The human hand is capable of both powerful grips and delicate, precise movements. This dexterity is possible due to an intricate network of nerves that transmit signals between the brain and the hand’s muscles and sensory receptors. Understanding the pathways of these nerves reveals their sophisticated organization.
Key Nerves and Their Pathways
Three primary nerves extend from the forearm into the hand: the median nerve, the ulnar nerve, and the radial nerve. Each follows a distinct anatomical route, supplying different regions of the hand.
Median Nerve
The median nerve descends through the forearm. Before reaching the hand, it passes through a narrow passageway at the wrist known as the carpal tunnel. Upon exiting the carpal tunnel, the median nerve branches out, with a branch supplying muscles at the base of the thumb and other branches extending into the fingers.
Ulnar Nerve
The ulnar nerve courses down the medial side of the arm, passing behind the medial epicondyle of the humerus at the elbow, an area commonly referred to as the “funny bone.” From the elbow, it continues into the forearm, traveling along the ulna bone. At the wrist, the ulnar nerve enters the hand through a space called Guyon’s canal, located near the pinky finger side of the palm. Within the hand, it then divides into superficial and deep branches.
Radial Nerve
The radial nerve descends along the back of the arm, wrapping around the humerus bone. As it approaches the elbow, it divides into two main branches: a superficial radial nerve and a deep radial nerve. The superficial branch continues down the forearm, primarily providing sensory innervation, and enters the hand on the thumb side. The deep branch provides motor innervation to muscles in the forearm that extend the wrist and fingers.
How Nerves Power Sensation and Movement
Each of these three major nerves plays a specific role in providing both sensation and movement to different parts of the hand. This division of labor ensures comprehensive coverage for complex hand functions.
Median Nerve
The median nerve is responsible for the sensation on the palm side of the thumb, index finger, middle finger, and the thumb side half of the ring finger. In terms of movement, the median nerve controls muscles that allow for bending of the wrist, thumb, index, and middle fingers, as well as the ability to rotate the forearm to turn the palm downward. It specifically innervates the muscles at the base of the thumb, enabling actions like grasping and pinching.
Ulnar Nerve
The ulnar nerve primarily governs sensation in the little finger and the pinky-side half of the ring finger, both on the palm and back of the hand. It is also responsible for the movement of most of the small muscles within the hand. These muscles enable fine motor skills such as spreading and bringing the fingers together, gripping objects, and other precise movements.
Radial Nerve
The radial nerve supplies sensory information to the back of the hand, particularly on the thumb side, including the web space between the thumb and index finger. Its motor functions are centered on extending the wrist and fingers. This allows for straightening the wrist and opening the hand from a clenched fist position.
Understanding Vulnerable Nerve Locations
Despite their protected pathways, certain anatomical locations make the hand’s major nerves susceptible to compression or injury. These areas often involve nerves passing through confined spaces or lying superficially.
Median Nerve
The median nerve is particularly vulnerable at the wrist as it passes through the carpal tunnel. This tunnel is a narrow passageway formed by wrist bones and a strong ligament, and any swelling or pressure within this space can compress the median nerve.
Ulnar Nerve
The ulnar nerve has two notable points of vulnerability. At the elbow, it passes through the cubital tunnel, a tight space behind the medial epicondyle, where it is close to the skin. Further down in the wrist, the ulnar nerve can also be compressed as it travels through Guyon’s canal, a narrow channel on the pinky finger side of the palm.
Radial Nerve
The radial nerve is susceptible to injury along the upper arm, especially as it wraps around the humerus bone. Fractures or direct pressure in this area can affect the nerve due to its close proximity to the bone.