Skeletal System

· Skeleton comes from the Greek word for "dried up body" or mummy

· Axial skeleton : skull, vertebral column, bony thorax

· The skull has a large cranial cavity and many smaller cavities (middle ear, nasal, orbitals, sinuses). It also has over 85 named openings.

· Bones have several functions : structure/support, protection, movements, mineral storage and blood cell formation

· Bones are classified by size, shape and gross anatomy. Different shaped bones have differing proportions of spongy and compact bone.

· Compact : smooth, homogeneous (aka dense)

· Spongy : composed of small needlelike or flat bone pieces and has a great deal of open space which is filled with red or yellow marrow. Also known as cancellous bone.

· Bones are classified by structure and by formation

· Long bones : longer than they are wide; consist of a shaft and two bulbous ends. Mostly compact bone, but ends and some interior are spongy. These develop from embryonic cartilage, and so are also called cartilage bone.

· Short bones : cube-like. Mostly spongy bone; thin compact bone covering. These are also cartilage bones.

· Flat bones : thin, flattened somewhat curved. Have two parallel compact bone surfaces with spongy bone between. These develop from embryonic membranes and so are also called membrane bone.

· Irregular bones : the miscellaneous bones. Complicated shapes, mostly composed of spongy bone with layers of compact bone overlaying. These can be cartilage bone or membrane bone, depending on where they are located.

· Gross Anatomy of a Bone

· The hollow part of the diaphysis is the marrow-filled medullary cavity.

· The epiphyses are covered with articular (hyaline) cartilage. The diaphysis is covered by periosteum, a double-layered membrane. The outer layer is dense, fibrous tissue. The inner layer is the osteogenic layer, composed of osteoblasts and osteoclasts.

· Blood vessels, nerves and lymph vessels enter the shaft by way of a nutrient foramen.

· Endosteum lines the canals passing through compact bone and covers the flat bone pieces of spongy bone.

· Marrow forms blood cells. Red marrow is found in the cavities of spongy bone. Yellow marrow is found in the medullary cavity.

· Microscopic Anatomy of a Bone

· Bones are arranged in a series of cylindrical osteons, also called Haversian systems. Each osteon is a group of hollow tubes (called lamellae), and the hole through the center of the tubes is called the Haversian canal. Blood vessels run through those, and the perpendicular Volkmann canals.

· Repair

· A fractured bone is repaired by reduction. Closed reduction involves physically moving the broken pieces into place.

· Open reduction involves surgery.

· Steps to bone repair :

· Hematoma

· Fibrocartilaginous callus

· Bony callus

· Bone remodeling

· Identifying bones

· Several "markings" are used to describe the bones of the skeleton, in addition to size and general shape. Some of these are :

· Condyle : a rounded process that usually articulates with another bone. Ex. occipital condyle on the base of the skull

· Epicondyle : raised area on or above a condyle

· Crest : a narrow, ridge-like projection. Ex. iliac crest on the ilium

· Fontanel : a soft spot in the skull

· Foramen : an opening into the bone

· Fossa : a relatively deep pit or depression. Ex. olecranon fossa on the humerus

· Process : a prominent projection. Ex. acromion process on the scapula

· Sinus : a cavity within a bone. Ex. frontal sinus

· Head : an enlargement at the end of a bone

· Tubercle : a small, knoblike process

· Tuberosity : large, rounded projection

· Trochanter : very large, blunt, irregularly shaped process. Only examples are on the femur.

· Spine : sharp, slender, often pointed process

· Facet : smooth, nearly flat, articular surface

· Meatus : a canal-like passageway. Ex. external auditory meatus

· Ramus : armlike bar of bone