The Skeletal System

Types of Skeletal Systems

  • Hydrostatic Skeleton:

    • Organisms with this system do not possess a hard skeletal structure.
    • Instead, they have body cavities filled with fluid under high pressure.
    • Movement is achieved through muscles acting against this fluid (hydrostatic pressure).
    • Example: Jellyfish.

  • Exoskeleton:

    • Composed of a hard outer layer that provides support and protects internal organs.
    • A significant characteristic is that it does not grow with the organism, often requiring molting.
    • Example: Praying mantis (insects).

  • Endoskeleton:

    • Found in all vertebrates.
    • The support system is internal and consists of bones, muscles, tendons, and ligaments.
    • Example: Cats, dogs, and humans.

Essential Biological Terminology

  • Cartilage: An elastic tissue usually found in association with bones.
  • Tendon: A tough, fibrous connection between a muscle and a bone.
  • Vertebrae: The individual bones that protect the spinal cord.
  • Cranial Bones: Bones that surround and protect the brain.
  • Patella: The bone that forms part of the knee (kneecap).
  • Clavicle: The scientific name for the collarbone.
  • Foramen Magnum: An opening in the skull through which the spinal cord passes.
  • Bipedal: Refers to an upright posture and walking only on two legs.
  • Canines: Large, pointed teeth in African apes used for tearing food.
  • Femur: The longest bone in the human body.

The Human Endoskeletal System

  • Main Sections:

    • The system is divided into two primary parts: the Axial Skeleton and the Appendicular Skeleton.

  • Core Functions:

    • Provides structure and support for the body.
    • Allows for the mechanism of hearing.
    • Serves as a storage site for minerals.
    • Provides protection for vital internal organs.
    • Responsible for the production of blood cells.

The Axial Skeleton

  • The axial skeleton includes all bones located around the central axis of the body.

  • The Skull:

    • Consists of the Cranium (encloses and protects the brain) and Facial Bones (Maxilla and Mandible).
    • Key Bones: Frontal, Parietal, Occipital, Temporal.
    • When compared to apes, the human cranium is much larger to accommodate a larger brain.
    • Foramen Magnum: The opening for the spinal cord. In humans, its position moved forward to a more central/ventral location to allow for a vertical entry of the spinal cord, which is essential for bipedalism.

  • The Vertebral Column:

    • Consists of 33 vertebrae bones encasing the spinal cord.
    • Vertebrae are separated by intervertebral disks.
    • Sections of the Spine:
      1. Cervical (includes Atlas and Axis).
      2. Thoracic.
      3. Lumbar.
      4. Sacral.
      5. Coccygeal.
    • Atlas (C1): Allows for nodding movements of the head.
    • Axis (C2): Allows for the rotation of the head.
    • Evolutionary Shape: The human spine is S-shaped to provide shock absorption, allow flexible movement, support the skull, and serve as an attachment for ribs. In contrast, an ape's spine is C-shaped.

  • The Rib Cage:

    • Composed of 12 thoracic vertebrae, 12 pairs of ribs, and the sternum.
    • Functions: Protects organs in the thoracic cavity, aids in breathing, provides attachment for pectoral muscles, and supports the pectoral girdle and upper limbs.

The Appendicular Skeleton

  • Consists of the bones that "append" or hang off the axial skeleton.

  • The Pectoral Girdle and Upper Limbs:

    • Scapula: Flat, triangular bone with a socket for the humerus.
    • Clavicle: The collarbone.
    • Acromium: Part of the scapula articulating with the clavicle.
    • Humerus: Longest bone in the arm; fits into the glenoid cavity (ball and socket joint).
    • Radius and Ulna: Bones of the forearm (radius is outer, ulna is inner).
    • Carpals: 8 bones forming the wrist joint.
    • Metacarpals: Bones in the palm of the hand.
    • Phalanges: Fingers (3 phalanges each) and thumb (2 phalanges).

  • The Pelvic Girdle and Lower Limbs:

    • Pelvis: Consists of three fused bones: Ilium, Ischium, and Pubis. It also includes the Sacrum.
    • Male vs. Female Pelvis:
      • Female: Ilium is flared; ischial tuberosities are farther apart; pubic angle is wider.
      • Male: Pubic angle is more acute; coccyx is more ventral.
    • Lower Limb Bones: Femur (thigh), Patella (knee), Tibia and Fibula (lower leg), Tarsals (ankle), Metatarsals (foot), and Phalanges (toes).

Anatomy of Bone and Connective Tissue

  • Long Bone Structure:

    • Epiphysis: The ends of the bone.
    • Diaphysis: The shaft of the bone.
    • Periosteum: Outer fibrous membrane.
    • Marrow Cavity: Central space in the diaphysis.
    • Compact Bone: High-density bone tissue.
    • Spongy Bone: Porous bone tissue found in the epiphyses.
    • Cartilage: Covers the ends of bones at joints.

  • Connective Tissues:

    • Ligaments: Connective tissue that attaches bone to bone; elastic enough to allow movement.
    • Tendons: Connective tissue that attaches muscle to bone; transmits the tension from muscle contraction to lift the bone.

Joints and Movement

  • Synovial Joint Components:

    • Hyaline cartilage: Reduces friction and acts as a shock absorber.
    • Synovial membrane: Produces synovial fluid.
    • Synovial fluid: Lubricates the joint.
    • Fibrous joint capsule.

  • Types of Synovial Joints:

    • Ball and Socket: (e.g., shoulder/hip).
    • Gliding: (e.g., between carpals).
    • Hinge: (e.g., elbow/knee).
    • Pivot: (e.g., atlas/axis).

  • Antagonistic Muscles:

    • Muscles work in pairs where one contracts while the other relaxes.
    • Example (Lifting Arm): The Biceps contract while the Triceps relax.

Skeletal Diseases and Injuries

  • Rickets: Caused by a lack of Vitamin D in children; results in soft, deformed bones. Treatment involves Vitamin D supplements and sunlight.
  • Osteomalacia: Vitamin D deficiency in adults; bones cannot hold body weight, leading to fractures. Treatment involves Vitamin D and sunlight.
  • Osteoporosis: Occurs when calcium is not replaced in bone; bones become brittle and porous. Vertebrae can weaken, causing compression of the spine.
  • Arthritis:
    • Osteoarthritis: Breakdown of cartilage; no inflammation, but makes movement difficult.
    • Rheumatoid Arthritis: Autoimmune disorder where the immune system attacks joints, causing inflammation, pain, and eventual immovability.
  • Injuries:
    • Strain: Damage or tearing of a muscle.
    • Sprain: Damage or tearing of a ligament.
    • Fractures: Broken bones, classified as incomplete (hairline, greenstick) or complete (simple, multi-fragmentary).
    • Dislocation: Bone is overextended out of its joint.

Educational Framework: CAPS and Bloom's Taxonomy

  • Differentiation in Assessment:

    • Assessments must cater to top, average, and weaker learners using different cognitive levels.
    • Scaffolding is used to show achievement across the learning spectrum.

  • Bloom's Taxonomy Levels (Life Sciences):

    1. Level A (Remembering): Find or remember information (List, Describe, Define). [40% weighting]
    2. Level B (Understanding): Making sense of information (Explain, Compare, Paraphrase). [25% weighting]
    3. Level C (Applying): Using information in new situations (Solve, Calculate, Diagram). [20% weighting]
    4. Level D (Analyzing/Evaluating/Creating): Take info apart, examine relationships, or create something new (Critique, Design, Organize). [15% weighting]

  • Instructional Verbs:

    • Name: Give the name of something.
    • Differentiate: Use differences to qualify between categories.
    • Tabulate: Draw a table with direct pairs.
    • Describe: State main points of a process in sentences.
    • Explain: Give answer in cause-effect or statement-reason sequence.
    • Compare: Give both similarities and differences.

  • Scientific Data Example:

    • Primate evolution brain volumes (cm3cm^3):
      • Ardipithecus ramidus (5.8 to 4.4 million years ago): 400 cm3400\,cm^3
      • Australopithecus afarensis (4 to 2.7 million years ago): 450 cm3450\,cm^3
      • Homo habilis (2.2 to 1.6 million years ago): 750 cm3750\,cm^3
      • Homo erectus (2 to 0.4 million years ago): 1000 cm31000\,cm^3
      • Homo neanderthalensis (0.3 to 0.23 million years ago): 1500 cm31500\,cm^3
      • Homo sapiens (0.2 to present): 1400 cm31400\,cm^3
      • Modern apes (0.2 to present): 500 cm3500\,cm^3