hi let's talk about the thoracic sympathetic trunks and splanchnic nerves in this video
we'll discuss the sympathetic trunks within the thorax we'll also detail the key ganglia of origin
constituent fibers and targets of the thoracic splenic nerves
when we discuss the sympathetic trunks
this is synonymous with sympathetic chains these are series both right and left of paravertebral
ganglia so these are to the side of the vertebrae which are connected by postganglionic fibers
now within the thorax we have a series of 12 ganglia so that would be the ganglion
associated with the first thoracic spinal nerve so that's t1 t2 t3 ganglion and so on and so forth
each of these ganglia communicate with a ventral primary ramus a vpr of a thoracic spinal nerve
the first ganglion tends to coalesce with the inferior cervical ganglion
so there would be a cervical region of each of these cords
and recall that the gangly of the cervical region are condensed into inferior middle and
superior ganglia in the inferior cervical ganglion and the first thoracic ganglion tend to coalesce
together as the cervicothoracic aka stellate ganglion so this is inferior cervical ganglion
plus the first thoracic ganglion after this all of these successive ganglia are numbered as they
maintain their relationships with ventral primary rami so t2 t3 and so on and so forth these ganglia
communicate with the ventral primary rami via rami communicantes these are communicating branches
rey my communicantes come in two flavors there are white rami communicantes which conduct
pre-ganglionic fibers from the vpr out to the ganglion there are also gray rami communicates
which conduct postganglionic fibers from the ganglion back to the ventral primary ramus
it's the white rami communicantes which have a limited distribution
so they can be found in association with ganglia from ventral primary rami of t1 through l2
t1 through l2 is the sympathetic outflow that's why oftentimes people refer to
the sympathetic portion of the autonomic nervous system as the thoracolumbar outflow
whereas the gray raymi communications those communicating branches that conduct
postganglionic fibers back to vpr will span the entire length of the vertebral column so they can
be found as high as the superior cervical ganglion at the base of the skull and as low as the coccyx
at the ganglion impar where right and left sympathetic trunks are going to join
from these ganglia various branches will go out to serve viscera either in the thoracic cavity if
we're talking about the thoracic sympathetic trunks or the abdominal pelvic cavities if
we're talking about abdominal um so or lumbar or sacral trunks there will also be special fibers
which leave various ganglia known as splanchnic nerves and there can be splenic nerves throughout
the sympathetic trunks but the splenic nerves in the thorax are quite special
they consist of preganglionic sympathetic fibers which never synapse within the ganglia so
they're not synapsing in these paravertebral ganglia they pass through these ganglia
such as these fibers here and these fibers here and they coalesce with other fibers to form
splanchnic nerves so splanchnic is greek for viscera or organs
and these thoracic splenic nerves are going to descend the thorax they're going to pierce
through the krura of the diaphragm and they are ultimately going to synapse in
pre-aortic ganglia so the ganglia of the chain are para vertebral ganglia
the ganglia that these will synapse within are called pre-aortic ganglia because
they are anterior to the aorta it also bears noting that visceral afferent fibers may be
associated with sympathetics or parasympathetics and within the thorax visceral afferent fibers
associated with sympathetic fibers are going to conduct pain visceral pain perceptions
so within the posterior mediastinum we can see splanchnic nerves descending down
just anterior to the bodies of vertebrae from t5 through t12 as they enter into the abdominal
pelvic cavity and there are typically three such aggregations of these fibers the most superior
and largest is called the greater thoracic splanchnic nerve and we have one on each side
the greater thoracic splanchnic nerve is typically supplied
of fibers from the fifth thoracic ganglion through the ninth and sometimes
the tenth thoracic ganglion these fibers are going to target the celiac ganglia
the aortico renal ganglion and go directly to the super renal i.e adrenal gland the greater
thoracic splenic nerves are always present they are the most constant among the splenic nerves
there's also a lesser thoracic splanchnic nerve this is supplied from ganglia t9 to t10
and its fibers target specifically the aortico renal ganglion and this nerve is typically present
there is also the least thoracic splanchnic nerve the least thoracic splenic nerve when present
comes from the t12 ganglion and it goes into the renal plexus
and it is rarely ever present now when we think about our dissections of the posterior mediastinum
when we think about the position of the diaphragm and how intractable
it's going to be given the fact that there are abdominal viscera still in association with it
we're going to have a very difficult time seeing the lesser and least thoracic splanchnic nerves
so that central tendon of the diaphragm is generally at about the level of t8 and so we will
barely be able to get a handle on the greater thoracic splanchnic nerves
visually so the lesser and least might be visualized best later on when we're able to
mobilize the liver and other abdominal organs and just for your edification uh so that these
are are structures that that you can kind of relate even not being familiar with
the the anatomy here because this will come later i wanted to show you some of these
autonomic plexuses and the pre-aortic ganglia that these thoracic splanchnic nerves are associated
with and let's look at their inputs just briefly so the greater lesser and least splenic nerves
can all be seen here we also have the posterior vagal trunk which we can see descending here
and we can see how the greater splenic nerve is feeding into the celiac ganglia
we call it the celiac ganglia because there are two of them and it's in association with the
celiac trunk that's the blood supply to the foregut
everything in green here is going to be mixed yellow and blue make green get it the
vagal fibers don't synapse in these ganglia they move through the ganglia but they also
intermix with the sympathetic fibers to form these autonomic plexuses so we have these celiac ganglia
and plexus there's also in communication with the celiac ganglion plexus a superior mesenteric
ganglion and plexus and because this is the superior mesenteric artery that's
the dominant blood supply to the mid gut and in association with the superior mesenteric artery
laterally we have the aortico renal so that is the target for the lesser
and then on the renal arteries which serve the kidneys we can see the renal plexuses these
renal plexuses are mixed and they are served by a variety of sources but from the thorax
if it's present we have the least thoracic splanchnic nerves so these autonomic ganglia
and the plexuses they're going to serve the the gut tubes they're also going to serve the the
vasculature that serves the gut tube so they'll have a variety of of uses most of which we'll
focus on when we discuss the gi system so we've discussed the sympathetic trunks within the thorax
their association with ventral primary rami of t1 through t12 white and gray rami communicates
as well as thoracic splanchnic nerves the greater the lesser and the least thoracic splenic nerves
their associated ganglia and their targets this is your summary slide thank you for your time