CH6 – Bones & Skeletal Tissue

Structure of a Long Bone

The long bone is a fundamental type of bone in the human body, characterized by a shaft and two ends. Understanding its anatomy is essential for identifying its functions and clinical relevance.

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

• Epiphyses: The ends of the bone, typically broader and composed of spongy bone surrounded by a thin layer of compact bone.

• Medullary Cavity: The central cavity within the diaphysis, containing yellow bone marrow in adults.

• Periosteum: A dense connective tissue membrane covering the outer surface of the bone, involved in bone growth and repair.

• Endosteum: A thin membrane lining the medullary cavity.

• Articular Cartilage: Hyaline cartilage covering the epiphyses at joints, reducing friction and absorbing shock.

Example: The femur is a classic example of a long bone.

Microscopic Anatomy of Compact Bone

Compact bone is organized into structural units called osteons, which provide strength and support.

• Osteon (Haversian System): Cylindrical structures containing a central canal surrounded by concentric lamellae.

• Central (Haversian) Canal: Contains blood vessels and nerves.

• Lacunae: Small spaces housing osteocytes.

• Canaliculi: Tiny channels connecting lacunae, allowing for nutrient and waste exchange.

• Lamellae: Layers of bone matrix arranged around the central canal.

Example: The dense outer layer of all bones is made of compact bone.

Bone Cell Types

Bones contain several specialized cell types, each with distinct functions in bone formation, maintenance, and remodeling.

• Osteoblasts: Cells responsible for bone formation; they secrete bone matrix.

• Osteocytes: Mature bone cells that maintain bone tissue; found in lacunae.

• Osteoclasts: Large cells that resorb or break down bone matrix.

• Osteogenic Cells: Stem cells that differentiate into osteoblasts.

Example: Osteoclast activity increases during bone remodeling and repair.

Bone Classification

Bones are classified based on their shapes and functions. The four main categories are:

• Long Bones: Longer than they are wide (e.g., femur, humerus).

• Short Bones: Cube-shaped, nearly equal in length and width (e.g., carpals, tarsals).

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis).

• Flat Bones: Thin, flattened, and usually curved (e.g., sternum, skull bones).

Example: The scapula is classified as a flat bone.

CH7 – The Skeleton: Axial Skeleton

Axial & Appendicular Skeleton

The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. Understanding their differences is crucial for anatomical classification.

• Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage (ribs and sternum).

• Appendicular Skeleton: Includes the limbs and girdles (shoulder and pelvic girdles).

Example: The vertebrae are part of the axial skeleton, while the femur is part of the appendicular skeleton.

Skull: Lateral, Posterior, and Inferior Views

The skull is a complex structure composed of multiple bones. Identifying bones and features from different views is essential for anatomical study.

• Lateral View: Shows the side of the skull, highlighting bones such as the temporal, parietal, and zygomatic.

• Posterior View: Displays the occipital bone and lambdoid suture.

• Inferior View: Reveals the base of the skull, including the foramen magnum and occipital condyles.

Example: The zygomatic arch is visible in the lateral view of the skull.

Skull Sutures: Lateral, Posterior, and Superior Views

Sutures are immovable joints between skull bones. Recognizing their locations is important for understanding cranial anatomy.

• Coronal Suture: Between frontal and parietal bones.

• Sagittal Suture: Between the two parietal bones.

• Lambdoid Suture: Between parietal and occipital bones.

• Squamous Suture: Between parietal and temporal bones.

Example: The sagittal suture runs along the midline of the skull.

Skull: Sphenoid and Ethmoid Bones & Features

The sphenoid and ethmoid bones are complex bones located at the base of the skull, contributing to the cranial floor and nasal cavity.

• Sphenoid Bone: Contains the sella turcica, which houses the pituitary gland.

• Ethmoid Bone: Forms part of the nasal septum and the medial wall of the orbit.

Example: The cribriform plate of the ethmoid bone allows passage of olfactory nerves.

Vertebrae: Bone Models & Diagrams, Various Views

The vertebral column consists of individual vertebrae, each with unique features depending on their region.

• Cervical Vertebrae: Seven vertebrae (C1–C7); C1 is the Atlas, C2 is the Axis.

• Thoracic Vertebrae: Twelve vertebrae (T1–T12); articulate with ribs.

• Lumbar Vertebrae: Five vertebrae (L1–L5); largest and strongest.

• Features: Vertebral body, spinous process, transverse process, vertebral foramen.

Example: The Atlas (C1) supports the skull and allows nodding motion.

Ribs & Sternum: Bone Models & Diagrams

The thoracic cage is formed by the ribs and sternum, protecting vital organs and supporting respiration.

• True Ribs: First seven pairs; attach directly to the sternum via costal cartilage.

• False Ribs: Pairs 8–12; do not attach directly to the sternum.

• Floating Ribs: Pairs 11–12; do not attach to the sternum at all.

• Sternum: Composed of the manubrium, body, and xiphoid process.

Example: The xiphoid process is the inferior tip of the sternum.

*Additional info: Academic context and examples have been expanded for clarity and completeness.*