Clinically Applied Anatomy – Thoracic Nerves

by Craig Canby, PhD

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    00:02 For clinically applied anatomy, let’s think about a specific type of lung tumor called a pancoast tumor. A pancoast tumor is a tumor of the lung that will occupy the posterior thoracic wall and grow upwards along the posterior thoracic wall and start to invade and involve some neurologic structures in and around the subclavian artery. One such structure here that’s involved or may be involved is the stellate ganglion. As mentioned previously, the stellate ganglion results from the fusion of the inferior cervical ganglion and the first thoracic ganglion. This is, again, part of the sympathetics and if it continues to grow, it can also involve some of the inferior roots of the brachial plexus, for example, T1 and even C8.

    01:07 If there is neural involvement of pancoast tumor with the stellate ganglion, you’ll inhibit the sympathetics and as a result of that, the individual will have ptosis, drooping of the eye lid, myosis as well as anhidrosis. Anhidrosis is an absence of sweating. If there is neurologic involvement in the inferior roots of the brachial plexus, the individual will have some sensory loss along the T1 and C8 dermatomal levels which would be the medial forearm and would have weakness of the intrinsic muscles of the hand.

    01:55 Cardiac referred pain helps us to apply some of the anatomy that we just went through.

    02:03 As you recall, the spinal cord levels for the preganglionic sympathetic neurons were housed where T1 to T4 may be even, as well as the T5. So, if you have pain coming from the heart through the afferents going back into those spinal cord levels, the neurologic processing confuses that with the sensory fibers that are coming from those dermatomes on the skin.

    02:30 And so, you will involve the T1 down to T4 dermatomal levels that will then continue on into the medial aspects of the arm and even forearm as well as the anterior part of the chest. This is showing the back, but the nipple is an excellent landmark here to help you understand where your dermatomes would lie anteriorly. The nipple lies within the T4 dermatome, so the other dermatomes would lie above that. So, if there is crushing pain and referred pain to the left upper chest, that’s radiating also into the medial arm and medial forearm, that would be somewhat typical of cardiac referred pain, but I think the general rule of thumb is to say that cardiac referred pain can be more than what is typical and there are gender differences as well, as cardiac referred pain has been known to radiate upwards into the jaw and also, can radiate to the back.

    03:48 Now, we have the important take-home messages from this presentation.

    03:53 The phrenic, the vagus conveying the parasympathetics and the sympathetics innervate thoracic viscera.

    04:02 The phrenic nerves are motor and sensory to the diaphragm.

    04:06 The parasympathetics conserve and restore because of their tremendous influence on the GI system to process nutrients and to absorb nutrients and to decrease the heart rate whereas sympathetics do the opposite. They elicit the fight or flight response, so they will increase the heart rate, increase the force of contraction and make us more responsive to these fight or flight events.

    04:37 Sympathetic preganglionic fibers originate from spinal cord segments T1 to as well as T5 when we look at innervation to thoracic viscera. These then will synapse some postganglionic neurons that reside in the ganglia of the sympathetic trunks and then from there, the post ganglionic axons are distributed to the thoracic viscera.

    05:02 Pharmacologic stimulation of the sympathetics is efficacious in promoting bronchodilation during asthmatic attacks.

    05:10 A pancoast tumor may produce neurologic symptoms due to involvement of the inferior roots of the brachial plexus and/or stellate ganglion.

    05:21 And lastly, cardiac referred pain may be explained by the dermatomes associated with the segmental sympathetic innervation.

    05:31 And thank you for joining me on this lecture of the nerves of the thorax.

    About the Lecture

    The lecture Clinically Applied Anatomy – Thoracic Nerves by Craig Canby, PhD is from the course Thoracic Viscera.

    Included Quiz Questions

    1. Increased sweating
    2. Ptosis
    3. Miosis
    4. Weakness of intrinsic hand muscles
    1. T4
    2. T1
    3. T2
    4. T3
    5. T5
    1. Sex of patient
    2. Age of patient
    3. Race of patient
    4. History of dental trauma
    5. History of exertion
    1. Reduced sweating
    2. Reduced salvation
    3. Reduced lacrimation
    4. Reduced urination
    5. Reduced transpiration

    Author of lecture Clinically Applied Anatomy – Thoracic Nerves

     Craig Canby, PhD

    Craig Canby, PhD

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