12.6 Innervation of the Upper Limb

Question 1

Which spinal levels comprise the brachial plexus?

Answer 1

C5-T1

Question 2

Dorsal scapular nerve root(s)

Answer 2

C5 (Imagine a handprint on the rhomboids; five fingers)

Question 3

Long thoracic nerve root(s)

Answer 3

C5-C7 (1,3,5,7,9; remove the three — SA runs from ribs 1-9, nerve roots are C5-C7)

Question 4

Subclavius nerve root(s)

Answer 4

C5-C6 (Six-five-ius)

Question 5

Which roots make up which trunks of the brachial plexus?

Answer 5

Superior trunk: C5-C6

Middle trunk: C7

Inferior trunk: C8-T1

Question 6

Which division of the brachial trunks that arise from the cervical spine correspond to flexors vs extensors?

Answer 6

Anterior division: flexors

Posterior division: extensors

Question 7

Suprascapular nerve root

Answer 7

C5-C6 (above scapula, and below clavicle [six-five-ius])

Question 8

Which divisions of which roots of the brachial plexus contribute to which cords? Around which blood vessel do the cords wrap?

Answer 8

• Anterior divisions of sup. and middle root create lateral cord
• Anterior division of inf. root creates medial cord
• Posterior divisions of all three create posterior cord (this one’s easy)

Question 9

Which nerves arise from the lateral cord of the brachial plexus?

Answer 9

• Lateral pectoral nerve
• Lateral root of median nerve
• Musculocutaneous

(Rugby mnemonic; “long legged movers”)

Question 10

Which nerves arise from the medial cord of the brachial plexus?

Answer 10

• Medial pectoral nerve
• Medial brachial cutaneous
• Medial antebrachial cutaneous
• Ulnar
• Medial root of medial nerve

(Rugby mnemonic; “make many moves using muscles”)

Question 11

Which nerves arise from the posterior cord of the brachial plexus?

Answer 11

• Upper subscapular
• Lower subscapular
• Thoracodorsal
• Radial
• Axillary

(Rugby mnemonic; “ULTRA competitive”)

Question 12

Which nerve innervates most forearm flexors?

Answer 12

Median nerve

Question 13

Which nerve innervates most intrinsic hand muscles?

Answer 13

Ulnar nerve

Question 14

Which nerve innervates all the extensors of arm, forearm, posterior skin of arm, forearm, and hand (but not fingers)?

Answer 14

Radial nerve

Question 15

Which are the three “interesting” nerves of the supraclavicular branches of the brachial plexus? Why?

Answer 15

• Dorsal scapular (rhomboids, levator scapulae, traps)
• Long thoracic (serratus anterior)
• Suprascapular (supra and infraspinatus)

Question 16

Is the long thoracic nerve deep or superficial to serratus anterior? Why is this important? Which muscle does this nerve pierce?

Answer 16

• Superficial to
• This makes it vulnerable to damage :(
• Pierces middle scalene

Question 17

Describe the course of the suprascapular artery and nerve relative to the AC ligament

Answer 17

Nerve: under
Artery: above

Therefore, nerve can get impinged

Question 18

Which area of the forearm skin does the musculocutaneous nerve innervate?

Answer 18

Lateral

Question 19

From which two cords of the brachial plexus does the median nerve arise? Which artery is this in front of?

Answer 19

Medial and lateral cords, in front of the axillary artery.

Question 20

Which nerve gives rise to the anterior interosseus nerve? What muscles does it innervate?

Answer 20

• Median nerve
• Innervates radial part of flexor digitorum profundis, flexor pollicis longus and pronator quadratus

Question 21

Which nerves innervate the thenar/hypothenar muscles?

Answer 21

Thenar: median
Hypothenar: ulnar

Question 22

Describe cutaneous innervation of the hand

Answer 22

Ulnar: medial 1.5 digits (on ulnar side)

Median: anterior of other digits + posterior distal phalanges of these

Radial: Lateral base of thumb and posterior aspect of 3.5 digits (except those fingertips)

Question 23

True or false: the whole median nerve passes through the carpal tunnel.

Answer 23

• False
• The palmar branch of the median nerve runs superficial to the flexor retinaculum

(Note: the ulnar nerve also has a palmar branch)

Question 24

What structures travel through the carpal tunnel?

Answer 24

• Median nerve
• Tendons of flexor digitorum profundus (4x)
• Tendons of flexor digitorum superficialis (4x)
• Tendon of flexor pollicis longus

Question 25

What does the ulnar nerve innervate?

Answer 25

• Flexor carpi ulnaris
• Medial half of FDP
• Intrinsic muscles of hand (other than thenar muscles and two lateral lumbricals)

Question 26

Describe the passage of the ulnar nerve across the elbow joint

Answer 26

Runs on the extensor (i.e., posterior) side of the elbow, in the ulnar groove of the medial epicondyle.

(This is why medial epicondyle fractures can cause damage to the ulnar nerve)

Question 27

The ulnar nerve enters the hand through the ______ canal, along with the ulnar artery and ulnar vein, which is between the _____ and _____ bones.

Answer 27

Guyon’s canal. Between pisiform and hamate bones.

Question 28

What muscles does the radial nerve innervate/not innervate?

Answer 28

• Upper arm: triceps
• ALL posterior compartment forearm muscles
• NO intrinsic hand muscles

Question 29

The median/ulnar/radial nerves travel through the two heads of which respective muscles?

Answer 29

Median: pronator teres
Ulnar: flexor carpi ulnaris
Radial: supinator

Question 30

Which major arteries do which of the median/ulnar/radial nerves travel with?

Answer 30

Median/Ulnar: Brachial artery
Radial: Profunda brachii

Question 31

Where does the superficial branch of the radial nerve run? What muscles does it innervate?

Answer 31

• Runs with radial artery under brachioradialis
• Superficial branch supplies brachioradialis, anconeus, and extensor carpi radialis longus

Question 32

The deep branch of the radial nerve becomes the ______. The counterpart to this nerve originates from the ____, and is called _____.

Answer 32

• Becomes the posterior interosseus nerve
• Counterpart is anterior interosseus nerve, which originates from median nerve

Question 33

Which muscles does the axillary nerve innervate? What are its roots?

Answer 33

• Deltoid
• Teres minor

Roots: C5-C6

Question 34

Which nerve innervates subscapularis and teres major? What are its roots?

Answer 34

• Subscapular nerve

Roots: C5-C6

Question 35

Describe the sensory innervation of the arm (not hand)

Answer 35

Lateral shoulder: axillary

Distal arm and posterior arm/forearm: radial

Lateral forearm: musculocutaneous