Human Body – The Skeletal System

Key Concepts

Overview of the Skeletal System

The human skeletal system is a complex and vital framework that provides structure, protection, and enables movement for the body. It consists of bones, joints, and connective tissues like cartilage, ligaments, and tendons. The adult human skeleton typically comprises 206 bones, categorized into axial and appendicular skeletons.

Major Bones

• Axial Skeleton (80 bones): Forms the central core of the body, providing support and protecting vital organs.
  • Skull: Includes the cranium, maxilla (upper jaw), and mandible (lower jaw).
  • Spine (Vertebral Column): Composed of 26 small bones, including cervical (neck), thoracic (upper back), and lumbar (lower back) vertebrae, sacrum, and coccyx (tailbone).
  • Chest (Thorax): Consists of the breastbone (sternum) and ribs.
• Appendicular Skeleton (126 bones): Includes the bones of the limbs and the girdles that attach them to the axial skeleton.
  • Arms: Collar bone (clavicle), shoulder blade (scapula), humerus (upper arm), radius, and ulna (forearm).
  • Hands: Wrist bones (carpals), metacarpals, and phalanges (finger bones).
  • Pelvis: Contains the hip bones.
  • Legs: Thigh bone (femur), kneecap (patella), tibia (shin bone), and fibula.
  • Feet: Tarsals, metatarsals, and phalanges (toe bones).

Bone Classification by Shape:

• Long bones: Found in limbs (e.g., femur, humerus) and aid in movement and support weight.
• Short bones: Cube-shaped, found in wrists and ankles (e.g., carpals, tarsals).
• Flat bones: Provide protection for internal organs (e.g., skull, ribs, scapula).
• Irregular bones: Have complex shapes (e.g., vertebrae).
• Sesamoid bones: Small, round bones embedded within tendons (e.g., patella).

Types of Joints

A joint is any place where two bones meet, allowing for movement or providing structural support. Joints are classified by their structure (the type of connective tissue) and their function (the amount of movement they allow).

Classification by Structure:

• Fibrous Joints: Connected by thick connective tissue, offering little to no movement. Examples include the sutures in the skull.
• Cartilaginous Joints: Bones united by cartilage, allowing limited movement. Examples include the joints between vertebrae.
• Synovial Joints: The most common type, characterized by a fluid-filled capsule that allows for a wide range of motion. They are further subdivided into:
  • Hinge joints: Allow movement in one direction (e.g., knees, elbows).
  • Ball and socket joints: Allow rotation and movement in almost any direction (e.g., shoulders, hips).
  • Condyloid joints: Allow circular motion, flexion, and extension (e.g., wrist).
  • Pivot joints: Allow rotation around an axis (e.g., joint between the first and second vertebrae in the neck).
  • Planar (Gliding) joints: Allow limited sliding movement (e.g., wrist, ankle bones).
  • Saddle joints: Allow movement back and forth and side to side, but no rotation (e.g., base of the thumb).

Classification by Function (Range of Motion):

• Synarthroses (Immovable): Provide structural support (e.g., skull sutures).
• Amphiarthroses (Slightly Movable): Offer a mix of stability and some motion (e.g., vertebrae).
• Diarthroses (Freely Movable): Allow the most movement (e.g., most synovial joints).

Functions of Bones and Joints

The skeletal system, including bones and joints, performs several critical functions:

• Support: Bones provide the body's shape and support its weight, acting as a scaffold.
• Movement: Bones serve as attachment points for muscles. Joints facilitate movement by allowing bones to articulate and act as levers when muscles contract.
• Protection: Bones protect internal organs from injury (e.g., skull protects the brain, ribs protect the heart and lungs, vertebrae protect the spinal cord).
• Mineral and Fat Storage: Bone tissue acts as a reservoir for essential minerals like calcium and phosphorus. Bones also store fat.
• Blood Cell Formation (Hematopoiesis): Bone marrow, found inside many bones, produces red blood cells, white blood cells, and platelets.

Importance of Good Posture

Good posture is the natural way you hold your body, whether sitting or moving, and involves the proper alignment of your body against gravity with minimal strain. It is important for:

• Reduces Aches and Pains: Helps avoid common back, neck, and shoulder pain by distributing body weight evenly and reducing strain on muscles and joints.
• Prevents Injuries: Maintains proper form during physical activity, reducing the risk of sports injuries.
• Improves Spine Health: Supports the spine, improves blood flow, and promotes the well-being of nerves and blood vessels.
• Reduces Wear and Tear: Decreases stress and wear and tear on joints, especially in the spine, which can help prevent issues like arthritis.
• Increases Energy Levels: Optimal muscle functioning and improved blood circulation contribute to higher energy levels.
• Enhances Confidence: Can indirectly boost confidence and improve physical appearance.
• Better Muscle and Joint Function: Promotes efficient muscle contraction and optimal use of muscles, preventing unnecessary tension.

Role of Calcium-Rich Foods

Calcium is a crucial mineral for building and maintaining strong bones. Adults typically need around 700mg of calcium per day. Calcium-rich foods include:

• Dairy Products: Milk, cheese, and yogurt are excellent sources of calcium, and the calcium in dairy is well-absorbed.
• Green Leafy Vegetables: Broccoli, cabbage, kale, collard greens, and bok choy are good sources (though spinach's calcium is less absorbed due to oxalates).
• Fish with Edible Bones: Sardines and canned salmon (when bones are eaten) are rich in calcium.
• Fortified Foods: Plant-based drinks (soya, almond, rice milk), orange juice, and some cereals and breads are often fortified with calcium.
• Legumes and Seeds: Soya beans, tofu (calcium-set), sesame seeds, chia seeds, and pulses.
• Nuts: Almonds.
• Other: Rhubarb, dried fruits (raisins, prunes, figs), and some cheeses like ricotta.

Vitamin D is also essential as it helps the body absorb calcium. Good sources include oily fish, egg yolks, and fortified foods. Sunlight is a primary source of vitamin D.

Exercises to Strengthen Bones and Muscles

Exercise is vital for keeping bones and muscles strong throughout life.

• Weight-Bearing Impact Exercises: These activities involve working against gravity and putting pressure on your bones, signaling the body to produce more tissue for stronger bones.
  • Walking, jogging, running
  • Dancing
  • Climbing stairs
  • Hiking
  • Sports like pickleball, tennis, squash, and paddle tennis.
• Muscle-Strengthening (Resistance) Exercises: These exercises build muscle strength, which in turn pulls on bones, stimulating bone growth and density.
  • Weightlifting (using dumbbells, resistance bands, or machines)
  • Bodyweight exercises (e.g., push-ups, squats, lunges)
  • Biceps curls, shoulder lifts.
  • Goblet squats (strengthens hips and spine).
  • Heel drops (strengthens lower body bones, especially hips).
  • Single-leg weighted dips (strengthens hip bones and muscles).
• Balance Training: Important for preventing falls, especially as one ages, which can lead to bone fractures.
  • Yoga (combines weight-bearing, resistance, and balance training).

It's important to note that exercises like swimming and cycling are great for general fitness and muscle strengthening but are not as effective for bone strength because they are not weight-bearing. Variety in exercise is also beneficial for bones.

Activities (for understanding, not part of notes)

• Draw major bones and joints, and classify them by type.
• Observe skeleton models/charts, identifying different bone shapes and joint types.
• Perform posture exercises and understand their benefits.
• Identify calcium-rich foods and discuss the importance of Vitamin D.
• Research common bone and joint conditions and their prevention.