What is the axial skeleton and the appendicular skeleton?

The human skeleton It is the part of the body made up of the bones. It has numerous functions, highlighting mechanical support, the articulation of body movements, the protection of internal organs and the production of blood cells (hematopoiesis).

The skeleton is usually divided into two large parts, the axial skeleton and the appendicular skeleton:

  • axial skeleton: is the skeleton of the trunk and head. It is made up of a total of 80 bones, including the skull, the bones of the middle ear, the spine, the ribs, and the sternum.
  • appendicular skeleton: is the skeleton of the upper extremities and the lower extremities, including the bones of the pelvis and the shoulder girdle. It is made up of 126 bones.
Axial skeleton and appendicular skeleton
Location of the axial skeleton and the appendicular skeleton

In this article we will see the main characteristics of the axial and appendicular skeleton, the bones that compose it and the functions of each one, emphasizing the differences between them.

What is the axial skeleton?

Axial skeleton structure
Axial skeleton structure

The axial skeleton is distributed around the central and vertical axis of the body forming the trunk and the head. It includes the bones of the skull and face, small bones of the middle ear, the neck, the rib cage, and the spinal column.

The axial skeleton encloses and protects the brain and vital organssuch as the heart or lungs.

The upright posture of humans is supported by the axial skeleton, which distributes the weight of the head, trunk, and upper limbs downward over the hip joints.

It also serves as the insertion of tendons and muscles that cross the shoulders and hips to move the extremities (appendicular skeleton), in addition to the muscles and tendons of the axial skeleton.

Bones of the axial skeleton

The axial skeleton It is made up 80 bones. It is usually divided into five parts:

  • 22 bones in the bony head or skull: 8 cranial bones and 14 facial bones.
  • 6 bones in the middle ear: 3 chains of ossicles in each ear (hammer, anvil and stirrup).
  • 1 hyoid bone: located in the neck, between the chin and the thyroid cartilage.
  • 25 bones in the rib cage or thorax: the sternum and 24 ribs (12 pairs).
  • 26 bones in the spinal column: 24 true vertebrae plus the sacrum and coccyx.

What is the appendicular skeleton?

Structure of the appendicular skeleton
Structure of the appendicular skeleton

The appendicular skeleton It is made up of the bones of the Superior limbs and the lower extremitieswhich can be considered appendages of the axial skeleton.

The upper extremities include the shoulder girdle and the lower limbs include the hipwhat are the structures of anchorage and articulation between the appendicular skeleton and the axial skeleton.

The upper extremities are made up of the hands, wrists, upper arms and forearms, and the shoulder girdle (scapula or shoulder blade and clavicle).

The lower extremities by the feet, the legs (calf and thigh) and the coxal bones (hipbones). The coxal bones, together with the coccyx and sacrum, these two of the axial skeleton, form the pelvic girdle.

Although they have a similar structure, the appendicular skeleton is very different between the lower and upper extremities. The bones of the lower extremities are adapted for weight-bearing and posture stabilization, as well as for walking and running.

In contrast, the bones of the upper extremities are much more mobile and can be used for a wide variety of activities and manipulation of objects, including a characteristic common to all primates: the opposable thumb against the palm of the hand.

Bones of the appendicular skeleton

The appendicular skeleton It is made up 126 bones:

  • 4 bones in the shoulder girdle: a clavicle and a scapula on each side.
  • 6 bones in the arms and forearms: 3 on each side, humerus, ulna and radius.
  • 58 bones in the hands: each hand is made up of 29 bones distributed in 8 carpus, 5 metacarpals, 14 phalanges and 2 sesamoid bones.
  • 2 coaxial bones: are the hip bones, there is one for each leg.
  • 8 leg bones: 4 in each leg, which are femur, tibia, fibula and patella.
  • 56 bones in the feet: tarsi, metatarsi, phalanges and sesamoids of the feet.
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