Brachial plexus

Brachial plexus
The right brachial plexus with its short branches, viewed from in front.
Details
Latin	plexus brachialis
From	C5, C6, C7, C8, T1
Innervates	Sensory and motor innervation to the upper limb
Identifiers
MeSH	A08.800.800.720.050
Dorlands /Elsevier	p_24/12647576
TA
TH	{{#property:P1694}}
TE	{{#property:P1693}}
FMA	{{#property:P1402}}
Anatomical terms of neuroanatomy [[[d:|edit on Wikidata]]]

The brachial plexus is a network of nerves, running from the spine, formed by the anterior rami of the lower four cervical nerves and first thoracic nerve (C5–C8, T1). The brachial plexus passes through the cervicoaxillary canal in the neck, over the first rib, and into the axilla (armpit region), where it innervates the upper limbs and some neck and shoulder muscles.

Structure

The brachial plexus is divided into five roots, three trunks, six divisions, three cords, and five branches. There are five "terminal" branches and numerous other "pre-terminal" or "collateral" branches that leave the plexus at various points along its length. A common structure used to identify part of the brachial plexus in cadaver dissections is the M or W shape made by the musculocutaneous nerve, lateral cord, median nerve, medial cord, and ulnar nerve.

Roots

The five roots are the five anterior rami of the spinal nerves, after they have given off their segmental supply to the muscles of the neck. The brachial plexus emerges at five different levels; C5, C6, C7, C8, and T1. C5 and C6 merge to establish the upper trunk, C7 continuously forms the middle trunk, and C8 and T1 merge to establish the lower trunk. Prefixed or postfixed formations in some cases involve C4 or T2, respectively. The dorsal scapular nerve comes from level C5 and innervates the rhomboid muscles which retract the scapula. The subclavian nerve originates in both C5 and C6 and innervates the subclavius, a muscle that involves lifting the first ribs during respiration. The long thoracic arise from C5, C6, and C7. This nerve innervates the serratus anterior, which draws the scapula laterally and is the prime mover in all forward-reaching and pushing actions.

Trunks

These roots merge to form three trunks:

• "superior" or "upper" (C5-C6)
• "middle" (C7)
• "inferior" or "lower" (C8, T1)

Divisions

Each trunk then splits in two, to form six divisions:

• anterior divisions of the upper, middle, and lower trunks
• posterior divisions of the upper, middle, and lower trunks
• when observing the body in an anatomical position, the anterior divisions are superficial to the posterior divisions

Cords

These six divisions regroup to become the three cords or large fiber bundles. The cords are named by their position with respect to the axillary artery.

• The posterior cord is formed from the three posterior divisions of the trunks (C5-C8,T1)
• The lateral cord is formed from the anterior divisions of the upper and middle trunks (C5-C7)
• The medial cord is simply a continuation of the anterior division of the lower trunk (C8,T1)

Branches

The branches are listed below. Most branch from the cords, but a few branch (indicated in italics) directly from earlier structures. The five on the left are considered "terminal branches". There have been several variations reported in the branching pattern but these are very rare.

Diagram

Anatomical illustration of the brachial plexus with areas of roots, trunks, divisions and cords marked. Clicking on names of branches will link to their Wikipedia entry.

Diagrammatic representation of the brachial plexus using colour to illustrate the contributions of each nerve root to the branches.

The brachial plexus, including all branches of the C5-T1 ventral primary rami. Includes mnemonics for learning the plexus' connections and branches.

Specific branches

Bold indicates primary spinal root component of nerve. Italics indicate spinal roots that frequently, but not always, contribute to the nerve.

From	Nerve	Roots	Muscles	Cutaneous
roots	dorsal scapular nerve	C4, C5	rhomboid muscles and levator scapulae	-
roots	long thoracic nerve	C5, C6, C7	serratus anterior	-
roots	branch to phrenic nerve	C5	Diaphragm	-
upper trunk	nerve to the subclavius	C5, C6	subclavius muscle	-
upper trunk	suprascapular nerve	C5, C6	supraspinatus and infraspinatus	-
lateral cord	lateral pectoral nerve	C5, C6, C7	pectoralis major and pectoralis minor (by communicating with the medial pectoral nerve)	-
lateral cord	musculocutaneous nerve	C5, C6, C7	coracobrachialis, brachialis and biceps brachii	becomes the lateral cutaneous nerve of the forearm
lateral cord	lateral root of the median nerve	C5, C6, C7	fibres to the median nerve	-
posterior cord	upper subscapular nerve	C5, C6	subscapularis (upper part)	-
posterior cord	thoracodorsal nerve (middle subscapular nerve)	C6, C7, C8	latissimus dorsi	-
posterior cord	lower subscapular nerve	C5, C6	subscapularis (lower part ) and teres major	-
posterior cord	axillary nerve	C5, C6	anterior branch: deltoid and a small area of overlying skin posterior branch: teres minor and deltoid muscles	posterior branch becomes upper lateral cutaneous nerve of the arm
posterior cord	radial nerve	C5, C6, C7, C8, T1	triceps brachii, supinator, anconeus, the extensor muscles of the forearm, and brachioradialis	skin of the posterior arm as the posterior cutaneous nerve of the arm. Also superficial branch of radial nerve supplies back of the hand, including the web of skin between the thumb and index finger.
medial cord	medial pectoral nerve	C8, T1	pectoralis major and pectoralis minor	-
medial cord	medial root of the median nerve	C8, T1	fibres to the median nerve	portions of hand not served by ulnar or radial
medial cord	medial cutaneous nerve of the arm	C8, T1	-	front and medial skin of the arm
medial cord	medial cutaneous nerve of the forearm	C8, T1	-	medial skin of the forearm
medial cord	ulnar nerve	C8, T1	flexor carpi ulnaris, the medial two bellies of flexor digitorum profundus, the intrinsic hand muscles except the thenar muscles and the two most lateral lumbricals	the skin of the medial side of the hand and medial one and a half fingers on the palmar side and medial two and a half fingers on the dorsal side

Function

The brachial plexus is responsible for cutaneous and muscular innervation of the entire upper limb, with two exceptions: the trapezius muscle innervated by the spinal accessory nerve (CN XI) and an area of skin near the axilla innervated by the intercostobrachial nerve. The brachial plexus communicates through the sympathetic trunk via gray rami communicantes that join the plexus roots.

Lesions can lead to severe functional impairment.

Clinical significance

Injury

Main article: Brachial plexus injury

Brachial plexus injury affects cutaneous sensations and movements in the upper limb. They can be caused by stretching, diseases, and wounds to the lateral cervical region (posterior triangle) of the neck or the axilla. Depending on the location of the injury, the signs and symptoms can range from complete paralysis to anesthesia. Testing the patient's ability to perform movements and comparing it to their normal side is a method to assess the degree of paralysis. A common brachial plexus injury is from a hard landing where the shoulder widely separates from the neck (such as in the case of motorcycle accidents or falling from a tree). These stretches can cause ruptures to the superior portions of the brachial plexus or avulse the roots from the spinal cord. Upper brachial plexus injuries are frequent in newborns when excessive stretching of the neck occurs during delivery. Studies have shown a relationship between birth weight and brachial plexus injuries; however, the number of cesarean deliveries necessary to prevent a single injury is high at most birth weights. For the upper brachial plexus injuries, paralysis occurs in those muscles supplied by C5 and C6 like the deltoid, biceps, brachialis, and brachioradialis. A loss of sensation in the lateral aspect of the upper limb is also common with such injuries. An inferior brachial plexus injury is far less common, but can occur when a person grasps something to break a fall or a baby's upper limb is pulled excessively during delivery. In this case, the short muscles of the hand would be affected and cause the inability to form a full fist position.

To differentiate between pre ganglionic and post ganglionic injury, clinical examination requires that the physician keep the following points in mind. Pre ganglionic injuries cause loss of sensation above the level of the clavicle, pain in an otherwise insensate hand, ipsilateral Horner's syndrome, and loss of function of muscles supplied by branches arising directly from roots—i.e., long thoracic nerve palsy leading to winging of scapula and elevation of ipsilateral diaphragm due to phrenic nerve palsy.

Acute brachial plexus neuritis is a neurological disorder that is characterized by the onset of severe pain in the shoulder region. Additionally, the compression of cords can cause pain radiating down the arm, numbness, paresthesia, erythema, and weakness of the hands. This kind of injury is common for people who have prolonged hyperabduction of the arm when they are performing tasks above their head.

Definition

Brachial plexus injuries are injuries that affect the nerves that carry signals from the spine to the shoulder. This can be caused by the shoulder being pushed down and the head being pulled up, which stretches or tears the nerves. Injuries associated with malpositioning commonly affect the brachial plexus nerves, rather than other peripheral nerve groups. Due to the brachial plexus nerves being very sensitive to position, there are very limited ways of preventing such injuries. The most common victims of brachial plexus injuries consist of victims of motor vehicle accidents and newborns.

Motorcycle accidents

Motorcyclists who are involved in accidents are very susceptible to brachial plexus injuries due to the nature of the collision. "Brachial plexus injuries were identified in 54 of 4538 patients presenting to a regional trauma facility… Motor vehicle accidents were the most frequent cause overall."

Many of these patients were forced to undergo reconstructive surgery. During physical therapy, the position of the brachial plexus became very important to avoid further damage. "The risk can be reduced by thorough release of the tissues from the inferior surface of the clavicle before mobilization of the fracture fragments." By wearing protective gear, like a helmet, a motorcyclist can help prevent nerve damage after collisions.

In this photo, the subject performs an example of a motorcyclist colliding with the floor at an angle, which may damage the brachial plexus nerves. The photo shows how head and shoulder are extremely separated, which may stretch or even tear the nerves in the between area. Protective gear can help prevent nerve damage by providing extra support on the opposite side of the head to prevent over-stretching the neck.

Sports Injuries

One sports injury that is becoming prevalent in contact sports, particularly in the sport of American football, is called a "stinger." An athlete can incur this injury in a collision that can cause cervical axial compression, flexion, or extension of nerve roots or terminal branches of the brachial plexus. In a study conducted on football players at United States Military Academy, researchers found that the most common mechanism of injury is, "the compression of the fixed brachial plexus between the shoulder pad and the superior medial scapula when the pad is pushed into the area of Erb's point, where the brachial plexus is most superficial.". The result of this is a "burning" or "stinging" pain that radiates from the region of the neck to the fingertips. Although this injury causes only a temporary sensation, in some cases it can cause chronic symptoms.

Penetrating Wounds

Most penetration wounds require immediate treatment and are not as easy to repair. For example, a laceration by a knife to the brachial plexus could damage and/or cut the nerve. According to where the cut was made, it could inhibit action potentials needed to innervate that nerve's specific muscle or muscles.

Injuries during birth

Brachial Plexus injuries also become an issue during the delivery of newborns. "…there were 80 brachial plexus injuries identified, for an incidence of 1–3 per 1000 live birth." Nerve damage has been connected to birth weight with larger newborns being more susceptible to the injury but it also has to do with the delivery methods. Although very hard to prevent during live birth, doctors must be able to deliver a newborn with precise and gentle movements to decrease chances of injuring the child.

Tumors

Tumors that may occur in the brachial plexus are schwannomas, neurofibromas and malignant peripheral nerve sheath tumors.

Imaging

Imaging of the Brachial Plexus can be done effectively by using a higher magnetic strength MRI Scanner like 1.5 T or more. It is impossible to evaluate the brachial plexuses with plain Xray, CT and ultrasound scanning can manage to view the plexuses to an extent; hence MRI is preferred in imaging brachial plexus over other imaging modalities due to its multiplanar capability and the tissue contrast difference between brachial plexus and adjacent vessels. The plexuses are best imaged in coronal and sagittal planes, but axial images give an idea about the nerve roots. Generally, T1 WI and T2 WI images are used in various planes for the imaging; but new sequences like MR Myelolography, Fiesta 3D and T2 cube are also used in addition to the basic sequences to gather more information to evaluate the anatomy more.

In anaesthetics

Main article: Brachial plexus block

Additional images

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  Mind map showing branches of brachial plexus

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  The axillary artery and its branches.

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  Nerves in the infraclavicular portion of the right brachial plexus in the axillary fossa.

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  Cutaneous nerves of right upper extremity.

• 

  Diagram of segmental distribution of the cutaneous nerves of the right upper extremity.

• 

  The right sympathetic chain and its connections with the thoracic, abdominal, and pelvic plexuses.

• 

  Dissection of brachial plexus

• 

  Brachial plexus

• 

  Brachial plexus

• 

  Brachial plexus

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  Spinal cord. Brachial plexus. Cerebrum.Inferior view.Deep dissection.

External links

• Brachial Plexus and Its Injury| Medchrome
• lesson3brachialplexus at The Anatomy Lesson by Wesley Norman (Georgetown University)
• Brachial Plexus Injury/Illustration, Cincinnati Children's Hospital Medical Center
• Learn the Brachial Plexus in Five Minutes or Less by Daniel S. Romm, M.D. and Dennis A. Chu Chu, M.D. [1]
• Video of the dissected axilla and Brachial Plexus