Brachial Plexus and Upper Limb Innervation

Overview of the Brachial Plexus

• Brachial plexus innervates the upper limb and arises from five spinal roots: C5-T1, with minor contributions from C4 and T2.
• Located between the anterior and middle scalene muscles.

Trunks of the Brachial Plexus

• Comprised of three trunks:
  • Superior trunk: C5-C6
  • Middle trunk: C7
  • Inferior trunk: C8-T1
• Each trunk divides into anterior and posterior divisions, which contribute to the formation of three cords.

Formation of Cords

• Lateral cord: Created from anterior divisions of the superior and middle trunks.
• Medial cord: Formed solely from the anterior division of the inferior trunk.
• Posterior cord: Comprises the posterior divisions of all three trunks.

Branches and Terminal Nerves

• Main functions are mediated through terminal branches (peripheral nerves) originating from each cord.
• Notable branches include:
  • Dorsal scapular nerve (C5): Innervates rhomboids and levator scapulae.
  • Long thoracic nerve (C5-C7): Innervates serratus anterior.

Long Thoracic Nerve Palsy

• Characterized by winged scapula due to weakness in the serratus anterior muscle, affecting shoulder movement.

Important Diagnostic Signs

• Erb-Duchenne palsy: Occurs due to trauma at Erb's point, affecting C5-C6 innervated muscles, leading to a "waiter's tip" posture.
• Klumpke’s palsy: Affects C8-T1, causes hand weakness and potential atrophy of hypothenar muscles.

Horner's Syndrome

• Results from damage to the T1 root, presenting symptoms like miosis and ptosis on the affected side.

Important Nerves and Their Functions

• Lateral pectoral nerve: Innervates pectoralis major.
• Musculocutaneous nerve: Innervates coracobrachialis, biceps, and brachialis; becomes lateral cutaneous nerve of forearm.
• Ulnar nerve: Governs finger movement, innervates flexors on the ulnar side.
• Median nerve: Controls thumb flexion and some intrinsic hand muscles, critical for grip.
• Axillary nerve: Involved in shoulder abduction and sensory supply to the skin covering the deltoid muscle.

Common Injuries and Their Effects

• Axillary nerve injury can lead to loss of shoulder abduction and sensory changes in the upper arm.
• Ulnar nerve injuries may cause claw hand or cubital tunnel syndrome, affecting hand function.
• Musculocutaneous nerve injuries are rare but can impact elbow flexion.

Cubitus Valgus and Guyon Canal Syndrome

• Cubitus valgus can result from elbow fractures, causing nerve compression.
• Guyon canal syndrome involves ulnar nerve compression, leading to motor deficits without sensory loss.

Additional Notes on Nerve Pathways

• Median nerve travels underneath the flexor muscle layer to enter the carpal tunnel, important for its relationship to carpal tunnel syndrome.
• The radial nerve is vital for extending the arm and hand and receives its origin from the posterior cord.

Clinical Implications

• Injury presentations depend on the level and structure affected within the brachial plexus, emphasizing the interconnectedness of arm function and potential complications from various accidents and surgeries.### Median Nerve
• Responsible for motor function in the thenar eminence: controls abductor, short flexor, and opponens muscles of the thumb.
• Palmar digital branches supply sensation to the fingertips of the index and middle fingers.
• Common lesions occur due to various causes:
  • Compression when sleeping awkwardly (honeymoon palsy).
  • Humeral fractures and shoulder dislocation.
  • Puncture wounds and wrist injuries (cuts or carpal tunnel compression).
• High lesion symptoms include:
  • "Preacher's hand" indicative of paralysis in flexors and pronators.
  • Loss of thumb opposition.
  • Reduced volume in the palm.
• Low lesion outcome: carpal tunnel syndrome, often due to repetitive wrist movements, pregnancy, or underlying health conditions like diabetes.

Radial Nerve

• Innervates muscles in the extensor compartment of the arm and forearm; provides sensory input to the back of the hand.
• Originates from the posterior secondary trunk near the armpit and travels along the radial sulcus, making it prone to injury from fractures.
• The nerve runs between the brachialis and brachioradialis muscles, branching into:
  • Cutaneous nerves supplying the upper limb.
  • Posterior interosseous branch associated with multiple extensor muscles.
• Lesion effects typically result in "wrist drop," characterized by impaired wrist and finger extension.

Cutaneous Innervation in Upper Limbs

• Different colors represent branches of the brachial plexus pertinent to sensory distribution:
  • Orange: supraclavicular branches
  • Grey: upper lateral cutaneous nerve
  • Ocher: medial cutaneous nerve of the arm
  • Red: lateral and posterior cutaneous nerves
  • Purple: medial cutaneous nerve of the forearm
  • Green: lateral cutaneous nerve of the forearm
  • Yellow: median nerve
  • Blue: ulnar nerve
• Understanding the distinct sensory branches is crucial for diagnosing peripheral nerve injuries.

Dermatomes of Upper Limbs

• Dermatomal distribution differs from cutaneous innervation due to the merging of spinal nerves in the brachial plexus.
• Each color in dermatomes aligns with spinal cord neuromeres, aiding in visualizing nerve damage locations.
• Knowledge of motor and sensory distributions is vital for effective treatment of peripheral nerve lesions.

This quiz covers the anatomy and innervation of the upper limb, specifically focusing on the brachial plexus as detailed in the Vercelli L02 lesson. You will explore the formation of the plexus from spinal roots and its significance in upper limb function. Test your knowledge on the structures involved and their respective contributions.