Skeletal and Muscular System

Functions of Skeletal System 1) Support - keep body upright, support organs, tissues 2) Protection - delicate organs surrounded or cradled by bony parts 3) Storage of minerals (calcium, phosphates) and lipids 98% of body’s calcium found in bones yellow marrow contains fat, is in shafts of bones 4) Blood cell production - blood cells made here, in red marrow in the ends of bones 5) Leverage - produces movements with skeletal muscles

Skeleton 206 bones in human body 6 are middle ear bones Axial Skeleton – Skull, vertebral column, rib cage is found in center or axis of body Appendicular Skeleton – bones of shoulders and arms and bones of pelvis and legs appendix- add-on, extra

Composition of Bone Non-living: 2/3 mass of bones is minerals Calcium and phosphate mainly protein fiber But also fluoride, Na+, magnesium, calcium carbonate these crystals are strong but brittle cell crystal Living: 1/3 bone mass is protein fibers (collagen) and bone cells Protein fibers are produced first and crystals are packed around the fibers, cells found in between strands The combination (fibers + crystals) gives the bone both strength and some flexibility

Bone cells – 4 types 1) Bone stem cells – can make new bone cells 2) Osteocytes – mature bone cells, maintain bone matrix 3) Osteoblasts – make new bone 4) Osteoclasts - destroy bone Osteoblasts and osteoclasts together remodel bones

Femur Two types of bone, both found in most bones Red marrow Periosteum shaft Yellow marrow

Red and yellow bone marrow Spongy bone under microscope http://medlib.med.utah.edu/WebPath/BONEHTML/BONEIDX.html

Compact bone still has cells in it They need nutrients (name 2) from the blood So compact bone has tubes called Haversian canals that run through the bone http://instruct1.cit.cornell.edu/courses/biog105/images/105slides/Unit10/index10.htm

These canals contain blood vessels and sensory neurons So if you break a bone – it bleeds! it hurts! http://instruct1.cit.cornell.edu/courses/biog105/images/105slides/Unit10/index10.htm

Exercise Bones remodel in response to stress (weight/ pressure) Weight-bearing exercise stresses bones, they respond by building more mass Conversely, absence of stress causes loss of bone mass especially a problem in space - no gravity long term astronauts may pass point of no return - bones too weak to live on Earth again