Skeletal System: Bones and Cartilages (Lab 4 Study Notes)

Overview of the Skeleton: Bones and Cartilages

Functions and Types of Cartilage

The human skeleton is supported and connected by various types of cartilage, each with specialized functions and locations.

• Elastic Cartilage: Provides flexibility and maintains the shape of certain structures. Location: External ear.

• Fibrocartilage: Highly compressible and strong, it resists tension and pressure. Location: Intervertebral discs, pubic symphysis, menisci of the knee.

• Hyaline Cartilage: Most abundant type; provides support with some flexibility. Location: Joint surfaces (articular cartilage), rib cage (costal cartilage), respiratory tract, external nose.

Classifications of Bones

Bones are classified by their shape and structure, which relate to their function in the body.

• Long Bones: Longer than they are wide; primarily found in limbs (e.g., humerus, femur).

• Short Bones: Cube-shaped; found in the wrist (carpals) and ankle (tarsals).

• Flat Bones: Thin, flattened, and usually curved; examples include the sternum, ribs, and skull bones.

• Irregular Bones: Complicated shapes; examples include vertebrae and certain facial bones.

Structure of a Long Bone

Long bones have a characteristic structure that supports their function in movement and weight-bearing.

• Diaphysis: The shaft of the bone, composed mainly of compact bone.

• Epiphyses: The ends of the bone, consisting of spongy bone covered by a thin layer of compact bone.

• Medullary Cavity: Central cavity within the diaphysis, containing bone marrow.

• Periosteum: Dense connective tissue membrane covering the outer surface of the bone.

• Articular Cartilage: Hyaline cartilage covering the joint surfaces of epiphyses.

Axial Skeleton: Thorax

Axial vs. Appendicular Skeleton

The skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton.

• Axial Skeleton: Consists of the skull, vertebral column, ribs, and sternum. Provides central support and protects internal organs.

• Appendicular Skeleton: Includes the bones of the upper and lower limbs, pectoral (shoulder) girdle, and pelvic girdle. Facilitates movement.

Spinal Curvatures

The vertebral column has four main curvatures that provide flexibility and resilience.

• Cervical Curvature: Concave posteriorly; supports the head.

• Thoracic Curvature: Convex posteriorly; accommodates the thoracic organs.

• Lumbar Curvature: Concave posteriorly; supports the lower back.

• Sacral Curvature: Convex posteriorly; forms the posterior wall of the pelvis.

Abnormal Curvatures:

• Scoliosis: Lateral curvature of the spine.

• Kyphosis: Excessive posterior thoracic curvature (hunchback).

• Lordosis: Excessive anterior lumbar curvature (swayback).

Vertebral Structure

Each vertebra has a common structural plan, with regional differences for function.

• Body (Centrum): Weight-bearing region.

• Vertebral Arch: Encloses the vertebral foramen (spinal canal).

• Processes: Spinous and transverse processes serve as attachment points for muscles and ligaments.

• Articular Processes: Form joints with adjacent vertebrae.

Thoracic Cage (Rib Cage)

The thoracic cage protects vital organs and supports the upper body.

• Sternum: Flat bone at the anterior midline of the thorax; consists of the manubrium, body, and xiphoid process.

• Ribs: 12 pairs; true ribs (1-7) attach directly to the sternum, false ribs (8-10) attach indirectly, and floating ribs (11-12) do not attach to the sternum.

• Costal Cartilages: Bars of hyaline cartilage connecting ribs to the sternum.

Relationship Between Ribs and Vertebrae

Ribs articulate with thoracic vertebrae at two points: the head of the rib with the vertebral body, and the tubercle of the rib with the transverse process.

• Head of Rib: Articulates with the costal facets on the bodies of two adjacent vertebrae.

• Tubercle of Rib: Articulates with the transverse costal facet of the corresponding vertebra.

Types of Cartilage in the Skeleton

Type of Cartilage	Main Locations	Function
Elastic Cartilage	External ear	Flexibility and shape maintenance
Fibrocartilage	Intervertebral discs, pubic symphysis, menisci of knee	Resists compression and tension
Hyaline Cartilage	Joint surfaces, rib cage, respiratory tract, external nose	Support with flexibility

Summary Table: Axial vs. Appendicular Skeleton

Skeleton Division	Main Components	Primary Function
Axial Skeleton	Skull, vertebral column, ribs, sternum	Support, protection of organs
Appendicular Skeleton	Upper and lower limbs, pectoral and pelvic girdles	Movement

Key Terms and Definitions

• Articulation: A joint; the point where two bones meet.

• Foramen: A round or oval opening through a bone.

• Process: Any bony prominence.

• Facet: Smooth, nearly flat articular surface.

• Condyle: Rounded articular projection.

Example Application

Understanding the structure and classification of bones is essential for identifying skeletal features on radiographs and in clinical practice. For example, recognizing the difference between a long bone (femur) and a flat bone (sternum) helps in diagnosing fractures and planning orthopedic treatments.