Flashcards in "The Brachial plexus, Nerves, and Vessels of the Upper Limb" Questions Deck (46)
What is meant by segmental nerve distribution in the body?
Body wall muscles, skin and limbs are supplied segmentally by the spinal nerves = segmental distribution as it is noted by which segments of spinal nerves are present. They are also supplied by other nerves but this is peripheral distribution.
What is a dermatome and a myotome?
Dermatome = area of skin supplied by a single spinal nerve root or spinal cord level
Myotome = region of skeletal muscle innervated by a single spinal nerve root or spinal cord level
Why might it be hard to detect the loss of singular spinal nerve/spinal cord levels?
Most muscles are supplied by two or more spinal roots and dermatomes overlap considerably so often the loss of one spinal cord level may go unnoticed.
What is 'crude' and 'light' touch used to test?
Integrity of sensory innervations of dermatomes in the upper limb
What does peripheral innervation comprise of and why might it be more obvious when peripheral innervation has been lost?
These carry nerve components from several spinal segments (roots) to muscles and skin areas
- damage to a peripheral nerve my result in wide ranging effects on more than one dermatomal area or muscle as the peripheral nerve affected provides the innervation to a large number of these.
What are the spinal segments supplying the sensory and motor nerve supplies to the upper limb?
How are the segmental supplies of the muscles of the upper limb divided?
Elbow flexors - C5-C6
Elbow extensors - C7-C8
Wrist movements and coarse hand movements - C6-C8
Fine hand movements - C8-T1
What nerve + spinal roots innervates the biceps brachii and its reflex?
How does one elicit the biceps brachii reflex?
Ask subject to rest comfortably with elbow semi flexed and hand pronated
- hold their forearm (so they are not flexing their elbow but it is in a "flexed" position)
Place your thumb on the biceps tendon and tap briskly with a tendon hammer on the nail bed of your thumb
If the reflex arc is intact, there will be a short contraction of the biceps causing flexion of the elbow
- compare with the other arm unless asked to only perform it on one side
What nerve + spinal roots innervates the triceps brachii and its reflex?
How does one elicit the triceps brachii reflex?
Ask subject to sit comfortably with elbow semi flexed and hand pronated
Hold their elbow with your non-hammer-holding arm
Briskly tap the triceps tendon directly with a tendon hammer
If the reflex arc is intact, there will be a brisk contraction of the triceps causing extension of the elbow
- compare with the other arm unless asked to perform it one one side
What is the physiological basis of muscle tendon reflexes?
When the tendon of the muscle is tapped, the muscle spindles are stretched slightly resulting in an involuntary (reflex) contraction of the muscle to prevent over-stretching
What is the spinal cord root that supplies the "regimental badge" area on the shoulder?
What are the approximate sensory segmental supplies to skin of the upper limb (dermatomes) and where would you test them?
Shoulder - C4
Lateral aspect of upper arm - C5
Lateral side of forearm and thumb/index finger - C6
Middle and ring finger - C7
Little finger, medial side of hand and forearm = C8
Medial side of upper forearm and arm = T1
Axilla = T2
C4 - regimental badge area
C5 - lateral side of upper arm
C6 - thumb
C7 - middle finger
C8 - little finger/medial forearm
T1 - medial upper arm
T2 - axilla
What is the function of the brachial plexus?
To rearrange the nerve fibres in C5-T1 (ventral rami) into bundles travelling to appropriate parts of the limbs
What are the 5 segments of the brachial plexus?
What are the roots in the brachial plexus?
5 anterior rami of the 5 spinal nerves involved (C5,6,7,8,T1)
What are the trunks in the brachial plexus and which spinal nerves are included in them?
Superior - C5, C6
Middle - C7
Inferior - C8, T1
What are the divisions in the brachial plexus and how many are there total?
Each TRUNK splits into an anterior and posterior division (6 total)
What are the cords of the brachial plexus, what forms each one and what are each of them called?
Lateral, posterior, medial
Lateral is formed from the anterior divisions from the upper and middle trunks
Posterior is formed from the 3 posterior divisions from all the trunks
Medial is formed as a continuation of the anterior division of the inferior trunk
What are the branches of the brachial plexus?
Nerve to subclavius
Medial cutaneous of arm
Medial cutaneous of forearm
What are the branches of the brachial plexus that branch in the roots segment of the plexus?
Dorsal scapular nerve (branches from C5 root)
Long thoracic nerve (branches from C5, C6, C7 roots
What are the branches of the brachial plexus that branch in the trunks segment of the plexus?
Suprascapular nerve (from superior/upper trunk)
Nerve to the subclavius (after suprascapular, also from superior trunk)
What are the branches of the brachial plexus that branch in the divisions segment of the plexus?
No branches in the divisions section
What are the branches of the brachial plexus that branch in the cords segment of the plexus?
Lots = 2 groups of 3, 2 posterior and 1 L.
Superior subscapular, thoracodorsal, inferior subscapular (1 group of 3), all from posterior cord
Medial pectoral, medial brachial, medial antebrachial (3 M's, all from medial cord)
Lateral pectoral (from lateral cord)
What are the terminal branches of the brachial plexus and which cords do they terminate from?
Radial - posterior cord
Axillary - posterior cord
Median - medial and lateral cord
Ulnar - medial cord
Musculocutaneous - lateral cord
Which cords do the nerve fibres supplying the different muscles of the upper limb run through?
Posterior = all extensors
Lateral = flexor muscles and is C5-C7 so muscles acting on the shoulder and elbow
Medial = flexor muscles and is C8-T1 so muscles in the forearm and hand
What are the two main nerves that the posterior cord divides into, what are their respective roots and what muscles do they supply?
Axillary - C5, C6
- winds around neck of humerus to supply fibres to the deltoid, teres minor and long head of triceps brachii
Radial - C7, C8, T1
- winds posterior to the humerus and travels in radial groove under the triceps, supplies all the muscles of the posterior compartment of the arm and forearm
What is the main nerve derived from the lateral cord?
Musculocutaneous - C5, C6, C7
- supplies elbow flexors and supinators (biceps + brachialis
What is the main nerve derived from BOTH lateral and medial cords?
Median nerve - C6-T1
- supplies most of the wrist/finger flexors in the forearm and most of the small muscles of the thumb and index finger
What is the main nerve derived from the medial cord?
Ulnar nerve - C8-T1
- mainly motor to muscles of forearm and the hand
- controls most of the small muscles in the hand except the fine motor muscles of the thumb and index finger (median nerve)
How can the axillary nerve be injured and what results from this?
Shoulder dislocations and upper humeral fractures
- motor - loss of abduction and eventual wasting of the deltoid
- sensory - shoulder joint + regimental badge region numbness
How can the radial nerve be injured and what results from this?
Fractures the shaft of the humerus
- motor - loss of function of the extensor muscles of the forearm and wasting of the triceps - WRIST DROP and weakness of the 'power grip'
- sensory - posterior surface of the thumb numbness however area is variable due to overlap with other nerves
How can the musculocutaneous nerve be injured and what results from this?
Well protected but can be cut during surgery for breast cancer
- loss of flexion of the elbow
How can the ulnar nerve be injured and what results from this?
Compression of the nerve, cutting of the nerve or fractures of the elbow at the point where it passes posterior to the medial epicondyle of the humerus
- weakness and wasting of many small muscles in the hand, clawing of the fingers may be seen due to unopposed median nerve-supplied long muscles of the fingers in the forearm
- claw is worse the more distal the injury (ulnar paradox, expected that the more proximal the injury, the worse it would be)
What is cubital tunnel syndrome?
Compression of the ulnar nerve at the elbow
- results in numbness in the little finger, medial half of ring finger and medial dorsal surface of the hand
- numbness and weakness deteriorate over time and ulnar claw develops late in the disease indicating nerve is severely affected
How can the median nerve be injured and what does this result in?
Can become entrapped as it passes through the carpal tunnel, can be injured above the elbow and at the elbow with different results
- above the elbow - loss of pronation and reduction in flexion of the hand at the wrist joint
- at the elbow - Hand of Benediction - loss of ability to flex 2nd/3rd digits at MCP/IP joints due to loss of innervation of lateral 2 lumbricals and lateral half of FDP
What can cause an upper brachial plexus lesion and which spinal nerve roots are affected?
Excessive lateral neck flexion away from shoulder
- commonly due to falling on neck at an angle (shoulder dystocia) or forceps delivery
- C5, C6 affected
What is the result of an upper brachial plexus lesion and which nerves are involved?
- loss of sensation in the arm, paralysis and atrophy of deltoid, biceps and brachialis
- this results in a medially rotated arm in the 'waiter's tip position' as the biceps and brachialis can't laterally rotate or supinate the arm
- suprascapular, musculocutaneous and axillary nerve involved
What can cause a lower brachial plexus lesion and which spinal nerve roots are affected?
Can arise due to difficulties in childbirth
- C8, T1 affected
What is the result of an lower brachial plexus lesion and which nerves are involved?
- ulnar nerve distribution numbness, claw hand, paralysis of all intrinsic hand muscles (since both median and ulnar nerves are deficient without C8+T1 fibres)
- T1 involvement may result in Horner's syndrome (ptosis (upper eyelid drooping) + miosis (excessive pupil constriction))
What is the difference in the effects on the hand by ulnar nerve lesion and Klumpke's (C8+T1) lesion?
Ulnar nerve lesion = claw-like hand
Klumpke's lesion - true claw (loss of all interossei so all fingers extended at MCP joint, flexed at IP joints)
Where are and what are the main arteries of the upper limb?
Subclavian artery - supraclavicular region between the clavicle and sternocleidomastoid muscle
Axillary artery - medial side of humerus posterior to tendon of short head of biceps
Brachial artery - medial bicipital groove behind medial border of biceps
Radial artery - lateral side of forearm/wrist
Ulnar artery - medial side of forearm/wrist
Which vein is most often used for venipuncture?
Median cubital vein
What structures are at risk during venipuncture of the median cubital vein?
Medial cutaneous nerve of forearm/median nerve
Risk of nerve compression if back/side wall of vein is punctured during access/infusion of fluids and fluid infiltrates the tissues = pressure build-up + compression