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Run in a Neurovascular Bundle
Introduction
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What’s up!
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Let’s go ahead and continue with our Peripheral Nervous System.
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Previously we’ve covered the cervical plexus, the brachial, lumbar and sacral plexuses.
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The next thing that we’re going to talk about now are nerves that’re located within
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the thoracic wall.
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The thoracic nerves we call them.
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So here we see a plan anterior view of the thorax.
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We see the costal bones, sternum, and the vertebra.
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The Intercostal space is the space between the ribs, as you see here.
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There are 11 spaces on each side and they are numbered according to the rib which is
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the superior border of the space.
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1st intercostal space under the 1st rib, 2nd intercostal space under the 2nd rib, and so
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on.
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It goes all the way down to the 11, so again we got 11 intercostal spaces.
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Now the Throacic nerves are distributed Now.
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The thoracic spine has 12 nerve roots.
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So from T1 all the way down to T12, there are nerves that go out from the spine on each
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side, similar to the rest of the spine.
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The anterior root of the nerves in the thoracic region branch off and control both the motor
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and the sensory signals in the thoracic and the abdominal wall.
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These nerves leave the thoracic spine, and are therefore referred to as the thoracic
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nerves.
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So we got one nerve that run underneath each rib, and are numbered according to each nerve
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that they run underneath.
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As you see here.
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If these thoracic nerves run within an intercostal space, they’ll get the name intercostal
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nerves.
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So we got 11 intercostal nerves, since we got 11 intercostal spaces.
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The last nerve that run underneath the 12th rib, is referred to as the subcostal nerve.
Content
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So in this video, we’re first going to go detailed into the intercostal nerves.
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We’ll talk about their course, and branches.
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And a traditional division of them called typical and atypical intercostal nerves.
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Then we’ll talk a little bit about the subcostal nerve so that we cover all the thoracic nerves
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that’re relevant to know regarding the peripheral nervous system.
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Awesome.
Intercostal Nerve Course
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So.
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Course.
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How do the intercostal nerves go?
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Here you see a plan anterior view of the thorax along with the intercostal muscles.
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If we now cross over the thorax like this, right over the rib.
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Then take away the upper part, and schematically draw what we’ll see from this view.
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What we now can see is the vertebra, let’s say T6, sixth thoracic vertebra.
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And the sternum.
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In the intercostal space, the most external muscle is called the external intercostal
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muscle.
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And remember, unlike the other two intercostal muscles, the external intercostal muscle does
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not retain its muscular character all the way to the sternum, and so the tissue that’s
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left towards the sternum is called the Anterior intercostal membrane, or the external intecostal
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membrane.
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Then we got the posterior intercostal memberane, or the internal intercostal memberane, from
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where the internal intercostal muscle come from.
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Then a little more internally.
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You know we’re at T6 so we might see a subcostal muscle.
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We can see the Innermost intercostals, which comprise the third and deepest layer of intercostal
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muscles.
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They are located deep to the internal and external intercostals, filling all the 11
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intercostal spaces between the ribs.
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And then more anteriorly we might have the Sternocostalis muscle.
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And then as you move even more internally you might find the parietal pleura.
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Alright.
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Let’s now add the spinal cord.
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Let me test your knowledge know.
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Off from the spinal cord comes two nerves that unite.
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These are called?
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The dorsal root and the ventral root.
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They unite and form the spinal nerve.
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The spinal nerve give off a branch called dorsal ramus, which carries information that
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supplies muscles and skin sensation to the back.
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They’re also connected to the sympathetic chain ganglion through the grey and white
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rami communicans.
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And then we got the anterior division.
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And the anterior division of the thoracic region T1 to T11 are called intercostal nerves.
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So let’s go ahead and grey out all the other nerves.
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The intercostal nerves enter their corresponding intercostal space between the posterior (internal)
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intercostal membrane and the parietal pleura.
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And then they run anteriorly towards either the sternum or the rectus abdominis muscle.
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The upper six goes to the sternum and the lower six goes towards the rectus abdominis
Intercostal Nerve Branches
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muscle.
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The typical intercostal nerves are mixed nerves carrying both motor and sensory innervation
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for the thoracic and abdominal walls.
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The motor branches for the intercostal muscles are branches that supply regional muscles.
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So, the intercostal nerves supply all the intercostal muscles, as well as muscles like
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the subcostal muscles, serratus posterior superior, levatores costarum and transversus
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thoracis muscles.
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The cutaneous branches are the lateral cutaneous branches, which further divide into anterior
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and posterior branches, and the anterior cutaneous branches which also divide into medial and
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lateral branches.
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These branches supply segmental sensory innervation to the skin of the anterolateral walls of
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the thorax and abdomen.
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And you know you can use this Dermatome map to see the sensory distribution of each dermatome
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across the body.
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And so, a dermatome refers to the area of the skin in which sensory nerves derive from
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spinal nerve root.
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The dermatomes related to the thorax and abdomen are T1-T12 anteriorly, each is quite evenly
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spaced, with T1-T6 being nearly horizontal lines that extend over the thoracic wall.
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While the dermatomes T7-T12 start horizontally in the thoracic wall, but anteriorly, they
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tend to dip inferiorly and extend onto the abdominal wall.
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And now you might be wondering why I’m showing you this.
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Well this type of mapping is a useful clinical way to localise lesions, damage, or injury
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to specific spinal nerves.
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So if you get a patient in which you suspect damage to the spinal cord.
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You can try to localize where the damage is by checking which dermatome the patient doesn’t
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feel any sensation at.
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Alright so that was the motor branches and the sensory branches.
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Another branch that we should talk about here is the collateral branches.
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Each intercostal nerve give a collateral branch.
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And they arise close to the angles of the ribs and course along the superior border
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of the inferior rib to innervate the intercostal muscles, parietal pleura, and the periosteum
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of the rib.
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And if we take a segment of the thoracic wall, you can see that the intercostal nerves run
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in a so called neurovascular bundle, located in the costal groove right underneath each
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rib, between the internal intercostal muscle and innermost intercostal muscle.
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It’s called neurovascular bundle so we got vessels here aswell, and they’re arranged
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as Vein, Artery and Nerve, from the most superior to the most inferior.
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An easy way to remember that is to use a mnemonic VAN.
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And notice how the collateral neurovascular bundle runs at the lower edge of the space,
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and the order is reversed, so we first have the nerve, artery and then vein from superior
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to inferior.
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You’ve probably heard about a procedure called thoracocentesis, or pleural tap.
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This procedure si done to evacuate fluid from the pleural space.
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And to do so you have to put a needle right above the superior margin of a rib.
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This ensures that the needle passes through the lower part of the intercostal space, avoiding
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the intercostal neurovascular bundle.
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That’s why it’s important to know the exact anatomy of the intercostal space so
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that you reduce the risk of complications while sticking needles in the patients thorax.
Typical vs. Atypical Intercostal Nerves
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Alright.
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So we’ve covered the course, we’ve covered the branches.
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Now.
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Although the majority of intercostal nerves follow a similar pattern from origin to course
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and branches, there are some differences among them.
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And these diffences are why we sometimes divide the intercostal nerves into typical and atypical
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intercostal nerves.
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The main reason for this division is that the typical intercostal nerves course solely
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in their own intercostal spaces, while the atypical spinal nerves go beyond the thoracic
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wall to supply other regions.
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The term ’typical’ refers usually to the third , fourth, fifth and sixth intercostal
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nerve, while the rest are considered to be atypical.
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So first and second intercostal nerve.
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As well as 7, 8, 9, 10 and 11 intercostal nerve.
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Alright.
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So.
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First intercostal nerve.
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The first nerve is special.
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It’s special because the anterior ramus of the first thoracic spinal nerve terminates
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by bifurcating around the neck of the first rib into two branches: superior and inferior.
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The larger, superior branch exits the thoracic cavity and joins the brachial plexus.
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As you see here While the inferior branch, also known as the
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intercostal branch, becomes the first intercostal nerve.
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This nerve goes within the first intercostal space below the rib, and ends as the first
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anterior cutaneous branch on the anterior chest wall.
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And note that we still have a collateral branch and a lateral cutaneous branch.
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The second intercostal nerve has exactly the same branches as all the other nerves, except
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that the lateral cutaneous nerve is longer.
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It’s longer because it’s referred to as the intercostobrachial nerve.
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So the intercostobrachial nerve is a lateral cutaneous branch of the second intercostal
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nerve that supplies sensation to the skin of the axilla.
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So It leaves the second intercostal space at the midaxillary line and then pierces the
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serratus anterior muscle to enter the subcutaneous tissues of the axilla.
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A little fun fact about this nerve is that it’s also referred to as the ‘tickle’
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nerve, given it supplies the skin of the axilla.
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Then we got all of those nerves right here.
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We got Intercostal nerve number 7, 8, 9, 10, 11.
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These nerves also enter and run in their corresponding intercostal spaces while still providing supply
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for the thoracic wall and the intercostal muscles.
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However, after they’ve run in the intercostal spaces, the nerves course behind the costal
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margin into the abdominal wall where it terminates as anterior cutaneous branches.
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These intercostal nerves supply skin and muscles of this region, as well as the parietal peritoneum.
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And since they innervate both thoracic and abdominal walls, these nerves are referred
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to atypical, and also sometimes also referred to as the thoracoabdominal nerves.
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So that was all the atypical nerves.
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The typical nerves, the 3rd, 4th , 5h and 6th intercostal nerve are typical because
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remember they keep their respected intercostal space.
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And they have the typical branches of the intercostal nerves.
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They have motor branches for all the muscles in their corresponding area.
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They have the lateral cutaneous branches, which remember divide into anterior and posterior
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branches, and the anterior cutaneous branches which also divide into medial and lateral
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branches.
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And they also have collateral branches, which course along the superior border of the inferior
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rib to innervate structures like the intercostal muscles, parietal pleura, and the periosteum
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of the rib.
Subcostal Nerve
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So that was all I had for the intercostal nerves.
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The last nerve is called the subcostal nerve.
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This nerve is the last and the largest of all the thoracic spinal nerves.
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For the most part of its course, the nerve follows the inferior margin of the 12th rib,
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running together in a neurovascular bundle with artery and vein.
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Then, it passes in front of the quadratus lumborum muscle and pierces the transversus
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abdominis muscle.
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On its course, the subcostal nerve gives off several types of branches, which are similar
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to the intercostal nerves.
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It gives off muscular branches, which innervate the muscles of the abdominal wall including
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the pyramidalis muscle, internal oblique, external oblique and transversus abdominis
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muscle.
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It also has the Lateral cutaneous branch; which pierces the internal and external oblique
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muscles and runs towards the gluteal region.
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It has a collateral branch, which is also similar to the intercostal branches.
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This branch innervates the parietal peritoneum and the peripheral parts of the diaphragm.
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It also has the anterior cutaneous branch, which you know is also a terminal.
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It terminates in the anterior portion of the abdominal wall supplying the skin over the
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lower abdomen, or the suprapubic region and the inguinal region.
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Now what’s special with the subcostal nerve is that it also give off the communicating
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branch.
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The communicating branch is a branch that merges with the iliohypogastric nerve to help
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form the lumbar plexus.
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Alright guys so that pretty much covers the thoracic nerves.
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Thank you so much for watching another one of my videos.
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