Human Skeleton Lecture Notes

Skeleton Overview

  • The skeleton is a framework for applying forces generated by muscles to produce movements.
  • Focus is on the human skeleton.

What is a Skeleton?

  • A skeleton is a framework of any structure.
  • In biological organisms, skeletons don't always consist of bones.
  • Three types of skeletons in biological organisms:
    • Endoskeleton: Internal skeleton, like in humans.
    • Exoskeleton: Hard covering on the outside of the body, such as a shell.
    • Hydrostatic skeleton: Fluid held under pressure within structures, like in worms.
  • Focus on the endoskeleton.

Functions of the Skeleton

  • Mechanical functions (primary focus):
    • Support of the body.
    • Protection of the body.
    • Movement of the body and external objects.
  • Metabolic functions:
    • Nutrient storage (e.g., minerals in bones).
    • Blood cell formation.

Detailed Mechanical Functions

  • Support:
    • Supports muscles and other body structures.
    • Maintains posture, body shape, and body functions.
    • Examples:
      • Ribs, sternum, and spine support the lungs.
      • Pelvis supports the pelvic organs.
  • Protection:
    • Protects vital organs.
    • Examples:
      • Skull protects the brain.
      • Spinal column supports the spinal cord.
      • Rib cage, spine, and sternum protect the lungs, heart, and major blood vessels.
  • Movement:
    • Converts muscle force into movement.
    • Muscles apply force to bones, and movement occurs around joints (articulations).
    • Requires a rigid structure (skeleton) for muscle forces to be exerted.

Axial vs. Appendicular Skeleton

  • Human skeleton consists of 206 bones.
  • Two primary divisions:
    • Axial skeleton
    • Appendicular skeleton

Axial Skeleton

  • Bones situated in the head and neck region.
  • Axial relates to forming an axis (the middle part of the skeletal structure).
  • Consists of 80 bones.
  • Includes:
    • Bones of the skull (protection of the brain).
    • Rib cage (protection of heart and lungs).
    • Vertebral column (protection of spinal cord).

Appendicular Skeleton

  • Bones in the limbs that append onto the axial skeleton.
  • Consists of 126 bones.
  • Includes:
    • Shoulder girdle, upper arm, forearm, and hand (support & allows the movement of the arm and hand, and protection through movement).
    • Pelvic girdle (protection of abdominal contents, supports the upper body, attaches to the lower limb for locomotion).
    • Lower limb (supports body weight and allows locomotion).

Example Question

  • Example question based on bone location rather than name:
    • e.g., "Is the femur (described as the large, long bone between the hip and knee joint) part of the axial or appendicular skeleton?"

Anatomical Planes

  • Essential for communication in paramedical and medical professions.
  • Three main planes:
    • Sagittal Plane
    • Frontal (Coronal) Plane
    • Transverse Plane

Sagittal Plane

  • Also known as the median plane.
  • Divides the body into left and right sides.
  • Movements in this plane do not cross the plane when standing in anatomical position.

Frontal (Coronal) Plane

  • Also known as the coronal plane.
  • Divides the body into dorsal and ventral parts (back and front) or posterior and anterior parts.

Transverse Plane

  • Also known as the horizontal plane.
  • Divides the body into cranial and caudal parts (head and tail) or superior and inferior parts.

Movements in the Sagittal Plane

  • Primarily flexion and extension.
  • Flexion and extension occur at joints, not in muscles (muscles concentrically or eccentrically contract).
  • Examples:
    • Flexion and extension of the spine.
    • Flexion and extension of fingers.
    • Flexion and extension of the wrist.
    • Flexion and extension of the shoulder (parallel to the sagittal plane).
    • Flexion and extension of the elbows.
    • Flexion and extension of the knee.
  • Dorsiflexion and plantar flexion at the ankle:
    • Dorsiflexion: Toes come up towards the back.
    • Plantar flexion: Toes point down (planting the foot).

Movements in the Frontal Plane

  • Abduction and adduction.
  • Abduction (AB-): Moving away from the midline.
  • Adduction (AD-): Moving towards the midline.
  • Examples:
    • Shoulder and hip

Movements in the Transverse Plane

  • Rotational movements.
  • Left and right rotation of the head and trunk.
  • Internal (medial) and external (lateral) rotation at ball and socket joints (shoulder and hip):
    • Internal rotation: Rotation towards the midline.
    • External rotation: Rotation away from the midline.
  • Supination and pronation (primarily forearm):
    • Supination: Holding a bowl of soup (palms up).
    • Pronation: Palms down.

Joint Structures

  • Joints (articulations) allow movement to occur.
  • Three types:
    • Fibrous Joints
    • Cartilaginous Joints
    • Synovial Joints

Fibrous Joints

  • Contain fibrous connective tissue; held tightly together.
  • Some have no movement, some have very little.
  • Examples: skull sutures and the joint between the fibula and tibia.

Cartilaginous Joints

  • Contain cartilage, acting as cushions to dampen forces.
  • Allow some range of motion.
  • Examples:
    • Intervertebral disc spaces.
    • Pubic symphysis.

Synovial Joints

  • Have a synovial cavity filled with fluid.
  • Allow the greatest range of motion.
  • Contain cartilage and ligaments.
  • Examples: hip joint (femur and pelvis).
  • Types:
    • Hinge joint
    • Ball-and-socket joint
    • Pivot joint
Hinge Joint
  • Allows movement in one direction (like a hinge on a door).
  • Example: Between the humerus and ulna.
  • Allows movement in the sagittal plane (flexion and extension).
  • Other examples include the knee, elbow, and fingers.
Ball and Socket Joint
  • Found where the humerus contacts the shoulder girdle (scapula).
  • Allows a wide range of motion in all anatomical planes.
  • Example: Shoulder and hip joint.
Pivot Joint
  • Enables rotation of one bone against another.
  • Example: Between the ulna and radius in the forearm.
  • Another example: Between the top two vertebrae in the neck.

Antagonist and Agonist Muscles

  • Antagonist muscle pairs: Muscles on opposite sides of a joint that act in opposite directions (e.g., biceps and triceps).
  • Agonist muscles: Muscles that work together to produce the same direction of movement around a joint (e.g., quadriceps).

Bone Composition and Structure

  • Bones need to be stiff and strong.
  • Collagen (40% of dry weight): Provides flexibility and fracture resistance.
  • Calcium and salts (60% of dry weight): Provide rigidity.

Bone Cell Types

  • Osteogenic cells: Stem cells that develop into osteoblasts.
  • Osteoblasts: Bone-forming cells that create the bone matrix.
  • Osteocytes: Maintain the bone matrix.
  • Osteoclasts: Reabsorb bone and dig tunnels in the direction forces are being applied.