THE SKELETON

The Skeletal System

• The Skeletal System serves many important functions; it provides the shape and form for our bodies in addition to supporting, protecting, allowing bodily movement, producing blood for the body, and storing minerals.

Functions:

• Its 206 bones form a rigid framework to which the softer tissues and organs of the body are attached.

• Vital organs are protected by the skeletal system. The brain is protected by the surrounding skull as the heart and lungs are encased by the sternum and rib cage.

• Bodily movement is carried out by the interaction of the muscular and skeletal systems. For this reason, they are often grouped together as the musculo-skeletal system. Muscles are connected to bones by tendons. Bones are connected to each other by ligaments. Where bones meet one another is typically called a joint. Muscles which cause movement of a joint are connected to two different bones and contract to pull them together. An example would be the contraction of the biceps and a relaxation of the triceps. This produces a bend at the elbow. The contraction of the triceps and relaxation of the biceps produces the effect of straightening the arm.

• Blood cells are produced by the marrow located in some bones. An average of 2.6 million red blood cells are produced each second by the bone marrow to replace those worn out and destroyed by the liver.

• Bones serve as a storage area for minerals such as calcium and phosphorus. When an excess is present in the blood, buildup will occur within the bones. When the supply of these minerals within the blood is low, it will be withdrawn from the bones to replenish the supply.

What are bones made of?Go to :http://kidshealth.org/misc/movie/bodybasics/bone.html for flash diagram

of bone

• The bones that make up your skeleton are all very much alive, growing and changing all the time like other parts of your body.

• Almost every bone in your body is made of the same materials:

• periosteum• compact bone• cancellous bone• bone marrow

Types of Bone:

• The bones of the body fall into four general categories: long bones, short bones, flat bones, and irregular bones. Long bones are longer than they are wide and work as levers. The bones of the upper and lower extremities (ex. humerus, tibia, femur, ulna, metacarpals, etc.) are of this type. Short bones are short, cube-shaped, and found in the wrists and ankles. Flat bones have broad surfaces for protection of organs and attachment of muscles (ex. ribs, cranial bones, bones of shoulder girdle). Irregular bones are all others that do not fall into the previous categories. They have varied shapes, sizes, and surfaces features and include the bones of the vertebrae and a few in the skull.

Divisions of the Skeleton

• The bones of the body are grouped into two major divisions.

• The axial skeleton consists of the bones, which lie around the longitudinal axis of the body. These include the SKULL, VERTEBRAL COLUMN, STERNUM & RIBS.

• The appendicular skeleton consists of the bones of the LIMBS, PECTORAL (shoulder) GIRDLE, & PELVIC (hips) GIRDLE.

Head (skull)The skull consists of 28 bones (22 not counting the 6 ear bones) and

protects the most important part of all, your brain. All of the bones are joined by sutures causing them to be rigid allowing for very little movement, except for the mandible. At birth humans have 45 bones in the skull and many fuse together.

Maxilla

Mandible

Frontal lobe

Nasal bone

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Spine (Vertebral Column)

• The spine lets you twist and bend, and it holds your body upright. It also protects the spinal cord, a large bundle of nerves that sends information from your brain to the rest of your body. The spine is special because it isn't made of one or even two bones: It's made of 26 bones in all! These bones are called vertebrae and each one is shaped like a ring

Spine contd.:• The first seven vertebrae at the top are called the cervical vertebra

e. These bones are in the back of your neck, just below your brain, and they support your head and neck. Your head is pretty heavy, so it's lucky to have help from the cervical vertebrae!

• Below the cervical vertebrae are the thoracic vertebrae, and there are 12 in all. These guys anchor your ribs in place. Below the thoracic vertebrae are five lumbar vertebrae. Beneath the lumbar vertebrae is the sacrum, which is made up of five vertebrae that are fused together to form one single bone.

• Finally, all the way at the bottom of the spine is the coccyx, which is one bone made of four fused vertebrae. The bottom sections of the spine are important when it comes to bearing weight and giving you a good center of gravity. So when you pick up a heavy backpack, the lumbar vertebrae, sacrum, and coccyx give you the power. When you dance, skip, and even walk, these parts help keep you balanced.

• In between each vertebra are small disks made of cartilage. These disks keep the vertebrae from rubbing against one another, and they also act as your spine's natural shock absorbers

The Ribs:• The ribs are thin, flat, curved bonesthat form a protective cage around the organs in the upper body. • They are comprised 24 bones arranged in 12 pairs.• The ribs serve several important purposes. They pro

tect the heart and lungs from injuries and shocks that might damage them. Ribs also protect parts of the stomach, spleen, and kidneys. The ribs help you to breathe. As you inhale, the muscles in between the ribs lift the rib cage up, allowing the lungs to expand. When you exhale, the rib cage moves down again, squeezing the air out of your lungs.

The Ribs contd.

• All 12 pairs of ribs attach in the back to the spine, where they are held in place by the thoracic vertebrae. The first seven pairs of ribs attach in the front to the sternum, a strong bone in the center of your chest that holds those ribs in place. The remaining sets of ribs don't attach to the sternum directly. The next three pairs are held on with cartilage to the ribs above them.

• The very last two sets of ribs are called floating ribs because they aren't connected to the sternum or the ribs above them, but don't worry, they are securely attached to the spine in the back

Sternum:

• The sternum is a flat, dagger shaped bone located in the middle of the chest. Along with the ribs, the sternum forms the rib cage that protects the heart, lungs, and major blood vessels from damage.

• The sternum serves an important function in the body. The ribs are connected to it by the costal cartilage. Without the sternum, there would be a hole in the bone structure in the middle of your chest, right above your heart and lungs. The sternum protects this vital area and completes the circle of the rib cage.

The Limbs (Arms):

• Each arm is attached to a shoulder blade or scapula, a large triangular bone on the upper back corner of each side of the ribcage. The arm is made up of three bones: the humerus, which is above your elbow, and the radius and ulna, which are below the elbow

• The clavicle, commonly called the collarbone, is a slender S-shaped bone that connects the upper arm to the trunk of the body and holds the shoulder joint away from the body to allow for greater freedom of movement. One end of the clavicle is connected to the sternum and one end is connected to the scapula.

• Did you know that the clavicle is the most frequently fractured bone in the human body?

Rear view

Clavicle

Scapula

Vertebrae

Sternum

Ribs

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The Limbs (Hands):• The hand consists of three parts (t

he wrist, palm, and five fingers) and 27 bones.

• The wrist, or carpus, consists of 8 small bones called the carpal bones that are tightly bound by ligaments.

• The palm or metacarpus consists of five metacarpal bones, one aligned with each of the fingers. The metacarpal bones are not named but are numbered I to V starting with the thumb. The heads of the metacarpals form the knuckles of a clenched fist.

• The fingers are made up of 14 bones called phalanges. A single finger bone is called a phalanx.

The Limbs (Legs):• Your legs are attached to a circular group of bones calle

d your pelvis. The pelvis is a bowl-shaped structure that supports the spine. It is made up of the two large hip bones in front, and behind are the sacrum and the coccyx. The pelvis acts as a tough ring of protection around parts of the digestive system, parts of the urinary system, and parts of the reproductive system.

• Your leg bones are very large and strong to help support the weight of your body. The bone that goes from your pelvis to your knee is called the femur, and it's the longest bone in your body. At the knee, there's a triangular-shaped bone called the patella, or kneecap, that protects the knee joint. Below the knee are two other leg bones: the tibia and the fibula. Just like the three bones in the arm, the three bones in the leg are wider at the ends than in the middle to give them strength.

The Limbs (Feet):• Your feet take a great amount o

f pressure from supporting up your entire body. There are 26 bones in each foot. Just like in the hands the feet have 6, not 8 like the hand, ankle bones called the tarsal, 5 foot bones called metatarsals, and 14 toe bones once again called phalanges. The calcaneus is your heel bone.

• Without all the bones of the foot working together, it would be impossible to balance properly.

Pelvis

Joints and Muscles:

• The joints and muscles of the body work in unison with the skeletal system (musculo-skeletal system) to enable us to move our bodies and perform actions that we take for granted everyday. We will look at these in more depth in the next lesson!