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MSK Week 1 > ICL 4.1: Brachial Plexus & Peripheral Nerves > Flashcards

ICL 4.1: Brachial Plexus & Peripheral Nerves Flashcards

1
Q

which nerve roots make up the brachial plexus?

A

C5-T1

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2
Q

which two nerves are the pre-plexus nerves of the brachial plexus?

A
  1. dorsal scapular nerve

2. long thoracic nerve

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3
Q

dorsal scapular nerve:

  1. nerve roots
  2. what does it innervate
A

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

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4
Q

long thoracic nerve:

  1. nerve roots
  2. what does it innervate
A

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

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5
Q

where does the brachial plexus come from?

A

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

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6
Q

what are the trunks of the brachial plexus and which nerve roots are they made of?

A

superior trunk = C5 + C6

middle trunk = C7

inferior trunk = C8 + T1

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7
Q

what is the suprascapular nerve and what is its origin?

A

originates from the superior trunk which is formed from C5 + C6

innervates supraspinatus and infraspinatus muscles of the rotator cuff

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8
Q

based on the location of the suprascapular nerve, what should you be worried about?

A

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

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9
Q

where are they divisions of the brachial plexus located? what are they?

A

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

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10
Q

what are the cords of the brachial plexus?

A

3 cords are formed and are named based upon their relationship to the axillary artery as it passes posterior to pectoralis minor

  1. lateral cord = comprised of the anterior divisions of the superior and middle trunks
  2. posterior cord = comprised of the 3 posterior divisions of each trunk
  3. medial cord = continuation of the anterior division of the inferior trunk
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11
Q

suprascapular nerve:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A
  1. sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
  2. root = C5, C6
  3. brachial plexus origin = superior trunk
  4. motor innervation = supraspinatus and infraspinatus of rotator cuff
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12
Q

lateral pectoral nerve:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A
  1. sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
  2. root = C5, C6, C7
  3. brachial plexus origin = lateral cord
  4. motor innervation = pectoralis major, inferior 2/3
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13
Q

medial pectoral nerve:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A
  1. sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
  2. root = C8, T1
  3. brachial plexus origin = medial cord
  4. motor innervation = pectoralis minor and sternocostal part of pectorals major
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14
Q

medial brachial cutaneous nerve:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A
  1. sensory innervation = cutaneous sensory ONLY
  2. root = C8, T1
  3. brachial plexus origin = medial cord
  4. motor innervation = NO MOTOR
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15
Q

medial antebrachial cutaneous nerve:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A
  1. sensory innervation = cutaneous sensory ONLY
  2. root = C8, T1
  3. brachial plexus origin = medial cord
  4. motor innervation = NO MOTOR
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16
Q

upper subscapular:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A
  1. sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
  2. root = C5, C6
  3. brachial plexus origin = posterior cord
  4. motor innervation = upper subscapularis
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17
Q

thoracodorsal nerve:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A

aka middle subscapular nerve

  1. sensory innervation = glenohumeral and acromioclavicular joints; NO CUTANEOUS
  2. root = C6, C7, T1
  3. brachial plexus origin = posterior cord
  4. motor innervation = latissimus dorsi
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18
Q

lower subscapular nerve:
1. sensory innervation

  1. root
  2. brachial plexus origin
  3. motor innervation
A
  1. sensory innervation = glenohumeral and acromioclavicular joints; NO CUTAN= EOUS
  2. root = C5, C6
  3. brachial plexus origin = posterior cord
  4. motor innervation = inferior subscapularis and trees major
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19
Q

which nerves provide sensation to the medial arm and forearm?

A

medial brachial cutaneous nerve

medial antebrachial cutaneous nerve

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20
Q

which nerves innervate the pectoralis major?

A
  1. medial pectoral nerve

a branch of the medial cord that innervates the inferior part of the pec major

  1. 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

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21
Q

axillary nerve:
1. root

  1. motor/sensory
  2. innervation
A
  1. C5-C6
  2. motor –> deltoid and teres minor

sensory –> over lateral deltoid

22
Q

radial nerve:
1. root

  1. motor/sensory
  2. innervation
A
  1. C5-T1
  2. 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)

23
Q

what does PIN stand for?

A

posterior interosseous branch of radial nerve

24
Q

how does the axial nerve root exit the brachial plexus? what’s its path?

A

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

25
Q

what is the region of unique axillary nerve cutaneous innervation?

A

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

26
Q

how does the radial nerve root exit the brachial plexus? what’s its path?

A

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

27
Q

what’s the course of the radial nerve in the forearm?

A

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

28
Q

how could you potentially injure the superficial radial nerve?

A

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

29
Q

what can you palpate/find in the anatomical snuffbox?

A

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

30
Q

what clinical symptoms are associated with problems related to the superficial radial and deep radial nerve?

A
  1. extensor indicis weakness with intact first – second dorsal web space sensation implies motor nerve neuropathy distal to radial nerve bifurcation at elbow
  2. 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

31
Q

medial cord contribution to the median nerve:
1. roots

  1. brachial plexus origin
  2. innervation
A
  1. C8, T1
  2. 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

32
Q

ulnar nerve:
1. roots

  1. brachial plexus origin
  2. innervation
A
  1. C8, T1
  2. 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

33
Q

what is the pathway of the ulnar nerve?

A

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

34
Q

what forms the borders of Guyon’s canal? what passes through it?

A

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

35
Q

what does the sensory vs. deep ulnar nerve innervate?

A 
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

36
Q

what is the function of the dorsal cutaneous branch of the ulnar nerve?

A

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

37
Q

lateral cord contribution to median nerve:
1. root

  1. brachial plexus origin
  2. innervation
A
  1. 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

38
Q

musculocutaneous nerve:
1. root

  1. brachial plexus origin
  2. innervation
A
  1. C5, C6
  2. terminal branch of lateral cord, motor –> Coracobrachialis
    Brachialis
    Biceps brachii

cutaneous sensory –> lateral forearm

39
Q

what compartment of the arm is the median nerve?

A

anterior compartment

no branches in the arm!

crosses elbow deep to bicipital aponeurosis

40
Q

what innervates the medial wad?

A

median nerve

  1. pronator teres
  2. palmaris longus
  3. flexor carpi radialis
  4. flexor digitorum superficialis

EXCEPT flexor carpi ulnas muscle and ulnar 1/3 of FDP which are innervated by ulnar nerve

41
Q

what does the anterior interosseous branch of the median nerve innervate?

A

deep anterior compartment (flexors):
1. pronator quadratus

  1. lateral ½ of FDP
  2. flexor pollicis longus
42
Q

how does the median nerve enter the hand?

A

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

43
Q

what is carpal tunnel syndrome?

A

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

44
Q

what does the median nerve innervate?

A

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)

45
Q

if you do a pin prick to the pad of your thumb, which nerve root are you testing?

A

C6

46
Q

if you do a pin prick to the pad of your middle finger, which nerve root are you testing?

A

C7

47
Q

if you do a pin prick to the pad of your small finger, which nerve root are you testing?

A

C8

48
Q

what does the posterior cord branch into?

A

radial and axillary nerve

49
Q

what does the medial cord branch into?

A

ulnar and median nerves

50
Q

what does the lateral cord branch into?

A

musculocutaneous and median nerve

51
Q

what are common sites of major nerve entrapment?

A
  1. median nerve at carpal tunnel
  2. ulnar nerve at the cubital tunnel, by the heads of flexor carpi ulnaris

3, PIN at supinator muscle

  1. radial nerve at the radial groove of the humerus

MSK Week 1 (11 decks)

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