The Brachial Plexus Flashcards
What is the brachial plexus?
A network of nerve fibres that supplies the skin and musculature of the upper limb
Where does the brachial plexus begin?
In the root of the neck
Where does the brachial plexus pass?
Through the axilla, and enters the upper arm
What is the brachial plexus formed by?
The anterior rami (divisions) of the cervical spines C5-8, and the first thoracic spinal nerve, T1
What is the brachial plexus divided into to aid explanation?
Roots, trunks, divisions, cords and branches
What is the functional difference between the parts of the brachial plexus?
None
What do the roots refer to?
The beginning of the brachial plexus
What are the roots of the brachial plexus formed by?
The spinal nerves C5, C6, C7, C8 and T1
What happens at each vertebral level?
Paired spinal nerves arise
How do paired spinal nerves leave the spinal cord?
Via the intervertebral foramina of the vertebral column
What happens when the paired spinal nerves have left the spinal cord?
Each nerve divides into the anterior and posterior nerve fibres
How are the roots of the brachial plexus formed?
By the anterior divisions of spinal nerves C5-T1
What happens to the posterior divisions of the spinal nerves C5-T1?
They go on to innervate the skin and musculature of the trunk
What happens to the anterior division of spinal nerves C5-T1 after their formation?
They pass between the anterior and medial scalene muscles to enter the base of the neck
What happens at the base of the neck?
The roots of the brachial plexus converge
What is formed when the roots of the brachial plexus converge?
Three trunks
What are the trunks of the brachial plexus named based on?
Their anatomical position
What are the three trunks of the brachial plexus?
Superior trunk
Middle trunk
Inferior trunk
What does the superior trunk consist of?
A combination of C5 and C6 roots
What does the middle trunk consist of?
A continuation of C7
What does the inferior trunk consist of?
A combination of C8 and T1 roots
What happens once the trunks have been formed?
They begin to move laterally, crossing the posterior triangle of the neck
What happens within the posterior triangle of the neck?
Each trunk divides into two branches
What happens to the two branches formed from the trunks of the brachial plexus?
One division travels anteriorly (towards the front the body) and the other posteriorly (towards the back of the body)
What happens once the divisions have been formed?
The divisions leave the posterior triangle and pass into the axilla region
What happens once the anterior and posterior divisions have entered the axilla?
They combine together to form three nerves
How are the three nerves formed by the trunks of the brachial plexus named?
By their position relative to the axillary artery
What are the three cords formed from the trunks of the brachial plexus?
Lateral
Posterior
Medial
What is the lateral cord formed by?
The anterior division of the superior trunk
The anterior division of the middle trunk
What is the posterior cord formed by?
The posterior division of the superior trunk
The posterior division of the middle trunk
The posterior division of the inferior trunk
What is the medial cord formed by?
The anterior division of the inferior trunk
What do the cords give rise to?
The five major branches of the brachial plexus
Where do the cords give rise to the major branches of the brachial plexus?
In the axilla and proximal aspect of the upper limb
What happens to the major branches of the brachial plexus?
They continue into the upper limb to provide innervation to the muscles and skin present
What are the major branches of the brachial plexus?
Musculocutaneous nerve Axillary nerve Radial nerve Ulnar nerve Median nerve
What is the M structure found when looking for the brachial plexus in a dissection formed by?
The musculocutaneous, median and ulnar nerves, arranged around the brachial artery
What does the brachial plexus have in addition to the 5 major branches?
A number of smaller nerves that arise
What nerves arise from the roots of the brachial plexus?
Dorsal scapular nerve
Long thoracic nerve
What nerves arise form the trunks of the brachial plexus?
Suprascapular
Nerve to subclavius
What nerves arise from the lateral cord of the brachial plexus?
Lateral pectoral nerve
What nerves arise from the medial cord of the brachial plexus?
Medial pectoral nerve
Medial cutaneous nerve of arm
Medial cutaneous nerve of forearm
What nerves arise from the posterior cord of the brachial plexus?
Superior subscapular nerve
Thoracodorsal nerve
Inferior subscapular nerve
What is an intact brachial plexus vital for?
Normal function of the upper limb
What are the major types of injuries that can affect the brachial plexus?
Upper brachial plexus injury
Lower brachial plexus injury
What does an upper brachial plexus injury affect?
The superior roots
What does a lower brachial plexus injury affect?
The inferior roots
When does Erb’s palsy commonly occur?
Where there is excessive increase in the angle between the neck and the shoulder
Why does excessive increase in the angle between the neck and the shoulder result in Erb’s Palsy?
It stretches (or can tear) the nerve roots, causing damage
What can Erb’s Palsy occur as a result of?
Difficult birth Shoulder trauma
What nerves affected by Erb’s Palsy?
Nerves derived solely from C5 or C6 roots- musculocutaneous, axillary, suprascapular and nerve to subclavius
What muscles are paralysed in Erb’s Palsy?
Supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid and teres minor
What motor functions are lost or greatly weakened in Erb’s Palsy?
Abduction at the shoulder
Lateral rotation of the arm
Supination of the forearm
Flexion at shoulder
What sensory functions are lost in Erb’s Palsy?
Loss of sensation down lateral side of arm
Why is the a loss of sensation down the lateral side of the arm in Erb’s Palsy?
Because this covers the sensory innervation of the axillary and musculocutaneous nerve
What happens to the affected limb in Erb’s Palsy?
The affected limb hangs limply, medially rotated
Why is the limb medially rotated in Erb’s Palsy?
Due to the unapposed action of the pectoralis major
Why is the forearm pronated in Erb’s Palsy?
Due to the loss of the biceps brachii
What is the characteristic position of Erb’s Palsy?
‘Waiters tip’
What does a lower brachial plexus injury result from?
Excessive abduction of the arm
What is a lower brachial plexus injury called?
Klumpke Palsy
How does the incidence of Klumpke Palsy differ from Erb’s palsy?
It is much lower
What nerves are effected in Klumpke Palsy?
Those derived form the T1 root- ulna and median nerves
What muscles are paralysed in Klumpke Palsy?
All the small muscles of the hand
Why are the flexor muscles in the forearm not paralysed in Klumpke Palsy?
Although they are supplied by the ulna and median nerve, they are innervated by different roots
What sensory functions are lost in Klumpke Palsy?
Loss of sensation along medial side of arm
What is the characteristic appearance of Klumpke Palsy?
Hand has a clawed appereance
What gives the hand a clawed appearance in Klumpke Palsy?
The metacarpophalangeal joints are hyperextended, and the interphalangeal joints are flexed
