Structure and Function of the MSK Flashcards
MSK made of two systems
- bones and joints
- soft tissues
Constituents of bone tissue
- Cells
- Fibers: collagen
- Ground substance: gelatinous material
- Crystallized minerals: especially calcium
Fibers: collagen
-Gives bones tensile strength-ability to hold itself together
Ground substance: gelatinous material
-medium for diffusion between bone and blood vessels
Crystallized minerals: especially calcium
-Provide rigidity
Factor-beta (TGF-B)
-is responsible for initiating, differentiating, and committing precursor cells into osteoblasts
Wnt Genes
- protein-signaling factors required for the development of body systems, including the MSK
- Bone formation, bone mass development, remodeling, and fracture healing
Osteoblasts
- derived from mesenchymal cells
- produce osteocalcin
- form new bone
- synthesize osteoid (nonmineralized bone matrix)
- bone is shaped according to its function
- become osteocytes that’re imbedded in bone
Osteocytes: bone maintenance
- develop dendritic processes that extend to either the bone surface or the bone’s vascular space
- help maintain bone by signaling osteoblasts and osteoclasts to form and resorb bone
- located in lacuna
- respond to parathyroid hormone
- coordinate osteoblast and osteoclast functions
Osteoclasts: bone resorption
- large multinucleated cells
- contain lysosomes filled w/ hydrolytic enzymes
- have microvilli called ruffled borders
- located in Howship lacunae
- attached to integrins by podosomes (helps bind to bone)
- osteoclasts loosen from bone surface
- osteoclasts become inactive and rest
Bone cells: nuclear factor kappa B ligand (RANKL)
-Induces osteoclast activation and bone resorption
Bone cells: osteoprotegerin (OPG)
- Is a glycoprotein
- coupling of osteoblasts and osteoclasts
- serves as a decoy receptor RANKL and blocks osteoclast activity
- balance between RANKL and OPG determines the quality of bone
Bone matrix
- 35% osteoid, 65% mineral component, 5-8% water
- organic: collagen fibers
- inorganic: Ca and phosphate minerals
- proteins, carbs, complexes, ground substances
Bone matrix: Collagen fibers
- essential for bone strength
- form fibrils that twist
- synthesized and secreted by osteoblasts
- have over 20 types
Bone matrix: Proteoglycans
- large complexes of numerous polysaccharides attached to a common protein core
- strengthen bone by forming compression-resistant networks between between collagen fibrils
- help Ca deposit and calcify in bone
Bone matrix: glycoproteins
- Carbs-protein complexes of bone
- control collagen interactions that lead to fibril formation
- play a role in calcification
Other proteins found in bone matrix
- Bone morphogenic proteins (BMPS)
- Sialoprotein (osteopontin)
- Osteocalcin
- Osteonectin
- laminin
- bone albumin
Bone formation
- First step: develop bone matrix
- Next step: calcification
- Final step: mineralization
Mineralization
- Final step in bone formation
- phases:
- -formation of the initial mineral deposit
- -proliferation or accretion or additional mineral crystals on the initial mineral deposits (growth)
- Majority of the mineral content in the body: hydroxyapatite-the end product
Types of bone tissue: Compact bone
- aka cortical bone
- 85% of skeleton
- solid and extremely strong
- haversian system
- haversian canal, lamellae, lacunae, osteocyte and canaliculi
Types of bone tissue: spongy bone
- AKA cancellous bone
- 15% of the skeleton
- filled with red bone marrow
- lack haversian system
- Trabeculae: plates or bars
Periosteum
- double layered connective tissue
- covers all bones
- outer layer: contains blood vessels and nerves
- inner layer: anchored to the bone by collagenous fibers
Characteristics of bones
- total of 206 bones in human skeleton
- Axial
- Appendicular skeleton
Axial skeleton
- 80 bones
- skull (cranium), vertebral disks/columns, thorax
- -first 7 ribs attach to sternum-true ribs
- -pair 8 is false
- -pars 11 and 12 are floating ribs
- -spine as 24 vertebral bones
Appendicular skeleton
- 126 bones
- upper and lower extremities, shoulder girdle, pelvic girdle
Long bones
- Diaphysis (medullary cavity contains fat: yellow marrow)
- metaphysis: broad neck
- epiphysis: (medullary cavity helps w/ blood formation-red marrow)
- Endosteum
Phases of remodeling
- activation of the remodeling cycle
- resorption
- formation of new bone (secondary bone)–takes 4-6 months
Bone heals itself: repair
- hematoma: clot forms
- Procallus: produces granulation tissue
- callus formation: forms membranous or woven bone
- callus replacement: replaces the callus w/ lamellar bone or trabecular bone
- remodeling
Joints
- site where two bones meet
- promote stability/mobility
- classifications are based on movements
Synathrosis (fibrous joint)
- immovable
ex. vertebral disks, sternum, skull, sutures, syndesmoses, gomphoses - directly united to bone by dense fibrous connective tissue
Amphiarthrosis (cartilage joint)
- Slightly movable
ex. pelvis, joints between the ribs and sternum, - connected by fibrocartilage or hyaline cartilage
- symphysis: bones are united by a pad or disk-
- synchondrosis-hyaline cartilage
Diathrosis (synovial joint)
- freely movable
- most complex
- synovial fluid: fills the joint cavity and lubricates the joint surface
- 6 types of synovial joints
Joint capsule
- connective tissue covers the ends of the bones where they meet in the joint
- richly supplied w/ nerves, blood vessels, and lymphatic vessels
Synovial membrane
- smooth, delicate inner lining of the joint capsule
- has a vascular layer and thin cellular layer
- Type A synovial cells:phagocytic
- Type B synovial cells:
Joint cavity
- called joint space
- enables two bones to move “against” one another
- filled w/ synovial fluid
Synovial fluid
- superfiltrated plasma fluid
- lubricates the joint surfaces and nourishes the pad of the articular cartilage
- contains free floating synovial cells and various leukocytes that phagocytize joint debris and micro-organisms
Articular cartilage
- reduces friction in the joint and distributes forces of weight bearing
- layered
- has no blood vessels , lymph vessels, or nerves (is insensitive to pain, and regenerates slowly after injury)
Proteoglycans
- act as a pump
- permit enough fluid to be pressed out to ensure that a fluid film is always present on the surface of the cartilage, even after hours of weight bearing
Myoblasts
- primarily cells responsible for muscle growth
- satellite cells when in dormant state
- once muscle is injured, satellite cells become activated to form myoblasts and assist in repair
Skeletal muscle composition
- 75% water, 20% protein, 5% organic and inorganic materials
- over 350 named muscles, most are paired
Fusiform muscles
- elongated muscles that are shaped similar to straps
- run from one joint to another
Pennate muscles
-broad, flat, slightly fan shaped
Whole muscle
- Fascia (organ encased in three part framework of connective tissue)
- epimysium (outermost layer an forms the tendon)
- tendon
- permysium
- fascicles
- endomysium
- Outer to inner: bone, tendon, fascia, muscle, epimysium, perimysium, endomysium, fascicle, muscle fiber/cell
Skeletal muscles: Voluntary
-directly controlled by CNS
Striated skeletal muscles
- striped pattern of skeletal muscle
- results from organization of muscle fibers into the contractile units called sacromeres
Extrafusal skeletal muscles
-distinguishes skeletal muscle fibers from other contractile fibers
Motor unit
- Anterior horn cells, its axon, and muscle fiber
- functional unit of the neuromuscular system
- behaves as single entity
Innervation ratio
- motor units per muscle
- greater the innervation ratio of a particular muscle, greater its endurance
- High: prevents fatigue
- Low: precision movement
Sensory receptors
- send signals to CNS
- spindles: mechanoreceptors that respond to muscle stretching
- secrete proteoglycan called neuroregulin
- responsible for muscle stretch response and tone
Muscle fibers
- each fiber is a single muscle cell
- myofibrils: functional units of contraction
- white muscle (type ll fibers): fast
- red muscle (type l fibers): slow
- muscle membrane
muscle membrane
- sarcolemma: propagates impulse
- basement membrane: maintains cell’s shape
Muscle fibers
- sarcoplasm (cytoplasm of muscle cell)
- sarcotubular system
- sarcomere (composed of proteins actin, myosin, titin, nebulin)
Muscle proteins and nonproteins
- M proteins contains creatinine kinase (CK)
- -Released when muscle cells are damaged
- actin and myosin (most abundant)
- muscle metabolism: nitrogen, creatine, creatinine, phosphocreatine, purines, uric acid, amino acids
Muscle contraction
- Ryanodine receptors (RyRs): primary ion channels that control calcium release in muscle
- -RyR1: skeletal muscle
- -RyR2: cardiac muscle
- -RyR3: diaphragm, smooth muscle, and brain
Phases of muscle contraction
-excitation, coupling, contraction, relaxation
Excitation
-spread of action potential from nerve terminal to the neuromuscular junction
Coupling
-release of Ca leaves actin free to bind w/ myosin
Contraction
- “All or nothing”
- cross bridge that causes muscle to shorten (sliding-filament theory or cross bridge theory)
Relaxation
-cross bridge detaches and a sarcomere lengthens as calcium is pumped back into the sarcoplasmic reticulum
Muscle metabolism
- Requires constant supply of adenosine triphosphate (ATP) and phosphocreatine
- oxygen debt: amount of oxygen needed to convert the buildup of lactic acid to glucose and replenish ATP and phosphocreatine stores
Muscle mechanics
Agonist -prime mover -contracts Antagonist -reciprocal muscle -relaxes
Electromyogram (EMG)
- Uses sensitive needle electrodes: muscle is recorded
- helps differentiate muscle diseases from peripheral nerve and neuromusclar junction disorders
