ICL 4.1: Brachial Plexus & Peripheral Nerves Flashcards
which nerve roots make up the brachial plexus?
C5-T1
which two nerves are the pre-plexus nerves of the brachial plexus?
- dorsal scapular nerve
2. long thoracic nerve
dorsal scapular nerve:
- nerve roots
- what does it innervate
C5 root
innervates rhomboid major and minor and the levator scapulae
the levator scapulae lifts the scapula while the rhomboid helps retract the scapula –> both originate from the medial border of the scapula
long thoracic nerve:
- nerve roots
- what does it innervate
C5, C6, C7 roots
innervates the serratus anterior
if you cut the LTN, the serrates anterior would become weak, maybe paralyzed – if it’s weak there won’t be any scapula support and you’ll get medial border winging of the scapula
this nerve sometimes gets clipped during mastectomy
where does the brachial plexus come from?
the nerve roots come from the proximal portion in the posterior triangle of the neck and then they pass in between the anterior and middle scalene muscles of the neck
this is a potential problem because it could lead to nerve entrapment which could cause tingling
what are the trunks of the brachial plexus and which nerve roots are they made of?
superior trunk = C5 + C6
middle trunk = C7
inferior trunk = C8 + T1
what is the suprascapular nerve and what is its origin?
originates from the superior trunk which is formed from C5 + C6
innervates supraspinatus and infraspinatus muscles of the rotator cuff
based on the location of the suprascapular nerve, what should you be worried about?
it traverses the scapular notch on its way to innervate the infraspinatus muscle
that notch is closed off by the transverse scapular ligament to form an opening for the suprascapular nerve to go through it so you should be worried about entrapment
so like if you get an edema or fatty tumor that could entrap the nerve it could lead to weak supraspinatus and infraspinatus which means you won’t be able to do abduction of the shoulder due to supraspinatus weakness or external rotation due to infraspinatus weakness
where are they divisions of the brachial plexus located? what are they?
divisions form between the 1st rib and the medial border of pectoralis minor
the anterior divisions supply the anterior or flexion compartment
the posterior divisions supply the posterior or extensor compartments of the upper limb
what are the cords of the brachial plexus?
3 cords are formed and are named based upon their relationship to the axillary artery as it passes posterior to pectoralis minor
- lateral cord = comprised of the anterior divisions of the superior and middle trunks
- posterior cord = comprised of the 3 posterior divisions of each trunk
- medial cord = continuation of the anterior division of the inferior trunk
suprascapular nerve:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
- sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
- root = C5, C6
- brachial plexus origin = superior trunk
- motor innervation = supraspinatus and infraspinatus of rotator cuff
lateral pectoral nerve:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
- sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
- root = C5, C6, C7
- brachial plexus origin = lateral cord
- motor innervation = pectoralis major, inferior 2/3
medial pectoral nerve:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
- sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
- root = C8, T1
- brachial plexus origin = medial cord
- motor innervation = pectoralis minor and sternocostal part of pectorals major
medial brachial cutaneous nerve:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
- sensory innervation = cutaneous sensory ONLY
- root = C8, T1
- brachial plexus origin = medial cord
- motor innervation = NO MOTOR
medial antebrachial cutaneous nerve:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
- sensory innervation = cutaneous sensory ONLY
- root = C8, T1
- brachial plexus origin = medial cord
- motor innervation = NO MOTOR
upper subscapular:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
- sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
- root = C5, C6
- brachial plexus origin = posterior cord
- motor innervation = upper subscapularis
thoracodorsal nerve:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
aka middle subscapular nerve
- sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
- root = C6, C7, T1
- brachial plexus origin = posterior cord
- motor innervation = latissimus dorsi
lower subscapular nerve:
1. sensory innervation
- root
- brachial plexus origin
- motor innervation
- sensory innervation = glenohumeral and acromioclavicular joints; NO CUTAN= EOUS
- root = C5, C6
- brachial plexus origin = posterior cord
- motor innervation = inferior subscapularis and trees major
which nerves provide sensation to the medial arm and forearm?
medial brachial cutaneous nerve
medial antebrachial cutaneous nerve
which nerves innervate the pectoralis major?
- medial pectoral nerve
a branch of the medial cord that innervates the inferior part of the pec major
- lateral pectoral nerve
a branch of the lateral cord that innervates the superior portion of the pec major
the pectoralis major attaches to the sternum, the menubrium and part of the clavicle all the way to the inter tubercular groove of the humerus
axillary nerve:
1. root
- motor/sensory
- innervation
- C5-C6
- motor –> deltoid and teres minor
sensory –> over lateral deltoid
radial nerve:
1. root
- motor/sensory
- innervation
- C5-T1
- motor –> triceps brachii, brachioradialis, extensor carpi radialis longus
superficial radial sensory –> dorsal 1st-2nd webspace skin
posterior interosseous branch of radial motor –> Extensor carpi radialis brevis
Supinator Extensor digitorum (communis)
Extensor digiti minimi (quinti)
Extensor carpi ulnaris
ABductor pollicis longus
Extensor pollicis brevis
Extensor pollicis longus
Extensor indicis (proprius)
what does PIN stand for?
posterior interosseous branch of radial nerve
how does the axial nerve root exit the brachial plexus? what’s its path?
it exits to the posterior axillary region through the quadranqular space, accompanied by the posterior circumflex humeral artery
it then encircles the surgical neck of the humerus which is why you have to worried about pinching the radial nerve if there’s a humerus fracture
what is the region of unique axillary nerve cutaneous innervation?
your upper forearm shoulder region
this region will be
anesthetic (numb) to pinprick after injury to axillary nerve in shoulder dislocations and humeral fractures at the surgical neck
how does the radial nerve root exit the brachial plexus? what’s its path?
it forms as a terminal branch of the posterior cord (along with the axillary nerve)
it then enters the posterior arm just inferior to the teres major through the triangular interval – here it enters and follows the radial groove of the humerus next to the profound brachii artery
what’s the course of the radial nerve in the forearm?
distal to the radial nerve split around the elbow, the main branch of the radial becomes the deep radial nerve
the deep radial pierces the supinator muscle and once it EXITS the supinator it becomes the posterior interosseous nerve (PIN) which innervates all muscles of the posterior/extensor forearm –> there are NO cutaneous branches from PIN
the superficial radial nerve runs down the lateral side of the forearm, crosses over the anatomical snuffbox superficial to the tendon of EPL down to the webspace between the thumb and pointer finger
how could you potentially injure the superficial radial nerve?
handcuffs
it’s because the superficial radial nerve crosses over the anatomical snuffbox superficial to the tendon of EPL, where it can be easily palpated as it separates into several branches
the superficial radial nerve is the ONLY cutaneous innervation over the 1st – 2nd dorsal webspace
**the radial nerve is usually tested sensorially in this region
what can you palpate/find in the anatomical snuffbox?
the anatomical snuffbox is the pocket that forms between the EPL and the EPB and APL tendons when the thumb is extended (slide 22)
the floor of the snuffbox contains the radial artery & scaphoid bone –> pain upon palpation of the floor strongly suggests a scaphoid fracture, even in the absence of radiographic findings of a fracture
EPL = extensor pollicis longus tendon
EPB = extensor pollicis brevis tendon
APL = abductor pollicis longus
what clinical symptoms are associated with problems related to the superficial radial and deep radial nerve?
- extensor indicis weakness with intact first – second dorsal web space sensation implies motor nerve neuropathy distal to radial nerve bifurcation at elbow
- extensor indicis weakness and numbness over the first – second dorsal webspace implies radial nerve injury proximal to bifurcation at elbow (or in plexus)
the most typical finding of general radial neuropathy is “wrist drop” since all the extensors are lost or weakened
sidenote: extensor indicis produces a weak MC-P extension of index finger if the radial motor nerve is injured or interrupted
medial cord contribution to the median nerve:
1. roots
- brachial plexus origin
- innervation
- C8, T1
- medial cord, motor main branch –> PT, FCR, PL, FDS, APB, ½ of FPB, OP, lateral 2 lumbricals
medial cord, motor anterior, interosseous branch –> FPL, lateral 1/2 FDP, PQ
cutaneous sensory –> sensory to radial half of palm to lateral side of 4th finger and thumb and fingers 1 and 2
ulnar nerve:
1. roots
- brachial plexus origin
- innervation
- C8, T1
- terminal branch of medial cord, motor –> FCU, medial ½ FDP, medial 2 lumbricals, FDM, ADM, ODM,
All 3 palmar interosseous, All 4 dorsal interosseous, AP
cutaneous sensory –> sensory medial half of ring and all of small finger
what is the pathway of the ulnar nerve?
it runs from its origin in the anterior compartment of the arm, with NO branches in the arm
it then crosses the elbow posterior to the medial epicondyle (elbow) , where it is susceptible to injury in medial epicondylar fractures
then it travels under the belly of flexor carpi ulnaris (FCU) and joins the ulnar artery in the distal ½ of the forearm
it crosses the wrist in Guyon’s canal superficial to the flexor retinaculum (transverse carpal ligament); NOT in the carpal tunnel
what forms the borders of Guyon’s canal? what passes through it?
the ulnar nerve passes through Guyon’s canal
the botton of Guyon’s canal is the traverse carpal ligament aka flexor retinaculum while the roof of the runnel is the volar carpal ligament
what does the sensory vs. deep ulnar nerve innervate?
the sensory ulnar nerve innervates the 5th digit and medial ½ of the 4th digit
the deep ulnar nerve separates from the sensory branch in the hypothenar eminence and innervates the hypothenar muscles all the interosseous muscles, medial two lumbricals and adductor pollicis muscle
what is the function of the dorsal cutaneous branch of the ulnar nerve?
it originates from the ulnar nerve approximately 1/2 way between wrist and elbow
sensory to the dorsal medial one half of the long, 3/4 of the ring and small finger
no motor action
lateral cord contribution to median nerve:
1. root
- brachial plexus origin
- innervation
- C6, C7
2. lateral cord, main branch, motor --> Pronator teres Flexor carpi radialis Palmaris longus Flexor digitorum superficialis Abductor pollicis brevis ½ of flexor pollicis brevis Opponens pollicis Lateral 2 lumbricals
lateral cord, anterior interosseous branch, motor –> Flexor pollicis longus
Lateral ½ flexor digitorum profundus
Pronator quadratus
cutaneous sensory –> Sensory to radial half of palm and to lateral side of 4th digit and thumb and fingers 1 and 2
musculocutaneous nerve:
1. root
- brachial plexus origin
- innervation
- C5, C6
- terminal branch of lateral cord, motor –> Coracobrachialis
Brachialis
Biceps brachii
cutaneous sensory –> lateral forearm
what compartment of the arm is the median nerve?
anterior compartment
no branches in the arm!
crosses elbow deep to bicipital aponeurosis
what innervates the medial wad?
median nerve
- pronator teres
- palmaris longus
- flexor carpi radialis
- flexor digitorum superficialis
EXCEPT flexor carpi ulnas muscle and ulnar 1/3 of FDP which are innervated by ulnar nerve
what does the anterior interosseous branch of the median nerve innervate?
deep anterior compartment (flexors):
1. pronator quadratus
- lateral ½ of FDP
- flexor pollicis longus
how does the median nerve enter the hand?
carpal tunnel
it shares the space with 9 tendons = flexor pollicis longus, flexor digitorum profundus (4), and flexor digitorum superficialis (4)
the median nerve is very superficial so it’s really vulnerable to injury
what is carpal tunnel syndrome?
when the median nerve is compressed in the carpal tunnel entering the wrist
the top of the tunnel is the flexor retinaculum aka transverse carpal ligament while the base of the tunnel is the proximal row of carpal bones
what does the median nerve innervate?
sensory = the lateral 3 digits and the lateral ½ of the 4th digit
motor = the lateral 2 lumbricals
and, via the recurrent branch,
the 3 muscles of the thenar eminence (APB, FPB, OP)
if you do a pin prick to the pad of your thumb, which nerve root are you testing?
C6
if you do a pin prick to the pad of your middle finger, which nerve root are you testing?
C7
if you do a pin prick to the pad of your small finger, which nerve root are you testing?
C8
what does the posterior cord branch into?
radial and axillary nerve
what does the medial cord branch into?
ulnar and median nerves
what does the lateral cord branch into?
musculocutaneous and median nerve
what are common sites of major nerve entrapment?
- median nerve at carpal tunnel
- ulnar nerve at the cubital tunnel, by the heads of flexor carpi ulnaris
3, PIN at supinator muscle
- radial nerve at the radial groove of the humerus
