Ch 50: Structure and Function of the Musculoskeletal System

What components make up the musculoskeletal system?

What components make up the musculoskeletal system?

• Bone

• Joints

• Cartilage

• Tendon and ligaments

• Skeletal muscle

What are the primary purposes of the skeletal system?

• Protects internal organs

• Provides bony attachments for muscles and ligaments

• Functional movement

• Stores mineral marrow elements for forming new blood cells

What is the composition of bone? What are the proportions of each composition?

• Organic matrix (collagen) → 22-25%

• Inorganic minerals (calcium and phosphorus)→ 65-67%

• Water → 10%

Describe dense and compact bone.

• Cortical

• Resistant to compression

Describe trabecular/spongy bone.

• Lighter

• Cancellous

• Laid down in response to stress and shape to accommodate loads placed on the bone

Where is trabecular/spongy bone found?

End of long bones, vertebral bodies, flat bones (pelvis)

What is the periosteum? Describe it.

• Fibrous membrane that covers all bones

• Highly vascular

• Not on the ends of bones

Where is the periosteum located?

On every bone except for the ends of bones

What are the functional properties of bone?

• Endochondral ossification

• Intramembranous ossification

• Altering its shape and density in response to mechanical demands

What is endochondral ossification?

Cartilage replacement by bone → stimulates longitudinal growth (long bones)

What is intramembranous ossification?

Connective tissue is transformed into bone → stimulates circumferential bone growth (flat bones)

What is Wolff’s Law?

• Bone is enhanced where needed; resorbed when not

• Without external forces (or loads) → Osteoclast activity is greater than osteoblasts activity → bone mass decreases

What effect can internal fixation have on bone strength?

• Can decrease bone strength

• Pin and metal implants → stress-relief osteoporosis

What fracture may lead to limb length discrepancy in children?

Fracture through epiphyseal plate

How does a bone fracture heal?

• Occurs by periosteal or external callus formation in fractures

• Managed by closed methods

What are the five stages of bone healing?

1. Hematoma formation

2. Fibrocartilage formation

3. Callus formation

4. Ossification

5. Consolidation/remodeling

Clinical healing is determines when what factors are met?

• Resume function

• No pain

• No gross movement in Fx site

• Radiologic proof

Define articulation

A joint or point of contact between points

What are the two categories of joints?

Synarthroses joints and diarthroses

What are the six categories of synovial joints? Describe each. Give an example of each.

1. Ball-and-socket joint → shoulder

2. Intervertebral joints

3. Cranial sutures

4. Hinge joint → elbow

5. Pubic symphysis

6. Ellipsoidal joint → wrist

What are the two types of cartilaginous joints?

Symphysis and synchondrosis joints

Describe symphysis joints and some examples.

• Connects bony segments by a fibrocartilaginous plate or disk

• Ex: symphysis pubis joint (joins the two pubic bones of the pelvis), intervertebral joints of the spine

Describe synchondrosis joints and some examples.

• Cartilage connects bony components

• Allows bone growth while providing stability

• Can be found at growth sites of the body

• Ex: the first sternocostal joint

What is synostoses?

When bone growth is complete → they ossify and become unions

What are some common features of synovial joints?

• A fibrous joint capsule

• A joint cavity enclosed by a joint capsule

• A synovial membrane that lines the inner surface of the capsule

• Lubricating synovial fluid that coats joint surfaces

• Hyaline cartilage that covers the opposing joint surfaces

What produces synovial fluid?

Fibroblast-like cells lining the joint capsule

What are the three main categories of synovial joints based on movement?

1. Uniaxial

2. Biaxial

3. Triaxial

Describe uniaxial joints and some examples.

• Allows motion around a single axis of movement

  • Hinge joints

  • Pivot joints

Describe biaxial joints and some examples.

• Has two axes of movement and permits movement in two planes

  • Condyloid joints

  • Saddle joints

Describe triaxial joints and some examples.

• Has three axes of movement and permits movement in three planes

• Permits gliding movement between two bones

• Is exemplified by the carpal joints of the hand

  • Carpal joints

  • Ball-and-socket joints

What is articular (hyaline) cartilage?

A specialized tissue designed to withstand stress imposed by movement of bony structures

Where is articular (hyaline) cartilage located?

Covering the ends of bones

What is its function of articular (hyaline) cartilage?

• Distributes joint loads over a wide area

• Decreases the stress of prolonged compression from contact joint surfaces

• Minimizes friction and deterioration with joint movement

Articular cartilage is devoid of…

Blood vessels, lymph channels, and nerves

What is the composition of articular cartilage? What is the proportions of the different compositions?

• Hydrophilic in nature → >70% water

• Inorganic salts, proteins, glycoproteins, and lipids make up the interstitial fluid

• Chondrocytes produce the organic components of the extracellular matrix

• Proteoglycan (especially aggregan) surround the extracellular matrix

What is the main cell type within articular cartilage? What is their function?

• Chondrocytes

• Function: to manufacture the organic components of the extracellular matrix of the cartilage

The extracellular matrix of the articular cartilage is composed of…

An intricate network of collagen fibrils, elastin, fibrillin, and other macromolecules → gives cartilage its flexibility and tensile strength

Proteoglycans surround the collagen network of the extracellular matrix of articular cartilage. What is the function of proteoglycans?

• Increases strength

• Provides structural rigidity

• Compression tolerance

What are the functions of tendons?

• Attach muscles to bones

• Assists in the generation of movement

What is the function of ligaments?

• Connects bone to bone

• Provides mechanical stability to joints

• Guides joint movements

What is the composition of tendons and ligaments?

• Dense connective tissue with collagen fibers in parallel alignment

• Composed of few cells and large amounts of extracellular matrix

• Tendons contain more collagen than ligaments

  • Collagen

  • Elastin

What kind of cross-links give strength to tissue and increase tolerance to mechanical stress?

Collagen

What do skeletal muscles enable bones to do?

• Move at the joint

• Provide strength, stability, and protection to the skeleton by distributing loads and absorbing shock

What is the composition of skeletal muscle? (HINT: start from the muscle fiber and know each step until the epimysium)

• Muscle fiber → sarcolemma → endomysium surrounds sarcolemma → perimysium surrounds fasciculi → epimysium surrounds entire muscle

What fibers attach tendons to bones?

Sharpey fibers

Is myosin the thick or thin filament?

The thick filament

What are actin’s regulatory proteins?

Troponin and tropomyosin

Describe the mechanics of muscle contraction.

• Increasing the amount of overlap of actin and myosin filaments → muscle shortening

• The Z lines at the end of the sarcomere move close together

• Myosin head groups grip binding sites on actin filaments and moves them towards the sarcomere’s center

• Each time a myosin head binds an actin bead, it forms a cross-bridge

• Requires one molecule of ATP

How does calcium affect muscle contraction? What if there is too much? Too little?

• If calcium is too little → Troponin induces tropomyosin to cover actin binding sites

• If calcium is too high → Troponin allows tropomyosin to move over and uncover binding sites

Early muscular activity after an injury is associated with what three factors?

• Quicker recovery of tensile strength

• Less atrophy

• Better circulation