Human Skeleton Anatomy

The Human Skeleton

• The adult human skeleton consists of 206 bones.
• Bones provide support, protection, leverage for movement, blood cell production, and storage.
• Hematopoiesis is the process of blood cell production within bone marrow.
• Bones vary in shape and size.

### Long Bones

• Long bones are longer than they are wide and are found in the extremities, except the patella and wrist/ankle bones.
• They provide structure, shape, and mobility.
• Diaphysis: The long shaft of the bone.
• Epiphysis: The enlarged ends of the bone, which strengthen joints and allow ligament/tendon attachment.
• Articular Cartilage: Smooth tissue lining the joint surfaces, reducing friction and acting as a shock absorber.
• Periosteum: Membrane covering the outer surface of the bone, responsible for growth, repair, and nutrition.
• Compact Bone: Dense outer layer of bone, providing strength and protection.
• Spongy Bone: Porous inner layer of bone that fills the epiphysis.

### Parts of a Long Bone

• Proximal Epiphysis: End of the bone closest to the body's center.
• Diaphysis: Shaft of the bone.
• Distal Epiphysis: End of the bone furthest from the body's center.
• Articular Cartilage: Covers the articular surfaces of the epiphyses, reducing friction during movement.
• Spongy Bone: Located within the epiphyses, helps distribute forces and contains marrow.
• Epiphyseal Line: Thin line formed when the growth plate fully ossifies, indicating the end of growth.
• Periosteum: Tough, fibrous membrane covering the outer surface of the bone, providing attachment points for tendons and ligaments.
• Compact Bone: Dense, hard outer layer, providing strong support and protection.
• Medullary Cavity: Hollow space within the diaphysis, filled with yellow marrow.
• Endosteum: Thin membrane lining the medullary cavity.
• Yellow Marrow: Fat storage area, also contains cells that produce leukocytes (white blood cells).
• Red Marrow: Site of blood cell production for red blood cells, platelets, and some white blood cells. Found in the spongy bone of some bones.

Other Types of Bones

• Short Bones: Same width and length, cube-like. Examples include the wrist (carpals) and ankle (tarsals).
• Flat Bones: Thin and broad, used for protection and muscle attachment. Examples include the sternum, ribs, scapula, and skull roof.
• Irregular Bones: Complex shapes, examples include vertebrae and some skull bones.
• Sesamoid Bones: Small, flat bones resembling a sesame seed. Develop within tendons, typically found near joints. The patella is an example.

The Skeletal System

• Axial Skeleton: Forms the trunk, including the skull, spinal column, ribs, and breastbone.
• Appendicular Skeleton: Forms the extremities, including the shoulder girdle (clavicle and scapula), arms, pelvic girdle, and legs.

The Skull

• The cranium surrounds the brain and consists of 8 bones:
  • 1 frontal
  • 2 parietal
  • 2 temporal
  • 1 occipital
  • 1 ethmoid
  • 1 sphenoid
• At birth, the cranium has spaces called fontanels ("soft spots") that allow brain growth. These spaces close around 18 months of age.
• There are 14 facial bones:
  • 1 mandible (lower jaw)
  • 1 maxilla (upper jaw)
  • 2 zygomatic (cheekbones)
  • 2 lacrimal (inner eye area)
  • 5 nasal
  • 2 palatine (roof of the mouth)

### Cranial Anatomy

• Sutures: Areas where cranial bones connect and fuse together.
• Sinuses: Hollow air spaces within the skull, part of the nasal and respiratory system, act as resonating chambers for voice production.
• Foramina: Openings in bones that allow nerves and blood vessels to enter or exit.

Facial Bones and their Functions

• Maxilla: Forms the upper jaw.
• Mandible: Forms the lower jaw.
• Conchae: Located within the nasal cavity.
• Nasal Bone: Located above the nasal cavity.
• Zygomatic: Positioned near the maxilla/cheekbone region.
• Lacrimal: Located near the eye sockets.
• Palatine: Found in the back part of the mouth/nose area.
• Vomer: Forms part of the nasal septum.
• Inferior Nasal Concha: Located within the nasal cavity.