Human Skeleton Structure

Overview of the Skeleton

• The adult human skeleton consists of 206 bones, while infants have around 270 bones.
• The skeleton can be divided into two main parts: the axial skeleton (80 bones) and the appendicular skeleton (126 bones).

Axial Skeleton

• The axial skeleton includes the skull, vertebrae, sternum, and ribs.
• The skull is made up of 8 bones: cranium, face, and auditory ossicles (maleus, incus, and stapes).
• The hyoid bone is also part of the axial skeleton.
• There are 26 vertebrae, including the sacrum and coccyx.
• The sternum consists of 1 bone.

Appendicular Skeleton

• The appendicular skeleton includes the shoulder girdles, upper and lower extremities.
• The shoulder girdles consist of 2 clavicles and 2 scapulae.
• The upper extremities include the humerus, radius, ulna, carpals, metacarpals, and phalanges.
• The pelvis (hip bone) is part of the appendicular skeleton.
• The lower extremities include the femur, patella, fibula, tibia, tarsals, metatarsals, and phalanges.

Classification of Bones

• Bones can be classified into four categories: long, short, irregular, and sesamoid bones.
• Long bones have two ends and one shaft, and are found in the limbs.
• Short bones are cube-shaped and are found in the wrists and ankles.
• Irregular bones have complex shapes and are found in the skull and vertebrae.
• Sesamoid bones are small and found in tendons, such as the patella.

Bone Characteristics

• The skull cap is a flat bone that develops from membrane.
• The mandible is an irregular bone that develops mainly from membrane.
• Ribs are flat bones that develop from cartilage.
• The sacrum and vertebrae are irregular bones that develop from cartilage.

Bone Shapes and Development

• The scapula is a flat bone that develops from membrane.
• The clavicle is a long bone that develops from membrane.
• The humerus is a long bone that develops from cartilage.
• The radius and ulna are long bones that develop from cartilage.
• The pelvis (hip bone) is an irregular bone that develops from cartilage.
• The femur is a long bone that develops from cartilage.
• The tibia and fibula are long bones that develop from cartilage.

Articulations

• The upper limb has several articulations: shoulder joint, radio-ulnar joints, elbow joint, and wrist joint.
• The lower limb has several articulations: hip joint, knee joint, and ankle joint.