L7.1 - Nerves of UL

Question 1

In the brachial plexus, how are cords named?

Answer 1

According to their relation to the axillary artery

Question 2

Pre-fixed brachial plexus?

Answer 2

Sometimes roots are higher (C4- 8)

Question 3

Post-fixed brachial plexus?

Answer 3

Sometimes roots are lower (C6 - T2)

Question 4

At which location are the following found:

a) Roots and trunks
b) Divisions
c) Cords and terminal branches

Answer 4

a) Roots and trunks - come from neck, supraclavicular
b) Divisions - behind clavicles, retroclavicular
c) Cords and terminal branches - infraclavicular

Question 5

Msc Nerve - Path it descends into

Answer 5

1) Pierces coracobrachiallis
2) Descends deep to biceps but superior to brachialis
3) Finishes at the lateral side of the elbow before it becomes cutaneous lateral to tendon of biceps, aka lateral antebrachial cutaneous nerve

Question 6

Injury to Msc nerve leads to?

Answer 6

Loss of motor innervation to arm and loss of cutaneous innervation of anterior lateral forearm (a bit of posterior lateral forearm as well)

Question 7

Ulnar Nerve - Path it descends into

Answer 7

1) Medial side of axillary artery (becomes brachial artery at lower border of teres major)
2) Passes behind medial epicondyle
3) Slips through 2 heads of FCU and under it. Lies superior to FDP
4) Goes over Flexor Retinaculum and into hand (tucked in under pisiform bone)

Question 8

Ulnar nerve - motor innervation?

Answer 8

Supplies all muscles of hand except what median nerve supplies:

• FCU
• FDP (medial half)
• Medial 2 lumbricals
• Hypothennar eminence
• Palmar and dorsal interossei
• Adductor Pol (the exception to the rule “all thenar muscles are supplied by the median nerve”)
• May or may not share thennar eminence with median nerve

Question 9

Ulnar Paradox

Answer 9

The ulnar nerve is vulnerable at two location:

• Behind the medial epicondyle
• At the flexor retinaculum

If damaged distally (at flexor ret), the hand displays a claw-like appearance as the medial lumbricals (responsible for MCP flexion and IP extension) are weakened and instead display MCP extension and IP flexion.

If damaged proximally (near elbow), the ulnar (medial) 1/2 of FDP, the flexor digitorum profundus muscle may be denervated and flexion of the IP joints is weakened, reducing the claw-like appearance of the hand. (Instead, the fourth and fifth fingers are simply paralyzed in their fully extended position rather than flexed.)

This is called the “ulnar paradox” because one would normally expect a more proximal and thus debilitating injury to result in a more deformed appearance.

Question 10

Cutaneous innervation of the hand - which nerves correspond to which regions?

Answer 10

Ulnar - Medial 1 1/2 digits
Median - Palmar 3 1/2 and nailbeds
Radial - Dorsal 3 1/2 minus nailbeds

Question 11

What terminal nerve roots correspond to which nerves?

Answer 11

Ulnar - (C7) C8 T1
Msc - C5 - 7
Median - C5 - T1
Axillary - C5 - 6
Radial - C5 - T1

Question 12

Median Nerve - motor innervation?

Answer 12

Supplies all forearm except FDP (medial half) and FCU

• Thennar muscles
• FDP (lat half)
• Lateral 2 lumbricals

Question 13

Median Nerve - Path it descends into

Answer 13

1) Descends to forearm, either lateral or superficial to the artery
2) Crosses artery and goes medial to brachial artery when ulnar nerve goes behind medial epicondyle
3) Descends through cubittal fossa
4) Slips under fibrous arch of FDS
5) Descends to middle of forearm, FDS is superficial to it, FDP deep to it
6) Through carpal tunnel and into the hand (palm)

Question 14

Median nerve - what splits before going through carpal tunnel?

Answer 14

The palmar branch of the median nerve which goes over the top of flexor retinaculum

Question 15

Axillary nerve - Motor and sensory innervation

Answer 15

Deltoid and regiments patch, has a posterior branch that innervates teres minor a little bit

Question 16

What space is the axillary nerve found in?

Answer 16

Quadrangular space - between long head of triceps, humerus, t min and maj

Question 17

Axillary Nerve - Path it descends into

Answer 17

1) Goes beneath shoulder joint before going above T.maj - hence endangered in inferior dislocation of shoulder joint
2) Anterior branch goes around surgical neck of humerus from back to front, feeding branches to lateral part and anterior part of deltoid

Question 18

Radial Nerve - Path it descends into

Answer 18

1) Goes through posterior wall of axilla to reach extensor compartment of arm and forearm
2) Exits below Teres Major
3) Goes in triangular interval between long and lateral head of biceps and Teres major
4) Spirals around back of humerus from medial to lateral in spiral groove
5) Piercing lateral intermuscular septum, exiting post compartment, going to ant compartment of arm
6) Tucks in under brachioradiallis
7) Splits into:
a) Sensory (superficial) which runs down lateral side of foream onto back of hand (lateral 3/1 digits on dorsum minus nail beds)
b) Motor (deep branch) pierces supinator and changes into posterior interosseous nerve after it goes through interosseous membrane

Question 19

What 2 extensor muscles attach to supracondylar ridge above CEO?

Answer 19

ECRL and Brachioradialis

Question 20

Interesting feature of radial nerve in regards to its branches?

Answer 20

Gives off branches early