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

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

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

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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.

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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)

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 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.