Chapter 7B

Chapter 8: The Skeletal System: The Appendicular Skeleton

Overview of the Appendicular Skeleton

  • Contains 126 bones primarily involved in movement.

  • Comprises the bones of upper and lower limbs.

  • Includes girdles that connect limbs to the axial skeleton.

Pectoral (Shoulder) Girdle

  • Clavicle (Collar Bone):

    • S-shaped.

    • Medial (sternal) end articulates with the manubrium of the sternum.

    • Lateral (acromial) end articulates with the acromion of the scapula (Shoulder Blade).

  • Scapula:

    • Flat bone situated between second and seventh ribs.

    • Contains the glenoid cavity, which connects to the humerus (upper arm bone).

Upper Limb (Extremity)

  • Humerus:

    • Articulates with scapula proximally (rounded head fits into glenoid cavity) and with the radius and ulna distally.

    • Key features include anatomical neck, greater/lesser tubercle, intertubercular sulcus, and deltoid tuberosity.

  • Radius and Ulna:

    • Ulna: Proximal end features olecranon and coronoid process forming trochlear notch for elbow joint formation.

    • Radius: Lateral bone in forearm; enables rotation via its articulation with the capitulum of the humerus.

  • Carpal Bones (Wrist):

    • 8 small bones in two rows:

      • Proximal row: Scaphoid, Lunate, Triquetrum, Pisiform.

      • Distal row: Trapezium, Trapezoid, Capitate, Hamate.

  • Metacarpals (Hand Bones):

    • 5 bones numbered I-V starting with the thumb; articulate with carpals and proximal phalanges.

  • Phalanges (Fingers):

    • Total of 14 (2 in thumb, 3 in each of the other four fingers).

Pelvic (Hip) Girdle

  • Composed of two hip bones (os coxa) that articulate with the sacrum.

  • Each hip bone comprises:

    • Ilium

    • Ischium

    • Pubis

  • The three bones fuse into one by the age of 23.

  • Acetabulum: Common area for hip bone articulation with the femur.

Differences in Male and Female Pelvis

  • Male Pelvis: Typically larger, heavier, and shaped more like a heart.

  • Female Pelvis: Wider and shallower, adapted for childbirth.

  • Pelvis comparison table indicating structural differences:

    • Females have a wider, oval-shaped pelvic brim compared to males’ narrow, heart-shaped shape.

Lower Limb (Extremity)

  • Femur (Thighbone):

    • The longest bone, articulates with the acetabulum (hip bone) and tibia (shinbone) at the knee joint.

    • Proximal end (head) and distal end (condyles).

  • Patella (Kneecap):

    • Triangular bone developing in the quadriceps tendon; articulates with femur posteriorly.

  • Tibia and Fibula:

    • Tibia: Proximal end articulates with femur and distal with talus (ankle).

    • Fibula: Lateral bone that supports the ankle but does not bear weight.

    • Mnemonic: "The fibuLA is Lateral."

  • Tarsal Bones:

    • 7 bones including talus, calcaneus, navicular, and 3 cuneiforms.

  • Metatarsals:

    • 5 bones similar to metacarpals, numbered I-V starting with the big toe.

  • Phalanges (Toes):

    • Arrangement similar to fingers (2 in big toe, 3 in other toes).

Foot Arches

  • Two types of arches:

    • Longitudinal Arch (medial and lateral portions)

    • Transverse Arch

  • Arches aid in weight support, leverage while walking, and weight distribution.

Development of the Skeletal System

  • Most skeletal tissue derives from mesoderm.

  • Skull bones develop through:

    • Neurocranium formation via endochondral ossification.

    • Viscerocranium from pharyngeal arch mesenchyme.

Role of the Skeletal System in Homeostasis

  • Supports all body systems by providing structure and calcium storage.

  • Key Contributions:

    • Red bone marrow for blood cell production.

    • Protection of vital organs.

    • Involvement in muscle attachment and movement facilitation.