Students will be able to:
For the purposes of this workbook the skeletal system consists of four components: bones, cartilage, tendons, and ligaments, the latter three may also be considered part of the articular system. There are 206 bones in the body creating the skeletal structural framework. This framework gives the body its shape, provides support and protection for tissues and organs, and serves as a storage site for minerals such as calcium and phosphorus. Bone tissue is also a site for blood cell production (hematopoiesis), and supplies the levers for movement, or kinesiology.
Axial Skeleton (80 bones)
Appendicular skeleton (126 bones)
Bone Structure - Classification & Function
There are three basic materials that make up the connective tissues throughout the body, 1) fibrous proteins (collagen and elastin), 2) ground substance, and 3) cells. Each will be described in more detail. The proportion and arrangement of these three materials determine whether the connective tissue forms articular cartilage, periarticular structures – ligament, tendon, bursa, joint capsule, meniscus, or bone.
Bone tissue is a type of connective tissue composed of bone cells and matrix.
Bone as a Living, Dynamic Tissue
When mechanical stress/pressure – compression via impact (e.g., plyometrics) or pulling via muscular contraction (resistance training) is placed on a tissue, a slight electric charge is produced in the tissue. This is known as the piezoelectric effect (“Piezo” means pressure). This causes a transient depolarization in the membranes of the osteocytes that are embedded in the bone matrix through stretch activated Ca++ channels. This depolarization causes the release of growth factors that stimulate nearby osteoblasts to produce matrix.
Osteoblasts can lay down bone matrix in any tissue, while osteoclasts are unable to resorb (break down) bone matrix from bone in piezoelectrically charged tissue. As a result, greater bone mass forms in regions of a bone that are under greater pressure producing stronger bones more capable of withstanding forces applied to them. On the other hand, mass is diminished in bone where there is a lesser stress applied. As such, there is a greater risk for bone damage from trauma and from the degenerative bone disease of osteoporosis.
Unfortunately, chronic unrelieved and unbalanced stress/pressure placed on a bone may result in excessive matrix being deposited in the bone. As the bone tissue becomes denser and denser the body starts to place calcium along the outer margins of the bone in an abnormal manner. This can result in bone spurs, degenerative joint disease, osteoarthritis, or abnormal formation of the bone, etc. Below are some examples of the effects of abnormal/unbalanced stress placed on bone tissue.
There are several different types of soft tissues in the body. Joints, the union formed between bones where body movement takes place, have various anatomical structures depending on the type or functional classification of the joint. The components of the periarticular soft connective tissue that forms many joints are the joint capsule, ligaments, tendons, articular cartilage, bursae, and fibrocartilage. Other soft connective tissues associated with the musculoskeletal system include retinaculum, tendon sheaths, aponeurosis, and fascia.
Joint Capsule – composed of an outer layer that provides support to the joint, and an inner layer, with synovial membrane that produces synovial fluid to lubricate the joint and nourish cartilage.
Ligament – thick fibrous band of connective tissue that connects bone to bone and functions to create stability at a joint by holding the bones together. Primarily composed of collagen fibers to provide strong tensile strength, with some elastin fibers.
Tendon – band of connective tissue that connects muscle to bone and functions to transmit the pulling force of a muscle contraction to its bony attachment. Primarily composed of collagen fibers (parallel fiber arrangement), for strong tensile strength, with elastin fibers as well.
Tendon Sheath – a synovium-filled sheath that envelopes a tendon to reduce the friction stresses between the tendon and other structures like retinaculum.
Retinaculum – connective tissue sheath that binds and holds tendons in place. Primarily found retaining the tendons that cross the wrist and ankle joint. Note: To minimize friction between the tendons and retinaculum, tendon sheaths are located in these regions. u
Cartilage – a firm, smooth, resilient, non-vascular
connective tissue composed of cartilage cells, matrix
fibers and ground substance. Types of cartilage:
Meniscus – a crescent shaped plate of cartilage that
functions to deepen an articular surface and serves to
provide shock absorption to joints like the knee and
sternoclavicular joints. (see Figure 7)
Labrum – a type of cartilage that deepens a joint socket and serves as an attachment site for the joint capsule. The glenoid of shoulder and acetabulum of hip are examples (see Figure 8)
Aponeurosis – a tendinous expansion of dense fibrous connective tissue sheath that anchors muscle to muscle or muscle to bone. (see Figure 9a)
Fascia – a sheet of fibrous connective tissue that envelopes, separates, or binds together parts of the body like muscles, organs, or other structures. (see Figure 9b)
Bursa – flattened sack of synovial membrane containing a film of synovial fluid. Bursae are typically located between a tendon and an adjacent joint structure, usually a bone, and help reduce the friction between the two structures.
Extensibility: the ability of a tissue to be stretched, becoming longer without injury or damage
Weight Bearing: the ability of a tissue to bear the compressive force of the weight of the body located above it, without injury or damage
Tensile Strength: the ability of a tissue to withstand a pulling force without injury or damage
Elasticity: the ability of a tissue to return to its normal resting length after being stretched
Plasticity: the ability of a tissue to have its shape altered or molded, and then to retain the new shape (elongation)
Elasticity and Plasticity Compared
Whenever a soft tissue of the body has been altered or deformed because a force has been applied to it (compressed or pulled) the tissue has a certain elastic ability to return to its original shape. If that elasticity is exceeded, then plasticity describes the fact that the shape of the tissue will stay permanently (or relatively permanently) altered or deformed to some degree. An example is a ligament that has been stretched. If it is only slightly stretched, its elastic ability allows it to return to its original length and provide the appropriate joint stability. However, if it is stretched to a greater degree (or repeatedly stretched) and its elastic ability is exceeded, the tissue will enter its plastic range and will become permanently (or relatively permanently) overstretched. This increased laxity results in a decrease in stability where the ligament is located.
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