INTRO TO THE

MUSCULOSKELETAL SYSTEM /

OVERVIEW OF BONES

P2, 4, 6

Composition of the Human Body

• How many bones

are in our body?

• 270+ (at birth)

• 206 (adult)

• How many skeletal

muscles are in our

body?

• ~640 skeletal muscles

Major Functions

SKELETAL SYSTEM

• Support

• Protection

• Movement

• Storage

• Blood cell formation

MUSCULAR SYSTEM

• Movement

• Maintaining posture

• Stabilizing joints

• Generating Heat

Functions of the Bones

• Support • Internal framework

• Supports & anchors all soft organs

• Protection • Skull brain

• Vertebrae spinal cord

• Rib cage organs of thorax

• Movement • Works w/ skeletal muscles,

tendons, & ligaments

• Storage • Fat internal cavities of

bones

• Minerals Ca & P

• Neural transmission, muscle contraction, blood clotting

• Controlled by hormones

• Blood cell formation • AKA hematopoiesis

• Occurs in marrow cavities of certain bones

Divisions of the Skeleton

• 2 divisions:

• Axial skeleton – bones that form the longitudinal axis of the body

• Appendicular skeleton – bones of the limbs and girdles

• Skeletal system includes joints, cartilages, & ligaments

Classification of Bones

• 2 basic types of

osseous (bone)

tissue:

• Compact bone –

dense, smooth-

looking, &

homogenous

• Spongy bone –

composed of small

needlelike pieces of

bone; lots of open

space

Classification of Bones (cont’d)

SHAPES

• Long bones

• Longer than they are wide

• Typically includes shaft with

heads at both ends

• Mostly compact bone

• Short bones

• Typically cube-shaped

• Mostly spongy bone

• Sesamoid – special short

bone formed w/in tendons

• Flat bones

• Thin, flattened, & usually

curved

• 2 thin layers of compact

bone sandwiching 1 layer of

spongy bone

• Irregular bones

• Bones that don’t fit any of the

other groups

STRUCTURE OF A

LONG BONE P1-3

Gross Anatomy

• Diaphysis – shaft of long bone • Composed of compact bone

• Protected by fibrous CT membrane called periosteum

• Secured by CT fibers called perforating (Sharpey’s) fibers

• Epiphyses – ends of long bone • Thin layer of compact bone enclosing area filled w/

spongy bone

• Covered by glassy hyaline cartilage called articular cartilage

• Epiphyseal line – remnant of epiphyseal plate • Epiphyseal plate – flat plate of hyaline cartilage that

causes lengthwise growth of long bone

• Yellow marrow (medullary) cavity – storage area for adipose tissue

• Red marrow – area for blood cell formation

Microscopic Anatomy (Compact Bone)

• (Refer to Fig. 5.3, pg. 135)

• Osteocytes – mature bone cells

• Found in tiny cavities w/in matrix called lacunae

• Lacunae arranged in concentric circles called lamellae around central (Haversian) canals

• Each complex called osteon (Haversian system)

• Tiny canals called canaliculi radiate outward from HC to all lacunae connects all bone cells to nutrient supply

• Perforating (Volkmann’s) canals run perpendicularly to HC & connect outside to interior

• KEY CHARACTERISTIC: Elaborate network bone cells well nourished

• Bone injuries heal quickly and well

Bone as a Material

• One of the hardest in the body Ca salt deposits

• Relatively light

• Flexibility & remarkable ability to resist tension & other

forces collagen fibers

BONE FORMATION,

GROWTH, & REMODELING

P2, 4, 6

Bone Formation & Growth

• Cartilage & bone strongest & most supportive

• Embryos hyaline cartilage

• Young child to adult bone • Remaining cartilage in isolated areas

• Process of bone formation = ossification • Controlled by growth & sex hormones

• Ends when epiphyseal plates completely converted to bone

• Most use hyaline structures as “models”

Bone Formation & Growth (cont’d)

• 2 major phases: 1. Hyaline cartilage model covered w/ bone matrix by osteoblasts

(bone-forming cells)

2. Enclosed cartilage model digested medullary cavity formed

• 2 regions left: • Articular cartilages for life

• Epiphyseal plates during childhood

• Lengthening: • Epiphyseal end of plate new cartilage grows

• Diaphyseal end of plate old cartilage ossifies

• Widening: • Osteoblasts in periosteum ADD bone to diaphysis

• Osteoclasts in endosteum REMOVE bone from diaphysis

Bone Remodeling

• Remodeled continually in response to ∆s to 2 factors:

• Calcium levels in blood

• Hypocalcemia: Ca ↓ PTH ↑ osteoclasts activate break down bone matrix release Ca ions to blood

• Hypercalcemia: Ca ↑ deposited in bone as hard Ca salts

• Pull of gravity & muscles on skeleton

• Become thicker & form large projections to ↑ strength

• Osteoblasts lay down new matrix & trapped w/in become osteocytes

• PTH when (or if)

• Stresses of muscle pull & gravity where

BONE FRACTURES P2, 4, 6

Bone Fractures

• Fracture – break in a bone

• Simple (closed) – clean break; does NOT break skin

• Compound (open) – clean break; does break skin