Muscles Crossing the Shoulder and Elbow Joints: Movements of the Arm and Forearm chapter 10 part 3

스터디 가이드 - 스마트 노트

자료에 맞춘 맞춤형 노트, 핵심 정의, 예시, 맥락을 확장해 제공합니다.

The Muscular System: Muscles Crossing the Shoulder and Elbow Joints

Overview of Muscles Crossing the Shoulder Joint

The shoulder joint is highly flexible, allowing a wide range of movements of the arm (humerus). Nine muscles cross the shoulder joint, inserting on and moving the humerus. These muscles originate from either the scapula or the axial skeleton and are responsible for actions such as flexion, extension, and adduction. The three prime movers of the arm are the pectoralis major, latissimus dorsi, and deltoid.

Prime Movers: Pectoralis major, latissimus dorsi, deltoid
Rotator Cuff Muscles: Supraspinatus, infraspinatus, teres minor, subscapularis
Synergists: Coracobrachialis, teres major

Muscles of the shoulder joint, posterior view

Rotator Cuff Muscles and Their Functions

The rotator cuff muscles act as synergists and fixators, originating on the scapula and reinforcing the shoulder capsule to prevent dislocation. These muscles are essential for stabilizing the shoulder joint during movement.

Supraspinatus: Initiates abduction of the arm; stabilizes shoulder joint
Infraspinatus: Rotates arm laterally
Teres Minor: Rotates arm laterally
Subscapularis: Medially rotates arm

Posterior view of shoulder muscles including rotator cuff

Muscles Crossing the Shoulder Joint: Table Summary

The following table summarizes the muscles crossing the shoulder joint, their descriptions, origins, actions, and nerve supply.

Muscle	Description	Origin (O) and Insertion (I)	Action	Nerve Supply
Pectoralis major	Large, fan-shaped muscle	O: Clavicle, sternum, ribs; I: Intertubercular sulcus of humerus	Prime mover of arm flexion; adducts, medially rotates arm	Lateral and medial pectoral nerves (C5–C8, T1)
Latissimus dorsi	Broad, flat, triangular muscle	O: Lower vertebrae, iliac crest, ribs; I: Intertubercular sulcus of humerus	Prime mover of arm extension; adducts, medially rotates arm	Thoracodorsal nerve (C6–C8)
Deltoid	Thick, multipennate muscle	O: Clavicle, acromion, spine of scapula; I: Deltoid tuberosity of humerus	Prime mover of arm abduction	Axillary nerve (C5, C6)
Supraspinatus	Named for its location above scapular spine	O: Supraspinous fossa of scapula; I: Greater tubercle of humerus	Initiates abduction of arm	Suprascapular nerve
Infraspinatus	Partially covered by deltoid and trapezius	O: Infraspinous fossa of scapula; I: Greater tubercle of humerus	Rotates arm laterally	Suprascapular nerve
Teres minor	Small, elongated muscle	O: Lateral border of scapula; I: Greater tubercle of humerus	Rotates arm laterally	Axillary nerve
Teres major	Thick, rounded muscle	O: Posterior surface of scapula; I: Intertubercular sulcus of humerus	Extends, medially rotates, and adducts arm	Lower subscapular nerve (C5, C6)
Coracobrachialis	Small, cylindrical muscle	O: Coracoid process of scapula; I: Medial surface of humerus shaft	Flexes and adducts arm	Musculocutaneous nerve (C5–C7)

Table of shoulder joint muscles

Muscles Crossing the Elbow Joint: Flexion and Extension of the Forearm

The elbow joint is moved by muscles that are divided into anterior and posterior compartments. The anterior muscles are primarily flexors, while the posterior muscles are extensors. The walls of fascia divide the arm into these two compartments.

Anterior Muscles: Biceps brachii, brachialis, brachioradialis
Posterior Muscles: Triceps brachii, anconeus

Cross-section of arm showing muscle compartments

Muscles Crossing the Elbow Joint: Table Summary

The following table summarizes the muscles crossing the elbow joint, their descriptions, origins, actions, and nerve supply.

Muscle	Description	Origin (O) and Insertion (I)	Action	Nerve Supply
Biceps brachii	Two-headed fusiform muscle	O: Short head—coracoid process; long head—supraglenoid tubercle; I: Radial tuberosity	Flexes and supinates forearm	Musculocutaneous nerve (C5–C6)
Brachialis	Strong muscle deep to biceps brachii	O: Distal humerus; I: Coronoid process of ulna	Major forearm flexor	Musculocutaneous nerve
Brachioradialis	Superficial muscle of lateral forearm	O: Lateral supracondylar ridge of humerus; I: Styloid process of radius	Synergist in flexing forearm	Radial nerve
Triceps brachii	Large fleshy muscle; three heads	O: Long head—infraglenoid tubercle; lateral head—posterior shaft of humerus; medial head—posterior shaft of humerus; I: Olecranon of ulna	Powerful forearm extensor	Radial nerve (C6–C8)
Anconeus	Short triangular muscle	O: Lateral epicondyle of humerus; I: Olecranon of ulna	Synergist in extension of forearm	Radial nerve

Table of elbow joint muscles

Muscles of the Forearm: Movements of the Wrist, Hand, and Fingers

The forearm muscles are divided into anterior and posterior compartments. Most anterior muscles are flexors and insert via the flexor retinaculum, while most posterior muscles are extensors and insert via the extensor retinaculum. These muscles are further divided into superficial and deep groups.

Flexors: Flex wrist, fingers, and thumb
Extensors: Extend wrist, fingers, and thumb
Pronators: Pronator teres and pronator quadratus pronate forearm
Supinators: Supinator acts as a synergist with biceps brachii in forearm supination

Cross-section of forearm showing muscle compartments

Summary Table: Actions of Muscles Acting on the Arm, Forearm, and Hand

The following tables summarize the actions of muscles acting on the arm, forearm, and hand, including flexion, extension, abduction, adduction, and rotation at various joints.

Muscle	Flexion	Extension	Abduction	Adduction	Medial Rotation	Lateral Rotation
Pectoralis major	x (PM)			x (PM)
Latissimus dorsi		x (PM)		x (PM)	x (PM)
Deltoid	x (anterior fibers)	x (posterior fibers)	x (PM)		x (anterior fibers)	x (posterior fibers)
Supraspinatus			x (PM)
Infraspinatus						x (PM)
Teres minor						x (PM)
Subscapularis					x (PM)
Coracobrachialis	x (weak)			x (weak)
Triceps brachii

Summary table of muscle actions at the shoulder

Muscle	Elbow Flexion	Elbow Extension	Pronation	Supination
Biceps brachii	x (PM)			x
Brachialis	x (PM)
Brachioradialis	x
Triceps brachii		x (PM)
Anconeus		x
Pronator teres			x (weak)
Pronator quadratus			x (PM)
Supinator				x

Summary table of muscle actions at the elbow

Muscle	Wrist Flexion	Wrist Extension	Abduction	Adduction	Finger Flexion	Finger Extension
Flexor carpi radialis	x (PM)		x
Flexor carpi ulnaris	x (PM)			x
Palmaris longus	x (PM)
Flexor digitorum superficialis	x (PM)				x (PM)
Flexor digitorum profundus	x (PM)				x (PM)
Extensor carpi radialis longus		x (PM)	x
Extensor carpi radialis brevis		x (PM)	x
Extensor carpi ulnaris		x (PM)		x
Extensor digitorum		x (PM)				x (PM)
Abductor pollicis longus			x (thumb)
Extensor pollicis longus						x (thumb)
Extensor indicis						x (index finger)

Summary table of muscle actions at the wrist and fingers

Key Terms and Concepts

Flexion: Decreasing the angle between two bones
Extension: Increasing the angle between two bones
Abduction: Movement away from the midline
Adduction: Movement toward the midline
Medial Rotation: Rotating toward the midline
Lateral Rotation: Rotating away from the midline
Synergist: Muscle that assists a prime mover
Fixator: Muscle that stabilizes the origin of the prime mover

Example: Application in Movement

During a push-up, the pectoralis major and triceps brachii are activated to flex and extend the arm at the shoulder and elbow joints, respectively. The rotator cuff muscles stabilize the shoulder joint, preventing dislocation.

Human Anatomy & Physiology textbook cover showing arm movement

Additional info:

Tables and images were interpreted and grouped logically to provide a comprehensive overview of the muscles acting on the shoulder, elbow, and forearm.
Muscle actions were expanded with academic context for clarity and completeness.