Skeletal System

Skeletal System OverviewThe adult human body consists of

approximately 206 bones, which are organized into an internal framework called the skeleton. Because the human skeleton is an internal structure, biologists refer to it as an endoskeleton. The variation in size and shape among the bones that make up the skeleton reflects their different roles in the body.

The Skeletona. The human skeleton is composed of 2

parts1. axial skeleton- the bones of the skull, ribs, spine, and sternum2. appendicular skeleton- the bones of the arms and legs, along with scapula,

clavicle and pelvis.b. provides a rigid framework against

which muscles can pullc. give shape and structure to the bodyd. support and protect delicate internal

organs

Bone Structurea. Bones are moist living tissues that make up less

than 20% of a body’s mass.b. periosteum- tough membrane covering a bone’s

surface.c. compact bone- hard material under the

periosteumd. spongy bone- network of connective tissue under

the compact bonee. bone marrow- soft tissue found in many bones

1. red bone marrow- found in spongy bone, produces red blood cells and certain types of white blood cells.2. yellow bone marrow- fills the shaft of long bones, consists mostly of fat cells and serves as an energy reserve

Jointsa. Joint is a place where 2 bones meet

1. fixed joint- prevent movement. Found in skull, connect bony plates2. semi-movable joint- permit limited movement. Vertebrae and spine, allow bending and twisting3. movable joint- wide range of movement. Several different types located throughout the body.

a. hinge- elbow (forward and backward movement)b. ball-and-socket- shoulder ( rotate in complete

circles)c. pivot- top 2 vertebrae (turn head from side to side)d. saddle- rotate thumb (grasp objects)e. gliding- small bones of the foot (allows foot to flex)

b. Tough bands of connective tissue called ligaments hold the bones of the joints in place.

Fixed Joint

Movable Joints

Hinge

Ball & Socket

Saddle

Gliding

• The human hand has 27 bones; your face has 14!

• The longest bone in your body? Your thigh bone, the femur -- it's about 1/4 of your height. The smallest is the stirrup bone in the ear which can measure 1/10 of an inch.

• Did you know that humans and giraffes have the same number of bones in their necks? Giraffe neck vertebrae are just much, much longer!

• You have over 230 moveable and semi- moveable joints in your body.