Lec 5- The Skeletal System: Appendicular Division – Study Notes

The Skeletal System: Appendicular Division

Introduction to the Appendicular Skeleton

The appendicular skeleton consists of the bones of the limbs and the supporting girdles that connect them to the axial skeleton. It plays a crucial role in movement and manipulation of the environment.

• Pectoral (Shoulder) Girdle: Connects the upper limbs to the trunk.

• Upper Limbs: Arms, forearms, wrists, and hands.

• Pelvic Girdle: Connects the lower limbs to the trunk.

• Lower Limbs: Thighs, legs, ankles, and feet.

Pectoral Girdle

Structure and Function

The pectoral girdle consists of two bones on each side: the clavicle and the scapula. It positions the shoulder joint and allows for a wide range of motion.

• Clavicle: S-shaped bone that acts as a strut to keep the scapula in position.

• Scapula: Flat, triangular bone that provides attachment for muscles and articulates with the humerus.

• Function: Maximizes range of motion and stabilizes the upper limb.

The Clavicle

• Articulates medially with the sternum (sternoclavicular joint) and laterally with the scapula (acromioclavicular joint).

• Acts as a brace to hold the arm away from the thorax.

• Common site of fractures due to falls on the shoulder.

The Scapula

• Broad, flat bone with several important landmarks:

  • Spine: Prominent ridge on the posterior surface.

  • Acromion: Lateral extension of the spine; articulates with the clavicle.

  • Coracoid Process: Anterior projection for muscle attachment.

  • Glenoid Cavity (Fossa): Shallow socket that articulates with the head of the humerus.

Sternoclavicular Joint

• Articulation between the clavicle and the manubrium of the sternum.

• Stabilized by several ligaments:

  • Sternoclavicular Ligament: Connects clavicle to manubrium.

  • Interclavicular Ligament: Connects the two clavicles across the top of the sternum.

  • Costoclavicular Ligament: Connects clavicle to the first rib.

• Allows movement of the pectoral girdle.

Movements of the Pectoral Girdle

• Elevation and depression (shrugging shoulders).

• Protraction and retraction (moving shoulders forward and backward).

• Rotation (raising the arm above the head).

The Upper Limb

Overview of Bones

• Humerus: Bone of the upper arm.

• Ulna and Radius: Bones of the forearm.

• Carpal Bones: Eight bones of the wrist.

• Metacarpal Bones: Five bones of the palm.

• Phalanges: Fourteen bones of the fingers.

The Humerus

• Proximal end articulates with the scapula at the glenoid cavity.

• Distal end articulates with the radius and ulna at the elbow joint.

• Key landmarks: head, greater and lesser tubercles, deltoid tuberosity, medial and lateral epicondyles, trochlea, and capitulum.

The Forearm: Radius and Ulna

• Radius: Lateral bone of the forearm (thumb side); participates in wrist joint.

• Ulna: Medial bone of the forearm (little finger side); forms the elbow joint with the humerus.

• Interosseous membrane connects the two bones along their length.

The Carpal Bones

The wrist contains eight carpal bones arranged in two rows:

Proximal Row	Distal Row
Scaphoid	Trapezium
Lunate	Trapezoid
Triquetrum	Capitate
Pisiform	Hamate

• Mnemonic: "So Long To Pinky, Here Comes The Thumb" (Scaphoid, Lunate, Triquetrum, Pisiform, Hamate, Capitate, Trapezoid, Trapezium).

• Carpal bones allow for limited sliding and twisting movements of the wrist.

Metacarpals and Phalanges

• Metacarpals: Numbered I-V from thumb to little finger; form the palm.

• Phalanges: Each finger has three phalanges (proximal, middle, distal), except the thumb, which has two (proximal and distal).

The Pelvic Girdle

Structure and Function

The pelvic girdle consists of two hip bones (coxal bones), each formed by the fusion of three bones: ilium, ischium, and pubis. It supports the weight of the upper body and protects pelvic organs.

• Articulates with the sacrum posteriorly and with each other anteriorly at the pubic symphysis.

• Provides attachment for lower limb muscles.

• Pelvic inlet and outlet are important for childbirth.

Pelvic Girdle Landmarks

• Ilium: Largest part; forms the superior region.

• Ischium: Forms the posteroinferior part.

• Pubis: Forms the anteroinferior part.

• Acetabulum: Deep socket for articulation with the femur.

• Obturator foramen: Large opening for nerves and blood vessels.

Comparison: Pectoral vs. Pelvic Girdle

Feature	Pectoral Girdle	Pelvic Girdle
Attachment to Axial Skeleton	Weak, allows mobility	Strong, allows stability
Function	Mobility of upper limb	Weight bearing, protection
Articulation	Clavicle to sternum	Hip bone to sacrum

Key Terms and Definitions

• Appendicular Skeleton: The portion of the skeleton consisting of the limbs and girdles.

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

• Articulation: A joint; the point where two bones meet.

• Ligament: A band of connective tissue that connects bones at a joint.

Summary Table: Bones of the Appendicular Skeleton

Region	Main Bones
Pectoral Girdle	Clavicle, Scapula
Upper Limb	Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges
Pelvic Girdle	Ilium, Ischium, Pubis
Lower Limb	Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges

Example Application: Understanding the structure and function of the appendicular skeleton is essential for analyzing movement, diagnosing injuries, and understanding the mechanics of the human body.