Nerves of the Arm and Hand

[Continued from above] . . . are sent from various parts of the brain and spinal cord; some come from sense organs located in the joints, ligaments, and tendons; and some come from the muscles themselves.

The nerves of the arm and hand include the brachial plexus, musculocutaneous, radial, median, and ulnar. The brachial plexus allows, for the most part, the whole upper limb to invert. It is actually a nerve fiber network that runs from the spine, along the neck and armpit area, and then enters the arm. The musculocutaneous nerve also starts in the spine and works its way throughout the arm’s lateral side.

The radial nerve supplies muscles on the back of the arms and the skin of the forearms and hands. The median nerve passes down the full length of the arm into the hand. It's a branch of the brachial plexus and is one of the main nerves in the arm. It is responsible for controlling the forearm and hand muscles. It also enables the rotation of the forearm palm-inwards. Feelings from the index finger, thumb, middle finger, part of the ring finger, and the area of the palm at the base of these fingers and thumb are conveyed by way of the median nerve. The ulnar nerves are branches stemming from the cervical nerves, which supply impulses to and from the muscles of the forearms and hands and from the skin of the hands.

As major sensory components of the body, the hands are the destination for a majority of the nerves in this part of the nervous system. They house a myriad of sensory nerve endings to detect pressure and temperature through the skin cells of the palm. Even the hand muscles, which perform very delicate and precise movements, are driven by about 200,000 neurons.

All of which allows the peripheral nerves in the arms and hands to collect information about the external conditions in relation to the body's internal state, to analyze this information, and to initiate appropriate responses to satisfy certain needs. The speed at which we can, for instance, remove our hand from a surprisingly hot surface exemplifies the power of the central and peripheral nervous systems in coordination within the upper extremities. Remarkably, the nervous system transmits such messages to the brain at speeds of 180 miles per hour!