The Skeletal System

The Skeletal System serves many important functions; it provides the shape and form for our bodies in addition to supporting, protecting, allowing bodily movement, producing blood for the body, and storing minerals.

Functions

Its 206 bones form a rigid framework to which the softer tissues and organs of the body are attached.

Vital organs are protected by the skeletal system. The brain is protected by the surrounding skull as the heart and lungs are encased by the sternum and rib cage.

Bodily movement is carried out by the interaction of the muscular and skeletal systems. For this reason, they are often grouped together as the musculo-skeletal system. Muscles are connected to bones by tendons. Bones are connected to each other by ligaments. Where bones meet one another is typically called a joint. Muscles which cause movement of a joint are connected to two different bones and contract to pull them together. An example would be the contraction of the biceps and a relaxation of the triceps. This produces a bend at the elbow. The contraction of the triceps and relaxation of the biceps produces the effect of straightening the arm.

Blood cells are produced by the marrow located in some bones. An average of 2.6 million red blood cells are produced each second by the bone marrow to replace those worn out and destroyed by the liver.

Bones serve as a storage area for minerals such as calcium and phosphorus. When an excess is present in the blood, buildup will occur within the bones. When the supply of these minerals within the blood is low, it will be withdrawn from the bones to replenish the supply.

Divisions of the Skeleton

The human skeleton is divided into two distinct parts:

The axial skeleton consists of bones that form the axis of the body and support and protect the organs of the head, neck, and trunk.

The appendicular skeleton is composed of bones that anchor the appendages to the axial skeleton.

Types of Bone

The bones of the body fall into four general categories: long bones, short bones, flat bones, and irregular bones. Long bones are longer than they are wide and work as levers. The bones of the upper and lower extremities (ex. humerus, tibia, femur, ulna, metacarpals, etc.) are of this type. Short bones are short, cube-shaped, and found in the wrists and ankles. Flat bones have broad surfaces for protection of organs and attachment of muscles (ex. ribs, cranial bones, bones of shoulder girdle). Irregular bones are all others that do not fall into the previous categories. They have varied shapes, sizes, and surfaces features and include the bones of the vertebrae and a few in the skull.

Bone Composition

Bones are composed of tissue that may take one of two forms. Compact, or dense bone, and spongy, or cancellous, bone. Most bones contain both types. Compact bone is dense, hard, and forms the protective exterior portion of all bones. Spongy bone is inside the compact bone and is very porous (full of tiny holes). Spongy bone occurs in most bones. The bone tissue is composed of several types of bone marrow embedded in a web of inorganic salts (mostly calcium and phosphorus) to give the bone strength, and collagenous fibers and ground substance to give the bone flexibility.

angle of jaw or mandible - back of jaw, the corner of the jaw where the mandible body turns upwards into the ramus

aveolar - process maxilla, root of teeth rugosities associated with tooth development

coronal suture - top of head between frontal and parietal cranial bones, one of the major joints or sutures between the plates of the frontal and parietal cranial bones

ethmoid bone - eye cavity, a cranial bone forming part of the eye cavity

frontal bone - top of face (forehead) and front top of head one of the major cranial bones that forms the forehead and front top of the head; roughly covers the frontal lobes of the brain glabella

lacrimal bone - inner corner of eye socket a small bone forming a cavity for the tear gland

maxilla- upper part of jaw the two maxillae form the center of the face with many attaching muscles; carry the upper teeth; form part of the eye orbit; act like keystones into which the other facial bones fit

nasal bone – nose forms the upper part of the nose and nasal bridge; the lower part of the bridge is formed of cartilage

occipital bone - the lower rear of the head a major cranial bone at the lower back of the head; covers occipital lobe of the brain

parietal bone - top and side of head a major cranial bone that froms part of the top, back, and side of the head and roughly covers the parietal lobe of the brain

sphenoid bone - temple and eye orbit area, a cranial bone that forms part of the eye cavity

temporal bone - side of the head, above the ear, a cranial bone on the side of the head that roughly covers the temporal lobe of the brain; it extends down behind the ear towards the jaw

zygomatic bone – cheek, the principal cheek bone; origin of zygomatic and other facial muscles

Spinal Cord

The spine is separated into 4 main section.

1. Cervical

2. Thoracic

3. Lumbar

4. Sacral

Dangers: Falling from a ladder could result in a broken femur.