Plexuses and Dermatomes – Anatomy of the Nervous System (Nursing)

00:01 So now that we've discussed the different branches of the spinal nerves, let's talk about the axons from the anterior rami that form networks on both the left and the right side of the body by joining with axons from adjacent nerves to form what we know as plexuses.

00:22 All of the anterior rami form plexuses with the exception of the anterior rami of T2 through T12.

00:32 These nerves are referred to as intercostal or thoracic nerves and they go directly to the intercostal spaces instead of forming these networks.

00:46 So the first of the plexuses that we will discuss is the cervical plexus.

00:51 This plexus supplies the skin and the muscles of the head, neck as well as the superior portion of the shoulders and chest and the diaphragm.

01:03 The cervical plexus extends from the anterior rami of C1 through C5.

01:11 And of these, one of the nerves that eventually comes from this plexus are the phrenic nerves.

01:19 The phrenic nerves are very important because they supply the diaphragm.

01:25 Damage to the phrenic nerve causes an inability to breathe.

01:32 The next plexus is the brachial plexus.

01:36 This plexus is a bit more complex.

01:39 It provides almost the entire nerve supply to the shoulders and the upper limbs.

01:46 It is made up of roots, trunks, cords, divisions and branches.

01:52 Because of the complexity of the brachial complex, let's take a closer look at the different components.

02:00 First you have your roots which are the anterior rami.

02:04 Next you have your trunks.

02:07 The roots or the anterior rami are going to unite to form trunks.

02:12 There are three types of trunks: the superior, the middle and inferior trunk.

02:18 After the trunks, you have divisions.

02:22 Posterior to the clavicle, the trunks are going to diverge into the anterior and posterior division.

02:30 In the axilla under the arms, these divisions are going to unite to form chords.

02:38 And finally, you have the branches which will form the principal nerves of the plexus.

02:47 The next plexus is the lumbar plexus.

02:51 This is going to supply the anterolateral abdominal wall, the external genitalia and parts of the lower limb.

03:01 This plexus is much less complex than the brachial plexus.

03:07 This plexus includes nerves that will go to the iliohypogastric, iliolinguinal, genitofemoral, lateral cutaneous nerve of t high, femoral, accessory obturator, obturator and the lumbosacral trunk.

03:32 The last plexus is the sacral plexus.

03:36 This plexus is going to extend from the rami of L4 through S5.

03:44 This is going to be divided into the posterior and anterior division.

03:50 In the posterior division, you have the superior gluteal, the inferior gluteal and the nerve of piriformis.

04:00 On the anterior division, you have the tibial as well as the common fibular nerve.

04:07 These two nerves together are going to form what's known as the sciatic nerve.

04:12 If you've ever had sciatica or nerve damage that results in shooting pain going down your leg, then you've had damage to the sciatic nerve.

04:26 So now let's talk about dermatomes.

04:29 A dermatome is an area of skin that provides sensory input to the central nervous system via a posterior root of one of the pairs of spinal nerves or via the trigeminal nerve which is not a spinal nerve but instead is a cranial nerve.

04:47 The trigeminal nerve is specifically gonna serve most of the skin of the face and the scalp.

04:54 So knowing which spinal cord segment supplies each dermatome makes it possible to locate damaged areas of the spinal cord.

05:04 As well, we use dermatomes in order to block pain using anesthetics.

05:11 The dermatomes however can overlap and if the overlap is considerable, then if you only damage one of the nerves, you may have very little loss in sensation.

05:24 As well if you're trying to block pain using anesthetics, you may need to block multiple nerves if there is considerable overlap as well.