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The facial nerve is responsible for providing motor innervation to facial muscles, as well as taste (anterior 2/3 of the tongue) and producing saliva and tears.
Introduction
0:05
[Music]
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what’s up time talkman here let’s
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continue our cranial nerve series
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cranial nerves are 12 pair of nerves
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that exit the brain and the brain stem
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and in this segment we will talk
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detailed about the seventh cranial nerve
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which is the facial nerve and we’ll do
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that by first making a quick scheme of
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the facial nerve pathway then we will
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talk through the functional components
0:28
and the nuclei of this nerve since it
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consists of different fibers and once we
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have that overview we’re going to look
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uh into the course and distribution by
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first going through the intracranial
0:40
course and then the extracranial course
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and once we have gone through that we
0:44
will talk a little bit about the
0:45
clinical
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relevance all right so the facial nerve
Facial Nerve Scheme
0:50
is responsible for providing motor
0:52
innovation of the facial muscles as well
0:54
as Taste of the anterior 2/3 of the
0:57
tongue and production of saliva and
0:59
tears
1:00
all right so here’s the scheme we will
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quickly run through it and then do it
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again in a little more detail within
1:07
pawns and the upper part of the medulla
1:09
we will find the motor nucleus which
1:11
sends out motor fibers we got the
1:14
superior salivatory nucleus which sends
1:17
out fibers to the salivary and the
1:18
lacrimal glands then we got some sensory
1:21
fibers coming in synapsing with the
1:23
spinal nucleus of the trinal nerve and
1:26
the uh nuclei of the solitary tract
1:29
these fibers will all go through the
1:31
Ponto medular Junction meaning uh in
1:34
between ponds and the medulla and they
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form two fibers they form the motor root
1:40
and a smaller sensory roote or commonly
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referred to as the intermediate nerve
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the motor route will travel through the
1:48
internal acoustic meatus and enter the
1:51
facial canal in the facial Canal the
1:54
facial nerve traverses forward and
1:55
laterally forming a bend the genu of the
1:59
facial nerve where the gulet gangon is
2:02
located in the posterior wall of the
2:04
middle ear it gives off the nerve to
2:07
stapedius supplying the stapedius muscle
2:10
and then it continues downwards towards
2:12
the styom fomen the superior salvat
2:16
nucleus will give off fibers that is
2:18
also going to go through the gicl
2:20
ganglion without synapsing with it and
2:23
give off the greater petal nerve on its
2:26
course towards the F laerum it merges
2:29
with the Deep petral nerve carrying
2:32
sympathetic fibers to form the nerve of
2:34
the PID Canal it travels to the pigo
2:38
palatin ganglion to provide pre
2:40
ganglionic parasympathetic inovation to
2:43
the lacrimal gland as well as mucous
2:45
glands of the nasal cavity maxillary
2:47
sinus and the
2:49
pallet fibers from the superior
2:51
salivatory nucleus will also Branch off
2:54
and give a nerve called Cordo tempany
2:57
cordan exits the skull by passing
3:00
through the panic fissure to enter the
3:03
infratemporal fosa here it terminates in
3:06
the submandibular ganglion which then
3:09
sends off postganglionic fibers to
3:12
innervate the submandibular and the
3:14
sublingual salivary glands Cordo tempany
3:17
consists of two fibers the general
3:19
visceral epin fibers here in purple
3:22
which comes from the superior salivatory
3:24
nucleus the other component are SVA
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fibers or sensor visceral afren fibers
3:31
is the Taste component of the
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cordan it comes from The Taste receptors
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from the anterior 2/3 of the tongue and
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then travel with the gve fibers as the
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Cordo tempany to syapse with the sensory
3:45
nuclei in the geniculate ganglion which
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then sends fibers towards the nuclei of
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the solitary tract a component of the
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facial nerve also provides sensory
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inovation around the external quistic
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meatus and the rro arular region and
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these fibers are known as general
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somatic afferent fibers which uh travels
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through the stylomastoid foran and
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through the facial Canal to signups with
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their respective nuclei in the
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geniculate ganglion which then sends off
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fibers towards the spinal nucleus of the
4:20
trinal
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nerve notice though that the geniculate
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ganglion only has cell bodies for
4:26
sensory neurons the other nerves pass
4:29
through it without synapsing here now
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for the facial muscles the motor fibers
4:35
or special visceral eant fibers they’re
4:38
going to travel further through the
4:40
facial canal and leave through the Stylo
4:43
M furen it then gives off the posterior
4:47
oricle nerve which branches off as the
4:50
occipital and the oricle segments to
4:52
innervate the occipital frontalis muscle
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and the instrinsic muscles of the ear it
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will give off a style of high branch and
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a digastric branch for the respective
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muscles the facial nerve then continues
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into the pared gland branching off
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forming the pared plexus which uh is a
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plexus of nerves that give off a
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superior branch and an inferior Branch
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or a superior Division and an inferior
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division the superior Branch give off
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the temporal zymatic and the Buckle
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branches while the inferior Branch give
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off the marginal mandibular and the
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cervical Branch all of these Supply
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different muscles of the face and we
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will go through them in detail once we
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get here all right so that was the
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General scheme awesome now the facial
Functional Components
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nerve is one of the most anatomically
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complex of all the cranial nerves
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because it transmits four different
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types of Innovations and so I want to
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start this video off by explaining these
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four functional components of this nerve
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before we dive into its pathway the
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first type of fibers are the special
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visceral eent fibers or the SV fibers
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they begin from the motor nucleus at the
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level of the lower ponds and Supply the
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muscles of facial
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expression then we got the general
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visceral eerin fibers or gve fibers
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which are preganglionic fibers meaning
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they arise in the superior salivatory
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nucleus then they go to two ganglia they
6:26
go to the submandibular ganglia to
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further inovate the submandibular and
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the sublingual salivar glands with the
6:33
post ganglionic fibers the other ganglia
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it goes to is toward SEO Paladin ganglia
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which sends fibers to inovate the lacal
6:43
gland then we got the special visceral
6:46
afferent fibers or SVA fibers and notice
6:50
they’re afferent fibers so they uh start
6:53
in the periphery or in this case uh
6:56
these fibers start from the taste buds
6:58
in the anterior 2/3 of the tongue then
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they sinapse with neurons in the
7:03
geniculate ganglion which sends fibers
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further towards the brainstem to talk
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with the upper part of the nucleus of
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the solitary tract the last fibers are
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the general somatic afferent fibers or
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GSA fibers those fibers come from the
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skin of the external ear primarily and
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then they also sinapse with cells in the
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GIC ganglion to then go further and
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syapse with the the spinal nucleus of
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the trial nerve so two efferent fibers
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leaving the brain stem and two effer
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fibers that come into the brain stem
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from the genic ganglion awesome now
Facial Nerve Nuclei
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let’s start with the nuclei of the
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facial nerve here we see a side view of
7:49
the central nervous system we can see
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the spinal cord the mingara cerebellum p
7:55
mlon and the dlon if we now remove the
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cere
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and focus on the brain stem from the
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posterior side we will see this so we
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see the mesencephalon PS and the midulla
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on the posterior side of the brain stem
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we can see something called the rbo fosa
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and the rbo fosa is a key location where
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several cranial nerve nuclei are
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situated and because it houses so many
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nerves and nuclei they form some
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external structures as you can see here
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in the middle we can see the median
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sulcus that divides the brain stem into
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two symmetrical halves on either side we
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can see the medial Eminence we can see
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the medular stria which divides PS and
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the mid blinga and just above the med
8:42
stria we can find the facial culus and
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this is what I want us to focus on here
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because the facial cicus is a grossly
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elevated area on the posterior side of
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Pawns that is formed because of the
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motor fibers of the facial nerve Hench
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the name facial culus here’s a
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cross-section of the distal part of PS
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here we see the abducent nerve nucleus
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and the facial nucleus when fibers from
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the motor nucleus of the facial nerve
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leaves they loop around the abducent
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nerve nucleus like this before it leaves
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laterally to the abducent nerve and this
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Loop that it makes forms the facial
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culus and here just for the visuals of
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it we got the motor nucleus of the
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facial nerve and here’s the nucleus of
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the six cranial nerve the abducent nerve
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fibers from the facial nerve will loop
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around the abducent nerve nucleus like
9:34
this then leave the brain stem on the
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anterior side between PS and abidullah
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blara and it will form the facial culus
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uh the elevation On The Backs side of PS
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the facial nerve is a bit special again
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because it consists of four fibers most
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literature divide this nerve into four
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fibers which go to four different nuclei
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so four nuclei are considered a part of
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the facial nerve the first one is the
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motor nucleus which give off SV fibers
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we got the superior salivatory nucleus
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giving off gve fibers there’s GSA fibers
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coming into signups with the spinal
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nucleus of the trinal nerve and we got
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the SVA fibers coming in to syapse with
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the nuclei of the solitary tract so the
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actual facial nerve arises from two
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divisions a motor root and a smaller
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sensor root commonly referred to as the
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intermediate nerve so the motor root
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contains motor fibers the intermediate
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nerve contains sensory and
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parasympathetic fibers of the facial
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nerve all right now let’s go through the
Facial Nerve Course
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course and distribution and I want to
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use this image to kind of illustrate
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just that the facial nerve has an
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intracranial course and an extra cranial
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course the intracranial course is
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everything from when the nerve is within
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the brain stem to the point where it
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exits the temporal bone and extra
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cranial course is when it’s actually
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outside of the cranium I think it’s
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easier to divide it this way so let’s
Intracranial Branches
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start with the intracranial
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course here again you see two nerves
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coming out from the junction between
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pwns and the medulla we see the motor
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roote of the facial nerve and we see the
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intermediate nerve they’re both going to
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penetrate the duramater and then go
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through the internal aquastic meatus as
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you see here to enter the facial canal
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in the petus part of the temporal bone
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where they fuse to form the facial uh
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nerve proper the nerve makes a sharp
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anterior to posterior turn at a point
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known as the geniculum of the facial
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nerve it also enlarges at this point as
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the geniculate ganglion which contains
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the cell bodies of sensory neurons in
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the facial nerve as you look at this
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image you will notice a large nerve
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going out from the GID ganglion this one
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is called the greater petal nerve the
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greater petal nerve consists of
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parasympathetic gve fibers the purple
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ones I showed you earlier that comes
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from the superior salivatory nucleus so
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they don’t syapse with the gulet
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ganglion they just come from the brain
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stem and run through the ganglion
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towards the F laerum on its way to
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towards the Pham laerum it merges with
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the Deep petal nerve that carries
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sympathetic fibers to form uh the nerve
12:36
of the pooid canal it travels uh to the
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pigo palatin gangon to provide pre
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ganglionic parasympathetic inovation to
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the lacal glands as well as the mucous
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glands of the nasal cavity the maxillary
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sinus and the pallet the second
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intratemporal branch of the facial nerve
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is the nerve to stapedius muscle
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supplying sve fibers or motor fibers to
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the sapidus muscle responsible for
13:05
dampening vibrations and protecting the
13:07
hearing apparatus when exposed to loud
13:10
sounds the final intratemporal branch is
13:14
the Corda tempany the Corda tempany
13:16
carries gustatory or taste sensory
13:19
Innovation from the front of the tongue
13:22
and it carries parasympathetic inovation
13:25
to the submandibular and the sublingual
13:27
salivary glands so there are two fibers
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that make up the cordan gve fibers and
13:33
SVA fibers cotan exits a skull by
13:38
passing inferiorly through the panic
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fissure to enter the infratemporal fosa
13:44
here Cordo tempani joins with the
13:46
lingual branch of the cranial nerve
13:48
number five and together these nerves
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travel anteriorly deep to the mendible
13:54
along the way the gve fibers diverge to
13:57
terminate in the sub mandibular ganglion
14:00
from here postganglionic neurons
14:03
distribute to the submandibular and the
14:05
sublingual salivary glands so gve fibers
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start from the superior salivatory
14:11
nucleus in the brain stem and go
14:13
straight to the submandibular ganglion
14:16
in contrast the SVA taste component of
14:19
the Cordo tempany remains with the
14:21
lingual nerve where it distributes to
14:24
taste receptors of the anterior 2/3 of
14:26
the tongue so it car sensory information
14:30
towards the neurons in the GIC ganglion
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which further sends neurons towards the
14:35
nucleus of the solitary
Extracranial Branches
14:36
tract so that was primarily the
14:39
intracranial course the facial nerve
14:42
exits the skull via the styom master
14:44
framen and now it’s outside of the skull
14:47
so let’s go through the extra cranial
14:49
course after it leaves the sty Master
14:52
for raymen once it exits the styo MTO
14:55
for rmen the facial nerve give off the
14:58
styo high IID branch and the digastric
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branch they carry motor Innovation to
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the respective
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muscles it also give off the posterior
15:07
arular nerve which divides into the
15:10
occipital Branch to provide motor
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Innovation to the occipital Belly of the
15:15
occipito frontalis muscle and the oricle
15:18
branch to supply mainly the intrinsic
15:21
oracular muscles and just for the sake
15:23
of theory we also got the general
15:26
somatic afren fibers or GS a fibers that
15:30
provide sensory inovation of the skin
15:32
around the external acoustic meus and
15:34
the Retro arular region which uh then
15:37
goes to syapse with the sensory nuclear
15:39
of the GID ganglion from which sends
15:42
fibers towards the spinal nucleus of the
15:44
trial nerve all right so that was dose
15:49
the facial nerve is then going to
15:52
continue into the pared gland as you see
15:54
here and if you fade the pared gland you
15:58
will see that that this nerve bifurcates
16:00
into a superior and an inferior chunk
16:04
which forms a network of nerves called
16:06
the pared plexus from here there are
16:10
five terminal branches that are going to
16:12
come off and they’re motor uh they
16:14
provide motor Innovation to facial
16:17
muscles the first one is the temporal
16:20
Branch innovating the facial muscles of
16:22
the forehead and the temporal region we
16:24
got the zygomatic branch that inovate
16:27
the orbicularis
16:29
zygomatic muscles and the muscles of the
16:31
nose there are the Buckle branches
16:34
innervating the muscles of the cheek and
16:36
the upper lip marginal mandibular Branch
16:39
innervating the muscles of the chin and
16:41
the lower lip uh so the depresso Lai
16:44
inferioris depressor angulis and the
16:46
mentalis muscle and then we got the
16:49
cervical branch that inovate the Prisma
16:52
and in some variations it also
16:54
participates in forming the superior
16:56
cervical Ana so that was primarily all I
Clinical Relevance
17:00
had for the course and the
17:02
distribution now the facial nerve can
17:05
get damaged at different levels and with
17:07
a neurological examination you’ll be
17:09
able to point out the most probable side
17:11
of lesions within this pathway a damage
17:14
might occur supran nuclearly the upper
17:18
motor neuron of the facial nerve is
17:20
located in the primary motor cortex of
17:22
the frontal lobe these upper motor
17:25
neurons will descend ipsilaterally uh as
17:28
the cortical bulbo tract via the genu of
17:31
the internal capsule and reach the
17:33
facial nucleus in the pontin pigmentum I
17:37
haven’t gone into this in detail but the
17:39
facial nucleus is divided into a dorsal
17:43
and a ventral region and so the dorsal
17:45
region supplies inovation of the muscles
17:48
of the upper face whereas neurons in the
17:51
ventral region interace muscles of the
17:53
lower
17:54
face the dorsal aspect of the facial
17:57
nucleus re receives input from both the
17:59
left and the right cerebral hemispheres
18:02
and this result in both hemispheres
18:04
having control over the muscles of the
18:06
upper face you with me so far so if
18:09
there’s a stroke of some sort that
18:11
affect the cortical B tract you know an
18:14
upper motor neural lesion that will
18:16
cause paralysis of the contralateral
18:19
middle and the lower part of the face
18:21
the muscles of the forehead and eyes are
18:24
spared because they’re innovated by both
18:26
hemispheres all right
18:28
now lesions that involve the facial
18:31
motor nucleus or lesions to the facial
18:33
nerve itself result in complete
18:36
paralysis of all the muscles on the
18:38
ipsilateral side and so since the whole
18:41
ipsilateral facial muscles are affected
18:44
the patient presents with drooping of
18:45
the mouth and eyelid as well as
18:48
flattening of the nasolabial fold Bells
18:50
pulsy is a form of facial nerve pulsy
18:53
it’s usually idopathic CA meaning we’re
18:56
not entirely sure uh what causes the
18:59
damage but one theory is that it is
19:01
caused by edema because of a viral
19:04
infection Bell’s pulsy can be
19:06
distinguished from other causes of
19:08
facial paralysis by rapid onset of
19:10
several hours and lack of trauma what is
19:13
more is that this kind of facial
19:15
paralysis is often self-limiting and the
19:18
patient usually recovers within days to
19:20
weeks and patients can benefit from
19:22
early initiation of steroids as this
19:25
prevents the progression of Edema
19:27
diminishing chances of further damage
19:29
all right so that was everything I had
Recap
19:31
for the facial nerve here we see the
19:33
scheme again of this nerve it’s not
19:36
detailed but it will help to gain a
19:38
general overview of this nerve so that
19:41
is this nerve the next video is going to
19:44
be about the eighth cranial nerve the
19:46
vestibulo clear nerve thank you so much
19:49
for watching another one of my videos If
19:51
you enjoyed learn something from it
19:53
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y’all
20:09
peace
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