Study Notes: The Appendicular Skeleton (Skeletal System III)

The Appendicular Skeleton

Overview

The appendicular skeleton is one of the two major divisions of the human skeletal system, the other being the axial skeleton. It consists of the bones of the limbs and the girdles that attach them to the axial skeleton, totaling 126 bones.

• Axial Skeleton: Includes the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Includes the pectoral girdle, pelvic girdle, and the bones of the upper and lower limbs.

Key Functions: Movement, support, and protection of vital organs.

Pectoral Girdle

Structure and Components

The pectoral (shoulder) girdle attaches the upper limbs to the axial skeleton. It consists of two bones: the clavicle and the scapula.

• Clavicle: S-shaped bone located on the anterior side of the shoulder. It is the only long bone that lies in a horizontal position in the body and is commonly fractured.

• Scapula: Flat, triangular bone located on the posterior side of the shoulder. It articulates with the clavicle and humerus, forming the shoulder joint.

Clavicle Regions

• Sternal (medial) end: Articulates with the sternum.

• Acromial (lateral) end: Articulates with the scapula.

• Shaft: Connects the two ends.

Scapula Borders and Processes

• Borders: Superior, medial, and lateral.

• Glenoid cavity: Articulates with the head of the humerus to form the glenohumeral joint.

• Coracoid process: Serves as an attachment for muscles of the chest and arm.

• Acromion process: Articulates with the clavicle, forming the acromioclavicular joint.

Upper Limb

Overview

The upper limb is divided into three regions: the arm (humerus), forearm (radius and ulna), and hand (carpals, metacarpals, phalanges). Each upper limb contains 30 bones.

Humerus

• Head: Articulates with the glenoid cavity of the scapula.

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

• Features: Contains numerous ridges and tubercles for muscle attachment.

Ulna

• Olecranon process: Forms the point of the elbow.

• Trochlear notch: Articulates with the humerus.

• Styloid process: Found at the distal end.

Radius

• Head: Disc-shaped structure that articulates with the humerus.

• Radial tuberosity: Attachment site for the biceps muscle.

• Styloid process: Found at the distal end.

Carpal Bones

• There are 8 carpal bones in each wrist, arranged in two rows.

• They form the carpus (wrist) and allow for a wide range of motion.

Metacarpal Bones

• Five metacarpal bones form the palm of the hand.

• They are numbered I-V from the thumb to the little finger.

Manual Phalanges

• Four fingers each have three phalanges: proximal, middle, and distal.

• The thumb (pollex) has two phalanges: proximal and distal.

Pelvic Girdle

Structure and Components

The pelvic girdle is composed of paired hip bones (coxal bones), which articulate with the sacrum and each other. Each hip bone is attached to the lower limb.

• Function: Supports the weight of the upper body and protects pelvic organs.

• Attachment: Serves as the attachment point for lower limbs.

Hip Bone Regions

• Ilium: Superior, broad portion of the hip bone. Forms the iliac crest and articulates with the sacrum.

• Ischium: Posterior, inferior portion. Forms the ischial tuberosity.

• Pubis: Anterior portion. Forms the pubic symphysis.

Ilium Features

• Iliac crest: Curved superior border.

• Greater sciatic notch: Passage for sciatic nerve.

Ischium Features

• Ischial tuberosity: Supports body weight when sitting.

Pubis Features

• Pubic symphysis: Cartilaginous joint uniting the left and right pubic bones.

Summary Table: Major Bones of the Appendicular Skeleton

Region	Main Bones	Key Features
Pectoral Girdle	Clavicle, Scapula	Shoulder attachment, mobility
Upper Limb	Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges	Arm movement, hand dexterity
Pelvic Girdle	Ilium, Ischium, Pubis	Weight support, lower limb attachment
Lower Limb (not covered in detail here)	Femur, Tibia, Fibula, Tarsals, Metatarsals, Phalanges	Locomotion, stability

Key Terms and Definitions

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

• Articulation: The joint or connection between bones.

• Phalanges: The bones of the fingers and toes.

• Symphysis: A cartilaginous joint where two bones meet.

Additional info:

• The lower limb bones (femur, tibia, fibula, tarsals, metatarsals, phalanges) are part of the appendicular skeleton but are not covered in detail in these notes.

• Understanding the structure and function of the appendicular skeleton is essential for comprehending human movement and clinical conditions such as fractures and joint disorders.