Skeletal System

Overview:- “skeleton” Greek for “dried up body”- Designed for protection and motion- The skeleton is a tower of bones

arranged in a way we can stand upright and balance

O The skeleton is divided into two divisions:O Axial skeleton

O Bones that form the longitudinal axis of the body

O Head, thorax

O Appendicular skeletonO Bones of the limbs and girdles

O Hips, arms, hands, legs and feet

O Also includes:O Joints, cartilages and ligaments

Functions of the BonesO Support

O form internal framework that supports and anchors all soft organs.

O Legs provide for support for our axial skeleton

O Rib cage supports the thoracic wall

O ProtectionO Provide protection for all soft organsO Skull::brain; rib cage::lungs, heart;

vertebrae::spinal cord

O Movement:O Skeletal muscles attached to bones

via tendons allow for movement of the skeletal system.

O Storage:O Bones provide a means of storing

fats, minerals (Calcium and phosphorus)

O “deposits” and “withdrawals” of calcium to and from bones take place all the time

O Blood cell Formation:O a.k.a hematopoiesis, occurs within

the marrow of certain cavities of certain bones.

Classification of BonesO 206 bones in adultsO Two basic types of osseus or bone tissue:

O Compact bone is dense and looks smooth and homogenous

O Spongy bone is composed of small needlelike pieces of bone and lots of open space.

O Bones come in a variety of shapes and sizes

O The unique shape of each bone fulfills a particular need.

Bone Classification: Shape

O Bones are classified according to shape into four groups:O LongO ShortO FlatO Irregular

Long BonesO Typically longer than they are wideO Composed of a shaft with a head at

each endO Mostly compact boneO All bones of the limbs other than

wrist and ankles

Short BonesO Generally cube-shapedO Contain mostly spongy boneO Wrist and ankles contain short bonesO Sesamoid bones, form with

tendons (kneecap)

Flat BonesO Thin, flattened and usually curvedO Two thin outer layers of compact

bone with a layer of spongy bone between them

O Ribs, sternum and most bones of the skull

Irregular BonesO Bones that do not fit one of the

preceding categoriesO Vertebrae and hips are examples

Structure of a Long Bone

O Diaphysis or shaftO Makes up most of the bones length O Compact boneO Covered and protected by a fibrous

connective tissue membrane called periosteumO The periosteum is secured to the bone

by many connective tissue fibers Sharpey’s fibers.

O Epiphyses are the ends of the long boneO Compact bone enclosing an area filled with

spongy boneO Covered with articular cartilage

O Articular cartilage (hyaline cartilage) it provides a smooth, slippery surface to reduce friction in joints

O In adult bones, a thin line of bony tissue throughout the epiphysis that is different in appearance. This is called the epiphyseal line, which is a remnant of the epiphyseal plate – a flat late of hyaline cartilage, cause the lengthwise growth of long bones. O E. P. – completely replaced by bone at the end of puberty

O In adults the cavity of the shaft is a primary storage for adipose tissueO a.k.a. yellow marrow, or medullary

cavityO In infants this area forms blood cells

and red marrow is found in the cavity

O In adults, red marrow is confined to the cavities of spongy bone of flat bones and the epiphyses of some long bones

Bone MarkingsO Bones are noticeably rough and scarred with

bumps, holes and ridges.O The markings reveal where the attachment

of muscles, tendons and ligaments attach and where blood vessels and nerves passed.

O Two categories:O Projections or Process – grow out from the

bone surface (all markings that begin with “t”)O Depressions or Cavities – indentations in

the bone (all markings that begin with “f” except facet)