SKELETAL SYSTEM
- the bones of your skeleton. OSSEUS TISSUE.
- Bone tissue is a type of connective tissue. Your skeleton performs several important functions.
Ø SUPPORT and PROTECTION
Ø BODY MOVEMENT – muscles “pull” on bones
Ø BLOOD CELL FORMATION – hemopoiesis à occurs in red bone marrow
Ø 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:
EPIPHYSIS – expanded ends of bone. ARTICULATES (forms a joint) with another bone.
DIAPHYSIS – shaft of the bone
ARTICULAR CARTILAGE – hyaline cartilage covering the ends of bones
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
Ø MATRIX composed of collagen and inorganic salts
Ø OSTEOCYTES (mature bone cells) are enclosed in tiny chambers called LACUNAE and form concentric “ring” (layers) around a passageway called the HAVERSION CANAL
Ø The osteocytes are connected by minute passages called CANALICULI (canaliculus) through which tiny “branches” or processes pass
Ø 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
Ø 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. ENCHONDRAL 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 built 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
2. AMPHIARTHOTIC – slightly moveable joint, vertebrae
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.
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. Mandilbe – 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 138
- 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
- False Ribs – last five pairs
- Floating ribs – last two pairs
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 carpels
Fingers – Metacarpels, 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.