The brachial plexus is a network of nerves that gives rise to all the motor and sensory nerves of the upper extremity. This plexus arises from the anterior rami of spinal nerves C5-T1 that undergo several mergers and splits into trunks and divisions, until they finally give rise to their terminal branches. These terminal branches are responsible for motor and sensory innervation of the upper limb, and they include the musculocutaneous, axillary, radial, median and ulnar nerves.
In addition to terminal branches, the brachial plexus gives rise to several preterminal branches called supraclavicular branches, which leave the plexus at various points along its length.
The brachial plexus can be a very challenging topic to understand due to its complex origin, branching, and relations and students often get lost while reading the textbooks. For this reason, we’ve prepared a clear and concise overview of the brachial plexus, as well as mnemonics and other learning hacks that will help you understand and memorize the brachial plexus.
This article will discuss the anatomy and functions of the brachial plexus.
|Roots||C5, C6, C7, C8, T1|
|Divisions||Three anterior divisions
- Anterior division of superior trunk
- Anterior division of middle trunk
- Anterior division of inferior trunk
Three posterior divisions
- Posterior division of superior trunk
- Posterior division of middle trunk
- Posterior division of inferior trunk
|Innervation||Complete sensory and motor innervation of the arm|
|Organization||'Rugby Teams Don't Cover Bruises'
(standing for: Roots, Trunks, Divisions, Cords, Branches
|Lateral cord branches||'Rugby players are Long Legged Movers'
(standing for: Lateral pectoral nerve, Lateral root of median nerve, Musculocutaneous nerve)
|Medial cord branches||'Rugby players Make Many Moves Using Muscles'
(standing for: Medial cutaneous brachial nerve, Medial cutaneous antebrachial nerve, Medial pectoral nerve, Ulnar nerve, Median root of median nerve)
|Posterior cord branches||'Rugby players are ULTRA competitive'
(standing for: Upper subscapular nerve, Lower subscapular nerve, Thoracodorsal nerve, Radial nerve, Axillary nerve)
(standing for Dropped wrist = Radial nerve lesion, Claw hand = Ulnar nerve lesion, Ape hand = Median nerve lesion)
- Supraclavicular branches
- Branches of the lateral cord
- Branches of medial cord
- Branches of posterior cord
- Clinical relations
So, the brachial plexus originates from the anterior rami of spinal nerves C5-T1, which are the roots of the brachial plexus. The roots quickly merge to form the trunks, which subsequently split into divisions. Finally, the divisions merge into cords of the brachial plexus, that give off the terminal branches of the brachial plexus.
Aside from the terminal branches of the brachial plexus, there are several nerves that branch off from previous segments of the plexus. These ‘preterminal branches’ arise from the trunks and roots and are collectively called the supraclavicular branches of the brachial plexus. The cords themselves are called the infraclavicular branches of the brachial plexus, while the nerves that branch off from the cords are the terminal branches of the brachial plexus.
The brachial plexus begins as the anterior branches of C5-T1 spinal nerves emerge from the spinal cord. Soon after their origin, these 5 nerve roots unite to form three trunks; superior, medial and inferior.
This segment of the brachial plexus gives rise to three lateral branches: dorsal scapular nerve, long thoracic nerve and intercostal nerve.
Each trunk has a well-known scheme of origin from the roots of the brachial plexus:
- The superior trunk is formed by the roots of C5 and C6.
- The middle trunk is formed from the root of C7 only.
- The inferior trunk is formed by the roots of C8 and T1.
How to easily remember this: imagine that your fingers are the five anterior branches (C5-T1), where C5 is the thumb and T1 is the little finger. When you connect the thumb (C5) with the index finger (C6), you get the superior trunk. The middle finger (C7) stands alone and forms the middle trunk, while the ring finger (C8) and the little finger (T1) connect to form the inferior trunk.
Upon their origin, the trunks pass over the base of the posterior triangle of the neck, traveling between the anterior and middle scalene muscles and behind the subclavian artery. The trunks then cross over the apex of the lung and the first rib and course towards the clavicle.
In this segment of the brachial plexus, the superior trunk gives rise to another couple of supraclavicular branches: the suprascapular nerve and the subclavian nerve (nerve to subclavius).
Flashcards are a really effective way to study the trunks of the brachial plexus. Find out how you can easily make your own ones!
As they reach the posterior aspect of the middle third of the clavicle, each of the 3 trunks divides into an anterior and posterior division. This yields a total of 6 divisions (3 anterior and 3 posterior), which continue to pass inferiorly behind the clavicle to enter the axillary region.
The divisions do not give rise to any branches. Instead, they go on to merge with one another to build the next segment of the brachial plexus: the cords.
The cords of the brachial plexus are formed by the 3 anterior and 3 posterior divisions that merge in a specific way:
- The lateral cord is formed by the merger of the anterior division of the superior trunk and anterior division of the middle trunk.
- The medial cord is a direct continuation of the anterior division of the inferior trunk.
- The posterior cord is formed by the merger of the posterior divisions of all three trunks.
The cords are placed around and named after their relationship with the second part of the axillary artery. Hence, it is easy to remember that the lateral cord is placed laterally, the medial cord lies medially, and the posterior cord lies posterior to the axillary artery.
The lateral and medial cords innervate the muscles of the anterior (flexor) compartment of the forearm, whereas the posterior cord innervates the muscles of the posterior (extensor) compartment of the forearm.
Each of the cords gives off one or more preterminal branches.
- The lateral cord gives rise to the lateral pectoral nerve.
The posterior cord gives rise to the upper subscapular nerve, thoracodorsal nerve and lower subscapular nerve.
The medial cord gives rise to the medial pectoral nerve, medial cutaneous nerve of the arm and medial cutaneous nerve of the forearm.
The cords terminate on the level of the inferior margin of the pectoralis minor muscle, by elongating into their respective terminal branches:
The lateral cord extends into the musculocutaneous nerve and the lateral root of the median nerve.
The posterior cord extends into the radial nerve and axillary nerve.
The medial cord extends into the ulnar nerve and the medial root of the median nerve.
Dorsal scapular nerve
The dorsal scapular nerve most commonly arises directly from the root of C5 spinal nerve. Occasionally, it can arise from the superior trunk of the brachial plexus. The dorsal scapular nerve provides motor innervation to the levator scapulae, rhomboid major and rhomboid minor muscles.
The suprascapular nerve emerges from the superior trunk and carries fibers of the C5 and C6. The suprascapular nerve provides sensory innervation to the glenohumeral and acromioclavicular joints, and motor innervation to the supraspinatus and infraspinatus muscles.
Long thoracic nerve
The long thoracic nerve arises from the merger of the roots of C5, C6 and C7. This nerve provides motor innervation to the serratus anterior muscle.
This nerve emerges from the superior trunk of the brachial plexus and contains fibers of C5 and C6 spinal nerves. The subclavian nerve provides motor innervation to the subclavius muscle.
Branches of the lateral cord
The lateral cord gives rise to a couple of preterminal branches; the lateral pectoral nerve and lateral root of median nerve. It also gives off one of the terminal branches of the brachial plexus, the musculocutaneous nerve.
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Lateral pectoral nerves
The lateral pectoral nerves arise from the lateral cord of brachial plexus and carry fibers of C5, C6 and C7 spinal nerves. Through the anastomoses with the medial pectoral nerves, the lateral nerves participate in the innervation of the pectoralis minor muscle.
Lateral root of median nerve
This is a short branch which is one of the two roots of the median nerve. It quickly merges with the medial root, a branch of the medial cord, to form the median nerve.
The musculocutaneous nerve is a terminal branch of the lateral cord of the brachial plexus, carrying fibers of C5-C7 spinal nerves. It is a mixed nerve that provides both motor and sensory supply to the upper limb.
The motor fibers of the musculocutaneous nerve innervate the muscles of the anterior arm, namely the biceps brachii, coracobrachialis and brachialis muscle. The sensory fibers of the musculocutaneous nerve innervate the skin over the lateral surface of the forearm via the lateral cutaneous nerve of the forearm.
Branches of medial cord
The medial cord gives off the medial pectoral nerve, medial brachial cutaneous nerve, medial antebrachial cutaneous nerve, medial root of median nerve, as well as the ulnar nerve (another terminal branch of brachial plexus).
Medial pectoral nerves
The medial pectoral nerves arise from the medial cord of the brachial plexus, containing fibers of C8 and T1 spinal nerves. This nerve provides motor innervation to the pectoralis minor muscle and the lower sternocostal part of the pectoralis major muscle.
Medial brachial cutaneous nerve
The medial brachial cutaneous nerve, also called the medial cutaneous nerve of the arm, arises from the medial cord carrying fibers of C8 and T1 spinal nerves. This nerve provides sensory innervation to the skin of the inferior portion of the medial side of the arm.
Medial antebrachial cutaneous nerve
The medial antebrachial cutaneous nerve, also called the medial cutaneous nerve of the forearm, arises from the medial cord carrying fibers of T1 spinal nerve. This nerve provides sensory innervation to the skin of the arm overlying the biceps brachii, and the skin of the medial side of the forearm.
Medial root of median nerve
The medial root of the median nerve is the second source of the median nerve. It merges with the above mentioned lateral root to form the trunk of the median nerve.
The ulnar nerve is a terminal branch of the medial cord of the brachial plexus that contains fibers of C8 and T1 spinal nerves. Similarly to the median nerve, the ulnar nerve is a mixed nerve that supplies motor and sensory innervation to the forearm and hand.
The ulnar nerves provides motor supply to the following:
- The remaining muscles of the forearm not supplied by the median nerve (flexor carpi ulnaris muscle, medial ½ of the flexor digitorum profundus).
- All intrinsic muscles of the hand, except for the LOAF muscles (lateral two lumbricals, opponens pollicis, abductor pollicis brevis and flexor pollicis brevis).
The ulnar nerve provides sensory supply to the following:
- Skin on the anterior and posterior aspect of the medial ½ of the palm.
- Skin on the anterior and posterior aspect of the medial 1½ fingers.
An easy way to remember the motor supply of the hand by the ulnar nerve is by using the following mnemonic.
The ulnar nerve supplies the HILA muscles of the hand:
Branches of posterior cord
The posterior cord of the brachial plexus gives rise to the subscapular, thoracodorsal and axillary nerves, as well as to the radial nerve (another terminal branch).
There are usually two of these nerves: superior subscapular and inferior subscapular nerve. Both of these nerves arise from the posterior cord carrying the fibers of C5 spinal nerve. The superior subscapular nerve innervates the superior portion of the subscapularis muscle, whereas the inferior subscapular nerve innervates the rest of the subscapularis muscle, as well as the teres major muscle.
The thoracodorsal nerve arises from the posterior cord of the brachial plexus and carries the fibers of C7 and C8. This nerve provides motor innervation to the latissimus dorsi muscle.
The axillary nerve is one of the terminal branches of the posterior cord, carrying fibers of C5 and C7 spinal nerves. This nerve is a mixed nerve that provides both motor and sensory innervation to the shoulder region. The axillary nerve supplies the deltoid and teres muscle, as well as the skin over the deltoid muscle.
The radial nerve is the second terminal branch of the posterior cord of the brachial plexus, that contains fibers of spinal nerves C5-T1. This nerve is a mixed nerve that provides motor and sensory innervation to the arm and forearm.
The radial nerve provides motor supply to the following:
- All muscles of the posterior compartment of the arm (triceps brachii muscle).
- All muscles of the posterior compartment of the forearm (brachioradialis, anconeus, supinator, extensor carpi radialis longus and brevis, extensor carpi ulnaris, extensor digitorum, extensor pollicis longus and brevis, extensor indicis, extensor digiti minimi, abductor pollicis longus).
The radial nerve provides sensory supply to the following:
- Skin on the posterior surface of the arm.
- Skin on the central, posterior surface of the forearm.
- Skin on the lateral surface of the dorsum of the hand.
- Skin on the posterior aspect of the lateral 2½ fingers.
The median nerve is formed by the merger of two roots that arise from the lateral and medial cord of the brachial plexus:
- The lateral root of median nerve, which is a terminal branch of the lateral cord.
- The medial root of median nerve, which is a terminal branch of the medial cord.
The median nerve courses over the entire upper limb and terminates in the hand by dividing into its terminal branches. It is a mixed nerve that provides motor and sensory innervation to several regions of the forearm and hand.
The median nerve provides motor supply to the following:
- All muscles of the anterior (flexor) compartment of the forearm except for the flexor carpi ulnaris and the medial ½ of the flexor digitorum profundus.
- All thenar muscles (abductor pollicis brevis, flexor pollicis brevis and opponens pollicis), except for the adductor pollicis.
- Two lateral lumbrical muscles.
The median nerve provides sensory supply to the following:
- Skin of the lateral ½ of the palm.
- Skin on the anterior aspect of the lateral 3½ fingers.
- Skin on the posterior aspect of the lateral 2½ fingers.
An easy way to remember the motor supply of the hand by the median nerve is by using the following mnemonic.
The median nerve supplies the LOAF muscles of the hand:
- Lateral two lumbricals
- Opponens pollicis
- Abductor pollicis brevis
- Flexor pollicis brevis
The overall organization of the brachial plexus is the basis of all subsequent nerve branches in the upper limb and thus is one of the favourite exam topics of anatomy professors. Prepare yourself on time and master it using the following mnemonic!
Rugby Teams Don't Cover Bruises
However, the above organization is a piece of cake compared to all the lateral and terminal branches of the brachial plexus and their sources. The following mnemonic can give you a hand to remember them!
Lateral cord branches: Rugby players are Long Legged Movers
- Lateral pectoral nerves
- Lateral root of median nerve
- Musculocutaneous nerve
Medial cord branches: Rugby players Make Many Moves Using Muscles
- Medial pectoral
- Medial cutaneous nerve of arm
- Medial cutaneous nerve of forearm
- Ulnar nerve
- Medial root of median nerve
Posterior cord branches: Rugby players are ULTRA competitive
- Upper subscapular
- Lower subscapular
- Thoracodorsal nerve
- Radial nerve
- Axillary nerve
Solidify your knowledge with our quiz:
Brachial plexus injury
Injuries to the brachial plexus affect both motor and sensory functions in the upper limb. Different injuries, such as inflammation, stretching, and wounds in the lateral cervical region of the neck or in the axilla may cause brachial plexus injuries, and the manifestations depend on the part of the plexus that is affected. In any case, injuries to the brachial plexus are followed by paralysis and anesthesia of the respective supply area of the affected nerves.
Median nerve injury
In case of the median nerve involvement, the injury causes a palsy that results in a hand deformity called ape hand. It manifests as an inability to abduct the thumb. In addition, it is accompanied by a loss of sensation in the lateral 3½ fingers.
Ulnar nerve injury
An injury of the ulnar nerve causes a characteristic hand deformity called the claw hand, which is a result of the paralysis of intrinsic hand muscles innervated by this nerve. The claw hand deformity is characterized by hyperextended metacarpophalangeal joints, and flexed interphalangeal joints.
Radial nerve injury
Injuries of the radial nerves result in a wrist drop, due to the paralysis of all the muscles of the posterior compartment of the forearm that are supplied by the radial nerve.
Here is a helpful mnemonic to help you remember the above nerve injuries and associated hand lesions.
- Drop = Radial nerve
- Claw = Ulnar nerve
- Median nerve = Ape (Apostle's) hand
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