Human Skeletal System Structure

Phalanges and Their Structure

• Phalanges refer to the finger bones, with each finger containing three phalanges and the thumb having two.
• The thumb metacarpal connects to the trapezium, allowing for a wide range of movement.

Lower Extremities

• The lower extremities consist of bones from the hip, thigh, leg, ankle, and foot.
• The pelvic girdle is formed by the fusion of three pairs of bones: ilium (largest), ischium (strongest), and pubis (anterior bones).

Femurs and Joint Connections

• Femurs are the longest and heaviest bones in the body, articulating with the acetabulum at the hip and the tibia at the knee.
• The patella (kneecap) protects the knee joint and overlaps the femur and tibia.

Facial Bones

• Key facial bones include two maxillary bones (upper jaw, nose), two zygomatic bones (cheekbones), two nasal bones (bridge of the nose), and the mandible (lower jaw).
• Other significant bones are two lacrimal bones (tear ducts), vomer (nasal septum), and two palatine bones (hard palate).

Spinal Column

• Comprises 24 vertebrae, sacrum, and coccyx, supporting the head and protecting the spinal cord.
• The spinal column consists of cervical (7), thoracic (12), lumbar (5) vertebrae, the sacrum, and the coccyx.
• Intervertebral disks cushion the vertebrae, allowing flexible movement and supporting balance.

Sacrum and Coccyx

• The sacrum, formerly os sacrum, is linked to the pelvic girdle.
• Coccyx, or tailbone, derives its name from the Greek word for cuckoo.

Chest and Ribs

• The sternum is a flat, sword-shaped bone anchoring the clavicles and protecting vital organs.
• Ribs attach to the thoracic spine; the first seven pairs are true ribs (attached to sternum), while the remaining five pairs are false ribs.

Appendicular Skeleton

• Includes upper and lower extremities; clavicles connect anteriorly to the sternum and laterally to scapulae.
• The humerus (upper arm) articulates with the ulna (little finger side) and radius (thumb side).

Bones of the Hand

• The hand consists of metacarpal bones forming the palm and phalanges (finger bones).
• Bones of the wrist comprise eight carpal bones linked by ligaments.

Tibia and Fibula

• The tibia (shinbone) is the largest lower leg bone, connecting proximally to the femur and distally to the fibula and talus.
• The fibula connects at both ends to the tibia and contributes to the ankle structure.

Foot Structure

• The foot maintains stability through an arch formed by seven tarsal bones: talus, calcaneus (heel), scaphoid (navicular), cuneiforms, and cuboid.
• Five metatarsal bones articulate with tarsals and phalanges, while fourteen phalanges in the toes mimic the fingers (three per toe except for the big toe, which has two).

Classification of Bones

• Bones are classified by shape:
  • Long bones: main limb bones (excluding the patella, wrist, and ankle bones).
  • Short bones: found in wrists and ankles.
  • Flat bones: include the sternum, scapulae, and cranium.
  • Irregular bones: consist of vertebrae and hip bones.