Brachial Plexus Anatomy
Describe Brachial Plexus Under The Following Heads
Table of Contents
1. Formation of brachial plexus,
2. Brachial Plexus Situation,
3. Relations of brachial plexus,
4. Brachial Plexus Branches, and
5. Brachial Plexus Applied anatomy.
Answer:
Brachial Plexus Introduction:
It is the network of nerves present at the junction of the neck and thorax. It supplies the muscles, joints, skin, and blood vessels of the anterior wall of the thorax, scapular region, and upper limb.
It is formed by ventral divisions of C5, C6, C7, C8, and T1.
1. Formation of brachial plexus: It may be fixed in two ways
- Prefixed: The contribution of C4 is large, and T2 is often absent.
- Post-fixed: The contribution by T1 is large, C4 is absent and C5 is reduced in size.
Brachial Plexus Nerves
2. Brachial Plexus Location
1. Roots of brachial plexus emerge between the scalenus anterior and scalenus medius muscles.
2. Trunks appear in the lower part of the posterior of the neck.
3. Divisions lie behind the clavicle.
Brachial Plexus Nerves
- Anterior divisions supply all the muscles present in the ventral part of the thorax and upper limb.
- Posterior divisions supply the muscles present on the dorsal part of the thorax and upper limb.
4. The cords are present in the axilla. The cords are related to the 2nd part of the axillary artery as per their names. The cords give branches around 3rd part of the axillary artery.
3. Relations of brachial plexus
- Supraclavicular part: It lies above the clavicle. It consists of the roots, branches of roots, and trunks of the brachial plexus.
- Retroclavicular part: It lies behind the clavicle. It consists of divisions of brachial plexus.
- Infraclavicular part: It lies below the clavicle. It includes cords and branches of the cord.
4. Brachial Plexus Branches
1. The nerves arising from roots supply the muscles which bring protraction and retraction of the shoulder girdle, i.e.
- Nerve to rhomboids (dorsal scapular nerve) (C5), and
- Nerve to serratus anterior (long thoracic) (C5, C6, and C7).
2. Trunks
1. Suprascapular nerve (C5 and C6) supplies
- Supraspinatus,
- Infraspinatus,
- Shoulder joint,
- Acromioclavicular joint, and
- Scapula.
Brachial Plexus Nerves
2. Nerve to subclavius (C5 and C6) supplies subclavius muscle.
3. Cords: Following are the branches from respective cords.
1. Lateral:
Lateral pectoral nerve,
The lateral root of the median nerve,
Musculocutaneous nerve
2. Medial:(The Word “Media”)
The branches of the medial cord begin with the letter “M” except the ulnar nerve.
Medial pectoral,
The medial root of the median nerve,
The medial cutaneous nerve of the arm,
The medial cutaneous nerve of the forearm, and
Ulnar nerve.
3. Posterior: (RUNAL)
Brachial Plexus Injury
RUNAL denotes an acronym for the branches of the posterior cord.
Radial nerve,
Upper subscapular,
Nerve to latissimus dorsi,
Axillary nerve, and
Lower subscapular.
5. brachial plexus nerves Applied anatomy
1. Injury to the brachial plexus can be discussed depending upon the severity, the frequency, and on ascertaining whether it is a partial or a total injury.
- The most severe injury of the brachial plexus is called global brachial plexus birth palsy. It is also called total brachial plexus birth palsy.
- It is more severe than Erb’s palsy. Here the upper and lower nerves are stretched.
- Next, the most common injury to the brachial plexus is by severe traction of an abducted arm in breech delivery.
2. The partial paralysis of the brachial plexus results from a shoulder dislocation.
3. The direct injury to the brachial plexus can result from a stab or gunshot wound.
4. Horner’s Syndrome: It is due to the involvement of the sympathetic nerve, which is contributed by T1 through white ramus communicans.It usually occurs due to injury at the root of the brachial plexus.
5..Erb’s paralysis: Injury to the upper trunk usually at the Erb’s point causes Erb’s paralysis.
6. Klumpke’s paralysis: Injury to the lower trunk of the brachial plexus.
7. Winging of the scapula: Injury to the nerve to serratus anterior.
8. Claw hand: Injury to the ulnar nerve.
Brachial Plexus Injury
Axilla How Does Nerve Plexus Is Formed
1. The lower part of the medulla oblongata continues as the spinal cord.
2. A transverse section of the spinal cord shows the grey and the white matter.
- The grey matter has a ventral and a dorsal horn.
- The nerve fibers arising from these horns are known as ventral and dorsal roots of the spinal nerve, respectively.
3. The dorsal roots bear a swelling that is formed by the cell bodies of neurons. It is called the ‘dorsal root ganglion.’
4. The dorsal and ventral roots join together to form a spinal nerve of the respective region.
- The body wall is segmentally supplied by the paired spinal nerves.
- Each paired spinal nerve divides into dorsal and ventral primary rami.
- A posterior longitudinal strip is supplied by dorsal rami.
- A lateral longitudinal strip is supplied by lateral branches of the ventral rami.
- An anterior strip is supplied by the anterior terminal branches of the ventral rami.
5. In the fetus, the limb buds grow out of the lateral strip.
6. They are supplied by the lateral branches of the anterior rami.
7. These lateral branches, by their anterior and posterior divisions, form the plexuses and supply the muscles and skin of the limbs.
Brachial Plexus Injury
To be remembered
- Dorsal rami never ever form plexus or plexuses, and
- Plexuses are not formed in the thoracic region.
Axilla What Is Brachial Plexus
Definition Of Brachial Plexus:
It is the network of nerves present at the junction of the neck and thorax.
- It supplies all the muscles of the upper limb, except the trapezius and levator scapulae.
- It supplies all joints of the upper limb.
- It also supplies the skin of the upper limb except for an area just above the point of the shoulder which is supplied by the supraclavicular nerves and the dorsal scapular area.
Axilla What Is Prefixed And Post-Fixed Brachial Plexus
The brachial plexus may be fixed in two ways:
- Prefixed, and
- Post-fixed.
The origin of the plexus may shift, i.e. one segment either upwards or downwards, resulting in a prefixed or post-fixed brachial plexus, respectively.
1. In the prefixed plexus,
- The contribution by C4 is large,
- The contribution by T1 is reduced, and
- T2 is absent.
2. In the post-fixed brachial plexus,
- C4 is absent,
- The contribution by C5 is reduced
- T1 is large, and
- T2 is always present.
Brachial Plexus Anatomy
Axilla What Are The Components Of Brachial Plexus
1. It has four basic components. They are roots, trunks, divisions, and cords.
2. It is remembered by the keyword RTDC.
It is a Short form for Rajasthan Tourist Development Corporation.
These components are compared to those of a tree.
3. Like a tree, the brachial plexus has roots, a trunk, divisions, cords, and branches.
4. There are only three roots. They are
- Roots of the spinal nerve,
- Roots of brachial plexus, and
- Roots of the median nerve.
5. The roots of the spinal nerve are the ventral and dorsal roots.
6. The roots of the brachial plexus are formed by ventral rami of 5, 6,7, 8 cervical, and 1st thoracic spinal nerves. The roots of the median nerve are branches of the medial and lateral cords of the brachial plexus.
- The most caudal root of a brachial plexus is the T1 root.
- It is distributed entirely to the flexor compartment of the upper limb.
7. The central root of the brachial plexus is C7 and it supplies flexor surfaces of the middle 3 fingers of the hand.
Brachial Plexus Anatomy
Axilla What Are Parts Of Brachial Plexus
It has a supraclavicular, a retroclavicular, and an infraclavicular part.
- The supraclavicular part includes roots and trunks. They lie above the clavicle.
- The sternoclavicular part includes divisions and lies behind the clavicle.
- The infraclavicular part includes cords and branches that lie below the clavicle.
Axilla Nomenclature Of Brachial Plexus
1. Trunks are named depending on the position in the lower part of the posterior of the neck.
- The upper trunk runs in the upper part of the posterior of the neck,
- The middle trunk is present in the middle part, and
- The lower trunk lies in the lower part of the posterior
2. The divisions of the brachial plexus are named on the basis of the distribution of the muscles of these branches.
- The branches of the anterior division supply all the flexor muscles of the upper limb.
- The branches of the posterior division supply all the extensor muscles of the upper limb.
3. The names given to cords of the brachial plexus depend upon their relations with the 2nd part of the axillary artery.
The medial cord lies on the medial side of 2nd part of the axillary artery.
The lateral cord lies on the lateral side of 2nd part of the axillary artery.
4. The posterior cord lies on the posterior side of 2nd part of the axillary artery.
Brachial Plexus Anatomy
Axilla Branches Of Roots And Trunks Of Brachial Plexus
Branches of roots, and trunks of brachial plexus
Branches from roots
1. The branches arising from roots are called R1 and R2.
- R1 is a dorsal scapular nerve which is also called the nerve to the rhomboids.
- R2 is a long thoracic nerve which is also called the nerve to the serratus anterior (nerve of Bell).
2. These nerves supply the muscles which act on the pectoral girdle.
Branches from trunks, only from the upper trunk. These are
- Suprascapular nerve, and
- Nerve to the subclavius.
Note: Both have the same root value as C5 and C6.
Axilla Branches Of Cords Of Brachial Plexus
Following are the branches from the cords.
1. The branches from the lateral cord are:
- Lateral pectoral,
- The lateral root of the median nerve, and
- Musculocutaneous nerve.
Brachial Plexus Branches
2. The medial cord has 5 branches. They are
1. Medial pectoral,
- The medial root of the median nerve,
- The medial cutaneous nerve of the arm,
- The medial cutaneous nerve of the forearm, and
- Ulnar nerve.
It is very interesting to note here that the 1st letter of the words “Medial cord”. and the 1st letter of all the branches of the medial cord begins with the alphabet “M.” The ulnar nerve is the only exception
3. The posterior cord gives 5 branches.
The word “RUNAL” is an acronym for the branches of the posterior cord.
The letter “R” stands for Radial,
The letter “U” stands for Upper subscapular,
The letter “N” stands for Nerve to latissimus dorsi,
The letter “A” stands for Axillary, and
The letter “L” stands for Lower subscapular
Axilla Dorsal Scapular Nerve
The dorsal scapular nerve is also called the nerve to the rhomboids.
1. Dorsal Scapular Nerve arises in the neck from the posterior aspect of the C5 root of the brachial plexus.
2. Dorsal Scapular Nerve passes through the scalenus medius and runs down deep to the levator scapulae.
3. Dorsal Scapular Nerve supplies levator scapulae and lies on the serratus posterior superior muscle.
4. Dorsal Scapular Nerve runs here on the medial side of the descending branch of the transverse cervical artery.
5. Dorsal Scapular Nerve supplies the rhomboid major and minor on the deep surface.
Brachial Plexus Branches
Axilla Branches Of Lateral Cord Of Brachial Plexus
Lateral Pectoral Nerve
- Lateral Pectoral Nerve arises from the lateral cord.
- Lateral Pectoral Nerve supplies pectoral muscles.
- The root value is cervical 5, 6, and 7.
- Lateral Pectoral Nerve pierces the clavipectoral fascia from the inside out and supplies the pectoralis major muscle.
- Lateral Pectoral Nerve has a communicating branch to the medial pectoral nerve.
- The branch crosses in front of 1st part of the axillary artery, and supplies pectoralis minor.
This piece of information is important while answering some of the most frequently asked MCQs on the upper limb.
Also, keep in mind that the lateral pectoral nerve does not have a cutaneous branch.
Axilla Horner’s Syndrome
It is Claude Bernard-Horner syndrome or is also known as oculosympathetic palsy. This is one of the most important and frequently asked topics in anatomy, surgery, and ophthalmology examination.
- Horner syndrome involves cranial and sympathetic nerves.
- The sympathetic contribution is from 1st thoracic spinal nerve.
- Horner syndrome usually occurs due to injury to the root of the brachial plexus.
The letters of the word “HORNER“ can act as an acronym to remember the clinical manifestations of Horner’s syndrome.
The letter “H” of Horner signifies Hypohydrosis. It means decreased sweating on the same side of the face.
1. The letter “O” of Horner indicates loss of Opening of an eye. The opening is impossible due to ptosis (drooping of the upper eyelid).
It is caused by loss of sympathetic innervation to the superior tarsal muscle or Müller’s muscle (smooth muscle of levator palpebrae superioris). In fact, it is pseudoptosis.
2. The letter “R” of HORNER should remind us of 3 “Rs”.
- Robertson pupil. It is constriction of the pupil due to paralysis of the dilator
- pupillae muscle. It is due to the unopposed action of sphincter pupillae.
- The second “R” stands for loss of vision.
- The third “R” stands for Redness of conjunctiva.
3. The letter “N” of HORNER signifies the Narrowing of the palpebral fissure due to drooping of the upper eyelid.
4. The letter “E” of Horner stands for Elevation of the lower eyelid.
5. The last letter “R” of HORNER stands for Retraction or sinking of the eyeball which is due to paralysis of the orbitalis muscle. It indicates a problem with the sympathetic nervous system, a part of the autonomic nervous system.
Brachial Plexus Branches
Axilla Erb’s Paralysis
Axilla Erb’s Paralysis Introduction:
It is the most common type of birth paralysis. It is a form of brachial plexus palsy. It is Wilhelm Erb who 1st described this condition.
1. Axilla Erb’s Paralysis Erb’s Point:
Injury occurring at Erb’s point is called Erb’s paralysis. The junction of 6 nerves is called Erb’s point. The following are the nerves contributing to the formation of
- Ventral division of 5th cervical nerve,
- Ventral division of 6th cervical nerve,
- Suprascapular nerve,
- Nerve to subclavius,
- The anterior division of the upper trunk, and
- Posterior division of upper trunk.
2. Axilla Erb’s Paralysis Site Of Injury:
Injury to the upper trunk usually at the Erb’s point causes Erb’s paralysis.
3. Axilla Erb’s Paralysis Incidence:
1:1000 vaginal deliveries. It is often caused when an infant’s neck is stretched to the side during a difficult delivery.
4. Axilla Erb’s Paralysis Causes Of Injury:
1. The most common cause of Erb’s palsy is shoulder dystocia, an abnormal or difficult labor or childbirth.
- Approximately 45% of Erb’s palsies are associated with shoulder dystocia.
- Erb’s palsy can occur if the infant’s head and neck are pulled towards the side, as the shoulders pass through the birth canal.
- The condition can also be caused by
-
- Excessive pulling on the shoulders during a cephalic presentation, i.e. delivery where the head is delivered first, or
- By pressure on the raised arms during a breech i.e. delivery where feet are delivered first.
2. Erb’s palsy can also result in neonates affected by the fracture of a clavicle.
3. Injury may be due to direct trauma. It includes
- Gunshot wounds, and
- Traction on the arm, or a
- A person falling on the shoulder.
Brachial Plexus Branches
5. Axilla Erb’s Paralysis Muscles Paralysed:
The muscles paralyzed in Erb’s palsy can be recollected by the mnemonics. (Damaged brachial plexus should be treated intelligently)
Deltoid, Latissimus Dorsi,
Biceps,
Supraspinatus, Subscapularis,
Brachialis,
Teres major and Teres minor, and
Infraspinatus.
Affected nerves, muscles paralyzed, and the clinical manifestations of Erb’s paralysis
Reasoning out of the position of the upper limb in Erb’s palsy.
1. There are no nerves from the ventral rami of C5 and C6.
2. Suprascapular nerve arises from the upper trunk. It innervates supraspinatus and infra- spinatus.
- Supraspinatus is an initial abductor of the shoulder joint. Paralysis of this muscle keeps the upper limb adducted.
- The infraspinatus is a lateral rotator. Paralysis of this keeps hands in medial rotation.
3. The lateral and posterior cords are involved.
- The musculocutaneous nerve arises from the lateral cord.
- Paralysis of this nerve results in loss of flexion of the elbow. As a result, the arm is kept in extended position.
- The biceps are also a strong supinator. This results in the pronated forearm.
4. The branches of the posterior cord are the upper subscapular, lower subscapular, nerve to latissimus dorsi, axillary nerve, and radial nerve.
- The upper and lower subscapular nerve supply subscapularis. They are medial rotators.
- Nerve to latissimus dorsi which, as the name suggests, supplies latissimus dorsi which is also a medial rotator and adductor of the shoulder joint.
- The ulnar nerve supplies all the small muscles of the hand.
- It would be wise to note here that the pectoral is the only muscle supplied by all five segments of the brachial plexus.
- It thus serves as a useful guide to localize the extent of the lesion.
Axillary Anatomy
5. Also remember, that there is a loss of sensation on the lateral side of the arm and forearm. This deformity is described as the ‘Policeman tip.’
Axilla Klumpke’s Paralysis
Klumpke’s Paralysis Introduction:
It is due to the injury of lower roots, i.e. C8 and T1 of the brachial plexus.
- Klumpkes Paralysis Site Of InjuryThe lower trunk of the brachial plexus.
- Klumpkes Paralysis Cause
-
- Klumpkes Paralysis is caused by breech delivery, where the arm remains above the head, causing birth injury.
- Undue abduction of the arm. This occurs, as the person clasps something with the hands after a fall from a height.
3. Klumpkes Paralysis Effect
-
- There is a sensory loss on the medial side of the forearm.
- The small muscles of the hand leading to claw hands are affected. The patient is not able to extend the fingers.
4. Klumpkes Paralysis Nerve roots involved: Mainly T1 and partly C8.
5. Klumpkes Paralysis Muscles paralyzed
- Intrinsic muscles of the hand (T1), and
- Ulnar flexors of the wrist and fingers (C8).
Klumpkes Paralysis
6. Deformity and position of the hand
1. Claw hand due to the unopposed action of the long flexors and extensors of the fingers. There is hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints.
2. Disability
- Complete clawhand
- Cutaneous anesthesia and analgesia in a narrow zone along the ulnar border of the forearm and hand.
3. Horner’s syndrome results in the lesion of 1st thoracic sympathetic ganglion. There is an injury of the T1 nerve proximal to white ramus communicans. The clinical manifestations are ptosis, miosis, anhidrosis, enophthalmos, and loss of ciliospinal reflex.
4. Vasomotor changes: The skin area with sensory loss is warmer due to arteriolar dilation.
5. Trophic changes: A long-standing case of paralysis leads to dry and scaly skin. The nails crack easily with atrophy of the pulp of fingers.
7. Surgical Approach
The C8 and T1 nerve is approached by exposing
- The supraclavicular part
- The infraclavicular part
1. The supraclavicular part can be exposed at the angle between the stereo cleidomastoid and the clavicle.
- The inferior belly of the omohyoid and lateral branches of the thyrocervical trunk are divided.
- The roots of the plexus are identified behind the scalenus anterior.
- They need to be retracted to visualize the lower trunk.
- Care should be taken to avoid damage to the phrenic nerve.
2. To expose the infraclavicular part,
- The deltopectoral groove is opened up.
- The pectoralis minor is detached from the coracoid process.
- The plexus and branches around the axillary artery can be dissected out from the axillary sheath.
- The middle part of the clavicle may have to be removed if more proximal exposure is needed.
Axilla Cervical Rib Cervical Rib Introduction:
A supernumerary rib arising from the cervical vertebra. It usually arises from the 7th cervical vertebra.
1. Cervical Rib Synonymous
-
- Costa cervicals.
2. Cervical Rib Effect of cervical rib
-
- It presses the lower trunk of the brachial plexus (C8, T1).
3. Cervical Rib Applied anatomy
-
- The cervical rib may compress the subclavian artery. This causes thrombi which are thrown as emboli in the vessels of the limb.
- They bring about vascular changes in the arm. It results in paraesthesia along the ulnar border of the arm and weakness and wasting of small muscles of the hand.
- A cervical rib may elevate the subclavian artery and render it unduly palpable. It simulates an aneurysm.
- In fact, there may be aneurysmal dilation of the artery distal to the edge of the cervical rib.
Axilla Sprengel’s Deformity
Sprengel’s deformity of the scapula (congenital high scapula)
- Sprengel’s deformity of the scapula causes failure of descent of the scapula leads to Sprengel’s deformity.
- Clinical manifestation
-
- The scapula is hypoplastic and situated in the neck region.
- An attempt to bring down the scapula by a surgical procedure may cause injury to the brachial plexus
Sprengel Deformity
Axilla Nerve Injuries Of Upper Limb
(DR CUMA)
Wrist Drop-Radial nerve injury
Claw hand-Ulnar nerve
Axillary Nerve Injury Signs
Ape Hand-Median nerve
Winging of scapula-nerve to serratus anterior
Causes of lesion of roots and cords of brachial plexus, muscles paralyzed, and clinical features
.Sprengel Deformity
Leave a Reply