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Functions of the Skeletal System
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• basic functional unit of compact bone is the osteon: layers of osseous tissue around the Haversian canal • osteocytes are found in the lacunae, sandwiched between layers of osseous tissue • perforating canals enter the bone • lacunae of a osteon are connected by small canaliculicompact bone• lack blood vessels • matrix forms trabeculae • nutrients reach cells through canaliculi that open onto the surface of the trabeculaespongy bonea connective tissue that is composed of specialized cells in a mineralized matrixbone• protein fibers: collagen • hydroxyapatite: inorganic component of matrix; deposits of calcium phosphate crystalsmakes up matrixosteochondral progenitor cellsstem cellscartilage comes in three types, what are they?hyaline, fibrocartilage, elastic cartilageperichondriumdouble layered connective tissue sheath covering most cartilagearticular cartilagehylaine cartilage, covers the ends of bones where they come together to form joints.chondroblastscartilage producing cellchondrocytesmature cartilage celldiaphysisshaft of the bone. consists of compact bone surrounding marrow cavityepiphysispart of the bone that develops from the center of ossification distinct from the diaphysis, end of bone-filled with spongy boneperiosteumsuperficial layer of bone, isolates bone from surrounding tissue, actively participates in bone growth(where bones grow in diameter)yellow marrowfat storage; in medullary cavity or in spaces of spongy bonered marrowconnective tissue in the spaces of spongy bone or in medullary cavity: site of hemopoises(blood cell procution)endosteumlines the marrow cavity active during bone growth or repair (inner cavities of bone)epiphyseal platearea of hyaline cartilage btwn the diaphysis and epiphysis: cartilage growth followed endochondral ossification results in growth in bone lengthepiphyseal linewhen bone stops growing in length the epiphyseal plate becomes ossified and is called thiswhen does bone development begin8 weeks after conception and continues through adolescencesintramembranous ossificationdermal ossification; osseous tissue develops from mesenchymal tissueendochondrial ossificationosseous tissue replaces existing cartilage modelprocess of intramembraneous ossification1. Mesenchymal cells cluster together and begin to secrete the organic components of the matrix. 2. Mesenchymal cells differentiate into osteoblasts. Some become trapped in bony pockets and mature into osteocytes. 3. Bone grows outward in small projections. Interconnection of projections traps blood vessels. 4. Mesenchymal cells divide and produce more osteoblasts. 5. Remodeling around blood vessels forms osteons. 6. Fibrous connective tissue around the bone becomes organized into periosteum.process of endochondrial ossification1. Cartilage enlarges reducing the matrix to thin struts. 2. Matrix becomes calcified, cutting off nutrients to the chondrocytes. 3. Chondrocytes die. 4. Blood vessels grow into the perichondrium. 5. Inner layer of the perichondrium is converted to periosteum 6. Thin layer of bone develops surrounding the shaft of the bone. 7. Blood supply to periosteum increases. Blood vessels enter the shaft of the bone providing a passageway for fibroblasts. 8. Calcified cartilaginous matrix breaks down. 9. Fibroblasts differentiate into osteoblasts and replace cartilaginous matrix with spongy bone. 10. Osteoclasts erode the spongy bone to form marrow cavity.how bones continue to grow in length• Ossification moves away from the center of the diaphysis • At the junction between the diaphysis and epiphysis: epiphyseal plate-composed of cartilage • More cartilage is produced on the epiphyseal side of the epiphyseal plate as ossification occurs on the diaphysis side • As long as the rate of new cartilage production = the rate of ossification, the bone will grow in length. • At puberty, rising levels of sex hormones, growth hormones and thyroid hormones increases the rate of ossification. • When the epiphyseal plate is reduced to a line, growth in length will stophow bones continue in diameterby appositional growth, growth at outer surface.factors affecting bone growth• calcium and phosphate • vitamin D • vitamin C • vitamins A, K and B12 • hormoneswhat is the most abundant ion in the body?calcium. (99% stored in bones)calcium ions is regulated by the interaction of what three ares?bones, intestines, kidneys.Calcium ion homeostasis is regulated bya negative feedback system involving two hormones with opposing effects:parathyroid hormone and calcitoninreleased by the parathyroid when levels of calcium are low; stimulates osteoclast activity, indirectly increases rate absorption at the intestines, decrease rate of excretion at kidneys• Parathyroid Hormone (PTH):released by the thyroid when calcium levels are high; inhibits osteoclasts activity, increase rate of excretion at kidneyscalcitonin4 components of skeletal systembomes, cartilage, tendons, and ligamentsligamentsstrong bands of fibrous connective tissue that attach to bones and hold them togethertendonsstrong bands of connective tissue, attach skeletal muscles to boneslong bonestype of bone that is longer than they are wide. most upper arm and lower limbs are long bones.flat bonestype of bone that is relatively thin, flattened shape and are usually curved. Ex: certain skull bones, the ribs, and the breastbone(sternum), and the shoulder blades(scapulae)short bonestype of bone that is round or nearly cube shaped. Ex: wrist(carpal bones), and ankle (tarsal bones)irregular bonestype of bone that does not fit readily into the other 3 categories. Ex:vertebrae and facial boneswhat are the two systems for classifying jointsstructural[type of tissue that binds the two bones] and range of motionwhat are the three types of joint structuresfibrous, cartilaginous, or synovialwhat are the three types of joint range of motionsynarthroses, amphiarthroses, diarthrosesfibrous jointsconsists of 2 bones connected by fibrous connective tissue, have no joint cavity, and exhibit little or no movement.fibrous joints are subdivided on basis of structure into what three categories?sutures, syndesmoses, and gomphosessuturesinterdigitation of the rough edges of two bones, dense connective tissue forms the ligament seams between the bones of the skull.syndesmosesbones are close but not touching. joined by ligaments. Ex: binds radius and ulna togethergomphosesspecialized joints consisting of pegs that fit into sockets and are held in place by fine bundles of regular collagenous connective tissue. Ex: teeth and socketscartilaginous jointsunite two bones by means of either hyaline cartilage or fibrocartilage.synchondrosesjoints containing hyaline cartilagesymphysesjoints containing fibrocartilage. serves shock absorber.synovialcontain synovial fluid and allow considerate movement between articulating bones. Most complex of the structures.6 types of synovial jointsplane, saddle, hinge, pivot, balland socket, and ellipsoid.plane joint(gliding joint) consists of 2 flat bones surfaces of about equal size between which a slight gliding can occur. uniaxial. Ex: acromion process of scapula and claviclesaddle joint2 saddle shaped articulating surfaces oriented at right angles to each other so that their complementary surfaces articulate. biaxial. Ex: joint of the thumbhinge jointconvex cylinder in one bone is applied to a a corresponding concavity in the other bone. uniaxial. Ex: elbow and knee jointspivot jointrestricts movement to rotation around a single axle. uniaxial. Ex:head of radius and proximal end of the ulna.ball and socket jointconsists of a ball at the end of one bone and a socket in an adjacent bone into which a portion of the ball fits. multiaxial. (wide range of motion in almost any direction) Ex: shoulder and hip joints.ellipsoid jointmodified ball and socket joint. articular surfaces are ellipsoid in shape rather than spherical as in regular ball and socket joints. biaxial. limits movement almost to hing motion. Ex: atlantoocipital joint of the neck.articular diska flat plate or pad of fibrocartilage that lies between the articular cartilages of the bones.articular cartilagea thin layer of hyaline cartilage that covers the articular surfaces and provide a smooth surface where the bones meet.meniscuspad of fibrocartilage situated between articulating bones. like articular disk with hole in center. Ex: knee and wrist.fat padsmasses of adipose tissue; act as packing materialtendonspass across or around joint, limit movement and provide supportbursaesmall fluid filled pockets in connective tissue, covered by synovial membrane; found where tendons or ligaments rub against other tissueligamentsaccessory ligaments reinforce the capsule; extracapsular ligaments pass outside the capsule; intracapsular ligaments help prevent extreme movementfunctions of the muscular systemMovement Maintain posture and body position Respiration Production of body heat Communication Constriction of organs and vessels Contraction of the heartwhat are the three types of muscle tissue?smooth, cardiac, and skeletalCharacteristics of the skeletal muscle tissue• voluntary • striated • attached to and cover bony surfaces • contract rapidly and forcefully • tire easily 40% of body's weightcharacteristics of the cardiac muscle tissueinvoluntary • striated • found only in the heart • contracts at a steady rate but can go faster if necessarycharacteristics of smooth muscle tissue?• involuntary • non-striated • in walls of hollow organs and vessels • slow but sustained contraction most widely distributedfunctions of skeletal muscle tissueresponsible for locomotion, facial expressions, posture, respiratory functions, many other body movements.functions of cardiac muscle tissueit's contractions provide the major force for moving blood through the circulatory system.functions of the smooth muscle tissuepropelling urine, mixing food in stomach and small intestine, dilating and contracting pupil of eye, and regulating flow of blood through blood vessels.muscleorgan consisting of hundreds of muscle cells, connective tissue, blood vessels, and nerve fiberswhat surrounds muscle fibers?endomysiumwhat surrounds muscle fascicule?perimysiumwhat surrounds whole muscles?epimysiumsarcolemmathe plasma membrane of a muscle fiber. small openings on it lead to transverse tubules. (T tubules)sarcoplasmcytoplasm of a muscle fiber, excluding the myofilamentssarcoplasmic reticulumform tubules that surround and run parallel to myofibrils; regulate intercellular levels of calcium ionsT tubulesserve as rapid telegraph systems to conduct nerve stimuli deep into the muscle fibermyofibrilscontractile element of the muscle fiber; bundles of myofilamentstriadcomplex formed by the terminal cisternae of two sarcoplasmic reticulum and a T tubulestructure of myofibrilscompose of linear arrangements of sarcomeres: repeating units containing actin and myosin filaments. 1-3 diameters. extend from one end of muscle to other.structure of sacromeresmallest functional unit. • A band: dark band, area with myosin and actin filaments • I band: light band, area with actin filaments only • H zone: region within the A band where only myosin filaments are present • M line: bisects A band, protein fibers secure the position of the myosin filaments • Z disk: boundaries of the sarcomere, point of attachment for actin filamentsstructure of myosin filaments• consists of 500 myosin molecules bundled together • each myosin molecule has myosin head (crossbridge) and rod-like tailstructure of actin filaments• F actin: twisted strands made up of hundreds of G actin molecules • tropomyosin: covers the active site on actin and prevents actin-myosin interaction • troponin: consists of 3 subunits, one binds to tropomyosin, one binds to G actin and one has a binding site for calciumneuromuscularIntercellular junction between muscle fiber and neuronmembrane potentialelectric charge difference inside a plasma membrane, measured relative to just outside the plasma membranewhat is the role of calcium ions in muscle contraction?bind to regulatory sites on troponin to remove contraction inhibitionwhat is the role of ATP in muscle contraction?supplies the energy needed by muscles to contracttwitchsingle stimulus-contraction-relaxation sequence in a muscle fiberwave summationa second stimulus arrives before the fiber has completely relaxed leading to greater tensiontetanya condition marked by intermittent muscular spasms, caused by malfunction of the parathyroid glands and a consequent deficiency of calcium.motor unita motor neuron and all muscle fibers it serviceswhat contributes to muscle fatigue?occurs when muscle cannot contract despite continued stimulation; due to either exhaustion of energy reserves.1. Depletion of ATP (due to depletion of energy sources and inefficient delivery of oxygen 2. Accumulation of EXTRACELLULAR K⁺ 3. Accumulation of INTRACELLULAR Phosphate 4. Accumulation of lactic acidwhat are the three major energy sources for skeletal muscle.ATP, creatine phosphate, and glycogenhow long does ATP last? and what regenerates it?stores are enough for about 6 seconds of contraction; ATP must be continuously regenerated by • interaction of ADP and CP • aerobic respiration • anaerobic respirationhow long does creatine phosphate last?stores are exhausted after 10 seconds of contractionwhat is glycogen used for?for fuel for respirationoxygen deficitThis is when oxygen is not taken in fast enough to keep the muscles supplied with all oxygen they need when they are working vigorously. Muscle fatigue is believed to result from this deficitfast fiberso most common in the body o large diameter and large glycogen reserves o fatigue rapidly because of low numbers of mitochondria o produce fast, powerful contractionsslow fiberso half the diameter as the fast fibers o take about 3 times longer to contract o specialized for aerobic respiration o capable of extended contractionhypertrophyenlargement of muscle through conditioningatrophyreduction in size, tone and power of musclerecovery periodwhen conditions in the muscle fiber are returning to normal; involves an oxygen debt in the bodytensionis the stress on a material produced by pull of forces. In muscles, tension is equal to the number of crossbridge attachmentsdescribe stimulation of muscle• the stimulation is the arrival of an action potential at the sarcolemma. • once the calcium is released from the SR, it cannot be capture quickly enough to prevent contraction • all triads within the fiber are affected by each APdescribe contraction of musclecalcificationgeneral term for deposition of calcium salts into any tissue. Many structures in body can calcify.canaliculiSmall channel or canal, as in bones, thwere they connect lacunae.central canalcerebrospinal fluid-filled space that runs longitudinally through the length of the entire spinal cord.lacunaeA small cavity or depression in a tissue such as bone, cartilage, and the erectile tissue.lamellar boneMature bone insheets called lamellae. Fibers oriented in one direction in each layer, but in different directions in different layers for strength. Extremely strong:resistant to bending, twisting, compacting. Osteocytes (w/lacunae) arranged in layers sandwiched between lamellae.medullary cavitylong cavity within the diaphysismetaphysistransition zone facing bone marrowossificationbone formationosteoncentral canal containing blood capillaries and the concentric lamellae around it; occurs in compact boneperforating canalcanal containing blood vessels and nerves and running through bone perpendicular to the haversian canals(Volkmann's canals)amphiarthrosesslightly movablesynarthrosesnonmovablediarthrosesfreely movableacetylcholinean organic molecule composed of acetic acid and cholinecrossbridgerecruitmentinvolves increasing the number of muscle fibers contractingrealaxtionoccurs when acetylcholine is no longer released at the neuromuscular junctionlag phasethe time between the application of the stimulus to the motor neuron and the beginning of contraction