Appendicular Skeleton: Structure and Function

Appendicular Skeleton

Overview of the Appendicular Skeleton

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

• Major Divisions: Pectoral girdle (shoulder), upper limbs, pelvic girdle (hip), and lower limbs.

• Total Bones: 126 bones in the appendicular skeleton (out of 206 total in the human body).

• Function: Facilitates locomotion and manipulation of objects.

Key Components:

• Pectoral Girdle: Clavicle and scapula

• Upper Limbs: Humerus, radius, ulna, carpals, metacarpals, phalanges

• Pelvic Girdle: Hip bones (coxal bones)

• Lower Limbs: Femur, patella, tibia, fibula, tarsals, metatarsals, phalanges

Pectoral Girdle

Structure and Articulations

The pectoral girdle connects the upper limb to the trunk and provides attachment points for muscles that move the shoulder and arm.

• Clavicle (collarbone): S-shaped bone that articulates medially with the sternum (sternoclavicular joint) and laterally with the scapula (acromioclavicular joint).

• Scapula (shoulder blade): Flat, triangular bone with several important landmarks for muscle attachment and articulation with the humerus.

• Joints:

  • Sternoclavicular joint: Between the clavicle and the manubrium of the sternum.

  • Acromioclavicular joint: Between the clavicle and the acromion of the scapula.

  • Glenohumeral joint: Between the glenoid cavity of the scapula and the head of the humerus.

Function: Provides a wide range of motion for the upper limb and serves as an attachment site for muscles.

Clavicle

Anatomy and Landmarks

The clavicle is a long bone that acts as a strut to keep the scapula in position, allowing the arm to hang freely.

• Ends:

  • Sternal end: Medial, articulates with the manubrium of the sternum.

  • Acromial end: Lateral, articulates with the acromion of the scapula.

• Surfaces:

  • Superior view: Shows the smooth upper surface.

  • Inferior view: Shows the conoid tubercle, a roughened area for ligament attachment.

• Orientation: The clavicle curves anteriorly on the medial side and posteriorly on the lateral side.

Clinical Note: The clavicle is the most commonly fractured bone in the body due to its subcutaneous position and the forces transmitted through the upper limb.

Summary Table: Major Bones of the Appendicular Skeleton

Region	Bone	Number (per side)	Main Function
Pectoral Girdle	Clavicle	1	Supports shoulder, transmits force to axial skeleton
Pectoral Girdle	Scapula	1	Attachment for muscles, articulates with humerus
Upper Limb	Humerus	1	Main bone of upper arm
Upper Limb	Radius	1	Lateral bone of forearm (thumb side)
Upper Limb	Ulna	1	Medial bone of forearm (pinky side)
Upper Limb	Carpals	8	Wrist bones
Upper Limb	Metacarpals	5	Palm bones
Upper Limb	Phalanges	14	Finger bones
Pelvic Girdle	Coxal (hip) bone	1	Supports trunk, attaches lower limbs
Lower Limb	Femur	1	Thigh bone, supports body weight
Lower Limb	Patella	1	Kneecap, protects knee joint
Lower Limb	Tibia	1	Main weight-bearing bone of lower leg
Lower Limb	Fibula	1	Stabilizes ankle, supports muscles
Lower Limb	Tarsals	7	Ankle bones
Lower Limb	Metatarsals	5	Foot bones
Lower Limb	Phalanges	14	Toe bones

Key Terms and Definitions

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

• Pectoral girdle: The set of bones (clavicle and scapula) that attach the upper limb to the trunk.

• Pelvic girdle: The set of bones (hip bones) that attach the lower limb to the trunk.

• Clavicle: The collarbone; a long bone that serves as a strut between the shoulder blade and the sternum.

• Scapula: The shoulder blade; a flat, triangular bone providing attachment for several muscles.

• Acromion: The lateral extension of the scapular spine, forming the highest point of the shoulder.

• Glenoid cavity: A shallow socket in the scapula that articulates with the head of the humerus.

Example: Clinical Relevance

• Clavicle Fracture: Commonly occurs from falls on the shoulder or outstretched hand. Presents with pain and deformity over the collarbone.

• Shoulder Dislocation: The head of the humerus is displaced from the glenoid cavity, often due to trauma.

Additional info: The notes above are expanded and clarified for academic completeness, based on standard Anatomy & Physiology curriculum.