Axial Skeleton

Bone Structure and Remodeling

Periosteum

  • Acts as an anchor for tendons and ligaments to bones.

  • Contains the osteogenic layer which is crucial for bone remodeling.

  • Bone is dynamic, adapting to stresses through remodeling.

Endosteal Layer

  • Inner lining covering diploic spongy bone surfaces and marrow cavity.

  • Plays a role in bone remodeling like the periosteum.

Osteoblasts

  • Cells responsible for building bone by depositing minerals.

  • Active in the endosteal layer on trabeculae (spongy bone).

  • Participate in remodeling based on stress and activity levels.

Osteoclasts

  • Cells that degrade or break down bone to release calcium into the blood.

  • Their activity increases with bone resorption, especially in osteoporosis.

Bone Remodeling Cycle

  • Characterized by the competition between osteoblasts and osteoclasts.

  • Essential for maintaining blood calcium levels.

  • Increased activity can lead to greater bone density if subjected to stress (e.g., exercise).

  • Osteoporosis occurs when bone resorption outpaces deposition, leading to weaker, porous bones.

Blood Supply and Healing Potential

  • Bones have a rich blood supply with networks like central and perforating canals.

  • Blood supply is critical for healing; bones have excellent healing potential.

  • Cartilage is avascular and relies on surrounding fluid for nutrients, making it harder to heal.

Axial Skeleton Overview

  • Comprised of the skull, vertebral column, and bony thorax (ribs and sternum).

  • Involves both cranial and facial bones in the skull.

Skull Anatomy

  • Cranial Bones: Protect the brain; include paired and unpaired structures.

  • Facial Bones: Form the structure of the face.

  • Sutures: Immovable joints connecting cranial bones, classified as:

    • Frontal or coronal suture

    • Sagittal suture

    • Lambdoid suture

    • Squamous suture

Vertebral Column

  • Consists of 26 bones in adults, some of which fuse (sacrum and coccyx).

  • Functions: Weight transmission, spinal cord protection, muscle attachment.

  • Cervical vertebrae support increasing weight as one descends the column.

Vertebrae Features

  • Spinous Process: Projects posteriorly, serving as muscle attachment.

  • Transverse Process: Projects laterally.

  • Vertebral Foramen: Hole for the spinal cord and nerves.

  • Facet Joints: Connect adjacent vertebrae, allowing movement.

  • Intervertebral Discs: Composed of:

    • Nucleus pulposus (gelatinous inner core)

    • Annulus fibrosis (outer ring of fibrocartilage)

Herniated Discs

  • Occurs when the nucleus pulposus protrudes through the annulus fibrosis, causing pain and discomfort.

Conclusion

  • Bone is a living structure that constantly remodels based on use and stress, while its rich blood supply greatly aids in healing. Understanding the axial skeleton is fundamental for grasping human anatomy.