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Anatomy > Brachial plexus and anterior arm > Flashcards

Brachial plexus and anterior arm Flashcards

1
Q

What does the brachial plexus innervate

A

Innervates muscles of the shoulder, arm, forearm and hand. Provides sensory innervation to the bones, skin, muscles and connective tissue of the shoulder and upper extremity.

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2
Q

When is a nerve plexus formed

A

formed when nerve fibres from 2 or more spinal segments intermingle then segregate to travel to a common anatomical region

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3
Q

What spinal segments does brachial plexus recieve motor and sensory fibres from

A

C5-T1

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4
Q

Where is the brachial plexus located

A

between the anterior and middle scalene

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5
Q

What are the different sections of the brachial plexus - in order

A

roots, trunks, divisions, cords, terminal branches

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6
Q

What are the roots

A

There is one root from each spinal segment and they are named from the spinal segment they represent (e.g., C5 root)

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7
Q

What are the different trunks

A

C5 and C6 roots join to form superior trunk. C8 and T1 roots join to form inferior trunk. C7 continues by itself to form middle trunk.

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8
Q

What do all trunks do

A

divide into an anterior and posterior division

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9
Q

Why is the segregation into anterior and posterior important

A

segregation because all fibres in anterior division will innervate anterior compartment muscles and all fibres in posterior division will innervate posterior compartment muscles

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10
Q

How does the mid-axillary line divide the arm

A

to form an anterior (pre-axillary/flexor) and a posterior (post-axillary/extensor) compartment.

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11
Q

How are the cords formed

A

The posterior divisions of the 3 trunks come together to form the posterior cord. The anterior division of the upper and middle trunk form the lateral cord. The anterior division of the lower trunk continues by itself to form the medial cord

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12
Q

How are the cords named

A

relative to their position to the axillary artery

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13
Q

What are the 5 terminal branches

A

axillary nerve, radial nerve, musculocutaneous nerve, ulnar nerve and median nerve

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14
Q

What does the posterior cord divide into

A

axillary and radial nerve

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15
Q

What does the lateral cord divide into

A

the musculocutaneous nerve and contributes to the median nerve by giving off the lateral root of the median nerve

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16
Q

What does the medial cord divide into

A

the ulnar nerve and contributes to the median nerve by giving off the medial route which joins the lateral route to form the median nerve proper.

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17
Q

What is the reference point to located components of the plexus

A

The terminal branches if the lateral and medial cords form the characteristic ‘M’ shape anterior to the axillary artery (most distinctive feature of plexus)

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18
Q

Which branch arises from the C5 root

A

the dorsal scapular nerve

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19
Q

What forms the long thoracic nerve

A

branches from C5, C6, C7 roots

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20
Q

What are the branches of the superior trunk

A

suprascapular nerve and the nerve to the subclavius

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21
Q

How many nerves do the cords give rise to in addition to the terminal branches

A

7

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22
Q

What branch does the lateral cord give off

A

lateral pectoral nerve

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23
Q

What branches does the posterior cord give off

A

upper and lower subscapular nerve and the thoracodorsal nerve

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24
Q

What branches does the medial cord give off

A

the medial pectoral nerve, the medial brachial cutaneous nerve and the medial antebrachial cutaneous nerve.

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25
Q

When does upper brachial plexus injury occur

A

during extreme lateral flexion of head (especially if shoulder is simultaneously depressed) – like when baby is being pulled out while its shoulders are trapped within the mother’s pelvis

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26
Q

What does upper brachial plexus injury damage

A

C5/C6 nerve roots or the superior trunk

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27
Q

What can upper brachial plexus damage result in

A

results in erb-duchenne paralysis (when arm hangs limply at the side and is internally rotated, forearm is also slightly pronated which slightly flexes the wrist)

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28
Q

What causes lower brachial plexus injury

A

during extreme abduction of the arm (e.g., falling from a ladder or a tree attempts to stop themselves by reaching for something overhead to hang on to)

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29
Q

What does lower brachial plexus injury damage

A

stress on C8-T1 root of inferior trunk itself

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30
Q

What does lower brachial plexus injury effect

A

causing muscles in the hand and forearm to be effected resulting in klumpke’s paralysis (claw hand – where fingers are flexed)

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31
Q

Which nerve innervates the serratus anterior muscle

A

the long thoracic nerve

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32
Q

Where is the long thoracic nerve located

A

travels along the lateral anterior wall, then is located on the superficial surface of the muscle

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33
Q

What does the serratus anterior do

A

protracts and upwardly rotates the scapula, it keeps the scapula tight against the thoracic cage during arm movements

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34
Q

What is a sign of long thoracic nerve injury

A

winging of scapula - it displays an obvious dorsal protusion

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35
Q

What does the axillary nerve innervate

A

the deltoid and teres major muscles. Provides sensory innervation to a portion of skin over the posterior lateral shoulder of the axillary.

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36
Q

Where does the axillary nerve travel

A

posteriorly through the quadrangular shape in order to innervate those muscles

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37
Q

When is the axillary nerve vulnerable to injury

A

when there is a fracture at the surgical neck of the humerus - could occur due to shoulder dislocation

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38
Q

What can axillary nerve injury result in

A

The loss of shoulder abduction above 15 degrees due to paralysis of the deltoid muscle. Paralysis of the teres minor muscle results in weakened external rotation at the shoulder and decreased stability of the shoulder joint because teres minor contributes to the rotator cuff. Loss of cutaneous sensation over the posterior lateral aspects of the shoulder.

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39
Q

What does the radial nerve supply

A

supplies all extensor compartment muscles of the arm and the brachioradialis and the supinator. It provides sensory innervation to the skin on the dorsal surface of the forearm and hand

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40
Q

Where does the radial nerve travel

A

It begins its distal journey by travelling posteriorly around the body of the humerus to lie within the radial groove, it comes to lie briefly within the flexor compartment of the arm as it travels across the elbow joint anterior to the lateral epicondyle of the humerus

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41
Q

At the elbow, what does the radial nerve divide into

A

superficial and deep branches

42
Q

Where does the superficial branch of the radial nerve travel

A

The superficial branch is cutaneous and travels distally along the radius to reach the hand

43
Q

What does the superficial branch of the radial nerve innervate

A

provides sensory innervation to the skin over the dorsum of the thumb and the radial half of the hand

44
Q

Is the deep branch motor or sensory innervation

A

motor

45
Q

Where does the deep branch of the radial nerve located

A

enters the posterior compartment of the forearm by piercing the supinator muscle within the posterior compartment of the forearm the radial nerve is now known as the posterior interosseous nerve (or PIN).

46
Q

What does radial nerve injury cause

A

Wrist drop - by loss of innervation to the extensor muscles in the forearm

47
Q

What do injuries proximal to the triceps innervation cause

A

Loss of elbow extension

48
Q

What are characteristics of radial nerve injury

A

loss of sensation or paraesthesia over the dorsum of the thumb and lateral aspect of the hand

49
Q

When is the radial nerve susceptible to injury

A

when there is a fracture of the shaft of the humerus or from compression due to the use of crutches etc…

50
Q

What does the musculocutaneous branch innervate

A

provides motor innervation to the coracobrachialis, brachialis and biceps brachii before ending as the lateral antebrachial cutaneous nerve which provides cutaneous innervation to the skin of the lateral aspect of the forearm

51
Q

What does damage to the musculocutaneous nerve cause

A

loss of its sensory component and loss of elbow flexion and weakened forearm supination

52
Q

Where is the ulnar nerve located

A

travels distally to enter the forearm by crossing the elbow joint immediately posterior to the medial epicondyle of the humerus. Once in the forearm the ulnar nerve is parallel to the ulnar artery, they both travel distally along the medial aspect of the forearm towards the hand.

53
Q

What does the ulnar nerve innervate

A

the flexor cardi ulnaris and half of the flexor digitorum profundus muscle. It provides cutaneous innervation to the medial 1/3 of the hand and motor innervation to the hypothenar muscles and all intrinsic hand muscles except thenar muscles and the first 2 lumbrical muscles

54
Q

How is ulna normally damaged

A

entrapment as it passes behind the medial epicondyle or fracture of the medial epicondyle of the humerus.

55
Q

What does ulnar entrapment cause

A

tardy ulnar palsy causing paraesthesia over the ring and little fingers and loss of fine motor control of the digits

56
Q

What does more severe ulnar damage result in

A

wrist causes paralysis of the abductors and adductors of the digits, resulting in claw hand (little fingers and ring fingers are hyper-extended at the metacarpal phalangeal joint and flexed at the interphalangeal joint due to loss of lumbrical and interosseus muscle function in the extensor expansion of these digits).

57
Q

Which artery does the median nerve accompany

A

the brachial artery as it crosses the elbow medial to the tendon of the biceps brachii

58
Q

Which nerve does the median nerve give off after entering the forearm

A

the anterior interosseous nerve

59
Q

What does the anterior interosseous nerve lie along

A

the interosseous membrane

60
Q

What does the median nerve and the anterior interosseous nerve supply

A

proper provide motor innervation to all of the flexor compartment muscles of the forearm except for the flexor carpi ulnaris and the ulnar ½ of flexor digitorum profundus

61
Q

How does the anterior interosseous nerve end

A

in the distal forearm - does not cross the wrist joint

62
Q

What branch does the median nerve give off as it exits the carpal tunnel

A

The recurrent branch of the median nerve (motor)

63
Q

What does the recurrent branch of the median nerve innervate

A

the 3 muscles of the thenar eminence

64
Q

What does the median nerve do after it has passed through the carpal tunnel

A

continues distally, innervating the first 2 lumbrical muscles before becoming cutaneous to the skin of the index and middle fingers as well as to the lateral half of the palm

65
Q

How does median nerve injury lead to carpal tunnel syndrome

A

Nerve is entrapped or inflamed as it enters the wrist under cover of the transverse carpal ligament

66
Q

What does mild carpal tunnel syndrome cause

A

causes paraesthesia and pain along the thumb, index and middle fingers.

67
Q

What does more severe carpal tunnel syndrome cause

A

cause atrophy of the thenar muscles and subsequent reduction of thumb movements

68
Q

Where does the anterior compartment of the arm lie

A

in front of the humerus and in front of the medial and lateral intermuscular septa

69
Q

What are the 3 muscles that make up the anterior compartment of the arm

A

the biceps brachii, the coracobrachialis and the brachialis.

70
Q

What is the most anterior muscle of the arm

A

biceps brachii

71
Q

Describe the shape of the biceps brachii

A

the 2 heads meet up to form a single belly, halfway down the arm. The belly narrows to form a 2 part tendon - the main part dives between the radius and the ulna and inserts on the radius tuberosity.

72
Q

What happens to the lateral edge of the tendon

A

the tendon fans out into a thin sheet of fascia (bicipital aponeurosis) becoming continuous with the deep fascia surrounding the forearm

73
Q

What does the bicepital aponeurosis give

A

an indirect attachment to the ulna

74
Q

Where does the short head of the biceps arise

A

arises in common from the tip of the coracoid process of the scapula with the coracobrachialis muscle

75
Q

Where is the long head of the biceps located

A

runs up the bicipital groove and passes inside the shoulder joint to reach its origin from the supraglenoid tubercle of the scapula

76
Q

Which muscle lies behind the biceps

A

the brachialis

77
Q

Describe the location of the musculocutaneous nerve

A

travels through the coracobrachialis muscle and then emerges deep to the biceps, where it runs down between biceps and brachialis to supply both of them. It then emerges to become the lateral cutaneous nerve of the forearm.

78
Q

Where does the brachialis arise

A

from a broad area on the anterior humerus

79
Q

What is the coracobrachialis

A

a slender muscle and a weak adductor

80
Q

Where on the ulna does the brachialis attach

A

to the front of the proximal ulna on the ulna tuberosity

81
Q

What happens when the brachialis contracts

A

it flexes the elbow joint

82
Q

Which nerve supplies the lateral third of the brachialis

A

the radial nerve

83
Q

Where do the biceps attach to the radius

A

at the proximal end on the radial tuberosity

84
Q

What is the function of the biceps brachii

A

flexor of elbow joint and is a supinator of the forearm

85
Q

When are the biceps more efficient at being a flexor

A

when the forearm is pronated - muscles are fully stretched

86
Q

Which 2 nerves start out close together and when do they diverge

A

the median and ulnar, half way down the arm they diverge

87
Q

Describe the location of the median nerve

A

stays close to the brachial artery, crossing in front of it. At the elbow it lies medial to the artery, then dives down between the brachialis tendon and pronator teres, and passes between the 2 heads of pronator teres to enter the forearm

88
Q

Describe the location of the ulnar nerve

A

slants backwards, and runs down just medial to the triceps tendon and behind the medial epicondyle. It turns a sharp corner round the underside of the medial epicondyle, where there is a fibrous tunnel for it. It passes between the 2 heads of flexor capri ulnaris to enter the forearm.

89
Q

What does the median nerve supply

A

pronator teres, flexor capri radialis, palmaris longus and pronator quadratus

90
Q

Describe the location of the radial nerve

A

Just below the latissimus tendon, the radial nerve runs back between the long head and the medial head of triceps. As it passes round the humerus, it lies right on the bone, running between the medial and latera head of triceps. It runs beneath the lateral head to emerge right on the bone, above brachioradialis. Under cover of brachioradialis it reaches the lateral epicondyle

91
Q

What does the radial nerve supply

A

the triceps, anconaeus, brachioradialis, all 3 wrist extensors and supinator.

92
Q

Where does the brachioradialis arise

A

arises halfway up the humerus, just below the deltoid tuberosity. It is inserted on the distal radius

93
Q

What is the function of brachioradialis

A

flexor of elbow

94
Q

What does contraction of triceps cause

A

extension of elbow

95
Q

What are the 3 heads of the triceps

A

long, lateral and a medial/deep head

96
Q

Where does the long head of the triceps arise from

A

the infraglenoid tubercle of the scapula

97
Q

Where does the lateral head of the triceps arise from

A

high up on the lateral side of the posterior humerus

98
Q

Where does the medial head of the tricsps arise

A

from a broad area, lower down and more medially

99
Q

When the 3 heads of the triceps converge where does its tendon insert

A

on the olecranon

100
Q

Where does the anconaeus run

A

from the lateral epicondyle to the lateral aspect of the proximal ulna

101
Q

What is the function of the anconaeus

A

a minor elbow extensor

Anatomy (21 decks)

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