INTRODUCTION
1. The skeletal system includes the osseous tissues of the body and the connective tissues that stabilize or interconnect them.
2. Functions of the skeletal system include support, protection, blood cell production, storage of minerals and nutrients, and acting as levers during locomotion or other movements.
OSSEOUS TISSUE
1. Osseous tissue is a connective tissue containing specialized cells, fibers,and a mineralized matrix.
2. The fibers provide resiliency and the minerals add structural strength.
Histological Organization:
1. The collagen fibers and the conditions for mineral crystal maintenance are maintained by osteocytes.
2. Osteocytes communicate with blood vessels via slender cytoplasmic extensions within canaliculi.
Histological Differences Between Compact and Spongy Bone
1. Compact bone contains osteons organized around central (Haversian) canals.
Functional Differences
1. Compact bone has great strength when stressed along the axis of the central canals.
2. Spongy bone consists of a series of trabeculae separated by marrow spaces.The trabeculae are arranged so that pressure applied to the epiphyses of a bone will be transferred to the compact bone of the diaphysis.
The Periosteum and Endosteum
1. A bone is surrounded by a periosteum and lined by an endosteum. The endosteum forms an incomplete lining for the marrow cavity, and endosteal cells are also found within the Haversian canals.
2. Osteoclasts dissolve the bony matrix through the process of osteolysis.
Development and Growth
1. Calcification refers to the deposition of calcium salts; ossification implies the construction of osseous tissue.
2. Osteogenesis involves the activity of osteoblasts.
3. Intramembranous ossification begins with the formation of trabeculae within a connective tissue, and ends with the creation of typical compact or spongy bone.
4. Endochondral ossification requires the formation of a cartilaginous model that is gradually replaced by bone.
5. The diameter of the bone increases through appositional growth. This requires the participation of osteogenic cells of the periosteum.
6. At an epiphyseal plate, interstitial growth of the epiphyseal cartilage is balanced by conversion of calcified cartilage to bone at the metaphysis.
7. The central portions of each epiphysis ossifies, leaving a cartilaginous epiphyseal plate and the articular cartilage of the joint.
* 8. Epiphyseal growth continues until hormonal stimuli cause the closure of the epiphyseal plates after puberty.
REMODELING AND HOMEOSTATIC MECHANISMS
1. Throughout life, activity in bone represents a balance between construction (osteogenesis) and destruction (osteolysis).
2. Mineral turnover in bone can be extremely rapid.
The Skeleton as a Mineral Reserve
1. The skeleton represents an important mineral storehouse.
2. The calcium ion concentration of body fluids is regulated by hormonal mechanisms. High or low levels are equally dangerous.
3. Calcitonin inhibits osteoclasts, decreases the rate of intestinal absorption of calcium, and increases the rate if calcium loss at the kidneys. This lowers the calcium ion concentration within body fluids.
4. Parathormone stimulates osteoclasts, increases the rate of intestinal absorption of calcium, and decreases the rate of calcium loss at the kidneys. This increases the calcium ion concentration within body fluids.
5. These two antagonistic hormones regulate calcium ion concentrations very effectively.
Injury and Repair
1. A fracture is a break or crack in a bone.
2. Repair of a fracture involves hematoma formation followed by appearance of the internal and external calluses.
3. Extensive remodeling and the removal of dead bone occurs before the repairs are completed.
ANATOMY OF SKELETAL SYSTEM
1. Bones may be categorized according to shape. They are either long, short, flat, irregular, sesamoid, or sutural bones.
2. Individual markings can be used to identify specific bones within each category.
3. Important terms referring to an elevation or projection include: ramus, process, head, trochanter, tuberosity, trochlea tubercle, facet, spine, crest, and line.
4. Important terms referring to depressions or holes include: fossa, sulcus, foramen, alveolus, fissure, meatus, antrum, and sinus.
ARTICULATIONS:
1. Articulations exist where bones contact one another. Major classes of articulations are based upon the range of permissible motion.
2. No movement occurs at a synarthrosis. Sutures (skull), gomphoses (jaw/teeth), synchondroses (epiphyseal plate), and synostoses (skull) are appropriate examples.
3. Amphiarthroses permit slight movement. Examples include syndesmoses (radius/ulna) and symphyses (coxae).
4. Diarthroses are highly mobile, and the ends of the articulating bones do not contact one another.They are covered by articular cartilages, bathed in synovial fluid, and enclosed within a joint capsule.
5. Other synovial structures include the synovial membrane, fat pads, menisci, and accessory ligaments.
6. Extremes of motion may produce damaging luxation (dislocation) or subluxation (partial dislocation) of a joint.Such movements are usually prevented by the joint capsule, accessory ligaments, the apposition of soft tissues, bony projections, tendons, and/or muscular contractions.
Planes of Motion
1. Primary movements may be classified as gliding, angular, or rotational.
2. Movement along one axis (forward/back, side/side, or rotational) is called monaxial; motion involving two axes is biaxial, and triaxial refers to movement in all three axes.
3. Monaxial joints include hinge joints (elbow, ankle) and pivot joints (radius/ulna).
4. Biaxial joints include gliding joints (ribs/vertebrae), ellipsoidal joints (palm/fingers), and saddle joints (palm/thumb).
5. Triaxial or ball-and-socket joints (hips, shoulders) are the most versatile.
Describing Dynamic Motion
1. Important descriptive terms in general use include: flexion, extension, hyperextension, rotation, circumduction, adduction, and abduction.
2. Movements of the foot may be described as: dorsiflexion, plantar flexion, inversion, and eversion.
3. Rotation of the radioulnar joint produces pronation or supination.
4. Protraction, retraction, depression, and elevation may be used to describe movements of the lower jaw and shoulder blades.