Anatomy 1; muscular skeletal system Flashcards

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Bone Types

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Classification of bones by shape, including long, short, flat, irregular, and sesamoid bones. Each type has distinct structural features and functional roles in support, protection, and movement.

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Long Bone

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A bone longer than it is wide with a shaft (diaphysis) and two ends (epiphyses). Long bones mainly facilitate movement and act as levers, and they contain a central medullary canal for marrow.

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Short Bone

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A cube-like bone with roughly equal length, width, and thickness, providing stability and some movement. Short bones are mostly composed of spongy bone covered by a thin layer of compact bone, as seen in the carpals and tarsals.

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Flat Bone

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Thin, flattened, usually curved bones that protect internal organs and provide broad surfaces for muscle attachment. Examples include the sternum, ribs, and most skull bones.

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Irregular Bone

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Bones with complex shapes that do not fit into other categories, such as vertebrae and some facial bones. Their unique shapes serve specialized protective and supportive roles.

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Sesamoid Bone

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Small, round bones embedded in tendons that protect tendons from stress and wear, and can improve mechanical advantage. The patella is the largest and most well-known sesamoid bone.

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Compact Bone

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Dense bone tissue forming the external layer of all bones and the bulk of the diaphysis. Compact bone contains osteons (Haversian systems) organized around central canals that carry blood vessels and nerves.

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Spongy Bone

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Also called cancellous bone; it has a porous, trabecular architecture that reduces weight while providing strength and space for marrow. Spongy bone is typically found in epiphyses and inside flat bones.

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Periosteum

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A fibrous membrane covering the outer surface of bone except at articular cartilage, containing blood vessels, nerves, and osteogenic cells. The periosteum aids in growth, repair, and attachment of tendons and ligaments.

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Endosteum

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A thin vascular membrane lining the inner surfaces of bone, including the medullary cavity and the trabeculae of spongy bone. It contains osteoprogenitor cells important for bone growth and remodeling.

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Epiphysis

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The rounded end region of a long bone that articulates with adjacent bones and often contains spongy bone and red marrow. Epiphyses are capped with articular cartilage to facilitate joint movement.

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Diaphysis

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The shaft or central tubular portion of a long bone composed mainly of compact bone surrounding a medullary cavity. The diaphysis provides leverage and weight support for the bone.

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Metaphysis

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The region of a long bone between the diaphysis and epiphysis that includes the growth plate in children and adolescents. In adults, the metaphysis contains the epiphyseal line where growth has ceased.

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Epiphyseal Plate

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A band of hyaline cartilage at the metaphysis of growing bones where longitudinal growth occurs via endochondral ossification. The plate is replaced by bone at puberty to form the epiphyseal line, marking growth cessation.

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Articular Cartilage

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Hyaline cartilage that covers the articular surfaces of bones at synovial joints, reducing friction and absorbing shock during movement. It lacks blood vessels and relies on synovial fluid for nutrient exchange.

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Osteoblast

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Bone-forming cells that synthesize and secrete the organic components of bone matrix (osteoid) and initiate mineralization. Osteoblasts can become embedded in matrix and differentiate into osteocytes.

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Osteocyte

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Mature bone cells derived from osteoblasts that maintain bone matrix and communicate via canaliculi. Osteocytes help regulate mineral homeostasis and coordinate remodeling in response to mechanical stress.

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Osteoclast

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Large, multinucleated cells responsible for bone resorption by secreting acids and proteolytic enzymes. Osteoclast activity helps remodel bone, regulate calcium levels, and shape bone during growth and repair.

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Bone Remodeling

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A lifelong process involving coordinated bone resorption by osteoclasts and bone formation by osteoblasts to repair microdamage and adapt to mechanical stress. Remodeling also regulates calcium and phosphate homeostasis.

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Intramembranous Ossification

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A bone formation process in which bone develops directly from mesenchymal connective tissue, forming flat bones like those of the skull and clavicle. Osteoblasts differentiate within the mesenchyme and deposit bone matrix without a cartilage precursor.

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Endochondral Ossification

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The process where bone replaces a hyaline cartilage model, responsible for formation of most bones including long bones. It involves cartilage growth, calcification, invasion by blood vessels, and replacement by bone tissue.

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Bone Matrix

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The extracellular matrix of bone composed of organic components (collagen fibers and ground substance) and inorganic mineral salts. The organic portion provides tensile strength while the inorganic hydroxyapatite crystals provide compressional strength.

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Hydroxyapatite

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The primary inorganic mineral in bone, a calcium phosphate mineral with the chemical formula $Ca_{10}(PO_4)_6(OH)_2$. These crystals deposit in the collagen matrix and give bone its hardness and resistance to compression.

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Bone Marrow

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Soft tissue within the medullary cavities and trabecular spaces; red marrow is hematopoietic and produces blood cells, while yellow marrow is rich in adipocytes and stores fat. In adults, red marrow is primarily found in axial skeleton and proximal epiphyses.

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Joint (Articulation)

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A site where two or more bones meet, allowing varying degrees of movement and providing mechanical stability. Joints are classified structurally (fibrous, cartilaginous, synovial) and functionally (synarthrosis, amphiarthrosis, diarthrosis).

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Synarthrosis

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A functional classification of a joint that permits little or no movement, often designed for protection or stability. Examples include sutures of the skull.

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Amphiarthrosis

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A joint type allowing limited movement, providing both stability and flexibility; commonly found in vertebral discs and the pubic symphysis. These joints often use fibrocartilage or hyaline cartilage as connective tissue.

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Diarthrosis

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A freely movable joint, typically a synovial joint, allowing a wide range of motion depending on its structural subtype. Diarthroses have features like a joint cavity, synovial membrane, and articular cartilage.

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Synovial Joint

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A joint characterized by a fluid-filled cavity between articulating bones, permitting significant movement and containing a synovial membrane and articular cartilage. Examples include the shoulder, hip, and knee joints.

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Joint Capsule

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A fibrous envelope surrounding a synovial joint composed of an outer fibrous layer and an inner synovial membrane. The capsule stabilizes the joint while the synovial membrane secretes synovial fluid for lubrication and nutrition.

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Synovial Fluid

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Viscous fluid produced by the synovial membrane that lubricates joint surfaces, reduces friction, and supplies nutrients to avascular articular cartilage. Synovial fluid also contains phagocytic cells to remove debris.

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Ligament

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Bands of dense regular connective tissue that connect bone to bone, stabilizing and guiding joint movement. Ligaments have limited elasticity compared to tendons and can be injured by overstretching.

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Tendon

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Dense regular connective tissue that attaches muscle to bone, transmitting the force of muscle contraction to produce movement. Tendons are composed largely of collagen fibers and are designed for tensile strength.

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Bursa

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A small fluid-filled sac lined with synovial membrane that reduces friction between tissues such as tendon and bone. Bursae are found near many joints and can become inflamed (bursitis) with overuse or trauma.

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Muscle Fiber

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A single muscle cell, often long and multinucleated, surrounded by the sarcolemma and containing myofibrils composed of contractile proteins. Muscle fibers are organized into fascicles and vary by metabolic and contractile properties.

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Myofibril

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A contractile organelle within muscle fibers composed of repeating sarcomeres containing actin and myosin filaments. Myofibrils align longitudinally and give skeletal muscle its striated appearance.

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Sarcomere

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The functional contractile unit of striated muscle defined by Z-discs, containing organized thick (myosin) and thin (actin) filaments. Sarcomere shortening via filament sliding produces muscle contraction.

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Actin

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The primary component of thin filaments in muscle sarcomeres, providing binding sites for myosin heads during contraction. Actin interacts with regulatory proteins troponin and tropomyosin that control access to binding sites in a calcium-dependent manner.

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Myosin

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The motor protein forming the thick filaments of the sarcomere with protruding heads that bind actin and hydrolyze ATP to generate force. Myosin head cycling and conformational changes produce the power stroke that moves actin filaments.

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Sliding Filament Theory

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The mechanism of muscle contraction where myosin heads pull actin filaments toward the center of the sarcomere, shortening muscle fibers without changing filament lengths. Contraction requires ATP and calcium, which regulate cross-bridge formation and release.

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Neuromuscular Junction

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The synapse between a motor neuron and a skeletal muscle fiber where acetylcholine release triggers muscle excitation. Binding of acetylcholine to receptors on the motor end plate initiates an action potential that leads to contraction.

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Motor Unit

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A motor neuron and all the muscle fibers it innervates, functioning as the basic unit of motor control. Recruitment of motor units of varying sizes and types allows graded force production and fine motor control.

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Excitation-Contraction Coupling

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The process linking an action potential in the muscle fiber to contraction, involving depolarization of the sarcolemma, calcium release from the sarcoplasmic reticulum, and activation of the contractile machinery. This sequence enables timely and coordinated muscle responses.

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ATP in Muscle

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Adenosine triphosphate provides the energy for cross-bridge cycling, powering myosin head detachment and re-cocking and fueling calcium pumps that restore resting ion gradients. Continuous ATP supply is essential for sustained muscle activity.

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Muscle Fiber Types

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Skeletal muscle fibers are categorized by contractile speed and metabolic pathway: slow oxidative (type I), fast oxidative-glycolytic (type IIa), and fast glycolytic (type IIb/IIx). Fiber types differ in endurance, force production, mitochondrial content, and fatigue resistance.

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Atrophy

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A decrease in muscle mass and strength due to reduced use, denervation, or disease, characterized by loss of myofibrils and decreased fiber size. Atrophy can be reversible with appropriate rehabilitation or can be permanent in severe cases.

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Hypertrophy

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An increase in muscle fiber size and contractile protein content in response to increased workload or resistance training. Hypertrophy improves strength and power by enlarging existing fibers rather than increasing fiber number.

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Agonist

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The primary muscle that produces a specific movement through concentric contraction. Agonists are countered by antagonists and often assisted by synergists to refine motion.

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Antagonist

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A muscle that opposes the action of the agonist, relaxing or contracting eccentrically to control or reverse movement. Coordination between agonists and antagonists ensures smooth and controlled motion.

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Synergist

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A muscle that assists the agonist in performing a movement, either by adding extra force or stabilizing a joint. Synergists help prevent unwanted actions by neutralizing inappropriate muscle components.

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Fixator

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A specialized synergist that stabilizes the origin of the agonist muscle, providing a stable base for efficient movement. Fixators are important for posture and precise limb control.

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Range of Motion

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The extent of movement possible at a joint, limited by bone structure, ligaments, muscles, and soft tissues. Joint flexibility and ROM are influenced by factors like age, injury, and training.

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Flexion/Extension

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Flexion decreases the angle between two bones at a joint, while extension increases that angle, typically returning to anatomical position. These are primary movements occurring in the sagittal plane.

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Abduction/Adduction

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Abduction moves a body part away from the midline, while adduction moves it toward the midline. These movements occur in the coronal (frontal) plane and are central to limb positioning.

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Pronation/Supination

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Rotational movements of the forearm: pronation turns the palm posteriorly (or downward), and supination turns it anteriorly (or upward). These movements result from the crossing and uncrossing of the radius over the ulna.

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Dorsiflexion/Plantarflexion

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Ankle movements where dorsiflexion brings the dorsal surface of the foot toward the shin and plantarflexion points the foot downward away from the leg. These movements are important for gait and balance.

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Fracture Types

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Fractures include simple (closed), compound (open), comminuted (multiple fragments), greenstick (partial break), and others. Each type has distinct clinical implications for treatment and healing.

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Callus Formation

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A stage in bone healing where a fibrocartilaginous callus forms bridging the fracture, later replaced by a bony callus through endochondral ossification. Subsequent remodeling restores normal bone structure over time.

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Bone Healing

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A coordinated sequence of inflammation, soft callus formation, hard callus formation, and remodeling that restores bone continuity and strength after fracture. Healing depends on blood supply, stability, and biological factors like age and nutrition.