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.
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.
Short bones : cube-like. Mostly spongy bone; thin compact bone covering.
Flat bones : thin, flattened somewhat curved. Have two parallel compact bone surfaces with spongy bone between.
Irregular bones : the miscellaneous bones. Complicated shapes, mostly composed of spongy bone with layers of compact bone overlaying.
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 example is 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