Anatomy of the Limbs 5 - The Brachial Plexus Flashcards
Which spinal segments is the sensory and motor nerve supply for the upper limb and its limb girdle?
C4 to T1
List the muscle supply of the upper limb
- Shoulder girdle muscles C3-C7
- Movements of the shoulder joint and elbow flexors C5 and 6
- Movements of the elbow joint C7 and 8
- C6-8 supply wrist and course hand muscles
- Movements of the fingers and thumb C8 and T1
What is the function of the brachial plexus?
To rearrange the nerve fibres from C5-T1 into bundles travelling to appropriate parts of the limb
What is in the posterior cord?
Nerves supplying extensor muscles
What is in the lateral and medial cord?
Nerves supplying the flexor muscles
What does the posterior cord divide into?
- 2 main branches
- Axillary nerve smaller (C5 and 6)
- Radial nerve larger (C7-T1)
What happens in the injury of the axillary nerve?
- Can be injured in shoulder dislocations and upper humeral fractures, resulting in loss of abduction and eventual wasting of the deltoid
- Also supplies teres minor
- Superior lateral cutaneous nerve supplies skin at the top of the arm and therefore can be used to test axillary nerve function
What happens in injury of the radial nerve?
- Damaged by fractures of the mid-humeral shaft, leading to loss of function of extensor muscles of the forearm
- Results in wrist drop and weakness of power grip (as extension is needed for power grip to reduce the work needed by the flexor muscles)
- Sensory loss affects the posterior surface of the thumb
What is the most important branch of the lateral cord?
- Supplies only flexor muscles
- Musculocutaneous branch
What is the lateral cord mainly concerned with?
Muscles acting on the shoulder and elbow, as it contains C5-7 fibres.
Describe the function of the musculocutaneous nerve and its risk of injury
- Low risk of injury, can be affected by upper brachial plexus nerve root injuries
- Surrounded by muscle, pierces through the coracobrachialis muscle
- May be damaged during surgery for breast cancer
- Supplies the biceps and branchialis (elbow flexors)
What does the medial cord supply?
- Only flexor muscles
- Mainly forearm and hand muscles (C8-T1 fibres)
What is the main branch of the medial cord?
Ulnar nerve
Describe the function and result of injury to the ulnar nerve
- Motor to most the intrinsic muscles of the hand (Hypothenar, interossei, 3rd and 4th lumbrical, adductor pollicis and palmaris brevis)
- Vulnerable to compression, cuts and fractures where it passes posterior to the medial epicondyle of the humerus at the elbow. Also vulnerable when people self harm
- Results in weakness and wasting of many small muscles of the hand, less serious than might be expected due to median nerve supply
- Clawing of the fingers may be seen due to lumbricals. Also affects PAD and DAB
- In the forearm supplies the medial half of flexor digitorum profundus and the flexor carpi ulnaris
- Sensory loss in ulnar nerve injury along the medial part of the hand
Which nerve is formed by contribution from both the lateral and medial cord?
- Median nerve
- C6-T1
What does the median nerve supply, and what is the result of damage?
- Supplies the wrist and finger flexors in the forearm
- Supplies most small muscles of the thumb and index finger
- Sensory to lateral part of the hand, making delicate tasks difficult when injured (as the lateral two lumbricals are affected)
- Injured when it becomes entrapped in carpal tunnel syndrome (one of the most common nerve entrapment conditions)
- Causes wasting of the thenar eminence
Which muscles are supplied by the long thoracic nerve?
Serrratus anterior muscle
What is seen in damage to the long thoracic nerve?
- Winging of the scapula when pressing against a wall
- This is because its main function is pulling the scapula inwards
- Damaged in car accidents
What is seen in upper root injury?
- Forearm is pronated due to lack of biceps supination
- Waiters tip position (unopposed flexion of the wrist, flexion of the elbow is difficult)
- Low limb mobility
What is seen in lower root injury?
- Damages T1 and sometimes C8
- Loss of activity of small muscles of the hand
- Clawed hand, as T1 supplies small muscles of the hand by the ulnar and medial nerves
Where is the radial nerve vulnerable to injury?
Where it winds posterior to the humerus in the radial groove from between the attachments of the medial and lateral heads of triceps.
Where is the axillary nerve vulnerable to injury?
Winds round the neck of the humerus to supply the deltoid
List the parts of the brachial plexus
- Roots (formed by anterior rami)
- Trunks (superior formed by C5 and C6, middle C7, inferior C8 and T1)
- Divisions (anterior, posterior come off each trunk)
- Cords (lateral formed by upper two anterior divisions, posterior formed from the three posterior divisions and medial from lower anterior division)
- Terminal branches (peripheral nerves), mainly come off the trunks
List the terminal branches coming off before the cords
- Dorsal scapular nerve (C5)
- Long thoracic nerve (C6 and C7)
- Supraclavicular nerve (before the clavicle
How are the cords named?
Based on their location relative to the axillary artery
What is the dermatome and cutaneous nerve pattern of innervation different?
- Due to fibre recombination
- Cutaneous nerves have innervation from different spinal nerves
What is the ulnar paradox?
More severe claw if you injure the ulnar nerve at the wrist rather than the elbow
- This is because the ulnar nerve also innervates half of the flexor digitorum profundus
- This results in weakened flexion of the interphalageal joints and as a result a less claw like appearance
What is erb-duchenne palsy?
Injuries to the upper roots
What causes upper root injury?
- Childbirth
- Falling onto the shoulders
- Stretching of the neck damages C5 an 6
What is Klumpke’s Palsy?
-Lower root injuries
What are the causes of lower root injuries?
- Over abduction
- Due to gripping overhead to break a fall
- Can happen during childbirth when one of the limbs emerges first
