Comprehensive Biology Study Notes: Iraqi Curriculum 2025 Translated Edition

Introduction to the Skeleton

The human body requires a hard support called the skeleton to maintain balance and harmony of movements and to provide attachment points for soft parts.

  • The Movement System is the combination of the muscles and bones. Muscle generate the power for movement, while bones provide the support and translate that power into motion.
  • Function: Rigid support, provides body shape and straightness, protects vital organs (e.g., skull protects the brain, thoracic cage protects the heart and lungs).

Bone Structure and Tissue

  • Tissue Composition: Composed of star-like bone cells called osteocytes.
  • Haversian Canal: A central canal discovered by Clapton Havers (1657-1702) around which osteocytes are arranged in circles.
  • Ossein: A solid substance secreted by osteocytes that makes bones hard.
  • Structure of a Long Bone (Example: Femur):
    • Diaphysis (Body): Covered by the periosteum, an external membrane containing nerves and blood vessels for nourishment.
    • Compact Bone: The hardest layer, located beneath the periosteum; contains the bone marrow.
    • Epiphysis (Ends): Two ends of the bone characterized as spongy bone. They are not covered by the periosteum but by a smooth, half-solid layer called cartilage.

Chemical Structure of Bones

  • Organic Materials (35%): Consists of colloidal proteins known as collagen and a mucous-like substance called mucole. Mucole resembles albumin (white of egg) and provides bone flexibility.
  • Inorganic Materials (65%): Consists of phosphate, carbonate, calcium fluoride, manganese phosphate, and sodium chloride. These materials are responsible for the hardness of bones.

The Human Skeleton: Main Divisions

  • The human skeleton is divided into two main parts: the Axial Skeleton and the Appendicular Skeleton.

Axial Skeleton: The Skull

  • Composed of 29 bones divided into three groups:
    • Cranial Bones (8 bones): Form a small box to protect the brain. Edges are serrated and interlocked, forming immovable joints. The foramen magnum is a large hole at the bottom for the spinal cord.
    • Facial Bones (14 bones): Surround eyes (sockets), nasal cavity, mouth, and ears. Only the lower jaw (mandible) is movable; the upper jaw is joined to the cranial bones.
    • Ear Bones (3 pairs): Tiny bones in the middle ear: malleus, incus, and stapes.
  • Infant Skull Characteristics: Large size relative to the body but small face; contains spaces called fontanelles covered with fibrous cartilaginous tissue.

Teeth

  • Definition: White, conical, or elongated structures used for cutting, tearing, and grinding food.
  • Count: 16 teeth per jaw (32 total in an adult).
  • Regions: Crown (visible), Root (transplanted in jaw), and Neck (between crown and root, surrounded by gum).
  • Structure:
    • Dentine: Solid basic substance containing calcic materials.
    • Enamel: Hard, shining white external layer on the crown.
    • Cementum: Rough brown solid substance on the neck and root.
    • Pulp: Inner cavity containing dental nerves and blood vessels.
    • Apical Foramen: Hole at the bottom of the root for nerve/vessel entry.
  • Types:
    • Deciduous (Milk/Temporal): Appear after 6 months, complete after 1 year, fall out at 6-7 years. Total count: 20.
    • Permanent: Appear after 7 years, completed after puberty (last teeth/wisdom teeth appear up to age 32).

Axial Skeleton: Vertebral Column and Thoracic Cage

  • Vertebral Column:
    • Length: 75 cm in an adult.
    • Composition: 33 bones called vertebrae.
    • Cartilaginous Discs: Located between vertebrae to enable bending, facilitate movement, and prevent friction.
    • Structure of a Vertebra:
    • Centrum: A flat disc-like portion at the front.
    • Vertebral Arch: Located at the back; forms the vertebral foramen. Vertically aligned foramina form the vertebral canal for the spinal cord.
    • Processes: Spinous process (for muscle connection), transverse processes (2 lateral, for ribs), and pairs of processes for articulating vertebrae together.
    • Regions:
    • Cervical (7 vertebrae): First is the atlas (joined to skull), second is the axis (has a long process for head turning).
    • Thoracic (12 vertebrae): Joined to the ribs.
    • Lumbar (5 vertebrae): Broad, flat sides.
    • Sacral (5 fused vertebrae): Forms the sacrum.
    • Coccygeal (4 fused vertebrae): Forms the coccyx.
  • Thoracic Cage:
    • Ribs (12 pairs):
    • True Ribs: First 7 pairs, directly connected to the sternum by cartilage pieces.
    • False Ribs: 3 pairs, connected to the cartilage of the 7th rib.
    • Floating Ribs: Last 2 pairs, not joined at the front.
    • Sternum: A long, level structure consisting of 3 cohesive bones in the front of the chest.

Appendicular Skeleton and Joint Specialties

  • Pectoral Girdle and Upper Limbs:
    • Pectoral Girdle: Includes the scapula (triangle bone on backside) and the clavicle (thin arch-like bone). The shoulder joint is formed where the humerus meets the scapula/clavicle cavity.
    • Upper Limbs:
    • Humerus: Long, strong bone of the upper arm.
    • Forearm: Composed of the ulna (longer, towards little finger) and the radius (towards thumb).
    • Hand (27 bones): Carpals (8 bones in 2 rows), metacarpals (5 bones), and phalanges (14 bones; 3 per finger, 2 for thumb).
  • Pelvic Girdle and Lower Limbs:
    • Pelvic Girdle: Two halves, each with three fused bones: ilium, ischium, and pubis. Females have wider, less deep pelves for pregnancy.
    • Lower Limbs:
    • Femur: Longest and strongest bone; has a spherical head that enters the acetabular cavity (ball and socket joint).
    • Leg: Composed of the tibia (inner/front) and fibula (thinner, outside edge). The patella bone is in front of the knee joint.
    • Foot (26 bones): Tarsals (7 bones), metatarsals (5 bones), and phalanges (Toes, 14 bones). The hallux (big toe) does not move like the thumb.

Supporting Structures and Joint Types

  • Ligaments: Strong flexible fibrous bands connecting bone to bone.
  • Tendons: Non-flexible firm fibrous cords connecting muscle to bone.
  • Cartilages: White, transparent, bendable structures covering bone heads.
  • Joint Types:
    • Ball and Socket: Extensive movement (e.g., shoulder, hip).
    • Hinge: Single-axis movement (e.g., elbow).
    • Cylindrical: e.g., junction of atlas vertebra with occipital bone.
    • Immovable: Bone plates held together (e.g., skull bones).

Skeletal Diseases and Recovery

  • Fracture: A split or break caused by contraction, external shock, or disease (TB, cancer). Recovery factors: fracture type, age (faster in young), nutrition (Vitamin D, Calcium), and immobilization (gypsum splint).
  • Dis-articulation: Separation of bones at a joint without breaking; damage to fibers instead of bone tissue.
  • Rickets: Affects children 1-2 years old. Cause: deficiency of Vitamin D and lack of sunlight. Symptoms: delayed teething, walking, and curved legs.