Part 2

The Skeleton

US-Mexico Border Fence Buenos Aires Wildlife Refuge

The Skeletal System

Human Skeleton• 206 bones

• Axial skeleton—skull, vertebral column, sternum

• Appendicular skeleton—pectoral girdle, pelvic girdle, limbs

Figure 5.5

Axial skeleton

Cranium (skull)MaxillaMandible

Sternum

Vertebrae

Sacrum

Appendicular skeleton

Clavicle

Humerus

UlnaRadiusCarpals

Metacarpals

Phalanges

Coxal bone

PatellaTibiaFibula

TarsalsMetatarsalsPhalanges

Ribs

Scapula

Femur

Axial Skeleton This Side Appendicula

r Skeleton This Side

• Long bones• Associated with large movement• Long and cylindrical with growth heads (epiphyses)• Examples—femur, radius, and ulna

• Short bones • Associated with small, complex movement • Somewhat cube-shaped and associated with smaller, more complex

movements. • Examples—carpals (small bones in the base of the hand) and

tarsals (in the feet)

• Flat bones• Protect the internal organs• Two thin layers of compact bone with spongy sandwiched between• Examples—skull (cranium), ribs, scapula (shoulder blade), sternum

(breast bone) and the pelvic girdle

Types of Bone by Shape

Types of Bone by Shape

• Irregular bones• Irregular in shape• Examples—vertebrae and some facial bones

• Sesamoid bones• Small bones held within tendon• Example—patella. Cartilage separates the femur and the patella and

acts as a shock absorber.

Axial Skeleton

• Vertebral column• Regions—cervical, thoracic, lumbar, sacral, coccygeal• Bones alternating with Intervertebral disks• Intervertebral disks

• Cushion vertebrae• Assist in movement and flexibility• Are composed of fibrocartilage

• Ribs• Twelve pairs• Two pairs are “floating,” not attached to sternum

• Sternum• Three bones fused together

Figure 5.7

Cervical vertebrae (7)

Thoracicvertebrae (12)

Lumbar vertebrae(5)

Sacrum(5 fused)

Coccyx (4 fused)

12

34567

123

45

6

7

8

9

10

11

12

1

2

3

4

5

Figure 5.8

Spinal cord

Intervertebraldisk

Main bodiesof vertebrae

b) A herniated disk.

Articulations with another vertebra

Spinal nerve

Articulation with ribs

a) Healthy disks.

Herniated areapressing againsta nerve

Figure 5.9

Sternum (breastbone)

Ribs

Cartilage

Vertebral column

Floating ribs

T11

T12

L1

L2

12

11

C7

T1 1

2

3

4

5

6

7

8910

Appendicular Skeleton

• Pectoral girdle (shoulder)• Clavicles• Scapulas

• Pelvic girdles (hip areas)• Coxal bones• Sacrum• Pubic symphysis

• Limbs• Arms—humerus, radius, ulna, wrist, hand bones• Legs—femur, tibia, fibula, ankle, foot bones

Figure 5.10

Pectoral girdle

Clavicle(collar bone)

Scapula (shoulder blade)

Humerus(upper arm)

Ulna

Forearm

Radius

8 Carpals (wrist)

5 Metacarpals (hand)

14 Phalanges (finger bones)

Figure 5.11

Coxal bones and sacrum (pelvis)

Femur (upper leg)

Patella (knee cap)

Lower legTibia

Fibula

7 Tarsals (ankle)5 Metatarsals (foot)

14 Phalanges (toe bones)

Pubic symphysis

Joints (Articulations)

Classified by degree of movement

• Fibrous joint• Relatively immovable• Example—fontanels

• Cartilaginous joint• Slightly movable cartilage connection• Example—intervertebral connections

• Synovial joint• Freely movable• Composed of

• Tendons—join bone to muscle• Joint capsule—synovial membrane (secretes lubricant) + hyaline

cartilage (provides smooth surface and cushions)

• Example—shoulder

Figure 5.12

b) A view of the knee with muscles, tendons, and ligaments in their normal position surrounding the intact joint capsule. The combination of ligaments, tendons, and muscles holds the knee tightly together.

Ligaments

Joint capsule

Tendon

Thigh muscles

Patella

Ligaments

a) A cutaway anterior view of the right knee with muscles, tendons, and the joint capsule removed and the bones pulled slightly apart so that the two menisci are visible.

Tendon

Patella

LigamentTibia

Fibula

Femur

Ligament

Meniscus

Hyaline cartilage

Posterior cruciate ligament

Anterior cruciate ligament

Meniscus

• Hinge joint—elbow

• Ball and socket joint—hip

• Gliding joints—the carpals of the wrist

• Pivot joint▬atlas-axial joint

• Condyloid (ellipsoid) joint—radiocarpal joint

• Saddle joints—joint of thumb (between the metacarpal and carpal)

Types of Synovial Joints