hello anatomy colleagues this is dr. Alsup and in this video we are going to talk the very basics of
every single cranial nerve all twelve of them and as we move through the course we will talk
about each one of these in much more detail and we've already talked about quite a few of these
at this point but this lecture is really meant to be a quick overview the basic function of
all twelve pairs so what I mean by basics we're going to include the name as well as the number
and are these nerves composed of only a ferrant or sensory fibers or only efferent and/or motor
fibers or do they have both types of axons and from this understanding then we'll talk about
the target organs of each nerve as in what do they innervate so this may seem like a lot but
I really hope that this feels more like a nice leisurely stroll through the cranial nerves
instead so let's just get started alright as you might have guessed we are going to start with
cranial nerve one and make our way to cranial nerve 12 so what is cranial nerve one why it
is the olfactory nerve of course or cranial nerve one this nerve is entirely sensory in
fact it is what is called special sensory so what does this mean what is so special about
this particularly this particular sensory fibers all this means is that this is composed of axons
or fibers transmitting unique sensations think of the five senses you grew up learning about
but with some bonuses so for the olfactory nerve this is going to be associated with the special
sense of smell and you probably could guess that from its name so sensation of odors that results
from detection of substances that are going to be a realized in the environment there will be
these cell bodies or all factory receptor neurons located in the olfactory part of the nasal mucosa
which is going to be located in say the roof of the nasal cavity so you can see some around this
region here we're actually looking at the nasal septum here so there's going to be little fibers
that are in this region as well and there's going to be some associated with the medial wall of the
superior nasal Concha and these fibers will connect to the olfactory bulb which typically
lies in contact with the orbital surface of the frontal lobe of the cerebral Hemisphere
and then these axons of the secondary neurons form the olfactory tract so the olfactory bulb
would be kind of in this region here connected to the olfactory tract which we can see here
and here so these are the olfactory tracts it is the olfactory tracts like you can see that
we typically see most clearly associated with the brain the olfactory bulbs and tracts are really
just anterior extensions of the forebrain making this one of the making it kind of unique in terms
of the fact that we refer to this as a cranial nerve so the too long didn't listen version of
this would be olfactory nerve is cranial nerve one and it will have special sensory fibers associated
with smell also entirely sensory and special sensory to boot is going to be the optic nerve
or cranial nerve two now although considered with the cranial nerves this optic the optic
nerve actually develops in a completely different manner and really these are interior extensions
of the forebrain and maybe better classified as central nervous system fiber tracts but we are
not going to do that as pretty much every other resource does and we're going to consider these
cranial nerves the optic nerve begins with the axons of the retinal ganglion and these will
pierce the sclera so the sclera is going to be kind of the whites of the eye in this region so
you can see the optic nerve very clearly here this large area and the optic nerve will exit
the optic canal to enter the middle cranial fossa where there's the formation of the optic chiasm
which you can see right here and these fights so they'll have fibers from the medial half of each
retina decussating or crossing in this chiasm and will join uncross fibers from the lateral
side so this partial crossing that occurs in the chiasm is essential for binocular vision moving
to cranial nerve 3 or the oculomotor nerve this is going to be an entirely motor nerve so no sensory
fibers associated with the oculomotor nerve the oculomotor nerve sends somatic motor motor fibers
to all extraocular eye muscles except for two which are going to be your superior oblique in
your lateral rectus muscles which are innervated by different cranial nerves so four out of the six
extra ocular eye muscles importantly oculomotor nerve also has pre ganglionic parasympathetic
fibers associated with it so they're going to be originating here and these pre ganglionic
parasympathetic fibers will synapse in the ciliary ganglion for innovation of the ciliary
body as well as the sphincter papillae muscle and that ciliary body is going to play a role
in accommodations and kind of helping in terms of keeping things in focus and the sphincter papillae
muscle does exactly what it sounds like it will which is constrict the pupils so we'll
spend a lot more time on those pre ganglionic when we talk about the eye the oculomotor nerve
will originate from the midbrain it will run in the lateral wall of the cavernous sinus and
will enter the orbital region through the superior orbital fissure and eventually split into superior
and inferior divisions the superior divisions been removed here and we can see a nice view of
your inferior division within the orbital region here next we have the trochlear nerve or cranial
nerve 4 which is entirely efferent or motor this nerve will innervate the superior oblique muscle
so you can see the trochlear nerve right here entering towards the superior oblique muscle
which you can see here and the nerve is actually named after the trochlea which you can see right
in this region of the superior oblique so it kind of changes the direction of the attachment for the
superior oblique muscle this nerve is unique in it emerges from the posterior aspect of the
brainstem so you can see it kind of popping out here from that posterior aspect and it will make
its way through the superior orbital fissure before reaching that superior oblique muscle
all right our first nerve with both sensory and motor fibers and this also happens to be your
largest cranial nerve which is the trigeminal nerve or cranial nerve five two of the three
divisions are entirely sensory so you have v1 or your ophthalmic nerve and v2 or your maxillary
nerve which are entirely sensory v3 which you can see v3 heading towards the framing of Valley right
here this would be your foramen rotundum and v1 will exit through your superior orbital fissure
v3 or the mandibular nerve has both a parent and efferent fibers and will provide somatic
muscle fiber innervation efferent innervation to muscles of mastication importantly the mylohyoid
muscle the anterior belly of the digastric and two tensor muscles the trigeminal nerve will
provide a fair and innervation to a huge expansive area which makes sense because it is the largest
of the cranial nerves and a good amount of its fibers are afferent so the expanse will include
but it's not limited to the skin of the face the teeth very important for most of you listening
gingiva mucous membranes of the nasal cavity paranasal sinuses and portions of the mouth so
very important in terms of afferent innervation the abducens nerve cranial nerve 6 is relatively
simple compared to the trigeminal nerve this nerve is entirely efferent and will innervate
the lateral rectus muscle which you can see right here here is your abducens nerve traveling to the
lateral rectus muscle the lateral rectus muscle will a be duct or abduct the eye thus the name
abducens nerve the abducens nerve is the cranial nerve that actually travels through the lumen of
the cavernous sinus before exiting through the superior orbital fissure to enter the orbit the
facial nerve or cranial nerve seven is another nerve that has both sensory and motor fibers and
we're really getting into one of the first complex nerves that has a lot of different
functions sensory fibers include both special sensory and somatic sensory so the special sensory
or excuse me that it will include just special sensory in terms of taste to the presulcul
or anterior portions of the tongue the somatic motor fibers are going to innervate muscles of
facial expression which you can see a lot of those branches right here which we'll talk about more in
the face session as well as some other muscles in the surrounding areas the visceral motor fibers
are their pre ganglionic parasympathetic fibers are going to be destined for the pterygopalatine
and submandibular ganglia so it will initiate secretion from the lacrimal gland as well as
the submandibular and sublingual salivary glands all right one of my favorite cranial nerves is
cranial nerve eight or the vestibulocochlear nerve which is entirely sensory a specifically special
sensory involving hearing equilibrium so we have hearing an equilibrium as well as motion or things
associated with motion vestibular cochlear nerve will enter into the internal acoustic
meatus which you can see clearly here which leads into the middle and inner ear region and it will
divide into the cochlear and vestibular nerve so important in terms of the inner ear region
the glossopharyngeal nerve is cranial nerve nine and has both a ferrant and efferent fibers again
there's a lot going on with the glossopharyngeal nerve a lot of it we've discussed already there
there will be special sensory fibers to the post suckle tongue as well as gence general
sensory fibers for that same area we also know that the glossopharyngeal nerve rods
sensory innervation for most of the pharynx as we discussed in previous session there will also
be pre ganglionic parasympathetic fibers that originated in the glossopharyngeal nerve which
will synapse in the otic ganglion and it will be those fibers are destined for the large largest
salivary gland your parotid gland and lastly it provides that somatic motor innervation to the
stylopharyngeus muscle which can really nicely see your style of trendiest muscle here and
your glossopharyngeal nerve right here we are becoming very familiar with this next cranial
nerve which is cranial nerve 10 or the vagus nerve so important roles in terms of efferent
innervation for the intrinsic laryngeal muscles as well as the pharyngeal muscles and we'll talk about
some in terms of the palate later on it will play a small role in pre ganglionic parasympathetics
in this general head neck region in regards to the tracheobronchial tree and the esophagus via
the pulmonary and esophageal plexus ease but most of its parasympathetic role is associated
with the gastrointestinal system associated with the abdomen the accessory nerve are quite
cranial nerve 11 was traditionally referred to as the spinal accessory nerve so you may hear
it referred to in that way this is an entirely motor or efferent nerve and we've talked about
the two muscles that it innervates already which are your sternocleidomastoid and your trapezius
muscle which you can see it kind of going in between the two right here and last but not
least we have the hypoglossal nerve or cranial nerve 12 this is also entirely efferent think
muscles of the tongue both extrinsic and intrinsic muscles of the tongue except colada glosses muscle
this nerve will originate on the medulla oblongata like you can see her on this brainstem model and
you can see how it will spread out all around this tongue region so we're in the extrinsic
tongue region and expanding into the intrinsic tongue region so those are the twelve pairs of
cranial nerves as mentioned at the big we will talk about each one of these in more detail in
either the previous sessions that we've already done or upcoming sessions but this video serves
as an overview of the basics at this point we're hoping that you know which ones are if totally
efferent totally a ferrant or both and kind of a general idea of their their target organs so
let's do a quick review of an important concept regarding pre ganglionic parasympathetics so the
question which of the following cranial nerves does not have presynaptic or pre ganglionic
parasympathetic fibers is it a the abducens nerve be the facial nerve see glossopharyngeal nerve D
oculomotor nerve or E the vagus nerve pause the video if you need a bit more time but for those
that are ready the correct answer is going to be a abducens so recall abducens is a purely efferent
nerve which innervates the lateral rectus muscle which is one of those extra ocular eye muscles
the facial nerve the glossopharyngeal nerve ocular motor in vagus all have presynaptic
parasympathetics associated with them so they are a source of those pre ganglionic parasympathetics
we will talk a lot about parasympathetics in this course so make sure you are beginning to
understand these sources and their destinations and we will continue to review these as we go
so that will do us for this video thank you for your time and attention have a great day