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Brachial plexus

Overview

The brachial plexus
Plexus
A plexus is a network. In biology the term plexus has multiple meanings:-Nervous system:In many animals the processes of neurons join together to form a plexus or nerve net.-In vertebrates:...

is an arrangement of nerve fibers, running from the spine, formed by the ventral rami of the lower cervical and upper thoracic nerve root

Spinal nerve

The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. The spinal nerve is the bit that passes out of the vertebrae through the intervertebral foramen. All spinal nerves are part of the peripheral nervous...

, specifically from below the fifth cervical vertebra to above the first thoracic vertebra (C5

Cervical spinal nerve 5

The cervical spinal nerve 5 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 5 ....

-T1

Thoracic spinal nerve 1

The thoracic spinal nerve 1 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 1 ....

). It proceeds through the neck, the axilla (armpit region), and into the arm.

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 intercostobrachialis nerve.

Because the majority of the upper limb muscles are innervated by the brachial plexus, lesions can lead to severe functional impairment.

One can remember the order of brachial plexus elements by way of the mnemonic, "Read The Damn Cadaver Book" (Or, alternatively, Real Teenagers Drink Cold Beer") - Roots, Trunks, Divisions, Cords, Branches or - Roots, Trunks, Divisions, Cords, Collateral/Pre-terminal Branches, and (Terminal) Branches.

The five roots are the five anterior rami of the spinal nerve
Spinal nerve
The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. The spinal nerve is the bit that passes out of the vertebrae through the intervertebral foramen. All spinal nerves are part of the peripheral nervous...

s, after they have given off their segmental supply to the muscles of the neck
Neck
The neck is the part of the body on many terrestrial or secondarily aquatic vertebrates that distinguishes the head from the torso or trunk. The Latin term signifying "of the neck" is cervical.-Bony anatomy: The cervical spine:...

.

These roots merge to form three trunks:
- "superior" or "upper" (C5
  Cervical spinal nerve 5
  The cervical spinal nerve 5 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 5 ....
  
  -C6
  Cervical spinal nerve 6
  The cervical spinal nerve 6 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 6 ....
  
  )
- "middle" (C7
  Cervical spinal nerve 7
  The cervical spinal nerve 7 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 7 ....
  
  )
- "inferior" or "lower" (C8
  Cervical spinal nerve 8
  The cervical spinal nerve 8 is a spinal nerve of the cervical segment.It originates from the spinal column from below the cervical vertebra 7 ....
  
  -T1
  Thoracic spinal nerve 1
  The thoracic spinal nerve 1 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 1 ....
  
  )

Each trunk then splits in two, to form six divisions:
- anterior division of the upper, middle, and lower trunks
- posterior division of the upper, middle, and lower trunks

These six divisions will regroup to become the three cords.

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Encyclopedia

Spinal nerve

, specifically from below the fifth cervical vertebra to above the first thoracic vertebra (C5

Cervical spinal nerve 5

The cervical spinal nerve 5 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 5 ....

-T1

Thoracic spinal nerve 1

The thoracic spinal nerve 1 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 1 ....

). It proceeds through the neck, the axilla (armpit region), and into the arm.

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 intercostobrachialis nerve.

Because the majority of the upper limb muscles are innervated by the brachial plexus, lesions can lead to severe functional impairment.

Path

One can remember the order of brachial plexus elements by way of the mnemonic, "Read The Damn Cadaver Book" (Or, alternatively, Real Teenagers Drink Cold Beer") - Roots, Trunks, Divisions, Cords, Branches or - Roots, Trunks, Divisions, Cords, Collateral/Pre-terminal Branches, and (Terminal) Branches.

The five roots are the five anterior rami of the spinal nerve
Spinal nerve
The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. The spinal nerve is the bit that passes out of the vertebrae through the intervertebral foramen. All spinal nerves are part of the peripheral nervous...

s, after they have given off their segmental supply to the muscles of the neck
Neck
The neck is the part of the body on many terrestrial or secondarily aquatic vertebrates that distinguishes the head from the torso or trunk. The Latin term signifying "of the neck" is cervical.-Bony anatomy: The cervical spine:...

.

These roots merge to form three trunks:
- "superior" or "upper" (C5
  Cervical spinal nerve 5
  The cervical spinal nerve 5 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 5 ....
  
  -C6
  Cervical spinal nerve 6
  The cervical spinal nerve 6 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 6 ....
  
  )
- "middle" (C7
  Cervical spinal nerve 7
  The cervical spinal nerve 7 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 7 ....
  
  )
- "inferior" or "lower" (C8
  Cervical spinal nerve 8
  The cervical spinal nerve 8 is a spinal nerve of the cervical segment.It originates from the spinal column from below the cervical vertebra 7 ....
  
  -T1
  Thoracic spinal nerve 1
  The thoracic spinal nerve 1 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 1 ....
  
  )

Each trunk then splits in two, to form six divisions:
- anterior division of the upper, middle, and lower trunks
- posterior division of the upper, middle, and lower trunks

These six divisions will regroup to become the three cords. The cords are named by their position with respect to the axillary artery
Axillary artery
In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla and the upper limb...

.
- The posterior cord
  Posterior cord
  The posterior cord is a part of the brachial plexus. It consists of contributions from all of the roots of the brachial plexus.The posterior cord gives rise to the following nerves:-External links: - "Axilla, dissection, anterior view"*...
  
  is formed from the three posterior divisions of the trunks (C5-T1)
- The lateral cord
  Lateral cord
  The Lateral cord is a division of the brachial plexus.The lateral cord gives rise to the following nerves:*The lateral pectoral nerve, C5, C6 and C7 to the pectoralis major muscle*The musculocutaneous nerve which innervates the biceps muscle...
  
  is the anterior divisions from the upper and middle trunks (C5-C7)
- The medial cord
  Medial cord
  The Medial cord is a division of the brachial plexus.The medial cord gives rise to the following nerves:*The median pectoral nerve, C8 and T1, to the pectoralis muscle*The medial brachial cutaneous nerve, T1...
  
  is simply a continuation of the anterior division of the lower trunk (C8-T1)

The branches are listed below. Most branch from the cords, but a few branch (indicated in italics) directly from earlier structures. The five in bold are considered "terminal branches".

Specific branches

One can remember the specific branches of lateral, posterior and medial cord using the mnemonic LML ULNAR M4U respectively.

LML - lateral pectoral nerve
Lateral pectoral nerve
The lateral pectoral nerve arises from the lateral cord of the brachial plexus, and through it from the fifth, sixth, and seventh cervical nerves....

, musculocutaneous nerve
Musculocutaneous nerve
The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis minor, its fibers being derived from C5, C6, C7.-Path:...

, lateral root of the median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....

.
ULNAR - upper subscapular nerve
Upper subscapular nerve
The upper subscapular enters the upper part of the Subscapularis, and is frequently represented by two branches. It is derived from C5, C6 nerve fibers, and branches from the posterior cord of the brachial plexus....

, lower subscapular nerve
Lower subscapular nerve
The lower subscapular nerve is a nerve that supplies the lower part of the subscapularis muscle, and also supplies the teres major muscle....

, nerve to latissmus dorsi (thoracodorsal nerve
Thoracodorsal nerve
The thoracodorsal nerve is a nerve present in humans and other animals. It is also known as the middle subscapular nerve or the long subscapular nerve. It supplies the latissimus dorsi muscle....

) , axillary nerve
Axillary nerve
The axillary nerve is a nerve of the human body, that comes off the posterior cord of the brachial plexus at the level of the axilla and carries nerve fibers from C5 and C6...

, radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm, as well as the associated joints and overlying skin.It originates from the posterior...

.

M4U - medial pectoral nerve

Medial pectoral nerve

The medial pectoral nerve arises from the medial cord of the plexus and through it from the eighth cervical and first thoracic....

, medial root of the median nerve

Median nerve

The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....

, medial cutaneous nerve of the arm , medial cutaneous nerve of the forearm , ulnar nerve

Ulnar nerve

In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar nerve is the largest unprotected nerve in the human body , and the only unprotected nerve that does not serve a purely sensory function...

From	Nerve	Roots	Muscles	Cutaneous Cutaneous innervation Cutaneous innervation refers to the area of the skin which is supplied by a specific nerve, that is, by a cutaneous nerve.Dermatomes are similar; however, a dermatome only specifies the area served by a spinal nerve...
roots	dorsal scapular nerve Dorsal scapular nerve The dorsal scapular nerve arises from the brachial plexus, usually from the plexus root of C5.It provides motor innervation to the rhomboid muscles, which pull the scapula towards the spine and levator scapulae muscle, which elevates the scapula....	C5 Cervical spinal nerve 5 The cervical spinal nerve 5 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 5 ....	rhomboid muscle Rhomboid muscle The rhomboid muscles, often simply called the rhomboids, are rhombus-shaped muscles associated with the scapula and are chiefly responsible for its retraction. There are two rhomboid muscles:* Rhomboid major muscle* Rhomboid minor muscle... s and levator scapulae	-
roots	long thoracic nerve Long thoracic nerve The long thoracic nerve supplies the Serratus anterior. This nerve characteristically arises by three roots from the fifth, sixth, and seventh cervical nerves but the root from C7 may be absent...	C5, C6 Cervical spinal nerve 6 The cervical spinal nerve 6 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 6 .... , C7 Cervical spinal nerve 7 The cervical spinal nerve 7 is a spinal nerve of the cervical segment..It originates from the spinal column from above the cervical vertebra 7 ....	serratus anterior	-
superior trunk	nerve to the subclavius Nerve to the subclavius The nerve to the Subclavius is a small filament, which arises from the point of junction of the fifth and sixth cervical nerves....	C5, C6	subclavius muscle Subclavius muscle The Subclavius is a small triangular muscle, placed between the clavicle and the first rib.Along with the pectoralis major and pectoralis minor muscles, the subclavius muscle makes up the anterior wall of the axilla.-Origin and insertion:...	-
superior trunk	suprascapular nerve Suprascapular nerve The suprascapular nerve arises from the trunk formed by the union of the fifth and sixth cervical nerves. It innervates the supraspinatus muscles and infraspinatus muscles....	C5, C6	supraspinatus and infraspinatus	-
lateral cord	lateral pectoral nerve Lateral pectoral nerve The lateral pectoral nerve arises from the lateral cord of the brachial plexus, and through it from the fifth, sixth, and seventh cervical nerves....	C5, C6, C7	pectoralis major (by communicating with the medial pectoral nerve Medial pectoral nerve The medial pectoral nerve arises from the medial cord of the plexus and through it from the eighth cervical and first thoracic.... )	-
lateral cord	musculocutaneous nerve Musculocutaneous nerve The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis minor, its fibers being derived from C5, C6, C7.-Path:...	C5, C6, C7	coracobrachialis, brachialis and biceps brachii	becomes the lateral cutaneous nerve of the forearm
lateral cord	lateral root of the median nerve Median nerve The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....	C5, C6, C7	fibres to the median nerve	-
posterior cord	upper subscapular nerve Upper subscapular nerve The upper subscapular enters the upper part of the Subscapularis, and is frequently represented by two branches. It is derived from C5, C6 nerve fibers, and branches from the posterior cord of the brachial plexus....	C5, C6	subscapularis (upper part)	-
posterior cord	thoracodorsal nerve Thoracodorsal nerve The thoracodorsal nerve is a nerve present in humans and other animals. It is also known as the middle subscapular nerve or the long subscapular nerve. It supplies the latissimus dorsi muscle.... (middle subscapular nerve)	C6, C7, C8	latissimus dorsi	-
posterior cord	lower subscapular nerve Lower subscapular nerve The lower subscapular nerve is a nerve that supplies the lower part of the subscapularis muscle, and also supplies the teres major muscle....	C5, C6	subscapularis (lower part ) and teres major	-
posterior cord	axillary nerve Axillary nerve The axillary nerve is a nerve of the human body, that comes off the posterior cord of the brachial plexus at the level of the axilla and carries nerve fibers from C5 and C6...	C5, C6	anterior branch: deltoid Deltoid Deltoid can refer to:* The deltoid muscle, a muscle in the shoulder* Kite , also known as a deltoid, a type of quadrilateral* A deltoid curve, a three-sided hypocycloid* A leaf shape* The deltoid tuberosity, a part of the humerus... 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 Radial nerve The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm, as well as the associated joints and overlying skin.It originates from the posterior...	C5, C6, C7, C8, T1	triceps brachii, supinator, anconeus, the extensor muscle Extensor muscle An extensor muscle is any muscle that opens a joint increasing the angle between components of a limb, such as straightening the knee or elbow and bending the wrist or spine. With the exception of the knee joint the movement is directed backward... s of the forearm Forearm The forearm is the structure and distal region of the upper limb, between the elbow and the wrist.. The term forearm is used in anatomy to distinguish it from the arm which is often misused to describe the entire appendage of the upper limb and technically means only the region of the upper arm... , and brachioradialis Brachioradialis Brachioradialis is a muscle of the forearm that acts to flex the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm; for this reason it is also called "the beer drinker muscle." It is attached to the distal styloid process of the...	skin of the posterior arm as the posterior cutaneous nerve of the arm
medial cord	medial pectoral nerve Medial pectoral nerve The medial pectoral nerve arises from the medial cord of the plexus and through it from the eighth cervical and first thoracic....	C8, T1	pectoralis major and pectoralis minor	-
medial cord	medial root of the median nerve Median nerve The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....	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 Arm In anatomy, an arm is one of the upper limbs of an animal. The term arm can also be used for analogous structures, such as one of the paired upper limbs of a four-legged animal, or the arms of cephalopods....
medial cord	medial cutaneous nerve of the forearm	C8, T1	-	medial skin of the forearm
medial cord	ulnar nerve Ulnar nerve In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar nerve is the largest unprotected nerve in the human body , and the only unprotected nerve that does not serve a purely sensory function...	C8, T1	flexor carpi ulnaris, the medial 2 bellies of flexor digitorum profundus, most of the small muscles of the hand Hand The hands are the two intricate, prehensile, multi-fingered body parts normally located at the end of each arm of a primate. They are the chief organs for physically manipulating the environment, used for both gross motor skills and fine motor skills...	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

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