8.1

The Skeleton Structure

  • Skeleton Overview

    • The human skeleton is divided into two main parts:

    • Axial Skeleton

      • Consists of 80 bones that form the head and body trunk.

    • Appendicular Skeleton

      • Comprises 126 bones that constitute the limbs and their attachments to the axial skeleton.

      • Bones are grouped into:

        • Limbs: Bones located within the limbs themselves.

        • Girdle Bones: Bones that attach the limbs to the axial skeleton.

Axial Skeleton and Appendicular Skeleton

  • Axial Skeleton

    • Includes the skull, vertebral column, and thoracic cage.

  • Appendicular Skeleton

    • Composed of:

    • Pectoral girdle

    • Pelvic girdle

    • Limb bones

    • Bones of the hands and feet.

Pectoral Girdle

Learning Objectives

  • By the end of this section, students will be able to:

    • Describe the bones that form the pectoral girdle.

    • List the functions of the pectoral girdle.

  • Components of the Pectoral Girdle

    • Includes the following bones:

    • Clavicle (Collarbone)

      • S-shaped bone located on the anterior side of the shoulder.

      • Medial end articulates with the sternum of the thoracic cage (axial skeleton).

      • Lateral end articulates with the scapula, slightly above the shoulder joint.

    • Scapula (Shoulder Blade)

      • Situated on the posterior side of the shoulder.

      • Supported by the clavicle; articulates with the humerus forming the shoulder joint.

Functions of the Pectoral Girdle

  • Provides attachment sites for muscles associated with shoulder and arm movement.

  • Allows the upper limbs to operate independently due to its structure.

  • Facilitates extensive mobility, enhancing shoulder and arm movements.

Clavicle: Structure and Function

  • Description of the Clavicle

    • The only long bone positioned horizontally in the body.

    • Functions:

    • Acts as a strut supporting the scapula, allowing for maximal freedom of motion for the upper limb.

    • Transmits forces exerted on the upper limb to the sternum and axial skeleton.

    • Protects underlying nerves and blood vessels during upper limb activities.

  • Regions of the Clavicle

    • Medial End (Sternal End)

    • Triangular shape, articulates with the sternum at the sternoclavicular joint.

    • This joint is crucial as it is the sole bony connection between the pectoral girdle and the axial skeleton.

    • Lateral End (Acromial End)

    • Articulates with the acromion of the scapula, forming the acromioclavicular joint.

  • Morphological Differences

    • Sex differences noted in the clavicle's morphology:

    • Women: Generally shorter, thinner, and less curved.

    • Men: Typically heavier, longer, and more curved.

  • Fractures

    • The clavicle is the most frequently fractured bone in the body, often due to falls or direct blows.

    • Common fracture sites: Middle and lateral portions.

    • Symptoms include sagging of shoulder and lateral clavicle due to weight of the upper limb.

Scapula: Structure and Function

  • Description of the Scapula

    • Lies on the posterior aspect of the shoulder, surrounded by muscles; does not articulate with the ribs.

Key Landmarks on the Scapula

  • Borders of the Scapula

    • Superior Border

    • Medial Border

    • Lateral Border

  • Angles of the Scapula

    • Superior Angle: Between medial and superior borders.

    • Inferior Angle: Between medial and lateral borders; serves as an attachment point for muscles.

  • Glenoid Cavity

    • Located between the superior and lateral borders; articulates with the humerus to form the glenohumeral (shoulder) joint.

  • Prominent Projections

    • Coracoid Process: A hook-like structure, projects anteriorly and curves laterally; serves as an attachment site for anterior chest and arm muscles.

    • Spine of the Scapula: A prominent ridge on the posterior aspect, extending laterally to form the acromion.

  • Fossae

    • Supraspinous Fossa: Found superior to the scapular spine.

    • Infraspinous Fossa: Located inferior to the scapular spine.

    • Subscapular Fossa: The broad anterior surface of the scapula.

    • All fossae provide attachment sites for muscles that cross the shoulder joint.

Acromioclavicular Joint

  • Significance

    • Allows force transmission from the limb to the clavicle.

    • Relatively weak ligaments may become injured due to falls or lateral shoulder impacts, leading to acromioclavicular joint injuries.

    • Coracoclavicular Ligament: A strong ligament that provides significant support to the acromioclavicular joint by connecting the coracoid process to the clavicle.

Acromioclavicular Joint Injuries

  • Shoulder Separation

    • Result from trauma such as a hard fall; can lead to dislocation of the acromioclavicular joint.

    • Symptoms include separation of the scapula from the clavicle, with possible downward retraction of the shoulder due to the upper limb's weight.