CHAPTER 8

Overview of the Appendicular Skeleton

  • Definition: The appendicular skeleton refers to the limb bones and their associated girdles, which include arm and leg bones, and the bones of the pelvis and shoulders.

Main Components of the Appendicular Skeleton

  • Upper Limbs:

    • Humerus: The bone of the upper arm.

    • Ulna: The inner bone of the forearm.

    • Radius: The outer bone of the forearm.

    • Carpals: Eight wrist bones.

    • Metacarpals: Five bones in the hand.

    • Phalanges: Finger bones (14 total in both hands, with each finger having its own bones).

  • Lower Limbs:

    • Femur: The thigh bone, the longest bone in the body.

    • Tibia: The larger bone of the lower leg (shinbone).

    • Fibula: The smaller lateral bone of the lower leg.

    • Tarsals: Seven ankle bones.

    • Metatarsals: Five bones in the foot.

    • Phalanges: Toe bones (14 total in both feet).

  • Girdles:

    • Pectoral Girdle: Composed of two clavicles (collarbones) and two scapulae (shoulder blades).

    • Pelvic Girdle: Comprises two hip bones (coxal bones).

Counting the Bones

  • Total of 126 bones in the appendicular skeleton:

    • Upper Limbs: 64 bones (32 per arm)

    • Lower Limbs: 62 bones (31 per leg)

Pectoral Girdle

  • Clavicle:

    • Sternal End: The thicker part that connects to the sternum.

    • Acromial End: The flatter part that connects with the acromion of the scapula, allowing for shoulder mobility.

  • Scapula:

    • Basic Features: Includes the acromion, coracoid process, and glenoid cavity (socket for humerus attachment).

    • Scapular Spine: The ridge on the posterior surface, used to identify orientation.

Glenoid Cavity

  • Function: Serves as a socket for the head of the humerus, enabling shoulder joint movement.

  • Attachments: Involves various ligaments wrapping around for stabilization during movement.

Upper Limb Articulations

  • Humerus:

    • Capitulum: Articulates with the head of the radius.

    • Trochlea: Articulates with the ulna (trochlear notch).

  • Forearm Bones: Allows for motion (flexion and extension) through articulations with the humerus.

Notable Features of the Ulna and Radius

  • Olecranon: The bony prominence of the ulna, often referred to as the elbow.

  • Radial Notch: A depression on the ulna allowing for articulation with the radius.

  • Interosseous Membrane: A connective tissue separating the ulna and radius, providing structural support.

  • Styloid Processes: Projections on both the ulna and radius for ligament attachment to wrist bones.

Carpal Bones

  • Mnemonic for Carpals: "Sally Left The Party To Take Cathy Home" can help remember the carpal bones: Scaphoid, Lunate, Triquetrum, Pisiform (Proximal row) and Trapezium, Trapezoid, Capitate, Hamate (Distal row).

  • Structure: Eight carpal bones, categorized into proximal and distal rows.

Metacarpals and Phalanges

  • Metacarpals:

    • Five long bones forming the framework of the palm, numbered I to V from thumb to pinky.

  • Phalanges:

    • Total of 14 finger bones (2 in the thumb; 3 in each of the other fingers).

    • Each phalanx has a proximal, middle, and distal section (except for the thumb which has only proximal and distal.)

Summary of Appendicular Skeleton

  • Overall, the appendicular skeleton is essential for movement and stability. It consists of 126 bones which provide functionality in the arms and legs, enabling interaction with the environment.