SKELETAL SYSTEM

- the bones of your skeleton. OSSEUS TISSUE.
- Bone tissue is a type of connective tissue. Your skeleton performs several important functions.

- SUPPORT and PROTECTION
- BODY MOVEMENT - muscles "pull" on bones
- BLOOD CELL FORMATION - hemopoiesis ' occurs in red bone marrow
- STORAGE of inorganic salts - especially calcium phosphate, but also magnesium, sodium, potassium, carbonates and others

ORGANIZATION - normally 206 bones
- 2 Main Divisions: AXIAL & APPENDICULAR

1. AXIAL: head, neck, trunk
SKULL, HYOID BONE (upper neck, under jaw, mandible)
VERTEBRAL COLUMN (spine/backbone)
THORACIC CAGE (rib cage-12 pairs)
STERNUM

2. APPENDICULAR: limbs and bones connecting the limbs to the:
PECTORAL GIRDLE (scapula & clavicle), UPPER LIMBS (arms)
PELVIC GIRDLE (coxal bones), LOWER LIMBS (legs)

BONE STRUCTURE: "LONG BONE" = typical bone

Major parts:
1. EPIPHYSIS - expanded ends of bone. ARTICULATES (forms a joint) with another bone.
2. DIAPHYSIS - shaft of the bone
3. ARTICULAR CARTILAGE - hyaline cartilage covering the ends of bones
4. PERIOSTEUM - tough membrane-like covering over entire bone, except for articular cartilage. Connects with tendons and ligaments. Forms bone tissue.

MEDULLARY CAVITY - hollow chamber within the diaphysis connects to spaces in spongy bone. Filled with soft specialized tissue called bone marrow.

" Red Marrow - mainly in spongy bone in adults. Produces blood cells
" Yellow Marrow - fat storage. Replaces much of the red marrow in diaphysis through childhood

ENDOSTEUM - lining of the medullary cavity

Two Types of Bone Tissue

1. COMPACT (cortical) BONE - wall of the diaphysis, solid, strong
2. SPONGY (cancellous) BONE - epiphysis. Covered with a thin layer of compact bone. Many branching, bony "plates"

Microscopic Structure

- MATRIX composed of collagen and inorganic salts
- OSTEOCYTES (mature bone cells) are enclosed in tiny chambers called LACUNAE and form concentric "ring" (layers) around a passageway called the HAVERSION CANAL
- The osteocytes are connected by minute passages called CANALICULI (canaliculus) through which tiny "branches" or processes pass
- The circular layers of matrix material and osteocytes, along with the haversian canal, forms a unit called a HAVERSIAN SYSTEM. Compact bone tissue is formed in this way
- The haversian canals are interconnected by passages called VOLKMANN'S CANALS. All of these canals contain blood vessels and nerve fibers

Bone Development and Growth:

There are two types of bone based on the way the bones form

1. INTRAMEMBRANOUS BONES = broad, flat bones of the skull. These bones form from membrane-like sheets of connective tissue

2. ENDOCHONDRAL BONES = all other bones.

• Bones first form as hyaline cartilage. The cartilage then gradually changes into bone tissue - a process called OSSIFICATION, which begins near the middle of the diaphysis in an area called the PRIMARY OSSIFICATION CENTER. Later the bone begins to ossify in the epiphysis - these areas are called the SECONDARY OSSIFICATION CENTERS.
  
• As long as growth is occurring, a "band" of cartilage (called an epiphyseal disk, growth plate) remains between the diaphysis and the epiphysis.
• Bones increase in length as these cartilage cells continue to reproduce and ossify
• Cartilage cells form cells called OSTEOBLASTS. These cells produce bone matrix and once the cell is enclosed in bone matrix it is considered to be a mature bone cell and called an OSTEOCYTE
• Growth in thickness of bone occurs as osteoblasts from beneath the periosteum produce bone matrix and build compact bone just underneath the periosteum
• Bone tissue is constantly being replaced as special cells called OSTEOCLASTS dissolve bone tissue from within the medullary cavity - a process called RESORPTION. At the same time new bone tissue is being added to the outside of the bone.
  

3 Basic Types of Joints (articulations):

1. SYNARTHROTIC - immoveable joint, such as bones in the skull, these junctions are called SUTURES. - Fibrous Joints

2. AMPHIARTHROTIC - slightly moveable joint, vertebrae - Cartilaginous Joints

3. DIARTHROTIC - freely moveable joint, such as shoulders, hips, knees, elbows, wrists, fingers…
--these joints are enclosed within a fibrous capsule which contains a lubricating fluid called SYNOVIAL fluid. These are called SYNOVIAL JOINTS.

Ball & Socket
Hinge
Pivot
Saddle

Bones of the Skull

1. Frontal - anterior portion above eyes
2. Parietal - one on each side of the skull, just behind frontal bone
3. Occipital - forms the back of the skull and base of the cranium
4. Temporal - forms parts of the sides and base of cranium
5. Sphenoid - wedged between several other bones in anterior portion of the cranium
6. Maxilla - forms upper jaws
7. Mandible - lower jaws, only moveable bone of the skull

Sutures

1. Coronal - between frontal and parietal bones
2. Lambdoidal - between occipital and parietal bones
3. Squamosal - between temporal and parietal bones
4. Sagittal - between parietal bones

Fontanels - "soft spots" of an infant's skull, see page 143
- anterior fontanel, posterior fontanel, sphenoid fontanel, mastoid fontanel

Foramen Magnum - Large opening through the underside of the skull, spinal cord enters skull

The Rest of the Bones

Ribs - Thoracic Cage, 12 pairs
- True Ribs - first seven pairs, attach directly to STERNUM by costal cartilage
(Vertebralsternal)
- False Ribs - last five pairs (Vertebralchondral)
- Floating ribs - last two pairs (Vertebral)

Pectoral Girdle: Shoulder. Two clavicles (collar bones) and two scapula (shoulder blade)

Arms: Upper arm - humerus. Lower arm - radius and ulna.
Wrist - 8 small bones called carpals
Fingers - Metacarpals, Phalanges

Pelvic Girdle: Hips. Two large bones called COXAL BONES

Legs: Upper leg (thigh) - FEMUR. Lower leg - tibia & fibula.
Ankle and Upper foot - 7 bones called TARSALS,
Largest is the heel bone called the CALCANEOUS
Toes - Metatarsals, Phalanges

What About Broken Bones?

• A complete fracture is when the bone has broken into two pieces.
• A greenstick fracture is when the bone cracks on one side only, not all the way through.
• A single fracture is when the bone is broken in one place.
• A comminuted (say: kah-muh-noot-ed) fracture is when the bone is broken into more than two pieces or crushed
• A bowing fracture, which only happens in kids, is when the bone bends but doesn't break
• An open fracture is when the bone is sticking through the skin.