The forearm is the region of the upper limb situated between the elbow and the wrist. It enables a wide array of movements integral to daily activities, providing the framework and muscle power for precise hand and finger movements.
Forearm Bones
The forearm is supported by two long bones, the Radius and the Ulna, which run parallel to each other. The Radius is located on the lateral side, aligning with the thumb when the arm is in the anatomical position, while the Ulna lies on the medial side, corresponding to the pinky finger. These bones articulate with the humerus at the elbow joint, forming a hinge that allows for bending and straightening of the arm.
At the wrist, the distal end of the Radius connects directly with some of the carpal bones of the hand, playing a significant role in wrist joint formation. The Ulna also articulates with the Radius at both its proximal and distal ends, forming the radioulnar joints. A strong sheet of connective tissue, the interosseous membrane, connects the shafts of the Radius and Ulna, providing stability and an attachment site for muscles while allowing for specific rotational movements.
Muscles and Connective Tissues
The forearm houses numerous muscles, broadly categorized into two main compartments: the anterior (flexor) compartment and the posterior (extensor) compartment. The muscles in the anterior compartment are responsible for bending, or flexing, the wrist and fingers. Conversely, muscles in the posterior compartment facilitate the straightening, or extension, of the wrist and fingers.
The forearm also contains a network of tendons, which connect muscles to bones, and ligaments, which connect bones to other bones, providing stability. Major nerves, including the median, ulnar, and radial nerves, traverse the forearm, conveying signals for both movement and sensation to the hand and fingers. Blood supply to these tissues is provided by the radial and ulnar arteries, which branch from the brachial artery near the elbow and extend down the forearm.
Forearm Movements
The arrangement of the Radius and Ulna allows for rotational movements of the forearm, known as pronation and supination. Pronation involves rotating the forearm to turn the palm downwards or backward. Conversely, supination is the movement that rotates the forearm to turn the palm upwards or forwards.
These rotational movements occur as the Radius crosses over the Ulna (pronation) or returns to its parallel position (supination) at the radioulnar joints. Forearm muscles also contribute to the flexion and extension of the wrist and fingers, enabling a wide range of actions. These movements enable everyday tasks, including turning a doorknob, using a screwdriver, and carrying objects.