Human Skeleton Overview

Overview

This lecture covers the organization of the human skeleton, distinguishing between the axial and appendicular skeletons, and detailing key bones and structures within each system.

Skeletal System Overview

• The adult human skeleton has 206 bones, along with cartilage, joints, and ligaments.
• The skeleton accounts for about 20% of total body mass.
• The skeleton is divided into the axial skeleton (skull, vertebral column, thoracic cage) and appendicular skeleton (limbs and girdles).

Axial Skeleton

Skull

• The skull consists of 22 bones: 8 cranial (protect brain) and 14 facial (form structure of face).
• Cranial bones are connected by sutures and include the frontal, parietal, occipital, temporal, sphenoid, and ethmoid bones.
• Sutures include coronal, sagittal, lambdoid, squamous, and occipitomastoid.
• Foramina are openings for nerves and vessels, with the foramen magnum allowing passage of the spinal cord.
• The hyoid bone, below the mandible, does not articulate with any other bone.

Vertebral Column

• The vertebral column comprises 26 irregular bones in 5 regions: 7 cervical, 12 thoracic, 5 lumbar, sacrum (5 fused), and coccyx (fused vertebrae).
• Ligaments stabilize the spine; main ones run anteriorly and posteriorly.
• Intervertebral discs (nucleus pulposus + anulus fibrosus) act as shock absorbers.
• Vertebrae have a body, vertebral arch, and various processes (spinous, transverse, articular).
• Structure varies by area: cervical (short process, large foramen), thoracic (long process, rib facets), lumbar (large, thick).

Thoracic Cage

• The thoracic cage includes the sternum (manubrium, body, xiphoid process) and 12 pairs of ribs.
• Ribs: 7 true (directly attached), 3 false (indirect), 2 floating (not attached).

Appendicular Skeleton

Pectoral Girdle and Upper Limb

• The pectoral girdle: clavicle (collarbone) and scapula (shoulder blade).
• Arm contains the humerus (upper limb bone).
• Forearm has radius and ulna, connected by the interosseous membrane.
• The hand: 8 carpals (wrist), 5 metacarpals (palm), 14 phalanges (fingers).

Pelvic Girdle and Lower Limb

• Pelvic girdle: sacrum and two hip bones (ilium, ischium, pubis).
• Thigh: femur (largest bone), with patella at the knee.
• Leg: tibia (larger, bearing weight) and fibula (thinner), also connected by interosseous membrane.
• Foot: 7 tarsals (ankle and heel), 5 metatarsals, 14 phalanges (toes).

Key Terms & Definitions

• Axial skeleton — central skeleton (skull, spine, ribs, sternum).
• Appendicular skeleton — limbs and girdles.
• Suture — immovable joint connecting skull bones.
• Foramen magnum — large skull opening for spinal cord.
• Intervertebral disc — cushiony pad between vertebrae.
• True/False/Floating ribs — based on attachment to sternum.

Action Items / Next Steps

• Review the names and locations of major bones in both skeleton sections.
• Prepare to study the structure and function of joints in the next session.