Musculoskeletal System I - Lecture NOTES

Musculoskeletal System I - Lecture NOTES - Musculoskeletal...

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Unformatted text preview: Musculoskeletal System I The Skeleton: An Overview 1. Bone Quick Facts: 0 Bone provides general structural support for the whole body and gives us shape. 0 Bone provides protection for the brain (skull) and internal organs (ribs, pelvis). 0 Bone provides a structural framework for the bone marrow (source of all blood cells and musculoskeletal cell progenitors). 0 Bone provides attachment sites for muscles. 0 Bones act as levers; joints are the fulcrums or pivot points, aiding efficient locomotion. 0 Bone provides a mineral reservoir of calcium and phosphate. 0 Bone is an excellent biomaterial: it is strong but light, it can adapt to functional demands and can self repair. II. Bone Shape. ~ The shapes of whole bones are varied and intimately related to their function. Despite the variation most bones fall into 3 main groups: Long Short After John D. Curry. Bones, 2002. Princeton Univ. Press a. Long Bones (Tubular) Examples of long bones are the humerus, radius, ulna, femur, tibiiL fibula, metacarpals and metatarsals. Long bones: 0 longer in one direction (usually length) than in other dimensions (usually width) the cross-section is often roughly circular wall thickness is usually about a fifth of the overall diameter hollow in their midsection expanded at their ends The expanded ends are often covered with a layer of hyaline cartilage forming part of a synovial joint. The lumen of long bones is filled with trabecular bone at the ends. Long bones are not simple tubes but have distortions such as flanges, ridges and tubercles for attachment of muscle and ligaments. Long bones occur typically in the limbs where they function as levers for locomotion. They are designed to carry both compressive loads and bending moments over long distances. Imposed loads can be large and the bones must withstand them without breaking or deforming too much. The major tubular part of the shaft is called the diaphysis; the expanded ends are called the epiphyses; the metaphysis is the flared end of the diaphysis where the shaft merges with the epiphysis. b. Short Bones Short bones are roughly the same size in all directions, i.e. have no dimension greater than the other and are roughly the shape of a cube. Examples are the bones comprising the carpus (carpal bones of the wrist) and tarsus (tarsal bones of the ankle) and the centra of the vertebrae. Several short bones may be grouped together to allow complex movements, for example in the carpus and the tarsus. Many of the phalanges are intermediate between short and tubular bones. Short bones have very thin cortices and are completely filled with trabecular bone. Short bones carry compressive loads over short distances. Short bones do not experience significant bending. c. Flat Bones Flat bones are thin in one dimension and much larger in the other two. Examples include the scapular and iliac blades and the bones of the vault of the skull. Generally flat bones consist of two sheets of cortical bone separated by some cancellous bone. Flat bones such as the scapular and iliac blades provide broad surfaces for the attachment of extensive muscles. Flat bones also serve to protect underlying soft tissues, for example the skull protecting the brain. III. The Axial Skeleton Skull, vertebral column, ribs and sternum. a. Vertebral Column 0 Typical vertebrae have a centrum or body, a neural arch and various processes. 0 The vertebral column functions as a segmented, flexible rod with attached limbs for locomotion. 0' Class Differences 0 Fish: vertebrae are relatively uniform, it resists compression and provides lateral flexibility for propulsion. o Mammals: there is regional specialization into Cervical, Thoracic, Lumbar, Sacral and Caudal vertebrae (Fig. 8.2). 0 Birds: Regionally specialized with increased number of cervical vertebrae and fused middle (notarium) and caudal (synsacrum) portions (Fig. 8.32). 4" b. Ribs Articulate with vertebrae and extend into body. Function to protect visceral organs and provide muscle attachments. 0 Fish: There are two sets of ribs with each vertebral segment, a dorsal laterally projecting set and a ventral set which arch ventrally in the lateral body wall. Ventral set fuse caudally to form the hemal arch (Figs. 8.17 and 8.6). Provide attachments for major locomotor muscles. 0 Mammals: Capitulum is the head of the rib which articulates between veterbrae at the lateral centra. The tuberculum articulates with transverse processes. There are stemal and asternal (false) ribs in higher tetrapods. Some vertebrates have two parts to the thoracic ribs: a costal rib adjacent to the vertebra and a distal, more ventral stemal rib (Fig. 8.7). 0 Birds: Have unique uncinate processes that are directed caudal to the adjacent rib to enhance the thoracic rib cage stability. c. Sternum A structure originating in tetrapods (fish lack a sternum). Its size and anatomical relationship are related to the utilization of the forelimbs in locomotion (Figs. 8.8, 8.31). The sternum offers a site of origin for chest muscles. It also secures the ventral tips of true ribs to complete the protective rib cage. The rib cage consists of ribs and stemal elements. Size and shape changes in the rib cage can act to compress or expand the lungs, promoting ventilation. The sternum may consist of a single bony plate or several elements in series. 0 Mammals: The sternum consists of a chain of ossified elements in series, the sternebrae. The most cranial sternebrae is called the manubrium and the most caudal the xiphoid process. 0 Birds: The sternum is one large bone from which the massive flight muscles arise. The sternum has a prominent ventral keel or carina which provides additional surface area for the attachment of muscle. IV. The Appendi ular Skeletornfl/m Composed of: pectoral and e Vic girdles and the skeleton of fins and limbs. The girdles provide the b r locomo ' u ting from fin and limb movement. a. Pectoral girdle O 0 Fish: Have lost the clavicle and fused the scapula and coracoid. The girdle is braced against the skull (Fig. 9.12). Mammals: have a more mobile girdle, no coracoid, sometimes diminished clavicle. Large scapula to support the body via a muscular sling (Fig. 9.28). Birds: have firm attachments to the sternum via coracoid’ and clavicle to brace wings against the axial skeleton. b. Pelvic girdle (Figs. 9.19 and 9.20) O O c. Limbs Fish: May not be attached to the axial skeleton — non weight bearing. Mammals and Birds: pubis, ilium and ishium form a socket called the acetabulum. Sacral veterebrae are strongly attached to the ilium. Birds often lack midline symphysis of pubis and ischium to provide a passageway for eggs. The bird pelvis is often called the innominant bone. Fish: Fins have a basic plan of a row of basal bones supporting a row of smaller radial bones. Cartilagenous fin rays extend from the radials to the end of the fin (Fig. 9.1). Mammals: Limbs have a basic plan of a single bone from the girdle attached to two bones which then support the manus or pes (Fig. 9.22). Birds: limbs are similar to mammal limbs but have reductions and fusions (Fig. 9.24). e.g. carpometacarpus, tibiotarsus, tarsometatarsus and fewer digits. d. Special Adaptations of the Limbs O O O V. Notes Soaring birds lengthen the radius and ulna with a membrane (patagium) across the brachium to the antebrachium. Bats elongate the metacarpals and digits to support the wings (Fig.9.42). Cetaceans increase the number of phalanges in the flippers. Adaptation for terrestrial locomotor speed: a change from plantigrade to digitigrade to unguligrade is associated with an increase in stride length (Fig. 9.36). Narrowing of the thorax and reduction of the clavicle (e.g. cat) provides more rotational movement of the pectoral girdle. Flexibility of the vertebral column may increase stride length by providing additional pivot points through the vertebral column (e.g. cheetah). Reduction in the number of digits by fusions increases strength and reduces weight (Fig. 9.38). ...
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This note was uploaded on 04/05/2011 for the course APC 100 taught by Professor Kelliewhited during the Spring '07 term at UC Davis.

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Musculoskeletal System I - Lecture NOTES - Musculoskeletal...

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