The Skeletal System -Introduction

The skeletal system consists of the 206 bones with their associated tissues, e.g., cartilage, ligaments, tendons, as well as, the joints (articulations).

I. General Functions

  1. Support for the body – The tubular structure of bones (dense, hard bone with a hollow center) affords the maximum support with the least materials.
  2. Protection for vital organs – The skull protects the brain, rib cage and sternum protects the heart and lungs, the pelvis protects reproductive organs.
  3. Anchorage for the action of muscles:
  1. point of origin – fixed point of a muscle to a bone
  2. point of insertion – the moving point of attachment of a muscle to a bone. The contraction of the muscle brings the insertion closer to the origin.

     D.  The joints or articulations where bones meet other bones permit varying degrees of movement.

     E.  Bones house marrow tissue – Marrow tissue is responsible for the formation of blood cells
     (hematopoiesis).

II. Types of Bones

A.  Long bones – Each long bone has ends or epiphyses, a shaft or diaphysis and marrow cavities. They are found in the upper and lower appendages, e.g., the humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals and phalanges.

B.  Short bones – are box-like in appearance. Externally, they are covered with compact bone. The interior contains spongy bone. Examples would be the wrist bones (carpals) and ankle bones (tarsals).

C.  Flat bones – are thin, plate-like bones consisting of two layers of compact bone sandwiching spongy bone. These bones are light but very strong. Examples would be the cranial bones (frontal, parietals, temporals and occipital) which protect the brain, the ribs, sternum and scapula.

D.  Irregular bones – are bones with complex shapes. Examples are the spinal vertebrae, the sphenoid and ethmoid.

E.  Sesamoid bones – are small, rounded and flattened. They form within tendons near joints at the knee, hand and feet. They are not commonly found except the one that everyone has, the sesamoid patella or knee cap bone.

F.  Wormian or sutural bones – are small, flat bones with an irregular shape found within a suture joint between skull bones. There is a great deal of variation in the number, shape and size of these bones in an individual.

III.  Divisions of the Skeletal System

A. The Axial Division consists of 80 bones making up the skull, rib cage and vertebral column. It carries out the following functions:

  1. Support and protection for the organs within the dorsal and ventral body cavities.
  2. Provides the framework for the attachment of muscles that:
    1. adjust the positions of the head, neck and trunk.
    2. Perform respiratory movements
    3. Anchor and stabilize the appendicular bones.

B.  The Appendicular Division consists of 126 bones making up the appendages and girdles that connect appendages to the body. The pectoral girdle consists of the clavicle and scapula. The pelvic girdle is formed by the two coxal bones which are fused anteriorly.