Brachial Plexus Anatomy

Brachial Plexus

Definition

• A network of nerve fibers that originate in the spinal cord and branch out to form the nerves of the upper limb
• Extends from the neck to the axilla (armpit)

Formation

• Formed by the ventral rami of spinal nerves C5-T1
• Divided into five roots, three trunks, six divisions, three cords, and five terminal branches

Roots

• Five roots: C5, C6, C7, C8, and T1
• Emerge from the spinal cord and combine to form trunks

Trunks

• Three trunks: superior, middle, and inferior
• Each trunk divides into an anterior and posterior division

Divisions

• Six divisions: three anterior and three posterior
• Divisions from each trunk merge to form cords

Cords

• Three cords: lateral, medial, and posterior
• Cords give rise to the terminal branches

Terminal Branches

• Five terminal branches:
  1. Musculocutaneous nerve
  2. Axillary nerve
  3. Radial nerve
  4. Median nerve
  5. Ulnar nerve
• These nerves distribute to the upper limb, controlling motor and sensory functions

Clinical Relevance

• Brachial plexus injuries can result from trauma, tumors, or birth injuries
• Symptoms include weakness, numbness, or paralysis in the upper limb
• Diagnosis involves physical examination, electromyography, and imaging studies

Brachial Plexus

Definition and Location

• A network of nerve fibers originating in the spinal cord and branching out to form the nerves of the upper limb
• Extends from the neck to the axilla (armpit)

Formation and Composition

• Formed by the ventral rami of spinal nerves C5-T1
• Composed of five roots, three trunks, six divisions, three cords, and five terminal branches

Roots

• Five roots emerge from the spinal cord: C5, C6, C7, C8, and T1
• Roots combine to form trunks

Trunks

• Three trunks: superior, middle, and inferior
• Each trunk divides into an anterior and posterior division

Divisions

• Six divisions: three anterior and three posterior
• Divisions from each trunk merge to form cords

Cords

• Three cords: lateral, medial, and posterior
• Cords give rise to the terminal branches

Terminal Branches

• Five terminal branches:
  • Musculocutaneous nerve
  • Axillary nerve
  • Radial nerve
  • Median nerve
  • Ulnar nerve
• These nerves distribute to the upper limb, controlling motor and sensory functions

Clinical Relevance

• Brachial plexus injuries can result from trauma, tumors, or birth injuries
• Symptoms include weakness, numbness, or paralysis in the upper limb
• Diagnosis involves physical examination, electromyography, and imaging studies

Brachial Plexus

Anatomy

• The brachial plexus is a network of nerves originating from the spinal cord (C5-T1) and extending from the neck to the axilla
• It is divided into five roots, three trunks, six divisions, three cords, and five branches
• The five roots (C5-T1) merge to form three trunks, which then divide into anterior and posterior divisions
• The three cords (lateral, medial, and posterior) are formed from the divisions, and various nerves arise from the cords

Injuries

• Brachial plexus injuries can occur due to trauma, such as motorcycle accidents or falls
• The severity of injuries can range from mild (neurapraxia) to severe (avulsion)
• Injuries can result in weakness or paralysis of the arm, numbness or tingling in the arm or hand, and pain or burning sensations in the arm or hand

Recovery

• Spontaneous recovery is possible in some cases, especially for mild injuries
• Physical therapy and occupational therapy are necessary to maintain range of motion and prevent contractures
• Surgical intervention may be necessary for more severe injuries
• Rehabilitation can be lengthy, taking months to years, and may require ongoing therapy

Nerve Roots

• The C5-C6 roots are primarily responsible for motor function, such as shoulder abduction and elbow flexion
• The C7 root has mixed motor and sensory function, including elbow extension and wrist flexion
• The C8-T1 roots are primarily responsible for sensory function, including hand sensation

Surgical Repair

• Surgical repair is indicated for severe injuries, such as avulsion or rupture
• The goals of surgical repair are to restore motor and sensory function and alleviate pain
• Techniques used in surgical repair include nerve grafting or transfer, nerve repair or reconstruction, and tendon or muscle transfer
• Surgical outcomes vary, and recovery can be lengthy and challenging

Muscles and Nerves of the Forearm and Arm

Forearm Muscles

• Pronator Teres:
  • Origin: Medial epicondyle (superficial head), coronoid process (deep head)
  • Insertion: Mid-lateral radius below anterior oblique line
  • Action: Pronation of radius and ulna, stabilization of elbow
• Flexor Carpi Radialis:
  • Origin: Medial epicondyle
  • Insertion: Base of 2nd and 3rd metacarpal
  • Action: Flexion of wrist, radial deviation, stabilization of elbow
• Palmaris Longus:
  • Origin: Medial epicondyle
  • Insertion: Palmar aponeurosis
  • Action: Flexion of wrist, stabilization of elbow
• Flexor Digitorum Superficialis:
  • Origin: Medial epicondyle, coronoid process, anterior oblique line of radius
  • Insertion: Sides of middle phalanx of digits 2-5
  • Action: Flexion of proximal interphalangeal and metacarpophalangeal joints, wrist flexion, stabilization of elbow
• Flexor Digitorum Profundus:
  • Origin: Proximal ¾ of medial and anterior ulna, adjacent interosseous membrane
  • Insertion: Bases of distal phalanges of digits 2-5
  • Action: Flexion of distal interphalangeal and metacarpophalangeal joints, wrist flexion
• Flexor Pollicis Longus:
  • Origin: Middle ½ of anterior radius, adjacent interosseous membrane
  • Insertion: Base of distal phalanx of thumb
  • Action: Flexion of interphalangeal and metacarpophalangeal joints, wrist flexion, stabilization of elbow
• Pronator Quadratus:
  • Origin: Distal ¼ of ulna
  • Insertion: Distal ¼ of radius
  • Action: Pronation of radius and ulna

Long Thoracic Nerve

• Innervates Serratus Anterior:
  • Origin: Upper 8 ribs at mid-axillary line
  • Insertion: Deep medial border of scapula
  • Action: Protraction of scapula, upward rotation, stabilization of scapula

Dorsal Scapular Nerve

• Innervates skin over deltoid region

Radial Nerve

• Passes through radial groove, sends off 6 branches
• Innervates:
  • Triceps Brachii (3 branches)
    • Origin: Long head (infraglenoid tubercle and capsule), lateral head (posterior humerus lateral to radial groove), medial head (posterior humerus medial to radial groove)
    • Insertion: Olecranon process
    • Action: Extension of elbow, adduction of humerus
  • Anconeous:
    • Origin: Lateral epicondyle
    • Insertion: Lateral olecranon and proximal shaft of ulna
    • Action: Stabilization of elbow
  • Skin of posterior arm and forearm
• Passes through radial groove, intermuscular septum between lateral head of triceps and brachialis, and innervates:
  • Brachioradialis:
    • Origin: Lateral supracondylar ridge
    • Insertion: Styloid process of radius
    • Action: Flexion of elbow
  • Extensor Carpi Radialis Longus:
    • Origin: Lateral supracondylar ridge
    • Insertion: Base of 2nd metacarpal
    • Action: Extension of wrist, radial deviation, stabilization of elbow
• Ends by dividing into superficial and deep radial nerves
• Superficial radial nerve: Innervates skin of dorsal hand and thumb
• Deep radial nerve: Innervates:
  • Supinator:
    • Origin: Posterior ulna below radial notch
    • Insertion: Posterior, anterior, and lateral proximal 1/3 of radius
    • Action: Supination of radius and ulna
  • Extensor Carp Radialis Brevis:
    • Origin: Lateral epicondyle
    • Insertion: Base of 3rd metacarpal
    • Action: Extension of wrist, radial deviation, stabilization of elbow