Download Dissection Instructions of the Superficial Nerves of the Neck, Arm

Dissection Instructions of the Superficial Nerves of the Neck, Arm and Forearm
Session One
1. Cadaver Positioning
a. Place the cadavers head and shoulders on an elevated platform such as the
big white bowl
b. Use a bungee cord and hook the external meatus of the cadaver and draw
it across the face under the nose and then wrap it around the leg of the
dissection table to help turn the head to the side
c. Your tools will be a Metz Scissors and a forceps
2. Superficial Cervical Plexus
a. Look at the sternocleidomastoid and imagine the center
i. Use the Metz to insert it into the most lateral or posterior aspect of
the muscle fibers
ii. As long as you are on this edge of the muscle look for a nerve that
is curving from under the muscle and crossing over its top on its
way to the middle of the neck. This is the transverse cervical nerve.
iii. These cervical nerves come from the same bundle of nerve tissue
so once you find this, it is a matter of looking for the other two.
iv. The greater auricular will then come form this same bundle of
nerves and angle up towards the ear
v. The lesser occipital will go along the lateral edge of the SCM
towards the occiput. Remember that the SCM is a wide muscle at
its insertion on the cranium and from the mastoid can be as much
as 3-4cm wide so the path of the lesser occipital will follow this
path
b. Now begin looking for the supraclavicular nerves. They are in a nerve
bundle that is separate and further caudad from the bundle of nerves that
were just found.
i. Once you find what looks like a tissue of nerves going towards the
middle third of the clavicle you can try tofollow it and look for
three branches, the middle that goes to the sternoclavicular joint,
the medial that goes towards the middle third of the clavicle and
the lateral which goies to the acromioclavicluar joint.
ii. You don’t have to follow these far as it is best to just demonstrate
them and their general direction and leave them attached to tissue
to keep them in place.
c. Put a tie on all the nerves you have found. Make the tie such that the knot
you throw down towards the nerve allows for a small loop. Otherwise, a
tight knot will eventually cut the nerve. Then leave the tie about 10cm
long and tie a knot in the end so it is easy to grab.
3. Accessory Nerve
a. Now begin looking for the accessory nerve.
i. First find the trapezius. This muscle is has a thin edge and its
insertion is on the lateral third of the clavicle. Find it here and then
lift any tissue above the muscle up and use your thumb to push the
muscle down and away from the overlying tissue and follow the
border of the trapezius up to the occiput if possible.
ii. Once you have exposed the middle third you can begin looking
under the edge of the muscle for the accessory that comes from
above the origin of the previously found superficial cervical plexus
nerves.
4. Practical application
a. The superficial cervical plexus can be blocked for carotid surgery, and any
surgery involving superficial dissection by the surgeon such as the
Portacath, dialysis catheter, vagal nerve stimulators and pacemakers. It can
even be used prior to starting the Internal Jugular stick for a central line.
b. Remember that the supraclavicular nerve innervate the skin over the
clavicle and down to about T4 and this is why when assessing the high
spinal you must go to the pinkie finger and pinch it to assess C8-T1
because these nerves do not really allow a proper assessment of the T1-T4
levels.
c. The accessory is blocked by placing the needle and giving local into the
upper part (junction of the upper and middle third) of the SCM. This helps
to disallow the patient from strongly turning their head towards the
surgical field and helps prevent the patient from lifting their shoulder. Bot
of these maneuvers get in the surgeons way
5. Dissection of the superficial nerves of the arm
a. Lateral Antebrachial Cutaneous
i. Use your hand to pinch the bicep and then incise the fascia
between the bicep and the brachialis. Spllit the fascia up and down
along the lateral border of the bicep.
ii. Now look at the bicep and lift it up to find the musculocutaneous
nerve under it and recall that the MCN goes through the
coracobrachialis then under the bicep and emerges on the lateral
side of the insertion of the bicep as the lateral antebrachial
cutaneous nerve.
iii. So once you have found the MCN under the bicep follow its path
and use you metz to insert the closed teeth along the path of the
nerve and then spread the teeth to open up the tissue along its path
and continue this process and follow this nerve as it travels just
inside the lateral edge of the forearm (antebrachium)
iv. Remember to leave it attached to tissue so you can demonstrate its
location and then place a tie around it.
b. The Radial Nerve and its cutaneous branches, namely the posterior
antebrachial cutaneous nerve
i. Having seen the bicep now look lateral to the bicep and note the
division of muscle between the bicep and the brachioradialis. Use
your metz to define the space between these two muscles and then
look for the brachialis and the radial nerve is found in between the
brachialis and the brachioradialis muscles
ii. Now follow the radial nerve cephalad up the arm and look for
nerves that go off diagonally. These are some of the cutaneous
nerves. The posterior antebrachial cutaneous nerve leaves the
radial nerve and descends right down the middle of the posterior
aspect of the arm between the ulna and radius bones
6. The intercostobrachial nerve
a. This nerve leaves the intercostal space between ribs T2 and T3 in the
anterior axillary line. It then travels posteriorly along the chest wall but
eventually goes across the axilla and crosses into the arm by going over
the junction of the Latissimus Dorsi muscle as it meets the triceps.
b. Use a bungee cord to hold the arm out as if it is on an arm board.
c. Remove fat and other tissue from over the pectoralis muscle and find the
lateral edge of the pectoralis major.
d. Now digitally dissect with your fingers to the chest wall.
e. Now feel for the first rib. It is wide and flat
f. Now count down to the second and third rib
g. Now use your Metz to try to find this nerve as it comes out of this
interspace. It is usually held by other tissue to appear as if it is exiting a rib
below but further dissection will show it comes out between ribs 2 and 3.
h. Follow it across the axilla to the junction of the Latissimus and the triceps
i. You may see some nerves coming from the area of the axillary vein and
artery and these are medial brachial cutaneous nerve that help take part
with the intercostobrachial in supplying the posteromedial and posterior
aspects of the arms
Session Two will involve dissecting the terminal nerves such as the radial ulnar and
median nerves as well as the medial antebrachial nerves and then having a lecture on all
the superficial nerves so that we can then move on in the following dissections of the
brachial plexus