KNOW YOUR NERVES: A CLOSER LOOK AT THE ULNAR NERVE

When it comes to understanding the human anatomy, every single part is crucial. Each nerve, muscle, and bone plays a crucial role in keeping our bodies functioning correctly. Today, let’s focus on the ulnar nerve, which is often overlooked but plays a critical role in the arm and hand movements.

ULNAR NERVE ORIGIN

The ulnar nerve is the terminal branch of the medial cord of the brachial plexus. It primarily receives input from nerve segments C8 to T1, as well as C7.

ULNAR NERVE PATH

Tracing the path of the ulnar nerve, it traverses down the medial aspect of the upper arm. It then passes posterior to the medial epicondyle, coursing down the forearm by passing between the Flexor Carpi Ulnaris (FCU) and Flexor Digitorum Profundus (FDP). It finally becomes superficial in the distal forearm.

ULNAR NERVE INNERVATIONS

The ulnar nerve innervates a variety of muscles, each of which is critical for different functions. These muscles include the Flexor Carpi Ulnaris (FCU), the Palmaris Brevis (PB), the ulnar half of Flexor Digitorum Profundus (FDP) in the forearm, and the hypothenar muscles. It also innervates the interossei muscles, lumbricals, and the skin of the hand medial to the axial line of digit 4.

MUSCLE ACTIONS

Each muscle innervated by the ulnar nerve performs unique functions.

• The FCU is responsible for wrist flexion and wrist abduction.
• The Lumbricals and Interossei primarily flex MCPs while extending IP joints.
  • Dorsal Interossei abduct the palm, while palmar ones adduct fingers.
• The Palmaris Brevis moves the skin of the hypothenar eminence and protects the ulnar artery and nerve.
• The Flexor Digitorum Profundus (FDP) is the only muscle to flex the distal interphalangeal joint of the fingers, with its ulnar portion giving innervation to 4th-5th digits.
• Hypothenar muscles are responsible for flexion, abduction, and opposition of the pinky finger.

CLINICAL PEARLS: ULNAR NERVE INJURIES

Ulnar nerve injuries can manifest in several ways, and present with unique findings depending on the location of the injury along the arm.

• An impact to the medial elbow, also known as hitting your “funny bone,” can cause parathesias to the median part of the dorsum of the hand. Cubital Tunnel Syndrome leads to numbness or tingling in the medial one half of the palm and the medial one and half fingers.
• Distal forearm injuries can cause loss of intrinsic and interossei function. Symptoms of such injuries include lateral hand deviation when trying to flex the wrist, no opposition ability leading to hyperextended MCPs, and difficulty flexing 4th & 5th digits. When trying to straighten fingers, one cannot extend IP of 4th and 5th fingers, leading to a condition known as “Claw Hand”.

Equipped with this knowledge, you are now more aware of the importance and functions of the ulnar nerve. For more nerve education, follow us @integrativedryneedling. Understanding our nerves is crucial in maintaining our health and promoting efficient body function.

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