the pectoral girdle bones, the upper and lower limbs, and the pelvic girdle. The pectoral girdles and the upper limbs are used for flexibility. The pelvic girdle and the lower limbs are used for weight sustaining. The femur, the largest, longest, and strongest bone in the body, is one of those bones. The femur is also about 1/4 of an individual's height.
The smallest is the stirrup bone in the ear which can measure 1/10 of an inch. At birth, the human body has well over 300 bones. As that little baby grew into an adult, some bones fused together, creating the result of a human adult having 206 bones. The human hand has 27 bones; the face has 14.
**BONE CHARACTERISTICS**
Long bones are different from short ones. For instance, long bones have a hyaline cartilage which covers both of its ends. It has a periosteum to cover the rest of it. A periosteum is a fibrous connective tissue. the epiphyses hold the spongy bone, which holds the red bone marrow.
Found in the medullary cavity of the diaphysis is the yellow bone marrow. The compacted bone forms the wall for the diaphysis.
Cells have a large duty when it comes to bones. they need to form bones, and even at some points, break down and absorb bone parts. These cells are osteoblasts, osteocytes, and osteoclasts. The skull's bones are examples of flat bones. These bones need fibrous connective tissue to separate them from colliding. These layers of tissue are called intramembranous ossification. Another time is endochondral ossification. this is here cartilaginous models of bones are actually replaced. A calcified bone matrix replaces it. Vitamin D as well as the growth and sex hormones contribute to the growth of a bone. If you are unfortunate enough to suffer from a breaking of a bone, perhaps by a skateboarding incident, your bone would repair itself in four steps: hematoma formtion, fibrocartilaginous callus, bony callus, and then remodeling. Sounds complicated.
**MUSCLES**
The human body has three different types of muscle tissues. There is smoot muscle, cardiac muscle and skeletal muscle. The skeletal muscle has many jobs: maintain posture, provide movement, provide heat, and protect organs. It is a voluntary muscle that has many muscle fibers in bunches. These are fascicles, and these are usally connected through tendons. The smooth muscle is involuntary, unlike the skeletal muscle. It is found in the walls of the internal organs. Finally, thecardiac muscle is also involuntary and is found in the heart's walls. Muscles help the body movvvvve. Most muscles are named for their characteristics including shape, location, siz, and direction number of attachments, or action.
Nerve impulses are carried on motor neurons and these stimulate the muscle fibers.
A muscle also has more neurofibers. These are several fibers tht are in control of another motor axon. The strength ofthe musle contraction varies acordin to the recruitment of the motor units. Muscles often contract. How is this? A muscle needs energy, otherwise known as ATP. A muscle can acquire this energy in three ways. One way would be to use creatine phosphate whih will send a phosphate to ADP and that would make a triphosphate or ATP. This is most common. Next would be fermentation. This process is able to produce ATP fast but it uses very little oxygen because the oxygen is used to metbolize the accumulated lactate. Third, would be cellular respiration. In this process, the ATP is produced in a large quantity. This gives the muscle the largest amount of ATP. However, the downside is that the process is much more enduring than the previous two. It happens during aerobic exercise and thereby burns the fat into glucose needed to energy. For athletes and the like, there are fast twitch muscles. These are used for weight lifting, jumping, any fast movement. These muscles are the power muscles but they burn out relatively quickly. Slow twitch fibers deal for runing and swimming, any exercise that is prolonging. Cross country runners use their slow twitch fibers in excess.
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