Module 7: The ASEAN World of Medicine
Table of Contents
Reading Text & Presentation
7.1 The human body
7.1.1 The skeletal system
The skeletal system consists of all the bones and joints in the body. Bones are made up of many cells, minerals and protein fibers. They act as a framework to provide support for the softer organs that make up the rest of the body. The skeletal system is also the anchor for muscles as it has attachment points to allow joint movement. In addition to these important functions, the red marrow inside of bones produces new blood cells. The bones of our skeleton are the body’s storehouse for iron, calcium, and provide energy in the form of fat.
An adult usually has 206 individual bones in the skeletal system. There are two major divisions: the axial skeleton and the appendicular skeleton. The axial skeleton has 80 bones which run along the body’s midline axis in the following regions: the skull, hyoid (between the chin and the thyroid cartilage), auditory ossicles, ribs, sternum, and vertebral column.
The 126 bones of the appendicular skeleton are in the following regions: the upper limbs, lower limbs, pelvic girdle, and pectoral (shoulder) girdle.
A The axial skeleton
- Skull
The skull is a composition of 22 bones, 21 of which fuse together to give strength and protection in adulthood. These bones are separate in children to allow for growth of the skull and brain. The mandible is the jaw bone, which is the only movable joint in the skull.
The cranium is the name given to the bones of the superior portion of the skull. It protects the brain from damage. The inferior and anterior portions of the skull are called facial bones and support the eyes, nose, and mouth.
- Vertebrae
The vertebral column of the skeleton has twenty-six vertebrae. They are named by their position:
Cervical (neck) – 7 vertebrae, Thoracic (chest) – 12 vertebrae, Lumbar (lower back) – 5 vertebrae, Sacrum – 1 vertebra, and Coccyx (tailbone) – 1 vertebra
For medical identity purposes (apart from the sacrum and coccyx), each vertebra is numbered with the first letter of its region as a prefix. The numbers denote the position along the superior-inferior axis. The top neck vertebra is C1 and the lowest one C7.
- Ribs and sternum
The ribs and sternum are mostly connected with a flexible connective tissue which we call cartilage. In this case it is termed costal cartilage. The sternum, or breastbone, is a knife-shaped bone located along the midline of the anterior side of the thoracic region of the skeleton. The sternum connects to 12 pairs of ribs which form the ribcage. The first seven ribs connect the thoracic vertebrae directly to the sternum through their own band of costal cartilage. They are known as “true ribs”. Ribs 8, 9, and 10 are known as “false ribs” because they connect to the sternum through cartilage connected to the cartilage of the seventh rib. Ribs 11 and 12 have no cartilage attachment to the sternum, so they are also false ribs but are considered to be “floating ribs”.
B The appendicular skeleton
- Pectoral girdle and upper limbs
Two clavicle bones and two scapula bones make up the pectoral girdle, which connects the upper limb (arm) bones to the axial skeleton. They consist of the left and right clavicles and left and right scapulae.
The upper arm is the humerus bone. It has a ball and socket joint at the shoulder with the scapula and an elbow joint with the lower arm bones. The lower arm bones are the radius and the ulna: the two bones of the forearm. The ulna forms the hinge joint with the humerus at the elbow. The radius allows forearm and hand movement at the wrist joint.
The radius and ulna form the wrist joint with a group of eight small bones called the carpals. These give added flexibility to the wrist. The carpals connect to five metacarpals which form the hand and connect to each finger. The four fingers have three bones known as phalanges, and the thumb has two phalanges.
- Pelvic girdle and lower limbs
The pelvic girdle is formed by the left and right hip bones (ilium). It connects the lower limb (leg) bones to the axial skeleton.
The only bone of the thigh (femoral) region is the femur. It is the largest bone in the body. The femur has a ball and socket hip joint with the hip bone and a knee joint with the tibia and patella (knee cap). The kneecap is unusual because it is one of the few bones that are not present at birth. It forms in early childhood to support the knee for walking and crawling.
The lower leg consists of the tibia and fibula bones. The tibia is the larger of the two and it bears most of the body’s weight. The fibula is used to help maintain balance, and is mainly a muscle attachment point. The tibia and fibula bones form the ankle joint with the talus to connect to the foot.
The foot consists of a group of seven small bones, the tarsals, which form the posterior end of the foot and heel. The tarsals have joints with the five long bones of the foot; the metatarsals. The metatarsals have a joint with the toes. Each toe has three phalanges, except for the big toe, which only has two.
