The term “brachial” refers to the arm, specifically the upper arm region situated between the shoulder and the elbow. This area is formally known as the brachium in anatomical terminology. The brachial region serves as a crucial segment of the upper limb, providing the leverage and mobility necessary for most activities of the hand and forearm. Contained within this section are several major structures, including a long bone, powerful muscle groups, and the main pathways for blood and nerve signals. Understanding the structures within the upper arm is important for appreciating the full function and potential issues that can arise in this part of the body.
Defining the Brachial Region
The boundaries of the brachial region extend from the shoulder joint down to the elbow joint. It is structurally defined by the humerus, a single long bone that connects the scapula to the bones of the forearm. This long bone provides the foundation for muscle attachments and movement in the upper arm.
The musculature of this region is divided into anterior and posterior compartments, separated by connective tissue known as septa. The anterior compartment primarily contains flexor muscles, such as the biceps brachii, which is responsible for bending the elbow. The posterior compartment contains the triceps brachii, the major extensor muscle that straightens the elbow. The collective action of these muscles allows for powerful movements and positioning of the forearm and hand.
Role of the Brachial Artery
The brachial artery is the principal blood vessel supplying oxygenated blood to the entire upper limb beyond the shoulder. It begins as a continuation of the axillary artery after passing the lower border of the teres major muscle. The artery then travels down the inner side of the arm, accompanying the median nerve for much of its course.
This vessel gives off several branches, including the deep brachial artery, which travels posteriorly to supply the triceps muscle and the humerus. The location of the brachial artery is significant in clinical practice. Its pulse can be easily felt and is the site where healthcare professionals typically place a stethoscope when measuring blood pressure.
Near the elbow, the brachial artery is situated close to the skin surface, making it an accessible point for medical evaluation. Within the cubital fossa, the brachial artery divides into its two terminal branches. These branches are the radial artery and the ulnar artery, which continue to supply the forearm and the hand.
Function of the Brachial Plexus
The brachial plexus is an intricate web of nerves that arises from the spinal cord (C5 through T1) to govern the motor and sensory functions of the entire upper extremity. Its main purpose is to relay signals from the brain to the arm muscles, initiating movement, and to carry sensory information back from the skin and joints.
The organization of the plexus follows a distinct anatomical hierarchy: Roots, Trunks, Divisions, Cords, and Branches. The five nerve roots combine to form three trunks, which then split into six divisions, ultimately regrouping to form three cords named for their relationship to the axillary artery. From these cords emerge the major peripheral nerves of the arm, including the musculocutaneous, axillary, radial, median, and ulnar nerves.
This neural pathway ensures that every muscle and area of sensation in the arm, forearm, and hand receives its proper nerve supply. The musculocutaneous nerve, for instance, supplies the anterior compartment muscles, such as the biceps, enabling elbow flexion. The radial nerve supplies the posterior compartment muscles, like the triceps, which are responsible for extension. Any disruption along the path of the brachial plexus can lead to widespread loss of movement or feeling in the limb.
Common Conditions Affecting the Brachial Area
The brachial region is susceptible to various conditions, many of which involve trauma to the humerus or the neurovascular structures. Fractures of the humerus, particularly spiral fractures in the middle shaft, can injure the radial nerve because of its close anatomical relationship as it wraps around the bone. Such damage can result in weakness of the wrist and finger extensor muscles.
Injuries to the brachial plexus often occur from excessive stretching or traction, such as those sustained in high-impact motor vehicle accidents or contact sports. These traumas can range from a mild stretch, known as neuropraxia, to the most severe injury, avulsion, where the nerve root is torn completely from the spinal cord. Depending on the location of the damage, a person may experience paralysis, loss of sensation, or intense pain in the arm and hand.
Other less common but serious conditions include a brachial artery occlusion, which is a blockage of the main blood vessel. Though the arm has alternative, smaller vessels for blood flow, a sudden, complete blockage can lead to ischemia, potentially causing severe muscle and nerve damage. Furthermore, trauma to the arm can sometimes lead to compartment syndrome, a condition where swelling and bleeding within the muscle compartments create dangerously high pressure that compromises blood flow and nerve function.