Ulnar, Radial, Median Nerve

Nerves

1. Ulnar Nerve

The ulnar nerve originates from the medial cord of the brachial plexus.  In the forearm it innervates only one and a half muscles.  The ulnar nerve does not give rise to branches during its passage through the arm.   It becomes superficial in the distal forearm.  In the hand, the ulnar nerve provides muscle innervations to most of the muscles. The “funny bone” is actually the point in the arm where the ulnar nerve, passes posterior to the medial epicondyle of the humerus at the elbow. 

                The ulnar nerve is the largest in the body that is unprotected by bone or muscle.  Ulnar nerve injury is common at the funny bone.  The injury results when the medial part of the elbow hits a hard surface and compresses the ulnar nerve. Severe compression produces pain at the elbow that radiates downward.  Ulnar nerve injury usually produces numbness and tingling of the medial part of the palm and the medial one and a half fingers.  Ulnar nerve injury can result in extensive motor and sensory loss to the hand.

Radial Nerve

                The radial nerve provides motor and sensory function in both the arm and forearm.  It branches from the brachial plexus.  The radial nerve divides into a superficial and deep branch in the forearm.   The radial nerve supplies the posterior upper limb muscles, as well as all 12 muscles in the posterior osteofascial compartment of the forearm.  The posterior cutaneous nerve of the forearm arises from the radial nerve in the posterior compartment of the arm and reaches the forearm independent of the radial nerve.  The superficial branch of the radial nerve is also a cutaneous nerve, but it gives rise to articular branches as well.  The deep branch of the radial nerve, also termed the posterior interosseous nerve, runs in between the superficial and deep extensor muscles of the forearm.

                The radial nerve is usually injured in the arm by a fracture of the humeral shaft.  Injury to the deep branch of the radial nerve may occur when wound of the posterior forearm are deep.  If the deep branch of the radial nerve is severed, the inability to extend the thumb and the joints of other digits could occur.  If the superficial branch of the radial nerve is severed, anesthesia occurs to the distal bases of the first and second metacarpals.

Median Nerve

                The median nerve arises from the brachial plexus.  The median nerve is the main source of innervations of the anterior compartment of the forearm.  The only branches that the median nerve has in the arm are small and travel to the brachial artery.  The median nerve branches more in the fore arm.  The major branch of the forearm is the anterior interosseous nerve.  The median nerve supplies branches to most of the muscles of the superficial and intermediate layers in the forearm.

                The most common site for lesion of the median nerve is where it passes through the carpal tunnel.  The median nerve is the most sensitive structure in the tunnel.  It has two terminal sensory branches that supply the sin of the hand.  The median nerve also has a terminal motor branch that serves the thenar muscles.  Loss of coordination and strength in the thumb may occur.  People with carpal tunnel syndrome are unable to oppose the thumb and have difficulty with every day tasks.

Clinically Oriented Anatomy

http://anatomy.med.umich.edu/musculoskeletal_system/hand_tables.html

http://en.wikipedia.org/wiki/Radial_nerve