Human Anatomy and Physiology - The Skeleton

Part 2: The Appendicular Skeleton

  • Definition: Consists of bones of the limbs and their girdles.
  • Pectoral Girdle:
    • Attaches upper limbs to body trunk.
  • Pelvic Girdle:
    • Attaches lower limbs to body trunk.

7.4 The Pectoral Girdle

  • Components:
  • Clavicles (anteriorly)
  • Scapulae (posteriorly)
  • Functions:
  • Attach upper limbs to axial skeleton.
  • Provide muscle attachment sites.
  • Offer mobility:
    • Scapulae are not attached to axial skeleton.
    • Shoulder joint has a shallow socket.

Clavicles

  • Description: Also known as collarbones, S-shaped.
  • Articulations:
    • Medial (sternal) end with sternum.
    • Lateral (acromial) end with scapula.
  • Function: Anchor muscles and hold scapulae and arms laterally.

Scapulae

  • Also called: Shoulder blades; thin, triangular bones on dorsal surface of rib cage (between ribs 2 and 7).
  • Borders:
  • Superior border: Shortest, sharpest.
  • Medial (vertebral) border: Parallel to spine.
  • Lateral (axillary) border: Ends superiorly in glenoid cavity (shoulder joint).
  • Angles:
  • Superior angle
  • Lateral angle
  • Inferior angle
  • Bone Features:
  • Spine, acromion, coracoid process, suprascapular notch, large fossae (e.g., supraspinous fossa).

7.5 The Upper Limb

  • Composition: 30 bones per upper limb.
  • Arm: Humerus.
  • Forearm: Radius and ulna.
  • Hand: 8 carpal bones (wrist), 5 metacarpal bones (palm), 14 phalanges (fingers).

Humerus

  • Description: Only bone of the arm; largest and longest of upper limb.
  • Articulations:
  • Proximally with glenoid cavity of scapula.
  • Distally with radius and ulna.
  • Features:
  • Head, anatomical neck, greater/lesser tubercles, surgical neck, radial groove, condyles, epicondyles.

Forearm

  • Bones: Ulna (medial) and radius (lateral).
  • Functional Connection: Connected by interosseous membrane.
  • Ulna: Major part of elbow joint, has features like olecranon, coronoid processes.
  • Radius: Articulates with humerus and ulna.

Hand

  • Structure: Composed of carpus, metacarpus, and phalanges.
  • Carpus: 8 bones in two rows (proximal: scaphoid, lunate; distal: trapezium, trapezoid, capitate, hamate).
  • Metacarpus: 5 bones forming palm.
  • Phalanges: 14 bones in fingers.

7.6 The Pelvic Girdle

  • Structure: Composed of 2 hip bones (coxal bones) and sacrum.
  • Functions:
  • Strong connection for lower limbs.
  • Supports pelvic organs.
  • Coxal Bone Composition: Ilium, ischium, pubis.
  • Form the acetabulum (socket for femur).

Ilium

  • Description: Superior region of coxal bone, articulates with sacrum.
  • Features: Iliac crest, greater sciatic notch, iliac fossa.

Ischium

  • Description: Posteroinferior part of hip bone.
  • Notable Markings: Ischial spine, lesser sciatic notch.

Pubis

  • Description: Anterior portion of hip bone, V-shaped.
  • Features: Pubic crest, tubercle, arch.

7.7 The Lower Limb

  • Structure: Comprises thigh, leg, and foot.
  • Weight Bearing: Carries the body's weight and withstands forces.

Thigh

  • Bone: Femur (largest and strongest, articulates with hip and knee).
  • Features: Fovea capitis, trochanters, condyles.

Leg

  • Bones: Tibia (weight-bearing) and fibula (not weight-bearing).
  • Structure: Connected by interosseous membrane.
  • Tibia Features: Condyles, tibial tuberosity, malleolus.
  • Bones: Includes tarsus, metatarsus, and phalanges.
  • Tarsus: 7 bones; weight carried by talus and calcaneus.
  • Metatarsals: 5 bones forming the instep.
  • Phalanges: 14 bones in toes.
  • Foot Arches:
  • Lateral longitudinal, medial longitudinal, transverse.

Clinical Considerations

  • Colles' Fracture: Break in distal end of radius, common in falls.
  • Carpal Tunnel Syndrome: Compression of median nerve.
  • Flat Foot (Pes Planus): Congenital/acquired; caused by age, weight, or activity.
  • Bimalleolar Fracture: Common sports injury, breaks in tibia and fibula.
  • Developmental Dysplasia of the Hip: Up to 2% of newborns; treatment varies.

Developmental Aspects of the Skeleton

  • Infant skull has more bones than an adult due to unfused structures.
  • Growth rate differences: limbs grow faster than torso leading to adult proportions.
  • Age-related changes: thinner discs, ossification of costal cartilages, height loss, and increased fracture risk.