hello anatomy colleagues this is your good friend dr. Alsup and in this video we are making our
first dive into the world of parasympathetics which will be really important in innervating
many of the exocrine glands associated with the head now the parasympathetics are part of
the autonomic nervous system which has also been referred to as its abbreviation ans or
more traditionally the visceral motor system so parasympathetic and sympathetic fibers which are
also part of the ANS consist of motor fibers that will innervate visceral tissues such as smooth
muscle or glandular tissue the parasympathetic system in most general terms is the calmer
partner to the sympathetic system sympathetics are often referred to as the fight-or-flight
system and the parasympathetic s-- are often lovingly referred to as the rest and digest
system so important in terms of homeostatic or energy conserving processes such as allowing
the body to feed and producing saliva is really important for the eating and digesting processes
so the focus of this video will be to discuss the innervation of the parotid gland which will
include parasympathetic innervation all right I gotta clear my my throat because we've got some
fun stuff to talk about the glossopharyngeal nerve is back this nerve is one of the more
complex cranial nerves it has both sensory and motor fibers so we remember that sensory really
important in terms of the pharynx and it is going to be important in this discussion because it's
one of the four cranial nerves that has pre ganglionic parasympathetics associated with
it so these fibers would be considered visceral efferent fibers unlike the somatic efferent
fibers that will innervate the stylopharyngeus muscle so I know this chart seems a little
overwhelming right now and we are going to take each one of these steps I step and slowly talk
our way through this and hopefully towards the end you will think oh what a delightful chart
that tells me all the information I need to know but first let's talk about each one of those these
steps one by one so the glossopharyngeal nerve carries preganglionic parasympathetic fibers
preganglionic parasympathetic it's hard to say it but I'm gonna do it quite a bit so I gotta
get used to it so the glossopharyngeal nerve carries preganglionic parasympathetic fibers
and this means fibers that have not yet synapse in a ganglion and so these the glossopharyngeal nerve
of course is going to originate from the brainstem now as I hope you are becoming increasingly aware
the glossopharyngeal nerve is going to exit via the jugular foramen which you can see right here
and if you if you're becoming more comfortable with where this is located this is going to be
between the temporal bone and the occipital bones so distinctly fairly irregularly shaped and after
exiting the jugular foramen specific fibers so those preganglionic parasympathetic fibers are
going to start to head for its target but it's going to take a very complex route so these pre
ganglionic parasympathetic fibers are going to kind of coalesce and form a nerve referred to
as the tympanic nerve and it will this tympanic nerve will actually re-enter the skull via the
tympanic canaliculus and I assume you're a little less familiar with this awesomely named
tympanic canaliculus to be honest many seasoned anonymous or not as comfortable is where it's
located and it looks like this tiny pinprick right here I just kind of colored over it just to kind
of give you a more cartoonish idea of where it's located and it's going to be between this carotid
canal the external opening of the carotid canal and the jugular foramen and when I say it looks
like a pinprick I really mean it that tympanic nerve is not a very large nerve at all so the
opening does not need to very large either now if I were to put my finger on this landmark region
right here and kind of flip it over to look on the inside of the cranium I would be looking at
the petrous part of the temporal bone so this nerve this tympanic nerve as it enters through
the tympanic canaliculus is heading into the inside of the petrous part of the temporal bone
which includes the middle and inner ears so the tympanic nerve has made its way into the middle
ear and we'll talk a lot more about the middle ear in our session associated with the ear but
you can kind of see what it would look like in this region at this point instead of being one
distinct nerve with nerve fibers wrapped up together with connective tissue to form one
nerve the fibers actually begin to spread out for a bit to form a portion of the tympanic
plexus which you can see on the promontory of the middle ear the promontory and you can see
there were in this region tear the promontory is actually going to be created by the basal part of
the cochlea so it's creating this bump and so you'll see small nerve fibers sitting right on
top of the promontory it's important to note that the tympanic plexus is not just composed of those
preganglionic parasympathetic fibers from the tympanic nerve but there are also postganglionic
sympathetic fibers that form part of this plexus as well and these sympathetic fibers
are postganglionic at this point because they have synapse in the superior cervical ganglion
now after being part of the tympanic plexus for just a short while those preganglionic
parasympathetic fibers will coalesce and join back together to form the lesser petrosal nerve the
lesser petrosal nerve will exit the skull via the foramen ovale so let's locate that right here and
while we're doing that think about why we know the foramen ovale why have we talked about the foramen
ovale already something much larger must reverse this foramen - necessitates that large foramen and
hopefully you recall that the mandibular nerve or v3 is also going to exit the skull via the frame
and a valley and this geographical relationship between those pre ganglionic parasympathetic
fibers and v3 is important so up to this point have we been talking about pre or post ganglionic
parasympathetic fibers we have been talking about pre ganglionic all right I've said preganglionic
probably at least 50 times in this video so we've been talking pre ganglionic so that means we need
to get to a ganglion for these preganglionic fibers to synapse and there just happens to be
the correct one just inferior to the foramen ovale you can see it here and here on the cartoon very
closely associated with the medial portion of v3 and this ganglion is going to be the otic ganglion
the otic ganglion is one of the for peripheral parasympathetic ganglia of the head so very
closely associated with v3 and this is where those pre ganglionic parasympathetic fibers will synapse
once those preganglionic fibers synapse now they are called postganglionic fibers alright so after
the synapse occurs they are post or after the ganglion and these post ganglionic parasympathetic
fibers need to reach their target or organ which in this case is the parotid gland and this will
happen by hitchhiking with another nerve that is already heading that way and this nerve is
the auricular temporal nerve the regulative aural nerve is a branch of v3 so remember
that geographic relationship to v3 is going to be important and the auricular temporal nerve is an
entirely afferent or sensory branch which will innervate skin of the anterior superior here as
well as skin around the temporomandibular joint so think about those structures and where they're
located that skin is very close to the parotid gland right so this is going to be a good way to
get those postganglionic parasympathetic fibers to the parotid gland so when stimulated this can
cause saliva secretion from the parotid all right so here's that chart again I hope it doesn't seem
as overwhelming but let's talk some big picture items the glossopharyngeal nerve is going to be
the source of the preganglionic parasympathetic fibers and that that nerve branch that kind of
joins together those preganglionic parasympathetic fibers are going to be referred to as the tympanic
nerve the tympanic nerve will spread out it's fibers to be a component of the tympanic plexus
and then they will join back together to form the lesser petrosal nerve which will exit the skull
through the foramen ovale so let's stop here for a moment if I were to ask you which nerve is the
source of the preganglionic parasympathetic fibers that innervate the product land what would your
answer be what is the source of these fibers OOP excuse me it would be the glossopharyngeal nerve
or cranial nerve nine now what if I asked you which nerve allows passage of the postganglionic
parasympathetic fibers to the parotid gland what would your answer be I hope your answer would be
the auricular temporal nerve but it's important to note that the auricular temporal nerve is
not a parasympathetic nerve it just allows those postganglionic parasympathetic fibers
to travel with a larger collection of fibers on its way to its target organ the parotid gland
alright so this may seem a bit of an overkill but I don't want us to move on to any other
topics until we get this so question true or false the parasympathetic fibers that
will innervate the parotid gland originate and the auricular temporal there's true or
false and I hope you have landed on that this is false the parasympathetic fibers
that will innervate the parotid gland originated in the glossopharyngeal nerve or cranial nerve
nine so it is going to be the glossopharyngeal nerve that is the source of the parasympathetic
fibers the postganglionic parasympathetic fibers synapse in the otic ganglion and then they hitch
a ride to the parotid gland via the auriculotemporal nerve so that is where the auriculo
temporal nerve comes into this process all right that hat that has been some fun times
with parasympathetics we only have three more peripheral parasympathetic ganglia to discuss
throughout the course thank you for your time and attention in this video and have a great day