Muscles, Bones, and Joints: Human Body Structure

Posted on Nov 20, 2024 in Physical Education

Muscles

Muscles are the engines of movement. A muscle is a bundle of fibers, with contractility as its most prominent property. When a muscle receives the proper signal, the fibers contract, shortening and pulling the attached bone or structure. After completing the action, it returns to its resting position.

There are three types of muscle tissue:

  • Striated or Skeletal Muscle
  • Smooth Muscle
  • Cardiac Muscle

Striated muscles are red, have fast twitch fibers, and are voluntary. They are inserted into bones through tendons. Examples include the muscles used for chewing, the trapezius (holding the head up), and the calf muscles (allowing toe movement). Here is a microscopic view of striated muscle:

Smooth muscles line pipes and ducts, have slow twitch fibers, and are involuntary. They are found in the digestive tract and blood vessels (arteries and veins).

Cardiac muscle (see Heart) is a special case, as it is striated but involuntary.

The human body has about 650 voluntary muscles, enabling a wide range of movements. Muscles vary in shape: flat (rectus abdominis), spindle-shaped (biceps), or short (interosseous metacarpal). Some are large (dorsal), while others are powerful (quadriceps). Muscles, along with bones, protect internal organs, shape the body, and contribute to facial expressions.

Muscles are composed of elongated cells called fibers, arranged in bundles within connective tissue sheaths that extend to form tendons. These tendons attach to bones. Muscles are typically spindle-shaped (thicker in the middle, thinner at the ends).

Muscle Properties:

  • Soft
  • Deformable
  • Contractible

Their main function is to move body parts supported by bones.

There are over 650 muscles in the human body. For a classification of muscles by form, click here.

Key Muscles:

Head:

  • Masseter muscles (chewing)
  • Orbicularis oris (lip movement)
  • Orbicularis oculi (eyelid movement)
  • Buccinator (blowing, whistling)

Neck:

  • Sternocleidomastoid (head bending and rotation)
  • Splenius (backward movement)

Trunk:

  • Intercostals, serratus, diaphragm (breathing)
  • Pectorals (arm forward movement)
  • Dorsal (arm backward movement)
  • Trapezius (shoulder movement, head support)

Here is a front view of the main trunk muscles:

Arms:

  • Deltoids (shoulder)
  • Biceps brachii (forearm flexion)
  • Triceps brachii (forearm extension)
  • Pronator and supinator (wrist and hand rotation)
  • Flexors and extensors (finger movement)

Lower Extremities:

  • Gluteals (buttocks)
  • Sartorius (leg crossing)
  • Biceps femoris (knee flexion)
  • Quadriceps (leg extension)
  • Calf muscles (walking, ending in the Achilles tendon)

Muscles work in extension and flexion by pulling bones, acting as levers. Muscle work also produces heat, aiding in nerve center regulation.

Muscles require oxygen and glucose. Intense or prolonged effort can lead to cramps and fatigue due to toxin buildup. Rest and massage improve blood circulation, removing toxins.

Bones

The human body is a complex structure with over 200 bones, over 100 joints, and more than 650 muscles working together. This collaboration enables movement and various actions.

The skeleton is formed by bones and cartilage.

Bones consist of bone cells (osteocytes), inert materials (calcium and phosphorus salts), and organic substances like collagen.

Skeletal Functions:

  • Supports the body
  • Protects organs (brain, heart, lungs)
  • Provides attachment points for tendons
  • Houses bone marrow (blood cell production)

The head is formed by the skull and face, protecting the brain and sensory organs (except touch).

The backbone (vertebral column) is a flexible pillar of 30 vertebrae, enclosing the rib cage and articulating with the ribs.

The thorax is a semi-rigid box involved in breathing.

  • Human Body Bones: 208
    • Vertebral column: 26
    • Skull: 8
    • Face: 14
    • Ear: 8
    • Hyoid bone: 1
    • Chest: 25
    • Upper limbs: 64
    • Lower limbs: 62
  • Bone Types:
    • Long (arm, leg)
    • Short (wrist, vertebrae)
    • Flat (head)

Examples of long, short, and flat bones:

  • Bone Characteristics:
    • Hard, composed of ostein and mineral salts
    • Long bones have a central channel with yellow marrow and ends with red marrow
  • Bone Functions:
    • Provide body structure
    • Support movement with muscles
    • Serve as erythrocyte maturation centers

Human Body Division:

  • Trunk
  • Head
  • Limbs

Bones of the Head

The skull has 8 bones protecting the brain. The face has 14 bones, including the maxilla (chewing). The hyoid bone at the tongue’s base aids in movement.

Bones of the Trunk

  • Clavicle and scapula (support upper limbs)
  • Ribs (protect lungs, form rib cage)
  • Sternum (rib attachment)
  • Vertebrae (spinal column, spinal cord protection)
  • Pelvis (support lower limbs)

Upper Limb Bones

  • Clavicle, scapula, humerus (shoulder joint)
  • Humerus (arm)
  • Radius and ulna (forearm)
  • Carpals (wrist, 8 bones)
  • Metacarpals (hand)
  • Phalanges (fingers)

Lower Limb Bones

  • Pelvis and femur (hip joint)
  • Femur (thigh)
  • Patella (knee)
  • Tibia and fibula (leg)
  • Tarsals (heel, 7 bones)
  • Metatarsals (foot)
  • Phalanges (toes)

Joints

Joints are areas where bones or cartilage meet. They are classified as:

  • Synarthroses (immovable, e.g., skull bones)
  • Symphyses (limited mobility, e.g., pubic bone)
  • Synovial joints (movable, e.g., shoulder, hip)

Immovable joints are held by bone growth or fibrous cartilage. Limited mobility joints are held by elastic cartilage. Movable joints have fibrous cartilage, ligaments, and synovial fluid for lubrication. Bursitis is inflammation of the bursae (containing synovial fluid).

Movable joint types include:

  • Ball-and-socket (hip, shoulder; free movement)
  • Hinge (elbow, knee, fingers; movement in one plane)
  • Pivot (first two vertebrae, head rotation)
  • Sliding (wrist, ankle; short movements)