The Skeletal System AP Biology

Divisions of the Skeletal System Subdivided into two divisions: Axial Skeleton – bones that form the longitudinal axis of the body Appendicular Skeleton – bones of the limbs and girdles Skeletal system also includes joints, cartilages, and ligaments The joints give the body flexibility and allow for movement.

Functions of Bones Support Protection Internal framework, support and anchor soft organs Bones of legs act as pillars to support body trunk Rib cage supports the throacic wall Protection Bones protect soft body organs Ex. The skull protects the brain Ex. The vertebrae surround the spinal cord.

Functions of Bones Movement Storage Skeletal muscles use the bones as levers to move the body. Remember – skeletal muscles are attached to the bones by tendons. Storage Fat is stored in internal cavities of bones. Bones store minerals, most importantly Calcium – important to muscles, nerves, and blood Phosphorous

Functions of Bones Blood Cell Formation Hematopoiesis = blood cell formation Occurs within the marrow of certain bones

Classification of Bones The adult skeleton is composed of 206 bones. 2 types of bone tissue: Compact bone – dense and looks smooth Spongy bone – composed of needlelike pieces of bone and lots of open space

Classification of Bones Bones are classified according to shape into 4 groups: long, short, flat, irregular Long: longer than they are wide, mostly compact bone Short: cube-shaped, mostly spongy bone Flat: thin, flattened, and usually curved, 2 thin layers of compact bone and a layer of spongy bone in middle most bones of the skull, ribs, and sternum Irregular: the vertebrae and the hip bones

Structure of a Long Bone The diaphysis makes up most of the bone’s length, composed of compact bone. Covered by a protective connective tissue membrane called the periosteum The epiphyses are the ends of the long bone. Mostly spongy bone Cartilage covers this part of the bone. Provides a smooth, slippery surface that lubricates the joints.

Structure of Bone Epiphyseal line – thin line of bony tissue on epiphysis Remnant of the epiphyseal plate Causes the lengthwise growth of a long bone. By the end of puberty, bones stop growing and epiphyseal plates are completely replaced by bone. Mark the previous location of epiphyseal plate Interactive Web

Structure of Bone In adults, the cavity in the shaft of the bone stores adipose tissue (fat). Yellow Marrow In infants, this area forms blood cells, and red marrow is found there. In adults, red marrow is only found in the cavities of spongy bone of flat bones and some long bones.

Bone Markings Bumps, ridges, and holes in bones. Indicate where muscles, tendons, and ligaments attach, and where blood vessels and nerves passed. p.115

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

Appendicular Skeleton limbs and bones connecting the limbs to the: PECTORAL GIRDLE (scapula & clavicle) UPPER LIMBS (arms) PELVIC GIRDLE (coxal bones) LOWER LIMBS (legs)

Microscopic Structure of Bone 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 small passages called CANALICULI (canaliculus) through which tiny “branches” or processes pass

Microscopic Structure of Bone The circular layers of matrix material and osteocytes, along with the haversian canal, forms a unit called a HAVERSIAN SYSTEM. The haversian canals are interconnected by passages called VOLKMANN’S CANALS. All of these canals contain blood vessels and nerve fibers

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

Vertebral Column 3 types of vertebrae: Cervical: First 7 (neck) Thoracic: 12 vertebrae Lumbar: Last 5 (lower back) Intervertebral disks: flexible cartilage, cushion vertebrae and absorb shock Sacrum: fusion of 5 vertebrae Coccyx: fusion of 3-5 small, irregularly shaped vertebrae. “tailbone”

Bones Ribs – Thoracic Cage, 12 pairs Pectoral Girdle: Shoulder. 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)

Bones 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

Broken Bones A simple fracture is when the bone is broken cleanly but does not penetrate the skin. A compound/open fracture is when the bone is sticking through the skin. A greenstick fracture is when the bone cracks on one side only, not all the way through. A comminuted (say: kah-muh-noot-ed) fracture is when the bone is broken into many fragments or crushed. A compression fracture is when the bone is crushed. A depressed fracture is when the bone is broken and pressed inward (typical of skull fracture). A spiral fracture is when a break occurs from excessive twisting forces applied to the bone.