Overview of Myology: Shoulder & Arm

Introduction

This study guide covers the anatomical basis of the major skeletal muscles of the shoulder and arm, focusing on muscle groups, compartments, origins, insertions, and their functions. Understanding these muscles is essential for comprehending upper limb movement and stability.

Key Learning Objectives

Muscle Compartments and Groups

• Compartment: A region of the limb containing muscles with similar functions, bound by fascia.

• Shoulder Muscles: Grouped differently in various texts; upper limb muscles are mostly found in distinct compartments.

• Main Functions: Each compartment/group has a common function and important attachment points.

Individual Muscles

• Identification: Be able to name and locate each muscle and its compartment/group.

• Function: Understand the main action of each muscle by observing its alignment and attachment points.

Etymology: Useful Word Roots for Key Terms

Prefixes and Regions

• Brach-: Arm

• Ante-: Before, preceding

• Sterno-: Breast/breastbone

• Carp-: Wrist

• Meta-: After, between, change

• Phalanx: Finger bone

Muscle Names

• Pect-: Breast, chest

• Serrat-: Saw-like, serrated

• Lat-: Wide, broad

• Teres: Round

• Levator: A lifter

Geometrical Shapes

• Delta: Triangle

• Rhomboid: 4 sides, parallel

• Trapezius: 4 sides, not parallel

Upper Limb Osteology

Pectoral Girdle

• Scapula

• Clavicle

Upper Limb Regions

• Arm: Humerus

• Forearm: Ulna, Radius

• Wrist: Carpal bones

• Hand: Metacarpals, Phalanges

Joints of the Upper Limb

Pectoral Girdle and Shoulder

• Sternoclavicular Joint: Synovial, ball & socket/saddle properties

• Acromioclavicular Joint: Synovial, gliding

• Glenohumeral Joint: Synovial, ball & socket

Elbow and Forearm

• Humeroulnar (and radial): Synovial, hinge

• Proximal radioulnar: Synovial, pivot

• Distal radioulnar: Synovial, pivot

Muscle Groups in the Shoulder & Arm

Classification

• Axial Muscles: Stabilize or move the trunk and head.

• Appendicular Muscles: Stabilize or move the limbs.

Shoulder/Pectoral Muscles

• Includes rotator cuff as the deepest group.

• Divided into posterior, anterior/lateral, and deep (rotator cuff) muscles.

Arm Muscles

• Anterior (Flexor) Compartment

• Posterior (Extensor) Compartment

Muscles of the Shoulder Region

Posterior Muscles

• Trapezius

• Levator scapulae

• Rhomboid major

• Rhomboid minor

• Teres major

Anterior & Lateral Muscles

• Pectoralis major

• Pectoralis minor

• Serratus anterior

• Deltoid

Deep Muscles: Rotator Cuff

• Subscapularis

• Supraspinatus

• Infraspinatus

• Teres minor

Rotator Cuff Functions at Glenohumeral Joint (GHJ)

Stabilization and Movement

• Dynamic Ligament: Rotator cuff muscles stabilize the GHJ by keeping the humeral head in the socket during movement.

• Abduction: Supraspinatus assists in abduction of the humerus.

• Rotation: Subscapularis mediates medial rotation; Infraspinatus and Teres minor mediate lateral rotation.

Muscles of the Arm

Anterior: Flexor Compartment

• Biceps brachii

• Coracobrachialis

• Brachialis

• Brachioradialis (primarily a forearm muscle, but flexes the elbow)

Posterior: Extensor Compartment

• Triceps brachii

Muscles & Movements

Movements of the Pectoral Girdle

• Elevation: Trapezius (upper fibers), Levator scapulae

• Depression: Trapezius (lower fibers), Pectoralis minor

• Retraction: Rhomboids, Trapezius (middle fibers)

• Medial (Downward) Rotation: Rhomboids, Levator scapulae

• Lateral (Upward) Rotation: Trapezius (upper and lower fibers), Serratus anterior

Movements of the Glenohumeral Joint (GHJ)

• Flexion: Pectoralis major, Deltoid (anterior fibers), Biceps brachii

• Extension: Latissimus dorsi, Deltoid (posterior fibers), Triceps brachii (long head)

• Abduction: Deltoid (middle fibers), Supraspinatus

• Medial Rotation: Subscapularis, Pectoralis major, Deltoid (anterior fibers)

• Lateral Rotation: Infraspinatus, Teres minor, Deltoid (posterior fibers)

Movements of the Elbow

• Flexion: Biceps brachii, Brachialis, Brachioradialis

• Extension: Triceps brachii

Arm Muscles Involved in Supination & Pronation

• Supination: Biceps brachii (inserts on radius), Supinator muscle

• Pronation: Pronator teres, Pronator quadratus (insert on radius)

• Elbow Flexion: Brachialis is the most important muscle for elbow flexion.

Table: Major Muscles of the Shoulder & Arm

Additional info:

• Some muscle origins and insertions are inferred from standard anatomical knowledge.

• Muscle actions are summarized for clarity and exam preparation.