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MSK Week 3 > 2.3.3. Brachial Plexus > Flashcards

2.3.3. Brachial Plexus Flashcards

1
Q

Define what the brachial plexus is - be as specific as you can (point of origin, path the nerves follow, where they terminate, what they innervate).

A

The brachial plexus is a network of nerve roots, trunks, divisions, and cords, running from the spine, formed by the ventral rami of the C5-C8 and T1 nerve roots.

It passes through the cervico-axillary canal to reach the axilla and innervates the brachium, antebrachium, and hand.

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2
Q

What are the five ROOTS of the brachial plexus? What is the anatomical name for these protrusions?

A

These are known as “anterior (or ‘ventral’) rami”

  • C5 nerve root
  • C6 nerve root
  • C7 nerve root
  • C8 nerve root
  • T1 nerve root
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3
Q

What are the three TRUNKS of the brachial plexus?

A
  • Superior
  • Middle
  • Inferior
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4
Q

What nerve roots unite to form the three trunks of the brachial plexus?

A
  • Superior trunk = C5 + C6 roots
  • Middle trunk = C7 root
  • Inferior trunk = C8 + T1 roots
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5
Q

What are the six DIVISIONS of the brachial plexus?

A

This is where it CAN get tricky, but NOT FOR YOU!

EACH trunk divides into TWO divisions:

anterior and posterior…

Use the relative anatomical positions of the trunks to name the divisions as follows:

  • Anterior divisions of the upper, middle, and lower trunks
  • Posterior divisions of the upper, middle, and lower trunks
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6
Q

What compartments of muscles do the anterior divisions of the trunks innervate?

A
  • Flexor (anterior) compartments

(think relative to the anatomical position - the belly of the forearm)

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7
Q

What compartments of muscles do the posterior divisions of the trunks innervate?

A
  • Extensor (posterior) compartments

(think relative to the anatomical position - the top of the forearm)

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8
Q

What are the three CORDS of the brachial plexus?

A
  • Lateral cord
  • Medial cord
  • Posterior cord
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9
Q

The anterior division of superior trunk and the anterior division of middle trunk form which cord of the brachial plexus?

A

The Lateral cord

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10
Q

The anterior division of the inferior trunk continues as which cord?

A

The Medial cord

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11
Q

Which divisions unite to form the posterior cord?

A
  • ALL THREE POSTERIOR DIVISIONS
    (post. superior + post. middle + post. inferior)
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12
Q

What are the five TERMINAL NERVES of the brachial plexus?

A

“My Aunty Raced My Uncle”

M = Musculocutaneous

A = Axillary

R = Radial

M = Median

U = Ulnar

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13
Q

From what roots does the musculocutaneous n. arise?

A
  • C5, C6, and C7
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14
Q

What motor functions does the musculocutaneous n. have?

A
  • It innervates the brachialis, biceps brachii, and coracobrachialis muscles
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15
Q

What sensory field does the musculocutaneous n. cover?

A

The lateral aspect of the forearm

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16
Q

From what roots does the axillary n. arise?

A

C5 and C6

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17
Q

What motor functions does the axillary n. perform?

A

It innervates the deltoid, teres minor, and the long head of the triceps brachii

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18
Q

What sensory field does the axillary n. cover?

A

Superolateral arm (over inferior part of the deltoid)

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19
Q

From what roots does the median n. arise?

A

C6, C7, C8, and T1

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20
Q

What motor functions does the median n. perform?

A

It innervates most of the flexor muscles in the forearm, the thenar muscles, and the two lateral lumbrical muscles that move the index and middle fingers

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21
Q

What sensory field does the median n. cover?

A

It innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand.

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22
Q

From what roots does the radial n. arise?

A

C5, C6, C7, C8, and T1

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23
Q

What motor functions does the radial n. perform?

A

Innervates the triceps brachii and the extensor muscles in the posterior compartment of the forearm

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24
Q

What sensory field does the radial n. cover?

A

Innervates the posterior aspect of the arm and forearm and the posterior aspect of the hand lateral to the axial line of digit 4

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25
Q

From what roots does the ulnar n. arise?

A

C8 and T1

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26
Q

What motor functions does the ulnar n. perform?

A

Innervates the flexor carpi ulnaris and medial half of the flexor digitorum profundus along with most intrinsic muscles of the hand

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27
Q

What sensory field does the ulnar n. cover?

A

Innervates the hand medial to the axial line of digit 4

28
Q

Describe the dermatome innervated by C5

A

Lateral aspect of the arm

29
Q

Describe the dermatome innervated by C6

A

Lateral forearm and thumb

30
Q

Describe the dermatome innervated by C7

A

Middle 3 fingers and center of posterior aspect of forearm

31
Q

Describe the dermatome innervated by C8

A

Pinky, medial side of hand and forearm

32
Q

Describe the dermatome innervated by T1

A

Medial aspect of forearm and inferior arm

33
Q

Describe the dermatome innervated by T2

A

Medial Aspect of superior arm and skin of the axilla

34
Q

Describe natomical relationship of the second part of the axillary artery to the cords of the brachial plexus.

(hint: this relationship is used to name them)

A

The cords bear the relationship to the second part of the axillary artery that is indicated by their names.

For example, the lateral cord is lateral to the axillary artery.

35
Q

Injury to the UPPER brachial plexus (C5, C6) results in…

A

Erb-Duchenne Palsy

(“Erb-er” - upper brachial plexus injury)

Results in musculocutaneous n. damage: deltoid, biceps and brachialis paresis.

Presentation: “waiter’s tip”

36
Q

Injury to the LOWER brachial plexus (C8, T1) results in…

A

Klumpke palsy

Results in Ulnar n. damage - hand clumsiness (intrinsic hand muscles affected), incoordination

Presentation: “total claw hand”

37
Q

Describe the pathological mechanism of the “total claw hand” sign.

A

Occurs after lower brachial plexus/lower cord injuries, leading to interosseous muscles no longer working (they flex the metacarpopharyngeal joints, aka MPJs, of the hand), meaning the extensors take over.

For now, just know that this is a palsy of the ulnar nerve.

38
Q

What are the FOUR supraclavicular branches of the brachial plexus?

A
  • Dorsal Scapular n.
  • Long Thoracic n.
  • Suprascapular n.
  • Subclavian n.
39
Q

Name as many of the infraclavicular branches of the brachial plexus as you can

(hint: there are 12 total - there’s a mnemonic for 5 of them…)

A
  • Lateral Pectoral
  • Medial Pectoral
  • Upper Subscapular
  • Lower Subscapular
  • Thoracodorsal (aka Middle Subscapular n.)
  • Medial cutaneous nerve of the arm
  • Median cutaneous nerve of the forearm

Recall the mnemonic: “My Aunty Raced My Uncle”

  • Musculocutaneous
  • Axillary
  • Radial
  • Median
  • Ulnar
40
Q

What muscles comprise the ANTERIOR / FLEXOR compartment of the arm?

What nerve supplies these muscles?

A

This contains 3 of the 4 major muscles of the arm: Biceps Brachii, Brachialis, and Coracobrachialis, which are all flexors.

They are supplied by the musculocutaneous n.

41
Q

What muscles comprise the POSTERIOR / EXTENSOR compartment of the arm?

What nerve supplies these muscles?

A

Contains the last of the four major muscles, the Triceps Brachii, which is an extensor.

It is supplied by the radial n.

42
Q

What type of joint is the sternoclavicular joint, and what articulates to form it?

A

Functions as a ball and socket joint but is technically a saddle synovial joint.

It is the only articulation between the upper limb and axial skeleton - 1st rib + clavicle + manubrium

43
Q

What type of joint is the acromioclavicular joint, and what articulates to form it?

A

A plane synovial joint, formed between the acromion and clavicle

44
Q

What type of joint is the glenohumeral joint.

A

A ball and socket synovial joint (has great mobility, but also has increased risk of injury).

45
Q

What two arteries are found in the posterior shoulder, and what do they supply?

A
  • Dorsal scapular artery: latissimus dorsi, levator scapulae, rhomboids (major & minor), and trapezius
  • Suprascapular artery: supraspinatus m. (and to a minor extent the sternocleidomastoid and subclavius)
46
Q

What artery comes off of the first part of the axillary artery?

Describe its course and what it supplies.

A

1 - Superior Thoracic Artery - Runs anteriorly and medially along border of pectoralis minor.

Supplies 1st and 2nd intercostal spaces and the superior portion of the serratus anterior

47
Q

What two arteries originate from the second part of the axillary artery?

Describe their course and what they supply.

A

1- Thoracoacromial artery - Curls around the superior medial border of pectoralis minor. This artery itself divides into four other arteries: the clavicular, acromial, deltoid, and pectoral .

(mnemonic: CADP - Cadavers Are Dead People)

It doesn’t directly supply any muscle - its branches do.

2- Lateral Thoracic Artery - Descends along axillary border of pectoralis minor and supplies the lateral aspect of the breast.

Supplies the serratus anterior, and pectoralis major.

48
Q

What arteries originate from the third part of the axillary artery?

Describe their course.

A

1- Anterior/Posterior Humeral Circumflex arteries: Encircle the surgical neck of the humerus and anastomose with each other laterally with the larger posterior branch traversing the quadrangular space (the anterior a. is much smaller than the posterior).

2- Subscapular artery: Along lateral border of scapular a., it divides into the circumflex scapular artery and the thoracodorsal artery.

3- Brachial artery: Branches off to Profunda brachii and the superior and ulnar collateral arteries.

49
Q

What muscles are supplied by the POSTERIOR Humeral Circumflex artery?

What muscles are supplied by the ANTERIOR Humeral Circumflex artery?

A
  • Posterior: supplies the teres minor, and deltoid.
  • Anterior: mainly supplies the head of the humerus.
50
Q

The circumflex scapular and thoracodorsal arteries arise which artery?

What do these two arteries individually supply?

A

They both arise from the subscapular artery.

  • The circumflex scapular a. supplies the infraspinatus m., the teres major m., and the teres minor m.
  • The thoracodorsal a. supplies the latissimus dorsi m.
51
Q

What is the Profunda brachii a.?

What does it supply?

A

It is the deep artery of the arm - Accompanies radial nerve along radial groove of humerus.

It supplies the posterior compartment of the arm.

52
Q

What nerve roots combine to form the Long Thoracic n.?

What muscle does this innervate?

A

C5, C6, and C7.

The Long Thoracic n. innervates the Serratus Anterior m.

53
Q

When injured, the Long Thoracic artery causes paralysis of which muscle?

This leads to what is called a “winged scapula” - with relation to the scapula, describe this in as much detail as possible.

A

The Serratus Anterior m. is paralyzed.

In a winged scapula, the medial border of the scapula moves laterally and posteriorly. When raising the arm, the medial side of the inferior angle pulls very far from the posterior wall.

54
Q

Name the SIX groups of axillary lymph nodes.

Describe their pyramidal pattern of drainage and confluence.

A

1- Pectoral (anterior) nodes

2- Subscapular (posterior) nodes

3- Humeral (lateral) nodes

These three make up the base of the pyramid, and they independently drain into #4:

4- Central nodes

This continues superiorly to the top of the pyramid:

5- Apical nodes

We’re at the “top” of the pyramid; only one more group lies above/supra to #5:

6- Supraclavicular nodes

55
Q

Where does the biceps brachii attach?

A

Short head attaches on the coracoid process of the scapula and the long head on the supraglenoid tubercle of the scapula.

They converge to attach distally on the fascia of the forearm and radial tuberosity via the bicipital aponeurosis

56
Q

What innervates the biceps brachii?

A

The musculocutaneous n.

57
Q

What action(s) does the biceps brachii perform?

A

It supinates the forearm, and the short head resists dislocation

58
Q

Where does the triceps brachii attach?

A

Long head attaches to the infraglenoid tubercle of the scapula, the medial head on the posterior surface of the humerus inferior to the radial groove and the lateral head on the posterior side of the humerus as well but superior to the radial groove.

They converge on the fascia of the forearm to attach on the olecranon of the ulna

59
Q

What innervates the triceps brachii?

A

The Radial n.

60
Q

What action(s) does the trieps brachii perform?

A

It is the main extensor of the forearm. Long head resists dislocation especially important during adduction

61
Q

Where does the coracobrachialis attach?

A

Coracoid process of scapula and the middle medial surface of the humerus

62
Q

What innervates the coracobrachialis?

A

The musculocutaneous n.

63
Q

What action(s) does the coracobrachialis perform?

A

It helps flex and adduct the arm, as well as resist dislocation

64
Q

Describe the geometry and anatomic importance of the cubital fossa.

A

This triangular intermuscular space is anterior to the elbow, and transmits nerves and vessels to the anterior compartment of the forearm

65
Q

What are the three boundaries of the cubital fossa?

(hint: think anterior/posterior, medial/lateral, etc)

A
  1. Superiorly - An imaginary line connecting the medial and lateral epicondyles
  2. Medially - The mass of flexor muscles off of the medial epicondyle, specifically the pronator teres
  3. Laterally - The mass of the extensor muscles coming off of the lateral epicondyle, most specifically the brachioradialis

MSK Week 3 (8 decks)

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