Session 5: The Brachial Plexus Flashcards
What are the 5 segments of the brachial plexus called?
Proximal to distal:
- roots
- trunks
- divisions
- cords
- terminal branches (peripheral nerves)
What are the names of the trunks of the brachial plexus? How many are there?
- 3
- superior, middle and inferior
Which nerve roots go into the brachial plexus?
- C5 (superior trunk)
- C6 (superior trunk)
- C7 (middle trunk)
- C8 (inferior trunk)
- T1 (inferior trunk)
Long thoracic nerve
- C5,6,7
- supplies serratus anterior
- Emerges from the root of the neck and runs over the surface of the serratus anterior muscle which it supplies.
supraclavicular and infraclavicular branches
x
Dorsal scapular nerve
- C5
- innervates rhomboids
Divisions
- anterior and posterior
- no terminal branches coming off diviisons
Trunks
- divisions recombine to form trunks
- upper 2 anterior divisions form lateral trunk
- all posterior fibers form the posterior trunk
- anterior trunk of inferior root forms median trunk
Summary of the motor nerves of the Upper limb (spinal levels)
- C3-7 supply shoulder girdle muscles
- C5-C6 supply shoulder joint muscles and elbow flexors
- C7-C8 supply elbow joint extensors
- C6-C8 supply wrist and coarse hand muscles
- C8-T1 supply small muscles of the hand (fine movements)
=> opposing movements are generally supplied by adjacent nerves -> see slide 13)
Dermatome vs. cutaneous nerve patterns
Because of all the fibre recombination that takes place in a plexus, the pattern of cutaneous nerve distribution is very different from the dermatome pattern.
Axillary nerve
- comes of the posterior branch of the brachial plexus
- passes posteriorly and then becomes lateral
- passes under the shoulder joint
- vulnerable to shoulder dislocation
- surgical neck of the humerus damage can also damage axillary nerve
- innervates deltoid muscle
What happens in axillary nerve damage?
- deltoid muscle wasting
- teres minor also supplied by that nerve
- superior lateral cutaneous nerve of arm -> loss of sensation in that area if that nerve is damaged
What does the axillary nerve innervate?
M:
- deltoid
- teres minor
S:
- name of the area
Radial nerve injury
- posterior muscle wasting if higher up
- wrist drop
- loss of power grip (you have to extend the wrist to get an efficient power grip)
=> depends on the level of the injury (where along the course of the nerve the damage occurs)
What is a plexus?
- nerve roots from different spinal levels merge together and produce peripheral nerves.
- these nerves usually have fibres from more than one spinal level
What are the names of the cords of the brachial plexus?
- lateral (anterior divisions of superior and middle trunk -> C5,6,7)
- posterior (made of all posterior divisions -> C5,6,7,8,T1)
- medial ( anterior division of inferior trunk -> C8,T1)
What are the names of the divisions of the brachial plexus?
- there are anterior and posterior divisions of each trunk (superior, middle, inferior)
What are the terminal branches of the brachial plexus called?
- musculocutanoues
What does the thoracodorsal nerve innervate?
Latissimus dorsi
What are the cords of the brachial plexus named in relation to?
- The cords of the brachial plexus are named according to their relationship to the axillary artery.
- The posterior cord is posterior to the artery etc.
Why are the dermatomes of the upper limb not as nice as the stripes on the torso? What are the dermatomes arranged like?
- If you lean forward and put your hands to the ground you can see the normal alignment.
- the dermatomes go around the upper limb in a circle (see slide 14)
What is the difference between dermatomes and the pattern of sensory nerve distribution?
- different than dermatomes due to nerve merging
- i.e. there are multiple nerves formed from a certain spinal level so the area that is innervated by a spinal nerve can be made up of several nerves that the spinal root formed.
- dermatome vs. cutaneous pattern: Because of all the fibre recombination that takes place in a plexus, the pattern of cutaneous nerve distribution is very different from the dermatome pattern.
- see slide 15 and 16
Where is the axillary nerve derived from?
- posterior cord
What does the axillary nerve supply?
- deltoid muscle
- teres minor muscle
How can the axillary nerve be damaged?
Commonly damaged through dislocations of shoulder and fracture of the surgical neck of the humerus.
What is the course of the axillary nerve?
- originated from the posterior cord
- passes inferiorly and laterally along the posterior wall to exit the axilla through the quadrangular space
- passes posteriorly around the surgical neck of the humerus
- innervates deltoid and teres minor
How does axillary nerve injury present?
- wasting of the deltoid muscle on that side
- there is an area of anaesthesia -> there is no sensory innervation on the side of the arm (area where you would usually get a vaccine)
- reported or observed weakness to the deltoid and teres minor muscles (Abduction and external rotation)
What is the course of the radial nerve?
- largest terminal branch of the posterior cord
- passes out of the axilla and into the posterior compartment of the arm by passing through the triangular interval between the inferior border of the teres major muscle, the long head of the triceps and the shaft of the humerus.
- accompanied through the trialgular interval by profound brachia artery
- innervates:
- all muscles in the posterior compartments of the arm and forearm
- AND the skin on the posterior aspect of the arm and forearm, the lower lateral surface of the arm and the dorsal lateral surface of the hand.
How does radial nerve injury occur?
- The radial nerve runs closely apposed to the shaft of the humerus, so can be damaged in humeral fractures.
How does radial nerve injury present?
- Wrist drop and anaesthesia of the dorsal hand
- Loss of muscle mass evident in the arm and forearm.
- loss of power grip (because this requires extension of the wrist, otherwise the hand muscles have a lot to do)
- presentation depends on where along the course of the nerve the damage occurs.
What is the course of the musculocutaneeous nerve?
- large terminal branch of the lateral cord
- passes laterally to penetrate the coracobrachilis muscle and pass between the biceps brachii and the brachilais muscles in the arm (BBC)
- innervates the three flexor muscles in the anterior compartment of the arm
- terminates as the lateral cutaneous nerve of the forearm.
How is the musculocutaneous nerve damaged usually?
- NOT injured by trauma generally as it is well protected by muscles
- however, it may be damaged during breast cancer surgery when the axial lymph nodes are being removed.
How does injury of the musculocutaneous nerve present?
?
What is the course of the ulnar nerve?
- large terminal branch of the medial cord
- passes through the arm and forearm into the hand where it innervates all intrinsic muscles of the hand except for the three thenar muscles and two lateral lumrical muscles. - branches of the ulnar n. innervate the FCU and the medial half of of the flexor digitorum profundus.
- sensory innervation to skin over the palmar surface of the little finger, medial half of the ring finger, dorsal surface of the medial part of the hand.
- does not supply anything in the arm
- FUNNY BONE (can be felt at the medial epicodyle region?)
What does the ulnar nerve innervate? What are the exceptions?
- innervates all intrinsic muscles of the hand except:
- the three thenar muscles
- two lateral lumbricals
- branches of the ulnar n. innervate the FCU and the medial half of of the flexor digitorum profundus.
- sensory innervation to skin over the palmar surface of the little finger, medial half of the ring finger, dorsal surface of the medial part of the hand.
How is the ulnar nerve commonly damaged?
- self harm (cutting wrist)
- Injuries to medial epicondyle of humerus cause injury to the ulnar nerve at the elbow (e.g. elbow fractures/dislocation)
- long term pressure on elbow or the base of the palm
How does ulnar nerve injury present?
- claw deformity of the hand
- Loss of lumbrical contraction means loss of flexion of the MPJs and weakened extension of the IPJs.
- Many small muscles of hand affected but thumb, index and middle finger movements largely spared (because their lumbricals are spared, innervated by the median nerve(ind and mid))
- Sensory problems inconvenient.
=> devastating for e.g. musicians
What is the ulnar paradox?
- Ulnar injury at the wrist results in a more severe deformity (clawing) than injury at the elbow, though you might normally expect a more proximal, and thus more debilitating, injury to result in a more deformed appearance.
- This is because the ulnar nerve also innervates the ulnar half of FDP, flexion of the IP joints is weakened, therefore less claw-like appearance.
- ‘the closer to the paw, the worse the claw’
What is the course of the median nerve?
- formed anterior to the third part of the axillary artery
- formed by the union of fibers from the lateral and medial roots from the lateral and medial cords of the brachial plexus
- passes into the arm anterior to the brachial artery and through the arm into the forearm where it innervates most of the muscles in the anterior compartment of the forearm (except FCU and the medial half of FDP which are innervated by the ulnar nerve)
- passes through the carpal tunnel!!
- continues into the hand to innervate
- the three thenar muscles associated with the thumb
- the two lateral lumbricals associated with movement of index and middle fingers
- the skin over the palmar surface of the lateral three and one-half digits and over the lateral side of the palm and middle of the wrist.
How does damage to the median nerve occur?
- compression due to carpal tunnel syndrome
- fracture or other traumatic injury
- compression due to fluid build-up following injury
How does damage to the median nerve show?
- wasting of thenar eminence (Abductor pollicis visible (supplied by the ulnar narve so it won’t be affected by the carpal tunnel syndrome))
- Loss of both sensation and fine movement in the lateral digits is a significant disability
How does damage to the long thoracic nerve present?
- Pressing against a wall will lead to “winging” of the scapula resulting from the loss of activity of serratus anterior.
How can damage to the long thoracic nerve occur?
- e.g. in car accidents
- e.g. stabbed in that area
What does injury to the upper roots called?
Erb-Duchenne Palsy
Erb-Duchenne Palsy
- damage to the upper roots (C5,C6)
- Stretching of neck relative to the shoulder, affecting roots; e.g. falling off a motorcycle)
- Can also happen during childbirth when pulling the head.
- causes “waiter’s tip” position
- Many muscles affected (shoulder, anterior arm). Forearm pronated by lack of biceps supination.
- general disability and wasting of the limb
- Unopposed flexion of the wrist
- Anterior arm and forearm tend to be pronated.
- devastating injury to limb mobility
What is injury to the lower roots called?
- Klumpke’s palsy
Klumpke’s Palsy
- injury to the lower roots
- Common cause is over-abduction due to gripping overhead to break a fall. T1 (and sometimes C8) -> fibers coming off the medial cord will be affected and also some from the posterior cord because some T1 fibres go posteriorly)
- T1 mainly supplies the small muscles of the hand via the ulnar and median nerves. Loss of their activity results in clawed hand.
Other nerve injuries
- The injuries considered here are the more common, serious injuries.
- Many other injuries are possible leading to a variety of motor and sensory deficits.
