The Skeletal System

1. The SkeletalSystem THE GENERAL framework of the body is built up mainly of a series of bones, supplemented, however, in certain regions by pieces of cartilage; the bony part of the framework constitutes the skeleton. The skeleton supports the body, protects vital organs, and works in conjunction with the muscles to cause movement.

2. Functions of Skeletal System Support • strong structural frame; every other part of the body is “hung” on bones like a hanger Protection • internal organs (brain by cranium, heart & lungs by ribs & sternum, spinal cord by spinal column) Aids in Movement • attachment for muscles that move us; lever systems; bones are hinged with muscles crossing the joints Blood Cell Formation • red marrow produces blood cells within internal structures of long bones Storage • calcium & phosphate storage; needed for muscle contraction, nerve cell function, & movement of materials across cell membranes Shape • relatively unique shape to organisms; height/weight/width; structure sub serves function

3. The Sexes • A baby's skeleton has 350 bones, but many of these fuse to give an adult a total of 206 bones. • A man's skeleton has broader shoulders than a woman's, a longer ribcage, and a narrow pelvic girdle optimized for walking/running/jumping. • A woman's skeleton has the same bone complement as a man's but is slightly smaller (lighter) and less robust, with a wider pelvic opening to assist childbirth. • There is a list of the major criteria shown in the chart on the following page to further distinguish between the sexes.

5. Axial & Appendicular Skeleton Axial • principle supportive structure of the body and is oriented along its medial longitudinal axis. • includes the skull, vertebrae, sternum, ribs, and hyoid bone. Appendicular • the joints make it possible for a considerable degree of freedom for the upper and lower limbs. • includes the pectoral and pelvic girdles and the bones of the arms, forearms, wrists, hands, thighs, legs, and feet. • Fractures and dislocations are more common in this part of the skeleton.

6. The skeletal system accounts for about 14% of our body weight. In the adult skeleton the 206 distinct bones, are allocated as follows:

7. BONES • Skeletal actually means “dried up”, bones appear lifeless but are living systems that grow, mature, repair & recycle (remodel) • Bones are composed of living tissue (bone cells, fat cells, blood vessels) and non-living tissue (H2O and minerals) • Bones are classified into 5 main types based on shape • Long bones • Short bones • Flat bones • Irregular bones • Sesamoid bones

8. Long Bones • Greater in length than width • Designed to absorb stress from body & leverage (used in locomotion & weight bearing) – STRUCTURE SUBSERVES FUNCTION! • Diaphysis (shaft) and epiphyses (ends of bone) • Bone marrow activity (production of blood cells) • Examples – arm (humerus), forearm (ulna & radius), hand (metacarpals), thigh (femur), lower leg (tibia & fibula), feet (metatarsals)

9. Short Bones • Equal in length & width • Form a shape roughly equal to a cube • No bone marrow activity • Examples – • wrist (carpals) and ankles (tarsals)

10. Flat Bones • Thin & flat • Offer protection & considerable surface area for muscle attachment • No bone marrow activity • Examples – head (cranial bones), ribs, sternum, shoulder blade (scapula)

11. Irregular Bones • Complex shapes • Not easily grouped into other 3 categories • No bone marrow activity • Examples – vertebrae, facial bones

12. Sesamoid Bones • Unusual bones • Small, flat bones wrapped within tendons • Move over bony surfaces • Examples – the patella