hi let's talk about the pulmonary plexuses in this video we'll discuss the basic structure
of the autonomic innervation of thoracic viscera with a special emphasis on the pulmonary plexuses
so there are three major visceral targets of autonomics each with their own devoted
set of plexuses within the thorax there are the cardiac plexuses that are going to serve the heart
and coronary vasculature there are the pulmonary plexuses which are going to serve the bronchial
trees as well as the pulmonary vasculature which will be the focus of this video and then there's
also the esophageal plexus which we'll discuss with the posterior mediastinum now all of these
plexuses are going to have exquisitely robust series of communications between
and among them so none of these are existing purely in a vacuum many of the fibers are
interwoven between these plexuses there is tremendous amounts of interplexus communication
it's important that we discuss them and that you understand their locations in theory because
within the laboratory as you clean off the uh the investing fascia of organs and other viscera and
vasculature you're going to remove much of these plexuses so it's
it's important that you understand where they are so as you're removing them you can appreciate them
now autonomic plexuses will have a variety of innervation sources uh so generally there are
both sympathetic and parasympathetic innervations to an autonomic plexus the thoracic viscera
are going to receive their innervation from the sympathetic side from both the cervical
and thoracic regions of the sympathetic chains now recall that the the pathways for sympathetics
involve both a pre and a post ganglionic series of fibers and the pre-ganglionic series of fibers
which serve the thorax predominantly arise from the spinal cord at spinal nerve levels t1
through t5 sometimes there may be fibers from t6 but the dominant outflow
via those white rami communicantes which we can see there are from levels t1 through t5
so those go out to the sympathetic trunk and keep in mind those white rami communicantes
are only found between the t1 and l2 levels of the spine whereas the sympathetic trunk or chain
is found from the base of the skull all the way down to the coccyx at the ganglion impar so the
inflow might be thoracolumbar but the sympathetic chain runs throughout and this is a good example
where we have an inflow from t1 to t5 but fibers can ascend all the way up to the
superior cervical ganglion of the cervical sympathetic trunk and then exit
and travel inferiorly to the thorax and so we'll see how the various levels of the
cervical and thoracic ganglia are going to serve the pulmonary plexuses it's also worth noting that
with respect to the pulmonary plexus typically the the fibers are coming from the t2 through t6
as well as the cervical ganglia but um all of these fibers will come back
along through that same pathway when we have the visceral afferent fibers that conduct pathway
the the pain pathways and so referred pain will typically refer to dermatomes covered by those
spinal nerve levels now the other constituent to the autonomic plexus will be the parasympathetic
and the vagus nerves cranial nerve 10 are the dominant parasympathetic
supplier to everything from the neck through the thorax through the fore and the mid-gut
and so we'll see how branches of the vagus nerves
and branches of branches from the vagus nerves will participate in these autonomic plexuses
now recall that there are visceral afferents associated with both the sympathetic and the
parasympathetic and whereas the visceral afferents associated with the sympathetic
are the visceral pain pathways the visceral afferents with the parasympathetic are for
feedback and for reflex fibers now let's focus on the thoracic outflow so t1 through t5 levels
are going to be the white rami communicates out so those are the pre ganglionics and coming off of
the sympathetic trunk we're going to see cardiac branches from the superior cervical ganglion
from the middle cervical ganglion and from the inferior cervical ganglion
as well as direct branches from the second thoracic through at least the fifth and
sometimes the sixth thoracic ganglion of the sympathetic trunk so those will all be
branches coming directly from the sympathetic trunk out to the pulmonary plexuses
there are the same branches also inclusive of t1 that are supplying the cardiac plexuses
and it's important to understand that a lot of these fibers are the same
so they're traveling in and amongst these two plexuses and they're serving
a similar function in terms of a sympathetic response as we'll see
now from the vagus nerve high in the neck there are going to be branches that arise directly
from each right and left vagus nerve called the superior cardiac branches sometimes they're called
the cervical cardiac branches and these are going to leave early and they're going to intermix with
some of those cardiac branches from the superior cervical ganglion as they descend down
within and adjacent to the carotid sheath towards the thorax they're also going to be
inferior cardiac branches which are also going to descend down
as they originate within the carotid sheath into the thorax now with the vagus there are two major
nerve branches that are going to arise from the vagus and they do so in an asymmetric fashion so
on the right side there is a right recurrent laryngeal nerve that wraps around the subclavian
artery and the root of the neck before it ascends superiorly to serve the larynx on the left side
the left vagus nerve makes it down to about the level of the arch of the aorta before the
left recurrent laryngeal nerve wraps around that concavity and ascends in that tracheoesophageal
groove on the way up to serve the larynx and both of these recurrent laryngeal nerves are going to
send branches to the cardiac and pulmonary plexuses as well as the esophageal plexus
and then the vagus nerves after are going to continue their descent distally along the
esophagus they move posterior to the roots of the lungs which we can see here and here
and that's going to be important because those pulmonary plexuses are going to be straddling the
roots of the lungs as we'll see and once the vagus nerves make it posterior to the roots of the lungs
they form a very close association with the esophagus the left vagus nerve is going to assume
more of an anterior orientation the right vagus nerve assumes more of a posterior orientation
and that they will then be known as the vagal trunks now the vagal trunks aren't exclusively
left versus right there are some fibers of each nerve in each trunk but predominantly the left
vagus nerve most of its fibers become the anterior vagal trunk
the right vagus nerve most of its fibers become the posterior vagal trunk and we can remember
this by the mnemonic LARP left anterior right posterior
now before the trunks come into existence those vagus nerves which have already supplied
cardiac branches high within the neck will also send more branches to the cardiac plexuses they'll
also serve dedicated bronchial branches to the pulmonary plexuses as well as various esophageal
branches as we'll see so the pulmonary plexuses are very difficult to differentiate from
the deep cardiac plexus and they're going to enjoy fibers from both cardiac plexuses so recall that
the superficial cardiac plexus is found in the concavity of the aorta the deep cardiac plexus
is found nestled between the bifurcation of the trachea and the arch of the aorta
and the pulmonary plexuses are going to be found straddling the roots of the lungs
and will be both anterior and posterior to those roots of the lung and so we'll have
continuity between the cardiac plexuses and the pulmonary plexuses such that it would be
nearly impossible from a gross perspective even with the the most perfect dissection to decide
if a fiber was of the pulmonary plexus or of the cardiac more of a cardiac plexus
now there are two types of pulmonary plexuses there are anterior plexuses and posterior plexuses
the anterior plexuses are very small they account for possibly about 25% of the total innervation
of the the pulmonary plexus they're absolutely contiguous with that superficial cardiac plexus
so all of the inputs for that plexus are going to be the same inputs for those anterior plexuses so
we're talking about the cardiac branches of the superior cervical ganglia as well as the
superior cervical cardiac branches of the vagus nerve in terms of the posterior plexuses which
are about three-quarters or 75% of the innervation to of the pulmonary plexuses
in total um all of the same innervations for the deep plexus which involve the cardiac branches
of the cervical ganglia as well all cervical ganglia so superior middle and inferior the
cardiac branches of thoracic ganglia t1 through t5 from the sympathetic trunk and then from the vagus
nerve there will be cardiac branches there will be branches from the recurrent laryngeal nerves
and then there will be dedicated bronchial branches from each vagus nerve to those plexuses
now let's think about what the pulmonary plexuses will do from a sympathetic standpoint the
sympathetic stimulus will lead to bronchodilation so we'll have a relaxation
of the smooth muscle that is going to line the airway so a greater ability to to move air
there's also going to be vasa constriction of the pulmonary arteries
so much of a sympathetic response will lead to vasoconstriction the only exception that that we
have now as an example will be that the coronary arteries vasodilate during a sympathetic response
parasympathetic responses are going to include bronchoconstriction and it's not that the
airway is narrow that much it's just more of a maintenance of the the tone of this smooth muscle
tissue that comprises the airway there will also be increased bronchiomucus production as well as
vasodilation of the pulmonary arteries when we think about an autonomic response with respect
to the lungs however typically we think of rates of respiration and so in terms of a sympathetic
response respiration rates will increase in terms of a parasympathetic response respiration rates
will decrease but those aren't being modulated by the pulmonary plexuses those are being
conducted by the phrenic nerves under the control of the the brain stem the medulla and the pons
so we've discussed uh the various autonomic plexuses of the thorax with our focus on the
pulmonary plexuses and their locations their particular inputs as well as the individual
sympathetic and parasympathetic responses this is your summary slide thank you for your time