Chapter 6

Axial Skeleton

80 bones; bones of skull, lorax, vertebral column, form the longitudinal axis

Appendicular Skeleton

126 bones; bones of the limbs and girdles that attach them to the Axial skeleton

Bones #total=206, Associated cartilages, ligaments and other connective tissues

Skeletal system components

Support, Storage of minerals and lipids, Blood cell production, protection, leverage

Functions of the skeletal system

1. Flat bones
2. sutural bones
3. long bones
4. irregular bones
5. sesamoid bones
6. short bones

Six categories of bone based on shape

tendon and ligament attachment, at joints where adjacent bones articulate)

elevations/projections

sites for blood vessels or nerves to lie alongside or penetrate bone

depressions/groves/tunnels

head, diaphysis, neck

Surface marking-general

Head

expanded proximal end of a bone that forms part of a joint

diaphysis (shaft)

elongated body of a long bone

neck

narrow connection between the head and diaphysis of a bone

process

any projection or bump

tubercle

small, rounded projection

tuberosity

small, rough projection that takes up a broad area

trochlea

smooth, grooved articular process shaped like a pulley

condyle

smooth, rounded articular process

trochanter

large, rough projection

facet

small, fist articular surface

crest

prominent ridge

line

low ridge, more delicate than a crest

spine

pointed or narrow process

ramus

extension of a bone that makes an angle with the rest of a structure

canal or meatus

large passageway through a bone

sinus

chamber within a bone, filled with air

foramen

small, rounded passageway for blood vessels nerves to pass through bone

fissure

elongated cleft or gap

sulcus

deep, narrow groove

fossa

shallow depression or recess in bone surface

epiphysis, metaphysis, diaphysis

long bone features

epiphysis

network of struts and plate, resists forces from various directions; directs body weight to diaphysis, joints, outer covering is of compact bone;strong organized bone

articular cartilage

covers portions of epiphysis that form articulations, avascular, so relies on synonal (joint) fluid or nutrients

diaphysis

long, tubular portion of the bone, wall composed of thick layer of compact bone, contains the medullary cavity

medullary cavity

filled with two types of marrow; red bone marrow involved in red blood cell production and yellow bone marrow adipose tissue; important as energy reserve

1 of each per bone

how many nutrient arteries and nutrient veins are there?

Nutrient foramen

tunnel providing access to marrow cavity, supply osteons of compact bone with blood

metaphyseal artery and metaphyseal vein

carry blood to/from metaphysis, connect to epiphyseal arteries/veins

Blood supply and innervation of the periosteum

smaller blood vessels supply superficial osteons, lymphatic vessels collect lymph from bone and osteons, sensory nerves innervate diaphysis meddulary cavity, and epiphyses

osteocytes

**maintain protein and mineral content of surrounding matrix, dissolve matrix to release minerals, rebuild matrix to deposit mineral crystals,** occupy lacunae, separated by layers of matrix, interconnected

lacunae

pockets that hold osteocytes

lamellae

layers of matrix

canaliculi

connect osteocytes, connect lacunae with each other and central canal

osteoblasts

**produce new bony matrix** (osteogenesis or ossification), become osteocytes once surrounded by bony matrix, add bone matrix under periosteum, produce bone faster than chondrocytes produce cartilage, actively replace cartilage with bone on diaphyseal side

osteogenic cells

osteoprogenitor cells, mesenchymal cells that produce cells that differentiate into osteoblasts, **important in fracture repair**

osteoclasts

**remove and remodel bone matrix, release acids and enzymes to dissolve matrix and release stored minerals** (process called osteolysis), remove matrix at inner surface to enlarge medullary cavity

\~1/3 bone weight-provide flexibility

collagen fibers

\~2/3 bone weight-provides strength

calcium phosphate

Compact bone

functional unit is osteon, concentric lamellae, osteocytes central canal, canaliculi, strong along it’s length, outer bone tissue layer

concentric lamellae

around a central canal

central canal

contains small blood vessels

circumferential lamellae

at outer and inner surfaces

interstitial lamellae

fill spaces between osteons

osteons

contain central canals (parallel to bone surface), connected by perforating canals (perpendicular to surface)

spongy bone

lamellae form struts and plates (trabeculae) creating an open network, reduces weight of skeleton, no blood vessels in matrix, red bone marry is found between trabeculae, innermost layer

Appositional growth in bones

increases bone diameter of existing bones-does not form of original bone

periosteum

wraps the superficial layer of compact bone, isolates bone from surrounding tissues, route for blood and nervous supply, actively participates in bone growth and repair, outermost layer

perforating fibers

collagen fibers from surrounding tendon, ligaments, and joint capsules cemented into circumferential lamellae, very strong attachment-excessive force will break a bone before snapping there fibers

endosteum

incomplete cellular layer lining medullary cavity, active during bone growth, repair, remodeling, covers spongy bone and lines central canals

endochondral ossification

initial skeleton of embryo formed of cartilage; it is gradually replaces by bone, uses cartilage as small model; bone grows in diameter and length

epiphyseal cartilage

(epiphyseal plate) separates epiphysis from diaphysis, bone grows in length, condrocytes actively produce more cartilage on epiphyseal side, epiphyses are pushed away by continued production of new cartilage

bone growth

at puberty, hormones stimulate increased bone growth, and epiphyseal cartilage is replaced, epiphyseal cartilage narrows until it disappears(process called epiphyseal closure; leaves behind epiphyseal line in adults)

intramembranous ossification

bone formation without a cartil aginous mudel; (stem) cells differentiate into osteoblasts within embryotic tissue or connective tissue

intramembranous ossification in fetal development

begins during the eight week of embyronic development; can see ossification centers and progressing bone formation at 10 weeks

fracture

most heal as long as blood supply and cellular parts of periosteum and endosteum survive

1. fracture hematoma formation
2. callus formation (internal callus and external callus)
3. spongy bone formation
4. compact bone formation

steps in fracture repair

closed or simple

completely internal, only seen on x-ray (no break in skin)

open or compound

project through skin, more dangerous due to infection and uncontrolled bleeding

transverse fractures

break shaft across long axis

spiral fractures

produce by twisting stresses

displaced fractures

result in new and abnormal bone arrangements

compression fractures

occur in vertebrae subjected to extreme stresses(osteoporosis)

greenstick fractures

one side of shaft broken, one side bent (generally occurs in children)

comminuted fractures

shatter affected area producing fragments

epiphyseal fractures

occur where bone matrix is calcifying (a clean transverse fracture of this type heals well)

pott’s (bimalleolar) fracture

occurs at ankle and affects both medial and lateral part of the bone

colles fracture

break in distal radius

metaphysis

connects epiphysis to shaft