Bone Structure and Classification

Week 4: Bone Structure and Classification

Organization of the Skeleton

  • Axial Skeleton: Skull

  • Axial Skeleton: Vertebral Column and Thoracic Cage

Why Do We Have Bones?

  • Functions of Bones:

    • Support the body.

    • Facilitate movement.

    • Protect internal organs.

    • produce blood cells (occurring in bone marrow).

    • Store and release minerals and fat (e.g., calcium).

How Many Bones Does the Human Body Have?

  • Total Count: 206 Bones.

  • Distribution of Bones:

    • Axial Skeleton: Bones within the mid-vertical axis.

    • Appendicular Skeleton: Bones located outside the mid-vertical axis, associated with limbs.

Why Do We Have So Many Bones?

  • Complex structure and variation to support various functions such as movement, protection, and support.

What Type of Tissue is Bone?

  • Bone Composition: Hard, dense connective tissue.

Classification of Bones

  • Total of 206 bones categorized into five categories:

    1. Long Bones (cylinder-shaped)

    • Location: Found in arms (e.g., humerus, ulna, radius) and legs (e.g., femur, tibia, fibula), as well as in fingers (metacarpals, phalanges) and toes (metatarsals, phalanges).

    1. Short Bones (cube-like)

    • Location: Carpal bones of the wrists and tarsal bones of the ankles.

    1. Flat Bones (thin and curved)

    • Examples: Cranial bones (skull), scapulae (shoulder blades), sternum (breastbone), and ribs.

    1. Irregular Bones

    • Examples: Vertebrae and facial bones.

    1. Sesamoid Bones (resembling sesame seed shape)

    • Example: Patella (kneecap).

Detailed Anatomy of Bone

  • Bone Functions:

    • Provides structural support to the body.

    • Facilitates movement through muscle attachment.

    • Offers protective encasement for internal organs.

    • Integral to hematopoiesis (production of blood cells) occurring in the bone marrow.

    • Acts as a reservoir for minerals including calcium and fat storage.

Metabolic Functions of Bone

  • Reservoir for Minerals:

    • Calcium and phosphorus essential for muscle contraction and nerve impulse transmission.

  • Bone Marrow Functions:

    • Yellow Marrow: Primary role in fat storage.

    • Red Marrow: Site for hematopoiesis (blood cell formation).

Types of Bone Cells

  • Osteocyte

    • Function: Maintains bone tissue.

  • Osteoblast

    • Function: Forms bone matrix.

  • Osteogenic Cell

    • Function: Stem cell that develops into osteoblasts.

  • Osteoclast

    • Function: Resorbs bone tissue.

Specific Bone Cell Locations

  • Osteogenic Cells: Located in deep layers of the periosteum and marrow.

  • Osteoblasts: Located in growing portions of bone, periosteum, and endosteum.

  • Osteocytes: Encased within the bone matrix.

  • Osteoclasts: Found on the surfaces of bones, particularly at sites of old, injured, or unnecessary bone.

Bone Structure

  • Long Bone Anatomy:

    • Epiphysis: Wider sections at each end filled with spongy bone.

    • Diaphysis: Hollow region known as the medullary cavity filled with yellow marrow; composed of dense compact bone.

    • Endosteum: Delicate membranous lining of the medullary cavity involved in bone growth, repair, and remodeling.

    • Periosteum: Fibrous membrane that covers the outer surface, containing blood vessels, nerves, and lymphatic vessels essential for nourishing compact bone. Attaches tendons and ligaments.

Compact vs. Spongy Bone

  • Compact Bone:

    • Location: Outer portion of bones; contains osteons.

    • Functions: Protection, calcium storage, and allows for movement.

  • Spongy (Trabecular) Bone:

    • Characteristics: Less dense, more vascular, greater metabolic activity, and contains red marrow.

    • Reinforces structural integrity by being arranged along the direction of mechanical load, capable of remodeling and adapting.

Bone Structure Overview

  • Collaborative Anatomy:

    • Compact Bone: Composed of osteons; where osteoblasts and osteocytes are located in lacunae, offering strength and durability.

    • Spongy Bone: Composed of trabeculae designed for strength while maintaining lightness.

Thoracic Cage

  • Comprised of ribs, thoracic vertebrae, and sternum.

  • Types of Ribs:

    • True Ribs (1-7): Directly attached to sternum.

    • False Ribs (8-12): Indirect or no attachment to the sternum.

    • Floating Ribs (11-12): No attachment to the sternum.

Skull Anatomy

  • Bones include:

    • Frontal

    • Sphenoid

    • Temporal

    • Parietal

    • Occipital

    • Ethmoid

    • Nasal

    • Zygomatic

    • Maxilla

    • Mandible

Vertebral Column Structure

  • Regions of the Spine:

    • Cervical (7 Vertebrae)

    • Thoracic (12 Vertebrae)

    • Lumbar (5 Vertebrae)

    • Sacrum (5, fused)

    • Coccyx (4, fused)

Intervertebral Discs

  • Between adjacent vertebrae, these discs consist of:

    • Anulus Fibrosus: Fibrous outer layer.

    • Nucleus Pulposus: Gel-like center that absorbs shock and maintains vertebral alignment.

Herniated Discs

  • Occurs when the anulus fibrosus weakens allowing protrusion of the nucleus pulposus, potentially compressing spinal nerves leading to pain or weakness.

Ligaments of the Vertebral Column

  • Anterior Longitudinal Ligament: Runs along the front of the vertebral bodies.

  • Supraspinous Ligament: Connects spinous processes of thoracic and lumbar vertebrae; expands in the neck to form the nuchal ligament.

Abnormal Curvatures of the Vertebral Column

  • Scoliosis: Abnormal lateral bending of the spinal column.

  • Kyphosis: Excessive convex curvature of the upper thoracic region.

  • Lordosis: Excessive anterior curvature of the lumbar region.

Summary of Skeleton

  • Structures such as the skull, ribs, and vertebrae are crucially interconnected with specific differences in shape and function, adapted to their roles within the body.