AHS 131 Lab Exam 2 Review: Compact Bone, Skeletal System, 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 organization is essential for understanding bone physiology and pathology.

• Osteon: The functional unit of compact bone, also known as the Haversian system. Each osteon appears as a circular structure in cross-section and consists of concentric layers of bone tissue surrounding a central canal.

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

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

• Concentric Lamellae: Rings of calcified matrix arranged around the central canal of each osteon, providing strength and resilience to the bone.

• Periosteum: A dense, fibrous membrane covering the outer surface of compact bone. It contains blood vessels, nerves, and cells important for bone growth and repair.

Example: The osteon structure allows compact bone to withstand compressive forces, making it ideal for weight-bearing bones such as the femur.

Ranges of Motion

Types of Joint Movements

Joints allow bones to move in specific directions, and each type of movement is defined by the anatomical planes and axes involved. Understanding these terms is essential for describing normal and pathological motion.

• 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 (anteriorly), while pronation rotates it so the palm faces down (posteriorly).

• 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; primarily found in the limbs (e.g., femur, humerus).

• Short Bones: Nearly equal in length and width; provide stability and support with little movement (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 the leverage of the quadriceps muscle.

Axial Skeleton

Components and Functions

The axial skeleton forms the central axis of the body and supports and protects the brain, spinal cord, and thoracic organs.

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

• Vertebral Column: Supports the body, protects the spinal cord, and allows flexible movement.

• Rib Cage: Protects the heart and lungs and assists in respiration.

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

Vertebrae and Ribs

Identification and Classification

The vertebral column is divided into regions based on the structure and function of the vertebrae. Ribs are attached to the thoracic vertebrae and protect thoracic organs.

• 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 long, downward-pointing spinous processes.

• 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 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 (ilium, ischium, pubis).

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

Additional info: The review sheet references specific slides and labeled images for identification, but the above content summarizes the core anatomical and physiological concepts required for the exam.