AHS 131 Lab Exam 2 Review: Compact Bone, Skeleton, and Ranges of Motion

Compact Bone

Structure and Function of Compact Bone

Compact bone is a dense, strong type of bone tissue that forms the outer layer of bones and provides structural support and protection. Its microscopic structure is organized into repeating units called osteons.

• Osteon: The functional unit of compact bone, appearing as a circular structure in cross-section. Each osteon consists of concentric layers of bone tissue surrounding a central canal.

• Lacunae: Small cavities within the bone matrix that house mature bone cells known as osteocytes.

• Canaliculi: Tiny channels that connect lacunae, allowing osteocytes to communicate and exchange nutrients and waste. These pathways are essential for bone remodeling and maintenance.

• Concentric Lamellae: Circular layers of bone matrix that surround the central canal of each osteon, providing strength and resilience.

• Periosteum: A dense, fibrous membrane covering the outer surface of compact bone. It contains nerves and blood vessels and plays a role in bone growth and repair.

Example: The osteon structure allows compact bone to withstand compressive forces, making it ideal for supporting the body's weight.

Ranges of Motion

Types of Joint Movements

Joints allow bones to move in specific ways, and each type of movement has a distinct anatomical definition. Understanding these movements is essential for describing how the body functions during activity.

• Flexion / Extension: Flexion decreases the angle between two bones (e.g., bending the elbow), while extension increases the angle (e.g., straightening the elbow).

• Adduction / Abduction: Adduction moves a limb toward the body's midline (e.g., bringing the arm to the side), while abduction moves it away (e.g., raising the arm sideways).

• Internal / External Rotation: Internal (medial) rotation turns a limb toward the body's midline, while external (lateral) rotation turns it away.

• Supination / Pronation: Supination rotates the forearm so the palm faces up, while pronation rotates it so the palm faces down.

• Inversion / Eversion: Inversion turns the sole of the foot inward, while eversion turns it outward.

Example: During walking, the ankle undergoes both inversion and eversion to adapt to uneven surfaces.

Bone Types

Classification of Bones by Shape

Bones are classified based on their shapes, which relate to their functions and locations in the body.

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

• Short Bones: Nearly equal in length and width; found in the wrist and ankle (e.g., carpals, tarsals).

• Irregular Bones: Complex shapes that do not fit other categories (e.g., vertebrae, some facial bones).

• Sesamoid Bones: Small, round bones embedded within tendons (e.g., patella).

Example: The patella is a sesamoid bone that protects the knee joint and improves leverage for thigh muscles.

Axial Skeleton

Components and Functions

The axial skeleton forms the central axis of the body and includes the skull, vertebral column, and thoracic cage. It provides support and protection for the brain, spinal cord, and thoracic organs.

• Skull: Protects the brain and forms the structure of the face.

• Vertebral Column: Supports the body and protects the spinal cord.

• Thoracic Cage (Ribs and Sternum): Protects the heart and lungs.

Example: The vertebral column is composed of 33 vertebrae, divided into cervical, thoracic, lumbar, sacral, and coccygeal regions.

Vertebrae and Ribs

Identification and Classification

The vertebral column consists of different types of vertebrae, each with unique features. The ribs form the thoracic cage and are attached to the thoracic vertebrae.

• Cervical Vertebrae: Seven vertebrae (C1–C7) in the neck; characterized by small bodies and transverse foramina.

• Thoracic Vertebrae: Twelve vertebrae (T1–T12) in the upper back; each articulates with a pair of ribs and has a heart-shaped body.

• Lumbar Vertebrae: Five vertebrae (L1–L5) in the lower back; large, robust bodies for weight-bearing.

• Ribs: Twelve pairs; true ribs (1–7) attach directly to the sternum, false ribs (8–12) do not, and floating ribs (11–12) have no anterior attachment.

Example: The atlas (C1) and axis (C2) are specialized cervical vertebrae that allow for head rotation.

Appendicular Skeleton

Upper and Lower Extremities

The appendicular skeleton includes the bones of the limbs and girdles, enabling movement and manipulation of the environment.

• Upper Extremity: Includes the humerus, radius, ulna, carpals, metacarpals, and phalanges, as well as the pectoral girdle (scapula and clavicle).

• Lower Extremity: Includes the femur, tibia, fibula, tarsals, metatarsals, and phalanges, as well as the pelvic girdle (hip bones).

Example: The femur is the longest and strongest bone in the body, supporting the weight of the upper body during standing and movement.