The brachial plexus is a network of nerves that originates in the spinal cord at the root of the neck, passes through the axilla, and runs through the entire upper extremity. It is formed by the anterior rami (divisions) of the cervical spinal nerves C5, C6, C7, and C8, and the first thoracic spinal nerve, T1. At the base of the neck, the roots of the brachial plexus converge to form three trunks: the Superior trunk (composed of C5 and C6 roots), the Middle trunk (continuation of C7), and the Inferior trunk (composed of C8 and T1 roots). The three trunks divide into two branches within the posterior triangle of the neck – an anterior division and a posterior division – which combine to form three cords, named by their position relative to the axillary artery: the lateral cord, the posterior cord, and the medial cord. These, in turn, give rise to the five major nerves of the brachial plexus, which are responsible for supplying the skin and musculature of the upper limb.
The five major branches of the brachial plexus are the Musculocutaneous Nerve, Axillary Nerve, Median Nerve, Radial Nerve, and Ulnar Nerve. The Musculocutaneous Nerve supplies the brachialis, biceps brachii, and coracobrachialis muscles, and gives off the lateral cutaneous branch of the forearm which innervates the lateral half of the anterior forearm, and a small lateral portion of the posterior forearm. The Axillary Nerve innervates the teres minor and deltoid muscles, and gives off the superior lateral cutaneous nerve of arm which innervates the inferior region of the deltoid. The Median Nerve innervates most of the flexor muscles in the forearm, the thenar muscles, and the two lateral lumbricals associated with the index and middle fingers, and gives off the palmar cutaneous branch, which innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand. The Radial Nerve innervates the triceps brachii, and the muscles in the posterior compartment of the forearm, and innervates the posterior aspect of the arm and forearm, and the posterolateral aspect of the hand. The Ulnar Nerve supplies the muscles of the hand (apart from the thenar muscles and two lateral lumbricals), flexor carpi ulnaris and medial half of flexor digitorum profundus, and innervates the anterior and posterior surfaces of the medial one and half fingers, and associated palm area.
In addition to the five major branches, the Brachial Plexus has a number of smaller nerves that arise from all five parts of the Plexus: the Dorsal scapular Nerve, Long thoracic Nerve, Suprascapular Nerve, Nerve to subclavius, Lateral pectoral Nerve, Medial pectoral Nerve, Medial cutaneous nerve of arm, Medial cutaneous nerve of forearm, Superior subscapular Nerve, Thoracodorsal Nerve, and Inferior subscapular Nerve. These nerves provide innervation to the muscles and skin throughout the upper limb.
Upper Brachial Plexus Injury, or Erb's Palsy, typically occurs as a result of a stretching injury during a difficult vaginal delivery and affects the C5-6 roots. It is characterized by weakness in the muscles of the upper limb, particularly those innervated by the C5-C6 spinal roots, and is typically associated with a lack of movement, reflexes, and sensation in the affected area.
The brachial plexus is an intricate network of nerves that provides innervation to the skin and muscles of the upper limb. It is composed of five major branches – the Musculocutaneous Nerve, Axillary Nerve, Median Nerve, Radial Nerve, and Ulnar Nerve – and numerous smaller nerves. Upper Brachial Plexus Injury, or Erb's Palsy, is a stretching injury that affects the C5-6 roots and is typically associated with a lack of movement, reflexes, and sensation in the affected area.
The brachial plexus is a specialized network of nerve fibres that supplies the skin and musculature of the upper limb. It unfolds from the root of the neck, passes through the axilla, and elongates into the entire upper extremity. Comprised of the anterior rami (divisions) of cervical spinal nerves C5, C6, C7 and C8, as well as the first thoracic spinal nerve, T1, the brachial plexus is formed by pairs of spinal nerves that branch off at each vertebral level and exit the spinal cord through its respective intervertebral foramina.
The brachial plexus consists of four roots, the superior trunk (formed by C5 and C6), the middle trunk (C7), and the inferior trunk (made up of C8 and T1). These roots converge to form three trunks at the base of the neck, two of which travel laterally through the posterior triangle of the neck. As they pass through the triangle, each trunk divides into an anterior and posterior division. The divisions leave the triangle and enter the axilla, where they recombine to form three cords – the lateral, the medial, and the posterior.
From the axilla and down the proximal aspect of the upper limb, the three cords give rise to five major branches. Each nerve continues into the upper limb to provide innervation to the muscles and skin present. These major branches are the musculocutaneous nerve, axillary nerve, median nerve, radial nerve, and the ulnar nerve.
Together, the musculocutaneous, axillary, suprascapular, and nerve to subclavius nerves, as well as the supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid, teres minor, abduction at shoulder, lateral rotation of arm, supination of forearm, and flexion at shoulder muscles are all innervated by the brachial plexus. This intricate network of nerve fibres serves to transmit sensory and motor signals between the spine and the upper extremity.
The brachial plexus is one of the most important, complex and sensitive structures in the body. It is responsible for a variety of important functions in the upper limb, making it vital for proper functioning and movement of the arms and hands. Any damage to this network of nerves can cause serious impairments and disabilities. It is, therefore, important to maintain a healthy lifestyle and consult a doctor at the first signs of any pain or discomfort in this area.
The brachial plexus is an intricate network of nerves that originate from the spinal cord and extend to the arm. It consists of five major nerve roots — the musculocutaneous, axillary, median, radial, and ulnar nerves — and an arrangement of nerves known as the “M” shape, which includes the ulnar, median, and musculocutaneous nerves. Minor branches from all five parts of the plexus are the dorsal scapular nerve, the long thoracic nerve, the suprascapular nerve, the nerve to subclavius, the lateral pectoral nerve, the medial pectoral nerve, the medial cutaneous nerve of the arm, the medial cutaneous nerve of the forearm, the superior subscapular nerve, the thoracodorsal nerve, and the inferior subscapular nerve.
Understanding the sensory functions of the brachial plexus is important for recognizing and locating it during a dissection of the upper limb. It can be difficult to recognize when dissecting due to it typically appearing as a mass of nerves. A key shape to look for is an ‘M’ shape, which is formed by the median, ulnar, and musculocutaneous nerves and is usually found superficial to the axillary artery.
Injuries to certain parts of the brachial plexus can cause significant medical issues, known as Erb's and Klumpke's palsies. Erb's palsy, otherwise known as Erb-Duchenne palsy, affects the C5-6 roots of the plexus, resulting in damage to the musculocutaneous, axillary, suprascapular, and nerve to subclavius nerves. Muscles commonly affected by Erb's palsy include the supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid, and teres minor. Motor functions affected by this condition include the abduction at the shoulder, lateral rotation of the arm, supination of the forearm, and flexion at the shoulder. Sensory functions affected include sensation over the lateral aspect of the upper limb.
Klumpke's palsy involves the C8-T1 roots of the plexus and results in damage to the ulnar and median nerves, along with the intrinsic hand muscles. Sensory functions are affected along the medial side of the upper limb. The most characteristic feature of Klumpke's palsy is a clawed hand due to paralysis of the lumbrical muscles.
When considering the practical relevance of the brachial plexus, understanding the anatomy and the sensory functions is crucial. The brachial plexus is responsible for motor and sensory functions of the upper limb, and identifying any abnormalities or deficiencies can have serious consequences. Thus it is important to have a comprehensive understanding of the anatomy and function of this complex network of nerves.
