KNOW YOUR NERVES: THE MEDIAN NERVE

Understanding the human body, especially the nervous system, can be a daunting task due to its intricate nature and complex functionality. Today, we will unravel the complexities of the median nerve, one of the principal nerves located in the human arm.

Characteristics of the Median Nerve

The median nerve is unique as it has no branches in the axilla or arm. However, it does supply articular branches to the elbow joint. Primarily, the median nerve innervates the anterior (flexor/pronator) muscle groups of the forearm. This nerve is critical in transmitting sensory and motor information between the spinal cord and parts of the arm and hand.

What Does the Median Nerve Innervate?

The median nerve innervates a large number of areas, including:

• the articular surfaces of the elbow joint,
• the sensation on the palmar side of the radial 3.5 fingers.
• muscles such as:
  • the Flexor Carpi Radialis (FCR),
  • Palmaris Longus (PL),
  • lateral half of Flexor Digitorum Profundus (FDP) (digits 2/3),
  • Flexor Digitorum Superficialis (FDS),
  • Pronator Quadratus (PQ)
  • Pronator Teres (PT).
  • 4 Thenar Muscles (abductor pollicus, adductor pollicis, oppenens pollicis, and flexor pollicis brevis)

Muscle Actions of the Median Nerve

Each muscle innervated by the median nerve has a specific function.

• The Flexor Carpi Radialis is responsible for wrist flexion and abduction.
• The Pronator Quadratus and Pronator Teres work together for the pronation of the forearm, with the latter helping hold the ulna and radius together.
• The Thenar Muscles are responsible for the flexion, abduction, and opposition of the thumb.
• The Flexor Digitorum Superficialis allows for the flexion of MCP and IP of all fingers independently, while the Flexor Digitorum Profundus is the only muscle that can flex the distal IP of fingers.

Clinical Pearls: Median Nerve Injuries

Due to its extensive distribution, the median nerve is often subject to injuries, leading to several syndromes.

Pronator Syndrome is one such condition, where median nerve entrapment in the pronator teres results in decreased sensation in the radial 3.5 digits.

Another condition is the Anterior Interosseous Syndrome, which impairs the flexion of digits 1-3, and weakness in digits 4 & 5; and distal phalanx flexion in digits 2 & 3 is absent. It’s often noticed when a patient is unable to make an “ok” sign.

A common median nerve injury is Carpal Tunnel Syndrome, which results in the weakness of the thenar muscles and progressively decreased sensation in the median nerve distribution of the hand.

Equipped with Knowledge

Understanding the median nerve helps us appreciate the intricacies of the human body and how every component plays a crucial role in our daily functioning. We hope this information has been helpful and informative. Follow us for more nerve education and take a deep dive into the fascinating world of human anatomy!

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Source: Clinically Oriented Anatomy; Keith L Moore et al; 8th edition