The Upper Extremity!
The Brachial Plexus:
Label your fingers from C5 (thumb) to T1 (pinky). Then recite after me:
The three musketeers (thumb, index and middle fingers extended)
Assassinated (make a gun with your thumb and index)
Five men (all five fingers)
And five rats (all five fingers)
But my uncle was ok (make an ok sign with your middle, ring and pinky extended)
That gives you the roots for the:
Musculocutaneous (C5, C6, C7)
Axillary (C5, C6)
Median (C5-T1)
Radial (C5-T1)
Ulnar (C7-T1)
Ok, going further down the arm. There is an arm and a forearm (wow!) and each is
divided into an anterior compartment and posterior compartment. Each compartment is
innervated by a single nerve (with a couple exceptions of course) But in general:
The Arm:
A. compartment: Musculocutaneous
P. compartment: Radial
Forearm:
A compartment: Median
P compartment: Radial
EXCEPTIONS!
Flexor Carpi Ulnaris, and the medial half of the flexor digitorum profundus, both in the A
compartment of the forearm, are innervated by the Ulnar nerve.
Think of it this way: the Ulnar nerve innervates all the muscles in the hand, with the
exceptions of the Thenar muscles, and the lateral half of the lumbricals, which are
innervated by the Median nerve.
So the Ulnar and Median nerves switch it up a little bit. Just to make for good trick
questions. Look out for these on tests!
P compartment of the forearm:
There are a lot of muscles here. Fortunately they travel through compartments to get to
the wrist, and separate themselves into a nice pattern: 2,2,1,2,1,1  kinda like a
palindrome, but not really. Starting from the lateral side (the side with the thumb dude!)
2: The abductor pollicis longus and extensor pollicis brevis travel together through the
first compartment and make the later border of your snuff box.
2: The extensor carpi radialis longus and brevis travel together through the second
compartment
1: The extensor pollicis longus travels by itself through the third compartment and takes
the long way around the carpi radiali (see above), forming the medial boarder of the snuff
box
2: The extensor indicis and extensor digitorum travel together through the fourth
compartment
1: The extensor digiti minimi is a loner (fifth compartment)
1: So is the extensor Carpi ulnaris (take a guess… the sixth!)
Bonus points! What goes through the snuff box? (The radial artery)
Miscellaneous upper extremity stuff:
The coracoid process has 3 muscles attached to it (pec minor, coracobrachalis, short head
of the bicep)
The palmaris longus goes outside of the flexor retinaculum, so when you flex your wrist
you can make it pop out.
A shoulder separation occurs at the AC joint. A shoulder dislocation occurs at the
humoral-scapula joint.
The Lower Extremity!
The lower extremity mirrors the upper with a couple modifications. It is also separated
into two halves, but we call them the thigh and the leg. This way we can liken people
more to chickens. There are now three compartment in each half, anterior, posterior and
medial in the thigh; and anterior, posterior, and lateral in the leg. Again, each
compartment in innervated by a single nerve (sorry, no mnemonic for the lumbar and
sacral plexi) with a couple exceptions as always.
The Thigh:
The A. compartment is the femoral nerve
The P compartment is the Tibial portion of the sciatic nerve
The M compartment is the Obturator nerve. What is the exception? (hamstring portion of
the obturator magnus is innervated by the tibial portion of the sciatic nerve)
The Leg:
The A compartment of the leg is the Deep fibular (peroneal) nerve
The P compartment is the Superficial fibular (peroneal) nerve
The L compartment is the Tibial nerve
Also for the leg, the deep muscles in the P compartment run behind the medial malleolus
in the following order:
Posterior Tibialis
Flexor Digitorum Longus
Flexor Hallucis Longus
The mnemonic here is Tom, Dick and Harry.
“And” can stand for the artery and nerve that also run through the tarsal tunnel behind the
medial malleolus. There is a vein there too.
The knee:
It’s there. Don’t forget about it.
There is an ACL, PCL, LCL, MCL. The MCL is attached to the Medial Meniscus, while
the LCL is not attached to the Lateral Meniscus.
The unhappy triad? (No it’s not you and your parents), it’s the MCL, ACL and Medial
Meniscus.
The ankle ligaments:
There are three on the lateral side and 4 on the medial side:
Lateral side, the fibula is unimportant, so it’s name always goes second:
Anterior talofibular
Posterior talofibular
Calcaneofibular
Medial side, the tibia is important (it does all the weight baring) so it’s name goes first:
Anterior tibiotalar
Posterior tibiotalar
Tibiocalcaneal
Note the first three are the exact same as the three on the lateral side! But we have an
additional bone on the medial side (the Navicular) so we need another ligament:
Tibionavicular  anyone surprised here?
This is a good way to remember that the Navicular is on the medial side of the foot.
Or just be lazy and call it the Deltoid ligament.
Misc. Lower Extremity stuff
The plantaris longus looks like a nerve. It runs between the Gastrocnemius and Soleous.
Be awares.
The pes anserinus is made up of the Gracillis, Sartorious, and Semitendinosis.
Reflexes:
There are a bunch of reflexes that god (according to Gov Palin) implemented to keep us
safe. Here’s how to remember which nerves do which:
1,2 The achilles reflex is mediated by S1 and 2
3,4 The knee reflex is mediated by L3 and 4
5,6 The bicep reflex is mediated by C5 and 6
7,8 The tricep reflex is mediated by C7and 8
Alright, there’s a run down of the stuff I can remember. I hope it’s readable, I think it’s
pretty error free. However, I did this in under an hour, so if you find one let me know
and I’ll buy you an ice cream or something. (misspellings don’t count!) If there are any
additional questions just email me (jao36@georgetown.edu)