The Skeletal System

• The skeletal system is a framework of bones giving shape and support to the body
• Bones join to form the skeleton
• The skeleton protects internal organs
• An adult human skeleton has 206 bones
• The skeletal system includes all the bones in our body and our joints
• Skull, backbone, rib cage, limbs, and hip girdle are parts of the skeleton

What are bones?

• Bones are hard parts in the body covered by skin
• Bones can be short, long, flat, or irregular
• Bones are made of minerals, mainly calcium and phosphorus
• Bones have a thick outer wall for support and protection
• Inside some bones is soft and spongy and called bone marrow
• Bone marrow has many blood vessels
• Babies have more than 300 bones
• Some bones join as we grow
• Bones keep growing making us taller and broader

Skull

• The skull is made of 22 bones; the upper part has 8 flat bones joined together
• The skull protects the brain and has holes for eyes, nostrils, mouth, and ears
• Teeth are attached to the skull
• The face and jaw consists of 14 bones
• The only movable part of the skull is the lower jaw
• The upper and lower jaw give structure to the mouth
• The skull protects the brain and the sense organs (eyes, ears, and nose)

Backbone (Spine)

• The skull is attached to the spine
• The spine has 33 small bones called vertebrae stacked on each other
• Each vertebra has a hole for the spinal cord to pass through
• The spinal cord is an extension of the brain, which is very delicate
• Many nerves branch out from the spinal cord
• The spine protects the spinal cord

Rib Cage

• The rib cage has 12 pairs of thin, curved bones
• The rib cage is attached to the spine at the back and the breast bone in front
• The last two pairs of ribs are joined to the backbone but not to the breast bone; these are floating ribs
• The rib cage protects our lungs and heart

Limbs (Arms and Legs)

• The bones in our limbs are long
• Each upper arm has a bone called the humerus
• Each lower arm has two bones
• The hands have many small bones
• The upper arm joins the spine with the shoulder blade and collar bone, forming the shoulder girdle
• Each thigh has a long bone called the femur, the longest bone in the body
• Each leg has two bones
• Each foot has many small bones
• The thighs connect to the hip girdle
• The bottom of the spine also joins the hip girdle

Importance of Bones

• Bones protect delicate organs
• The skull protects the brain and eyes
• The rib cage protects the lungs and heart
• The spinal cord is protected inside the backbone
• The hip girdle supports the stomach, intestines, and other organs

Importance of Muscles

• Muscles are required for bones to move
• Muscles are attached to bones and help them move
• Muscles help in digestion, breathing, smiling, frowning, opening/closing eyes, and swallowing food

Voluntary Muscles

• Voluntary muscles can be moved or stopped at will because they are under our control
• Arms, legs, hands, and feet have voluntary muscles
• All muscles that can be moved when you want to are voluntary muscles
• Voluntary muscles are long and cylindrical with bands all over and are called striped muscles

Involuntary Muscles

• Involuntary muscles are those that cannot be controlled
• Examples are blood vessels, stomach, food pipe, and intestines
• Involuntary muscles are short and spindle-shaped, without bands, and are called smooth muscles

Cardiac Muscles

• Cardiac muscles are present in the heart
• Cardiac muscles are responsible for pumping blood throughout the body
• Cardiac muscles look similar to voluntary muscles but are branched
• Cardiac muscles continuously work day and night and are involuntary