An upper extremity, also known as an upper limb, is the part of the human body that extends from the shoulder to the fingertips. It is a highly functional unit that allows for complex interactions with the surrounding environment. This anatomical region includes the arm, wrist, and hand, providing capabilities for a wide range of daily activities.
Anatomical Regions of the Upper Extremity
The upper extremity begins with the shoulder girdle, which forms the connection to the main body. This girdle consists of two bones: the clavicle (collarbone) and the scapula (shoulder blade). These bones work together to stabilize the shoulder region and allow for broad movements of the arm.
Extending from the shoulder is the arm proper, medically termed the brachium, which spans the area between the shoulder and the elbow joint. This segment contains a single long bone, the humerus. The forearm, or antebrachium, follows, located between the elbow and the wrist. It comprises two parallel bones, the radius and the ulna, which enable rotation of the hand.
The final segment is the hand, or manus, which includes the wrist, palm, and fingers. The wrist, or carpus, serves as a flexible connection between the forearm and the hand. Beyond the wrist, the palm is supported by metacarpal bones, leading to the phalanges that form the fingers and thumb.
Underlying Structures
Each upper limb contains 30 bones, forming the skeletal framework for support and movement. These include the clavicle, scapula, humerus, radius, ulna, and the bones of the wrist and hand.
Joints connect these bones, allowing for a wide array of motions. The shoulder joint, known as the glenohumeral joint, is a highly mobile ball-and-socket type, facilitating extensive arm movement. The elbow joint enables bending, straightening, and rotation of the forearm. The wrist joint connects the forearm to the carpal bones, and smaller joints are present within the hand and fingers.
Muscles overlay these bones and joints, providing the force for movement and maintaining stability. These include muscles around the shoulder, such as the deltoid and rotator cuff, which control arm elevation and rotation. Muscles in the arm, like the biceps and triceps, bend and straighten the elbow. The forearm contains muscles responsible for wrist and finger movements, while intrinsic hand muscles allow for fine dexterity.
An intricate network of nerves, primarily originating from the brachial plexus in the neck and shoulder, extends throughout the upper extremity. Major nerves, including the median, ulnar, and radial nerves, transmit signals from the brain to the muscles, enabling voluntary movement, and carry sensory information back to the brain. Blood vessels, comprising arteries and veins, ensure a continuous supply of oxygen and nutrients to the tissues and remove waste products. The subclavian, axillary, brachial, radial, and ulnar arteries deliver blood, while corresponding veins return it to the heart.
Critical Roles in Daily Life
The upper extremity performs essential roles in human daily life, enabling interaction with the environment. It facilitates reaching for objects, grasping them, lifting items, and carrying various loads. These actions involve coordinated movements across the shoulder, elbow, and wrist joints, supported by the strength of the arm and hand muscles.
Fine motor skills, which rely on the small muscles of the hands and fingers, are performed extensively by the upper extremity. Tasks such as writing, typing on a keyboard, fastening buttons, tying shoelaces, and manipulating small tools or utensils depend on these precise movements. Threading beads or turning the pages of a book are additional examples of activities that showcase the dexterity of the hand.
The upper extremity also engages in gross motor skills, which involve larger, more sweeping movements. Examples include throwing a ball, catching an object, waving, or pushing heavy items. These actions require the coordinated effort of larger muscle groups in the arm and shoulder. Beyond manipulation, the upper limb plays a role in communication through gestures and writing, and is fundamental for personal self-care activities like eating, dressing, and grooming.