Appendicular Skeleton

Overview

The appendicular skeleton consists of the bones of the limbs and their girdles, which attach the limbs to the axial skeleton. It is essential for movement and manipulation of the environment.

• Pectoral girdle: Attaches upper limbs to the body trunk.

• Pelvic girdle: Attaches lower limbs to the body trunk.

The pectoral girdle consists of the clavicles and scapulae, providing attachment sites for muscles and offering a high degree of mobility. The scapulae are not attached to the axial skeleton, allowing for greater movement.

Pectoral Girdle

Clavicle (Collar Bone)

The clavicle is a slender, S-shaped bone that connects the arm to the trunk. It is prone to fractures due to its exposed position.

• Sternal end: Articulates medially with the sternum.

• Acromial end: Articulates laterally with the scapula.

• Serves as a brace to hold the scapula and arms out.

Scapula (Shoulder Blade)

The scapula is a thin, triangular flat bone located on the dorsal surface of the rib cage, between ribs 2 and 7. Each scapula has three borders and three angles.

• Angles: Superior, lateral (axillary), and inferior.

• Spine: Prominent ridge on the posterior surface.

• Acromion: Lateral projection that articulates with the clavicle.

• Coracoid process: Attachment site for muscles.

• Fossae: Infraspinous, supraspinous, and glenoid cavity (shoulder joint).

Upper Limb

Structure

Each upper limb consists of 30 bones, forming the framework for the arm, forearm, and hand.

• Arm: Humerus (only bone of the arm).

• Forearm: Radius and ulna.

• Hand: Carpus (wrist), metacarpus (palm), and phalanges (fingers).

Humerus

• Head: Articulates with the scapula.

• Deltoid tuberosity: Site of muscle attachment.

• Radial groove: Carries the radial nerve.

• Condyles: Trochlea (medial), capitulum (lateral).

• Epicondyles: Medial and lateral, sites of muscle attachment.

Forearm

• Radius: Lateral bone, forms the wrist joint.

• Ulna: Medial bone, forms the elbow joint.

• Colles fracture: Break in the distal end of the radius, common from falls.

Hand

• Carpus (Wrist): 8 bones arranged in two rows.

• Metacarpus: 5 bones forming the palm.

• Phalanges: 14 bones, numbered 1-5 (thumb is 1, pinky is 5).

• Carpal tunnel syndrome: Inflammation and overuse of tendons compress the median nerve, causing tingling and numbness.

Pelvic Girdle

Structure and Function

The pelvic girdle, also called the hip girdle, is formed by two hip bones (coxal bones) and the sacrum, joined at the pubic symphysis (hyaline cartilage). It supports pelvic organs and provides stability.

• Less mobility than the shoulder joint, but more stability.

• Three fused bones form each coxal bone: ilium, ischium, and pubis.

• Ilium: Superior region, articulates with the sacrum.

• Ischium: Posteroinferior part, consists of body and ramus.

• Pubis: Anterior portion, joins at pubic symphysis.

• Acetabulum: Deep socket formed at the fusion point, receives the head of the femur.

• Iliac crest: Thickened superior margin of the ilium.

• Greater sciatic notch: Passage for the sciatic nerve.

• Gluteal surface: Contains ridges for muscle attachment.

Comparison of Male and Female Pelves

Lower Limb

Structure

The lower limb carries the entire weight of the erect body and is subjected to exceptional forces during activities such as jumping or running. It consists of three segments: thigh, leg, and foot.

• Thigh: Femur (largest and strongest bone in the body).

• Patella: Sesamoid bone in the quadriceps tendon, protects the knee joint.

• Greater and lesser trochanters: Sites for muscle attachment.

• Leg: Tibia (medial, weight-bearing) and fibula (lateral).

• Foot: Tarsus, metatarsus, and phalanges.

• Pott's fracture: Break in the fibula.

Foot

• Tarsus: 7 bones forming the posterior half of the foot.

• Metatarsals: 5 bones forming the sole.

• Phalanges: 14 bones forming the toes.

Spinal Curvatures

Primary and Secondary Curvatures

The vertebral column exhibits curvatures that are important for balance and flexibility.

• Primary curvatures: Thoracic and sacral regions are convex at birth, resulting in a C-shaped spine.

• Secondary curvatures: Cervical and lumbar regions develop convex anteriorly as the child grows.

Key Terms and Definitions

• Girdle: A set of bones that attach the limbs to the axial skeleton.

• Fossa: A depression or hollow in a bone, often serving as an articulation site.

• Condyle: A rounded articular projection.

• Trochanter: Large, blunt, irregularly shaped process (femur).

• Epicondyle: Raised area on or above a condyle.

• Sesamoid bone: A bone embedded within a tendon (e.g., patella).

Summary Table: Bones of the Limbs

Additional info:

• Some anatomical terms and bone features were expanded for clarity and completeness.

• Comparative table of male and female pelvis was inferred from standard anatomical knowledge.

• Definitions and summary tables were added for exam preparation.