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## Levers for Movement Bones serve as attachment sites for skeletal muscles, other soft tissues, and some organs. Muscles attached to the bones of the skeleton contract and exert a pull on the skeleton which then functions as a system of levers. The bones of the skeleton can alter the direction an...

## Levers for Movement Bones serve as attachment sites for skeletal muscles, other soft tissues, and some organs. Muscles attached to the bones of the skeleton contract and exert a pull on the skeleton which then functions as a system of levers. The bones of the skeleton can alter the direction and magnitude of the forces generated by the skeletal muscles. Potential movements range from powerful contractions needed for running and jumping to delicate and precise movements required to remove a splinter from the finger. ## Hematopoiesis Hematopoiesis (he'ma-to-poy-e'sis; haima = blood, poiesi = making) is the process of blood cell production. It occurs in red bone marrow connective tissue, which contains stem cells that form blood cells and platelets. (The process of hematopoiesis is described in greater detail in section 18.3a.) ## Storage of Mineral and Energy Reserves Most of the body's reserves of the minerals calcium and phosphate are stored within and then released from bone. **Calcium** is an essential mineral for such body functions as muscle contraction (see section 10.3b), blood clotting (see section 18.4), and release of neurotransmitter from nerve cells (see section 12.8d). **Phosphate** is a structural component of ATP, other nucleotides, and phospholipids (see sections 2.7d and 2.7b) and is an important component of the plasma membrane (see section 4.2a). When calcium or phosphate is needed by the body, some bone connective tissue is broken down, and the minerals are released into the blood In addition, potential energy in the form of lipids is stored in yellow bone marrow in the shafts of some adult bones. ### What Did You Learn? * What two minerals are stored in bone, and what are their functions in the body? ## 7.2b Classification of Bones ### Learning Objective * Compare and contrast the four major classes of bones as determined by shape. Bones appear in various shapes and sizes, depending upon their function. The four classes of bone as determined by shape are long bones, short bones, flat bones, and irregular bones (Figure 7.2). * **Long bones** are greater in length than width. These bones have an elongated, cylindrical shaft (diaphysis). This is the most common bone shape. Long bones are found in the upper limbs (namely, the arm, forearm, palm, and fingers) and lower limbs (thigh, leg, sole of the foot, and toes). Long bones vary in size. The small bones in the fingers and toes are long bones, as are the femur, tibia, and fibula of the lower limb. * **Short bones** have a length nearly equal to their width. Examples of short bones include the carpals (wrist bones) and tarsals (bones in the foot). Sesamoid bones, which are small, sesame seed-shaped bones along the tendons of some muscles, are also classified as short bones. The patella (kneecap) is the largest sesamoid bone. * **Flat bones** are so named because they have flat, thin surfaces that may be slightly curved. They provide extensive surface areas for muscle attachment and protect underlying soft tissues. Flat bones form the roof of the skull, the scapulae (shoulder blades), the sternum (breastbone), and the ribs. * **Irregular bones** have elaborate, sometimes complex shapes and do not fit into any of the preceding categories. The vertebrae; the ossa coxae (hip bones); and several bones in the skull, such as the ethmoid, sphenoid, and maxilla, are examples of irregular bones. ### What Did You Learn? * What are several examples of flat bones in the body? ## 7.2c Gross Anatomy of Bones ### Learning Objectives * Describe the structural components of a long bone. * Compare the gross anatomy of other bones to that of a long bone. * Explain the general function of blood vessels and nerves that serve a bone. Our discussion continues with details of the gross anatomy of a long bone. First we compare it to other classes of bones, then we discuss the vascularization and innervation of bone. Chapter Seven Skeletal System: Bone Structure and Function 213