Brachial plexus Flashcards
What can cause the nerves of the brachial plexus to get trapped?
- Enlarged scalene muscles can compress nerves
2. Additional cervical rib can cause thoracic outlet syndrome
What is the path of the brachial plexus to the upper limb?
- Originates at the cervical vertebrae
- Emerges between the anterior scalene and medial scalene muscles and runs through the posterior triangle of the neck
- Passes behind the clavicle at approx. the midpoint [where it runs alongside the axillary artery to the upper limb]
What makes up the posterior triangle of the neck?
Anterior = posterior border of sternocleidomastoid muscle Posterior = anterior border of the trapezius muscle Inferior = middle 1/3 of the clavicle
Which spinal roots form the brachial plexus?
Ventral rami of C5-T1
Which spinal roots form each trunk of the brachial plexus?
Upper trunk = C5 + C6
Middle trunk = C7
Lower trunk = C8 + T1
Which divisions of each trunk form the cords of the brachial plexus?
Anterior divisions of the upper and middle trunks form the lateral cord
Posterior divisions of the upper, middle and lower trunks form the posterior cord
Anterior division of the lower trunk forms the medial cord
What are the cords of the brachial plexus named in relation to?
Anatomical position in relation to the axillary artery
What terminal branches of the brachial plexus does the lateral cord contribute to?
Musculocutaneous
Median
What terminal branches of the brachial plexus does the posterior cord contribute to?
Radial
Axillary
What terminal branches of the brachial plexus does the medial cord contribute to?
Median
Ulnar
What muscles does the musculocutaneous nerve innervate?
Anterior arm compartment muscles (long and short head of the biceps brachii and the coracobrachialis)
What are the functions of the biceps brachii?
Supination of forearm
Arm flexion at shoulder
Elbow flexion
What are the functions of the coracobrachialis?
Arm flexion at shoulder
Weak adduction
What would loss of innervation from the musculocutaneous nerve cause?
Loss of anterior compartment muscles (biceps brachii and coracobrachialis) leading to weakness of flexion of shoulder and elbow and weakness of supination of forearm
[Nb. uncommon to damage this nerve as is protected by muscles]
What muscles does the axillary nerve innervate?
Deltoid
Teres minor
What can damage the axillary nerve?
Shoulder dislocation
Fracture of the surgical neck of humerus
What would loss of innervation from the axillary nerve cause?
Loss of innervation to the deltoids would cause loss of ability to abduct the arm and weakness in flexing and extending the arm at the shoulder
Loss of innervation to the teres minor would cause weakness in lateral rotation of the arm at the shoulder
What does the median nerve innervate?
Anterior compartment of the forearm (except the flexor carpi ulnaris), thenar muscles (base of thumb) and lumbricals 1 + 2 (index and middle finger)
How can the median nerve be damaged?
Penetrating injury to medial arm, laceration to anterior wrist or carpel tunnel
What muscles does the radial nerve innervate?
Posterior arm compartment (three heads of the triceps brachii) and the posterior forearm compartment
How can the radial nerve be damaged?
Fracture of humeral shaft (through spiral groove)
Dislocated or fractured head of radius (can affect the posterior interosseous nerve)
What muscles does the ulnar nerve innervate?
Majority of the intrinsic muscles of hand
How can the ulnar nerve be damaged?
Fracture of the medial humeral epicondyle
Injury to anterior wrist
How can the C5 root and the upper trunk be damaged?
Penetrating neck injury
What nerve roots does the radial nerve carry?
C5-T1
What nerve root of the brachial plexus is vulnerable to damage from a Pancoast (apical lung) tumour and what can this result in?
T1 nerve root
Damage can cause wasting of the small muscles of the hand
What muscle does the lateral pectoral nerve innervate?
Clavicular head of pectoralis major
What muscles does the suprascapular nerve innervate?
Supraspinatus and infraspinatus rotator cuff muscles
What muscles does the dorsal scapula nerve innervate?
Rhomboids
Levator scapulae
What does damage to the suprascapular nerve result in?
Limits lateral rotation of shoulder and shoulder stability
How can you identify damage to the long thoracic nerve?
Winging of the scapula (due to damage to the serratus anterior muscle)
What can cause damage to the long thoracic nerve?
Axillary region surgery
Incorrect thoracostomy
Thoracotomy incision
What muscles does the medial pectoral nerve innervate?
Sternal head of pectoralis major
Pectoralis minor
How can damage to the brachial plexus be identified?
Abnormal resting position of the limb (due to loss of functionality in some muscles, remaining functional muscles pull limb into different position)
What is Erb’s Palsy and how can it be caused?
Damage to the C5 + C6 upper root/ trunk damage
Caused by:
Forced separation of the neck from the shoulder (e.g. through trauma such as cycling accident or during childbirth) causing stretching of nerves or evulsion of nerves from spinal cord
Stab wound or laceration to the neck
What resting limb position does an Erb’s Palsy cause?
‘Waiters tip’ - limb is medially rotated, forearm pronated and hangs limp. Wasting of deltoid muscle.
What is Klumpke’s Palsy and how can it be caused?
Damage to the C8 + T1 root damage or compression Caused by: Upward traction of upper limb Apical lung tumour Compression via cervical rib
What does a Klumpke’s Palsy result in?
‘Claw hand deformity’ - extension of metacarpophalangeal joints and flexion of interphalangeal joints at rest
Can also cause wasting of small muscles of hand
