Bone Trivia •206 bones in human adult

- at birth -3 vertebrae in spine- during adulthood- 4 vertebrae fuse to form coccyx; 5 vertebrae fuse to form sacrum

 •Smallest bones-stapes (stirrups) in ear •Bone surface not smooth but with markings/projections (depressions)  -more prominent bone projections occur where active muscles are attached (e.g. weight lifters)  -thickenings at insertion sites of active muscles •Lesser used bone in fetus- comparatively smoother and featureless •Unused bone atrophies

THE SKELETAL SYSTEM

• Skeleton- hardened part of the body

• Functions:• protection• support• aids in locomotion

Three types of skeleton: 1. Hydrostatic skeleton-consists of fluid held under pressure in a closed body compartment.

•type of skeleton in most cnidarians, flatworms, nematodes and annelids•by alternate contraction of the circular and longitudinal muscles in the body wall, pressure is applied to the fluid and the earthworm is able to move•provide no protection and couLd not support a large animal living on land

Hydrostatic skeleton

2. exoskeleton- forms a hard cover in the animal’s body surface -exoskeleton of arthropods can not enlarge once it is deposited and must periodically be shed

(molted) and replaced by a larger case during growth

Examples: calcareous exoskeleton of corals Shells of snails and clams Chitinous exoskeletons of arthropods such as the carapace of crabs Skin derivatives plumage and pelage,antler and horn, claws, nails and hoofs

3. endoskeleton- consists of hard supporting elements (bones and cartilages) buried within the soft tissues of an animal •few invertebrates with endoskeletons: spicules of sponges, dermal ossicles of echinoderms and chitinous pens of squids and cuttlebone of cuttlefishes

Endoskeleton cont.•vertebrates have complete endoskeleton

Human skeletal systemMade up of 206 individual bones.

• Axial Skeleton (80 bones) support main body axis.

– Skull, Backbone, and Rib Cage.

• Appendicular Skeleton (126 bones) support arms and legs.

– Pectoral girdle

– Pelvic girdle

Bone Tissue

• Bone is produced when needle-shaped crystals surround and impregnate collagen fiber.– Outer bone layer is dense and compact (compact bone).– Interior of bone is open lattice structure (spongy bone).

• New Bone Formed in Two Stages:– Collagen secreted by osteoblasts which lay down matrix of fibrils.– Calcium minerals impregnate fibrils.

• Layers form as series of tubes around narrow central channel (Haversian Channel) running parallel to length of bone.

THE BONE- vascular tissue which became ossified (hardened) due to calcium

deposition-composed of: 1/3 organic matter (e.g. collagen, polysaccharides) and

2/3 inorganic salts (calcium phosphate)

Type of Bone cells

•osteoblasts-embryonic, bone formation•osteocytes- maintenance•osteoclast- resorption; promotes active erosion of bone minerals

Bone growth( Ossification)

• Types of Joints in the Human Body• The point where two or more bones meet is called a joint. The joints of the skull

are known as sutures (top, left). Sutures do not have a wide range of movement. Instead, they allow for growth and very limited flexibility. Hinge joints (top, right) allow for movement in one plane. The hinge joints of the elbow and knee, for example, bend up and down. Two flat-surfaced bones that slide over one another make up a gliding joint (bottom, right). Gliding joints, such as those in the wrist and the foot, provide for limited movement. Ball-and-socket joints (bottom, left) allow for the greatest range of motion. The ball-and-socket joints of the shoulder and hip, for example, can rotate in a complete circle.

Clinical applications

Common FracturesIn a greenstick fracture, the bone does not break all of the way through. Fractures are called simple, or closed, when the bone breaks but the skin does not. A compound, or open, fracture is when the broken bone tears through the skin, introducing the dangerous possibility of infection. The area around a break swells and discolors, but some fractures can be detected only by X ray. The weakened bones of the elderly are especially susceptible to fractures.

• Slipped Disk• A slipped disk, or disk prolapse, occurs when an intervertebral disk, one of the

cartilage disks that separates and cushions the bones of the spinal column, pushes against the spinal cord. The result of injury or age-associated degeneration, slipped disks can cause severe and even disabling pain. Most slipped disks occur in the lower back, but the bones of the upper back are also vulnerable. Depending on severity, doctors may prescribe painkillers, bed rest, or surgery to treat slipped disks.