Bone Structure and Function Quiz

Musculoskeletal System

• The musculoskeletal system is composed of bones, cartilage, and ligaments
• Provides support and protection for the body
• Site of hematopoiesis (blood cell production)
• Stores calcium and phosphorus
• Allows body movement
• Skeletal system is composed of dynamic living tissues: osseous tissue, cartilage, fibrous CT, blood, and nervous tissue.
• Continuously rebuilds and remodels itself throughout a lifetime
• Works in conjunction with other organ systems

General Osteology and Arthrology

• Osteology: The study of bones
• Bones: Organs of the skeletal system.
• Skeletal System: Bones and associated cartilages.
• Arthrology: The study of joints (fulcrum of movement)
• Endoskeleton: Internal skeleton (endo- = inside)

Skeletal System

• Composed of bones in the skeleton, cartilage, and other connective tissues that stabilize or connect the bones
• Includes:
  •  bones
  • cartilage
  • ligaments
  • Other connective tissues, which stabilize or connect the bones.

Functions of The Skeletal System

• Support: Framework for the entire body, supports legs, pelvic girdle, vertebral column, mandible (teeth), and various organs/tissues
• Protection: Shields against trauma. Protects brain, lungs, heart, and spinal cord
• Movement: Skeletal muscles use bones as levers to move the body
• Reservoir: Reservoir for minerals (99% of body's calcium, and 85% of body's phosphorous) and adipose tissue (found in the marrow of certain bones)
• Hematopoiesis: Also known as blood cell formation, occurs in the marrow of certain bones.

Cartilage

• Characteristics:
  • Weaker than bone
  • More flexible than bone
  • Cells in an abundant matrix
• Types: Hyaline, fibrocartilage, elastic
• Functions:
  • Supporting soft tissues
  • Providing a gliding surface at articulations (joints)
  • Providing a model for the formation of most bones

Types of Cartilage

• Hyaline cartilage: Most abundant type, has a perichondrium (membrane), associated with synovial joints, most bones first modeled in hyaline cartilage.
• Fibrocartilage: Has collagen fibers, intervertebral discs, pubic symphysis
• Elastic cartilage: Has elastic fibers, ear, respiratory tubing

Classification of Bones by Organization

• Axial skeleton: Forms the long axis of the body (skull, vertebral column, rib cage)
• Appendicular skeleton: Bones of the upper and lower limbs and girdles (shoulder bones and hip bones), attaches to the axial skeleton and involved in locomotion and manipulation of the environment

Classification of Bones by Shape

• Long bones: Much longer than they are wide (all limb bones except the patella), consist of a shaft plus 2 expanded ends
• Short bones: Roughly cube shaped (wrist and ankle)
• Flat bones: Thin, flattened, and usually a bit curved (scapulae, sternum, costae, and most skull bones)
• Irregular bones: Have irregular shapes that fit none of the 3 previous classes (vertebrae, hip bones, some skull bones)

Bone Structure

• Bones are organs, composed of multiple tissue types:
  • Bone tissue (osseous tissue)
  • Fibrous connective tissue
  • Cartilage
  • Vascular tissue
  • Lymphatic tissue
  • Adipose tissue
  • Nervous tissue
• Osteons (Haversian systems) are cylindrical structural units functioning as weight-bearing pillars, that are arranged parallel to one another along the long axis of compact bone

Bone Cells

• Osteoprogenitor cells: Stem cells, derived from mesenchyme, produce other stem cells and osteoblasts
• Osteoblasts: Synthesize and secrete collagen and other organic components, initiate calcification, found in periosteum and endosteum
• Osteocytes: Mature bone cells, trapped by the matrix, no longer secrete matrix, responsible for maintaining bone tissue
• Osteoclasts: Huge cells derived from fusion of monocytes, digest bone matrix, part of normal bone growth, concentrated in the endosteum

Bone Matrix

• Consists of organic and inorganic components (1/3 organic, 2/3 inorganic by weight).
• Organic components: Secreted by osteoblasts, composed of several materials, collagen fibers, and other organic materials provide bone resilience
• Inorganic components: Consists mainly of calcium phosphate and calcium hydroxide (form compound hydroxyapatite), contain smaller amounts of magnesium, fluoride, and sodium, give bone its hardness.

Structure of Long Bone

• Diaphysis: Shaft
• Epiphyses: Expanded ends (proximal and distal)
• Metaphysis: Region between diaphysis and epiphyses
• Epiphyseal line: Remnant of epiphyseal plate
• Articular cartilage: Hyaline cartilage covering epiphyses
• Medullary cavity: Marrow cavity

Structure of Short, Irregular and Flat Bone

• Thin plates of periosteum-covered compact bone on the outside and endosteum-covered spongy bone within.
• Have no diaphysis or epiphyses since they are usually not cylindrical
• Contains bone marrow between trabeculae, but no marrow cavity
• In flat bones, the internal spongy bone layer is known as diploë, resembling a stiffened sandwich

Bone Marrow

• General term for soft tissue
• Occupies medullary cavity of long bones and among trabeculae of spongy bone
• Two types:
  • Red bone marrow: Blood cell-forming tissue (hematopoietic)
  • Yellow bone marrow: Fatty marrow

Ossification (Osteogenesis)

• Bone tissue formation.
• In embryos, leads to the bony skeleton.
• As children & young adults, part of bone growth and repair.
• In adults, part of bone remodeling & repair.
• Begins in embryo (eighth-twelfth weeks): from mesenchyme OR hyaline cartilage models.
• Intramembranous ossification: Development of bone from a fibrous membrane.
• Endochondral ossification; Replacement of hyaline cartilage with bone.

Bone Growth

• Interstitial growth: Occurs in epiphyseal plate as chondrocytes undergo mitosis; growth in length
• Appositional growth: Occurs within periosteum; growth in diameter

Bone Remodeling

• Continual deposition of new bone tissue and removal (resorption) of old bone tissue
• Helps maintain calcium and phosphate levels in body fluids
• Occurs at periosteal and endosteal bone surfaces

Wolff's Law

• Bones adapt to loads under which they're placed
  • Increased loading leads to stronger bones
  • Decreased loading leads to weaker bones

Axial Skeleton

• Includes the skull, vertebral column, and thoracic cage

Appendicular Skeleton

• Includes the bones of the upper and lower limbs, also includes the girdles (pectoral girdle and pelvic girdle)

The Skull

• Cranial and facial bones form the cranium
  • complete, rounded structure that surrounds and encloses the brain
  • facial bones protect the entrances to the digestive/respiratory systems
  • attach to facial muscles
• Mandibular bone makes up the lower jaw; Forms lower jaw
• Cavities of the skull: large cranial cavity, orbits, oral cavity, nasal cavity, and paranasal sinuses

Sutures of the Skull

• Immovable fibrous joints that form between cranial bones
• Dense regular connective tissue forms the cranial bones together
• Allows cranium to grow and expand during childhood

Muscular System

• Three types of muscle tissue:
  • skeletal
  • cardiac
  • smooth
• Skeletal: Attached to bones, enable body movement
• Cardiac: Only in the heart, moves blood through the circulatory system
• Smooth: Primary muscle of internal organs and tubes

Skeletal Muscle

• Make up the bulk of muscle in the body
• Typically attached to bones by tendons of collagen
• Origin: End near the trunk or more stationary bone
• Insertion: End near the more distal or mobile attachment
  • Flexor: Muscle causing bones to move closer
  • Extensor: Muscle causing bones to move farther apart

Antagonistic pairs

• Most joints contain antagonistic muscle pairs (flexors and extensors)
  • Contraction pulling a bone in one direction, but also requires an opposing muscle preventing opposite motion.
• Muscles pulling in opposite directions
• E.g., biceps and triceps in the arm
• Muscles acting in coordinated fashion

Motor unit

• A motor neuron and the skeletal muscle fibres it controls .
  • A motor neuron can innervate many muscle fibers
  • A motor unit is the basic functional unit of contraction
• Contraction is initiated when a somatic motor neuron fires an action potential, causing all muscle fibers in the motor unit to contract.

Basic Mechanics of Body Movement

• Isotonic contractions: Muscle contracts, shortens, and/or moves a load (e.g., picking up a weight)
• Isometric contractions: Muscle contracts but does not change length and does not move a load (e.g., holding a weight)

Bones and Muscles Around Joints (levers)

• Lever: A rigid bar that pivots around a point (fulcrum)
• Fulcrum: The flexible joint that forms the pivot point.
• Load: Object pulled or pushed during movement.
• Muscle force: Muscles attached create this force by contracting.
• Lever systems: Bones act as levers, joints are fulcrums, and muscles provide force.

Classification of Joints

• Fibrous joints: Held together by dense connective tissue.
  • Gomphoses (e.g., teeth)
  • Sutures (e.g., skull)
  • Syndesmoses (e.g., tibia/fibula connection)
• Cartilaginous joints: Joined by cartilage, lack a joint cavity.
  • Synchondroses (e.g., epiphyseal plate)
  • Symphyses (e.g., pubic symphysis)
• Synovial joints: Has a fluid-filled synovial cavity between articulating bones; enclosed in a capsule and joined by ligaments
• Synarthrosis: An immovable joint (e.g., suture of skull)
• Amphiarthrosis: A slightly movable joint (e.g., symphysis pubis)
• Diarthrosis: A freely movable joint (e.g., elbow joint)

Accessory Structures of Synovial Joints

• Bursae: Fibrous sacs that contain synovial fluid reduce friction
• Fat pads: Found around synovial joints act as packing material

Types of Synovial Joints

• Classified by their shape:
• Plane or gliding: Flat or slightly curved surfaces, small movements (e.g., intercarpal)
• Hinge: Convex and concave surfaces, one axis of movement (e.g., elbow)
• Pivot: Cylindrical surface rotating within a ring (e.g., proximal radioulnar)
• Ellipsoid/condyloid: Oval articular surface within a depression, two axes of movement (e.g., wrist between radius & carpals)
• Saddle: Articular surfaces with both a concave & convex region, two axes of movement (e.g., carpometacarpal of thumb)
• Ball-and-socket: Spherical head fits within a cup-shaped socket, multiaxial movement (e.g., shoulder)

Other details

• Sinuses: Hollows within bones in the skull that are lined with mucous membranes, lighten skull, serve as resonant chambers for voice.
• Hyoid bone: U-shaped bone located in the neck; does not articulate directly with other bones in the skeleton; provides sites for attachment of ligaments and muscles of the neck and tongue