skeleton

The Musculoskeletal System Study Notes

Introduction to the Musculoskeletal System

The musculoskeletal system comprises the skeletal framework of the human body, categorized primarily into two types: the exoskeleton made from chitin, typically seen in some invertebrates, and the internal skeleton, which is the focus of human anatomy.

Functions of the Skeleton

The skeleton serves multiple essential functions:

  1. Protection of organs: The skull provides a protective enclosure for the brain.

  2. Movement: Skeletal muscles pull on bones, enabling bodily movement.

  3. Production of blood cells: Blood cells are produced in the bone marrow.

  4. Support and Structure: The skeleton maintains body form and keeps the body upright.

Types of Skeleton

The human skeleton can be broadly divided into two groups:

  1. Axial Skeleton

    • Consists of bones that make up the central axis of the body, which includes the:

      • Skull

      • Sternum

      • Rib cage

      • Spine

  2. Appendicular Skeleton

    • Consists of the bones that make up the limbs and girdles, which include the:

      • Pectoral girdle (clavicle and scapula)

      • Pelvic girdle (pelvis, femur, patella, tibia, fibula)

Detailed Components of Axial and Appendicular Skeleton

  • Axial Skeleton:

    • Skull

    • Sternum

    • Rib Cage

    • Spine (also known as the backbone): Comprised of 33 vertebrae grouped into five regions:

      • Cervical: 7 vertebrae (neck region)

      • Thoracic: 12 vertebrae (chest region)

      • Lumbar: 5 vertebrae (lower back)

      • Sacrum: 5 fused vertebrae (hip region)

      • Coccyx: 4 fused vertebrae (tailbone)

  • Appendicular Skeleton:

    • Pectoral Girdle:

    • Composed of the clavicle (collar bone) and scapula (shoulder blade).

    • Connects the upper limbs (arms) to the body; includes humerus, radius, ulna, carpal, metacarpal, and phalanges.

    • Pelvic Girdle:

    • Composed of the bones forming the pelvis and the lower limb bones including femur, patella, tibia, and fibula.

Structure of Bones

Types of Bone Structure

  • Long Bones: Contain a hollow central region known as the medullary cavity, filled with yellow bone marrow for fat storage.

  • Periosteum: A tough fibrous layer that envelops each bone.

  • Cartilage: Coats the ends of bones at joints, minimizing friction and acting as a shock absorber, primarily composed of collagen.

Internal and External Structures of Bone

  • Compact Bone: Composed of:

    • Living components: Osteoblasts (bone-forming cells).

    • Non-living components: Composed of calcium and collagen, providing strength and some flexibility.

  • Spongy Bone: Contains red bone marrow, located at the ends of bones, characterized by a lightweight structure due to hollow spaces, responsible for blood cell production.

  • Medullary Cavity: Contains red marrow in spongy bone areas, with yellow marrow in the hollow section of the diaphysis that stores fat and may convert to red marrow when necessary. In adults, it mainly consists of inactive yellow marrow.

Bone Development and Growth

Ossification Process

  • Bone formation starts at week 8 of embryonic development, characterized by a growth plate made of cartilage allowing increase in length.

Growth Plate Functionality

  • The activity of growth plates diminishes over time, leading to their eventual replacement by bone, typically concluding growth in length at age 18 for females and 21 for males.

Bone Renewal Process

  • Bone is a living tissue, continuously undergoing breakdown and replacement through:

    • Osteoclasts: Cells that digest bone.

    • Osteoblasts: Cells responsible for bone formation.

    • Excess calcium from bone remodeling enters the bloodstream for purposes such as nerve function, muscle action, blood clotting, and tooth formation.

Factors Influencing Bone Renewal

  1. Physical activity: Exercise stimulates osteoblast activity.

  2. Hormone levels: Parathyroid and growth hormones regulate bone renewal rates.

  3. Diet: Adequate calcium and vitamin D are essential for strong bones.

Types of Joints

  • A joint is defined as the location where two bones meet. There are different joint classifications:

    • Immovable joints: Allow no movement (e.g., the fused bones of the skull).

    • Partially movable joints: Allow limited movement (e.g., the joints between vertebrae).

    • Freely movable joints (synovial joints):

    • Ball and socket joints: Such as in the hip or shoulder, permitting 360-degree movement.

    • Hinge joints: Such as in the knee or elbow, allowing movement in one plane only.

Joint Terminology

  • Ligaments: Connect bone to bone.

  • Tendons: Connect muscle to bone. Both structures are collagen-rich connective tissues but serve different functions.

Muscle Types and Functionality

Muscle Classification

  1. Skeletal Muscle: Attached to bones, responsible for voluntariness in movement, and tires quickly.

  2. Smooth Muscle: Compounds that line bodily systems, facilitating involuntary processes and are slow to tire.

  3. Cardiac Muscle: Found in the heart, characterized as involuntary and slow to tire as well, maintaining rhythmic contractions.

Antagonistic Muscles

Antagonistic muscles work in pairs, with one muscle contracting while the other relaxes:

  • Example: Biceps (for lifting the arm) and Triceps (for lowering the arm). The contraction of the biceps pulls on the radius to bend the forearm, while the contraction of the triceps pulls on the ulna to straighten it out.

Health Implications

Arthritis

  • A common condition characterized by inflammation of joints, often caused by wear on cartilage in synovial joints. Preventative measures include proper footwear during exercise. Treatment may involve exercises for maintaining mobility and anti-inflammatory medications to alleviate pain.

Exam Questions

Higher Level Questions:

  • 2023 Q5

  • 2022 DP Q15(a)(b) p.45

  • 2022 Q16(c) p.72

  • 2021 Q7 p.84

  • 2019 Q14(c) p.142

Ordinary Level Questions:

  • 2023 Q17(a) P.255

  • 2022 Q16(d) p.276

  • 2022 Q16(c) P.299

  • 2021 Q7 P.309

  • 2019 Q12(c) P.357