Appendicular skeleton — A/L Biology

What must I remember about Appendicular skeleton?

• The human appendicular skeleton consists of 126 bones organized into the Pectoral (Shoulder) Girdles, Upper Limbs, Pelvic (Hip) Girdle, and Lower Limbs, designed for broad mobility and bipedal locomotion.
• Pectoral Girdle (4 bones): Each side comprises a slender Clavicle (collarbone articulating medially with manubrium of sternum and laterally with acromion) and a flat triangular Scapula (shoulder blade with spine, acromion, coracoid process, and shallow Glenoid Cavity articulating with head of humerus).
• Upper Limb (60 bones, 30 per limb): Humerus (arm), Radius (lateral forearm, articulates with scaphoid/lunate for pronation/supination) and Ulna (medial forearm, olecranon process forms elbow hinge), 8 Carpals (scaphoid, lunate, triquetrum, pisiform, trapezium, trapezoid, capitate, hamate), 5 Metacarpals, and 14 Phalanges (proximal, middle, distal; thumb has only 2).
• Pelvic Girdle (2 hip / coxal bones): Each os coxae is formed by fusion of three embryonic bones — Ilium (flaring superior blade with iliac crest), Ischium (inferior-posterior with ischial tuberosity for sitting support), and Pubis (anterior, joined at fibrocartilaginous pubic symphysis); all three converge at the deep Acetabulum articulating with femoral head.
• Lower Limb (60 bones, 30 per limb): Femur (longest, strongest bone in body), Patella (sesamoid knee bone), Tibia (medial weight-bearing shinbone with medial malleolus), Fibula (lateral non-weight-bearing bone for muscle attachment with lateral malleolus), 7 Tarsals (talus, calcaneus heel bone, navicular, cuboid, 3 cuneiforms), 5 Metatarsals, and 14 Phalanges.

Test yourself (1 minute)

1. Shoulder vs Hip joint mobility/stability tradeoff

   Shoulder joint (shallow glenoid fossa) provides extreme range of multiaxial motion at the expense of dislocation vulnerability; Hip joint (deep acetabulum cup + powerful iliofemoral ligaments) maximizes stability and weight-bearing at the expense of mobility.

2. Male vs Female pelvis distinctions

   Female pelvis is broader, lighter, and shallower, with an oval/round pelvic inlet, wider pelvic outlet, greater sciatic notch >90°, and pubic arch angle >90° (vs <90° in males) adapted for childbearing.

3. Foot arch functional biomechanics

   Three arches (medial longitudinal, lateral longitudinal, transverse) maintained by bones, plantar ligaments, and tendons distribute body weight and act as dynamic springs during walking and running.

Practise Appendicular skeleton questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 5

What should I study first?

What comes next?

Next in the syllabus

Where does Appendicular skeleton fit in the syllabus?

Year 2 · Term 1