TWO SUBDIVISIONS OF THE SKELETAL SYSTEM Axial –Skull, vertebrae, ribs, and sternum Appendicular –Upper/lower limbs –Hands/feet –Pelvic/pectoral girdles
SKULL Composed of cranial and facial bones Cranial bones – protects brain, organs of hearing, and organs of equilibrium Facial bones – forms the framework of the face, protects eyes, and has opening for food air and organs of smell
FETAL SKELETON Fontanels – areas of hyaline cartilage Allow skull to be compressed as it passes through birth canal Allows for brain to grow during pregnancy and infancy Gradually convert to bone by 22 to 24 months
Cervical vertebrae Concave (called cervical curvature) 7 vertebrae – named C 1 – C 7 1 st – atlas – lets one nod “yes” –Contains depression for the occipital condyles of the skull 2 nd – axis – pivot point for atlas and skull –Lets one nod “no” C 3 – C 7 – typical shape
THORACIC VERTEBRAE Convex curvature 12 vertebrae T 1 – T 12 Spinous process is long and hooks downward 2 articulating surfaces ( costal facets) which receives the heads of the ribs
LUMBAR VERTEBRAE 5 vertebrae L 1 – L 5 Very sturdy Supports most of the stress of the vertebral column
SACRUM Composed of 5 fused vertebrae Articulates with L 5
COCCYX Humans tailbone Remnant of other animal’s tails
INTERVERTEBRAL DISCS Pads of fibrocartilage between each vertebrae absorbs shock cushions the vertebrae younger person - discs are about 90% water as we age, the water content decreases
S SHAPE OF THE COLUMN Prevents shock as we walk, run, and exercise primary curve - present when we are born. Found in the thoracic and sacral regions. Secondary curves - develop later –cervical - starts forming when a baby raises his head –lumbar - develops when baby begins to walk
JOINTS Place where 2 bones come together. If it is a joint where bones move, the joint must not allow the bones to rub against each other. Also called articulation
FUNCTIONS OF JOINTS Secure bones together. Allows rigid bones to move
PERIOSTEUM Fibrous connective tissue membrane that covers the diaphysis. Sharpey’s fibers secure it to the diaphysis. They are connective tissue.
EPIPHYSIS Ends of the long bones. Inside is spongy bone. Layer of compact bone on top of the spongy. Articular cartilage covers the ends of the epiphysis.
MEDULLARY CAVITY Yellow marrow - stores adipose red marrow - forms RBC’s –infants - found in long bones –adults - found in spongy bone, flat bones, and some long bones.
Epiphyseal plate - causes length wise growth of long bones. If damaged it can affect growth of the bone. Epiphyseal line - in adults marks where plate was.
OSTEOGENESIS Embryo’s skeleton is entirely cartilage Occurs 6 weeks after conception Ossification occurs Embryo’s cartilage serves as the template
PROCESS OF OSTEOGENESIS Cartilage template develops periosteum Inner surface of periosteum - cartilage cells change into osteoblasts Osteoblasts secrete Ca into collagen matrix Osteoclasts remove Ca from the collagen matrix to form a medullary cavity
Blood vessels grow in the cartilage model and into the cavity This causes more cartilage cells to become osteoblasts Site of primary ossification center Process works toward epiphysis
At epiphysis – site of secondary ossification center Same process occurs but spongy bone develops No medullary cavity appears By birth most hyaline cartilage has been converted to bone except for articular cartilage and epiphyseal plate
GROWTH New cartilage is formed on the external face of the articular cartilage and epiphyseal plate Old cartilage nearer the medullary cavity is broken down and replaced by bone Controlled by growth hormone and sex hormones Ends at puberty
EXERCISE AND BONE TISSUE Mechanical stress with strength bone and increase deposition of mineral salts and production of collagen fibers. Mechanical stress – main source is the pull of skeletal muscles and the pull of gravity