Identify The Highlighted Structure Upper Limb

The human upper limb, a marvel of biomechanical engineering, allows us to interact with the world in incredibly diverse and nuanced ways. Identifying the structures of the upper limb, from the shoulder girdle to the fingertips, is crucial for healthcare professionals, athletes, and anyone interested in understanding the intricacies of human movement and potential sources of injury. This comprehensive guide will walk you through the key structures of the upper limb, combining anatomical detail with practical relevance.

The Shoulder Girdle: Foundation of Upper Limb Movement

The shoulder girdle, comprised of the clavicle (collarbone) and scapula (shoulder blade), serves as the foundation for upper limb movement. It connects the upper limb to the axial skeleton, providing a wide range of motion and flexibility.

• Clavicle: This S-shaped bone articulates with the sternum (breastbone) at the sternoclavicular joint and the scapula at the acromioclavicular joint. Its primary functions include supporting the upper limb, transmitting forces from the upper limb to the axial skeleton, and protecting underlying nerves and blood vessels.

• Scapula: This flat, triangular bone lies on the posterior aspect of the thorax. Key features of the scapula include:

  • Glenoid Fossa: A shallow socket that articulates with the head of the humerus (upper arm bone) to form the glenohumeral joint (shoulder joint). This joint is known for its wide range of motion but also its instability.
  • Acromion: A bony process that extends laterally from the scapula and articulates with the clavicle at the acromioclavicular joint.
  • Coracoid Process: A hook-like process that projects anteriorly and provides attachment points for several muscles and ligaments.
  • Spine of the Scapula: A prominent ridge on the posterior surface of the scapula that divides it into the supraspinous fossa and infraspinous fossa. These fossae serve as origins for the supraspinatus and infraspinatus muscles, respectively, both crucial components of the rotator cuff.

Muscles of the Shoulder Girdle: Several muscles attach to and act upon the shoulder girdle, enabling movements such as elevation, depression, protraction, retraction, and rotation of the scapula. Key muscles include:

• Trapezius: A large, superficial muscle that extends from the occipital bone of the skull to the thoracic vertebrae and laterally to the clavicle and scapula. It elevates, depresses, retracts, and rotates the scapula.
• Rhomboids (Major and Minor): Located deep to the trapezius, these muscles retract and rotate the scapula.
• Levator Scapulae: This muscle elevates the scapula.
• Serratus Anterior: This muscle protracts and rotates the scapula, allowing for movements such as reaching forward and upward. It also helps to stabilize the scapula against the rib cage.
• Pectoralis Minor: Located deep to the pectoralis major, this muscle depresses, protracts, and rotates the scapula.

The Upper Arm: Humerus and Associated Muscles

The upper arm, also known as the brachium, extends from the shoulder to the elbow and contains the humerus, the longest and largest bone in the upper limb.

• Humerus: This bone articulates with the scapula at the glenohumeral joint and with the radius and ulna (forearm bones) at the elbow joint. Key features of the humerus include:
  • Head: A rounded proximal end that articulates with the glenoid fossa of the scapula.
  • Anatomical Neck: A groove that encircles the head of the humerus.
  • Surgical Neck: A narrower region distal to the anatomical neck, which is a common site for fractures.
  • Greater Tubercle: A large prominence on the lateral aspect of the humerus, providing attachment points for the supraspinatus, infraspinatus, and teres minor muscles.
  • Lesser Tubercle: A smaller prominence on the anterior aspect of the humerus, providing attachment for the subscapularis muscle.
  • Intertubercular Groove (Bicipital Groove): A groove between the greater and lesser tubercles that houses the tendon of the long head of the biceps brachii muscle.
  • Deltoid Tuberosity: A rough area on the lateral aspect of the humerus, serving as the insertion point for the deltoid muscle.
  • Lateral and Medial Epicondyles: Bony projections at the distal end of the humerus, providing attachment points for muscles of the forearm.
  • Capitulum: A rounded projection on the lateral aspect of the distal humerus that articulates with the head of the radius.
  • Trochlea: A spool-shaped projection on the medial aspect of the distal humerus that articulates with the ulna.
  • Olecranon Fossa: A deep depression on the posterior aspect of the distal humerus that accommodates the olecranon process of the ulna when the elbow is extended.

Muscles of the Upper Arm: The muscles of the upper arm are divided into anterior and posterior compartments, primarily responsible for flexion and extension of the elbow joint, respectively.

• Anterior Compartment:
  • Biceps Brachii: A two-headed muscle that flexes the elbow and supinates the forearm.
  • Brachialis: A muscle deep to the biceps brachii that is a powerful elbow flexor.
  • Coracobrachialis: A muscle that flexes and adducts the arm at the shoulder joint.
• Posterior Compartment:
  • Triceps Brachii: A three-headed muscle that extends the elbow.

The Forearm: Radius, Ulna, and Interconnecting Muscles

The forearm, also known as the antebrachium, extends from the elbow to the wrist and contains two bones: the radius and the ulna. These bones articulate with each other at the radioulnar joints (proximal and distal) and with the humerus at the elbow joint, allowing for pronation and supination of the forearm.

• Ulna: Located on the medial side of the forearm, the ulna articulates with the humerus at the elbow joint and with the radius at the radioulnar joints. Key features of the ulna include:

  • Olecranon Process: A prominent bony projection that forms the point of the elbow and articulates with the olecranon fossa of the humerus.
  • Coronoid Process: A triangular projection that articulates with the trochlea of the humerus.
  • Trochlear Notch: A concave surface between the olecranon and coronoid processes that articulates with the trochlea of the humerus.
  • Radial Notch: A small depression on the lateral aspect of the coronoid process that articulates with the head of the radius.
  • Ulnar Head: The distal end of the ulna, which articulates with the radius at the distal radioulnar joint.
  • Styloid Process: A pointed projection at the distal end of the ulna.

• Radius: Located on the lateral side of the forearm, the radius articulates with the humerus at the elbow joint, with the ulna at the radioulnar joints, and with the carpal bones (wrist bones) at the wrist joint. Key features of the radius include:

  • Head: A disc-shaped proximal end that articulates with the capitulum of the humerus and the radial notch of the ulna.
  • Radial Tuberosity: A bony prominence distal to the head that serves as the insertion point for the biceps brachii muscle.
  • Styloid Process: A pointed projection at the distal end of the radius.
  • Ulnar Notch: A depression on the medial aspect of the distal radius that articulates with the ulnar head.

Muscles of the Forearm: The muscles of the forearm are divided into anterior and posterior compartments, primarily responsible for flexion and extension of the wrist and fingers, as well as pronation and supination of the forearm.

• Anterior Compartment (primarily flexors and pronators):
  • Superficial Layer:
    • Pronator Teres: Pronates the forearm.
    • Flexor Carpi Radialis: Flexes and abducts the wrist.
    • Palmaris Longus: Flexes the wrist (not present in all individuals).
    • Flexor Carpi Ulnaris: Flexes and adducts the wrist.
  • Intermediate Layer:
    • Flexor Digitorum Superficialis: Flexes the wrist and the middle phalanges of the fingers.
  • Deep Layer:
    • Flexor Digitorum Profundus: Flexes the wrist and the distal phalanges of the fingers.
    • Flexor Pollicis Longus: Flexes the thumb.
    • Pronator Quadratus: Pronates the forearm.
• Posterior Compartment (primarily extensors and supinators):
  • Superficial Layer:
    • Brachioradialis: Flexes the elbow (unique in its location and function).
    • Extensor Carpi Radialis Longus: Extends and abducts the wrist.
    • Extensor Carpi Radialis Brevis: Extends and abducts the wrist.
    • Extensor Digitorum: Extends the wrist and fingers.
    • Extensor Digiti Minimi: Extends the little finger.
    • Extensor Carpi Ulnaris: Extends and adducts the wrist.
  • Deep Layer:
    • Supinator: Supinates the forearm.
    • Abductor Pollicis Longus: Abducts the thumb.
    • Extensor Pollicis Brevis: Extends the thumb.
    • Extensor Pollicis Longus: Extends the thumb.
    • Extensor Indicis: Extends the index finger.

The Wrist and Hand: Carpal Bones, Metacarpals, and Phalanges

The wrist and hand are complex structures that allow for fine motor control and manipulation of objects. The wrist consists of eight carpal bones arranged in two rows, while the hand consists of five metacarpal bones and fourteen phalanges.

• Carpal Bones: These eight small bones are tightly packed together and arranged in two rows:

  • Proximal Row (from lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform.
  • Distal Row (from lateral to medial): Trapezium, Trapezoid, Capitate, Hamate.
  • The scaphoid is the most commonly fractured carpal bone.

• Metacarpal Bones: These five bones form the palm of the hand. They are numbered I to V, starting with the thumb. Each metacarpal consists of a base, a shaft, and a head. The heads of the metacarpals form the knuckles.

• Phalanges: These bones form the fingers. Each finger (except the thumb) has three phalanges: proximal, middle, and distal. The thumb only has two phalanges: proximal and distal.

Muscles of the Wrist and Hand: The muscles that control the wrist and hand are located primarily in the forearm, with tendons extending into the wrist and hand. However, there are also intrinsic muscles located within the hand that contribute to fine motor control.

• Extrinsic Muscles (located in the forearm): As described in the forearm section, these muscles primarily flex and extend the wrist and fingers.
• Intrinsic Muscles (located within the hand): These muscles are responsible for fine motor movements of the fingers and thumb. They include:
  • Thenar Muscles (thumb): Abductor Pollicis Brevis, Flexor Pollicis Brevis, Opponens Pollicis, Adductor Pollicis.
  • Hypothenar Muscles (little finger): Abductor Digiti Minimi, Flexor Digiti Minimi Brevis, Opponens Digiti Minimi.
  • Interossei (between the metacarpals): Dorsal Interossei (abduct the fingers), Palmar Interossei (adduct the fingers).
  • Lumbricals: Flex the metacarpophalangeal joints and extend the interphalangeal joints.

Nerves and Blood Vessels of the Upper Limb

Understanding the innervation and vascular supply of the upper limb is critical for diagnosing and treating injuries and conditions affecting this region.

Nerves: The major nerves of the upper limb originate from the brachial plexus, a network of nerves formed by the ventral rami of spinal nerves C5-T1. The main nerves arising from the brachial plexus are:

• Musculocutaneous Nerve: Supplies the anterior compartment muscles of the upper arm (biceps brachii, brachialis, coracobrachialis) and provides cutaneous innervation to the lateral forearm.
• Axillary Nerve: Supplies the deltoid and teres minor muscles and provides cutaneous innervation to the lateral shoulder region.
• Radial Nerve: Supplies the posterior compartment muscles of the upper arm and forearm (triceps brachii, extensors of the wrist and fingers) and provides cutaneous innervation to the posterior arm, forearm, and dorsal hand.
• Median Nerve: Supplies most of the anterior forearm muscles (except flexor carpi ulnaris and ulnar half of flexor digitorum profundus) and thenar muscles of the hand (except adductor pollicis) and provides cutaneous innervation to the palmar aspect of the thumb, index, middle, and lateral half of the ring finger. It passes through the carpal tunnel at the wrist.
• Ulnar Nerve: Supplies the flexor carpi ulnaris and ulnar half of the flexor digitorum profundus in the forearm and most of the intrinsic muscles of the hand (except thenar muscles supplied by the median nerve). It provides cutaneous innervation to the palmar and dorsal aspects of the little finger and medial half of the ring finger.

Blood Vessels: The main artery supplying the upper limb is the subclavian artery, which becomes the axillary artery as it passes into the axilla (armpit). The axillary artery then becomes the brachial artery in the upper arm. The brachial artery divides into the radial artery and ulnar artery in the forearm, which supply the wrist and hand.

Common Injuries and Conditions of the Upper Limb

Understanding the anatomy of the upper limb is essential for recognizing and managing common injuries and conditions, including:

• Rotator Cuff Tears: Tears of the tendons of the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) are common, especially in athletes and older adults.
• Shoulder Impingement Syndrome: Compression of the rotator cuff tendons and bursa in the subacromial space, leading to pain and limited range of motion.
• Clavicle Fractures: Common fractures, especially in children and adolescents, often resulting from falls or direct blows to the shoulder.
• Elbow Dislocations: Displacement of the ulna and radius from the humerus at the elbow joint, often caused by falls onto an outstretched hand.
• Lateral Epicondylitis (Tennis Elbow): Inflammation of the tendons that attach to the lateral epicondyle of the humerus, causing pain on the outside of the elbow.
• Medial Epicondylitis (Golfer's Elbow): Inflammation of the tendons that attach to the medial epicondyle of the humerus, causing pain on the inside of the elbow.
• Carpal Tunnel Syndrome: Compression of the median nerve in the carpal tunnel at the wrist, leading to pain, numbness, and tingling in the hand and fingers.
• De Quervain's Tenosynovitis: Inflammation of the tendons of the abductor pollicis longus and extensor pollicis brevis muscles at the wrist, causing pain on the thumb side of the wrist.
• Fractures of the Radius and Ulna: Common fractures, often resulting from falls or direct blows to the forearm.
• Scaphoid Fractures: Fractures of the scaphoid bone in the wrist, which can be difficult to diagnose due to poor blood supply and risk of nonunion.
• Trigger Finger: A condition in which a finger gets stuck in a bent position and then snaps straight, caused by inflammation of the tendons in the finger.

Conclusion

Identifying the structures of the upper limb requires a thorough understanding of its complex anatomy, including the bones, muscles, nerves, and blood vessels. This knowledge is essential for healthcare professionals in diagnosing and treating injuries and conditions affecting the upper limb, as well as for athletes and anyone interested in understanding the mechanics of human movement. By mastering the anatomy of the upper limb, you can gain a deeper appreciation for the intricate design and function of this remarkable part of the human body. From the powerful movements of the shoulder to the delicate precision of the fingertips, the upper limb allows us to interact with our environment in countless ways. A strong understanding of its anatomy is the key to maintaining its health and optimizing its performance.