Anatomy of Fourth Ventricle and Rhomboid Fossa

What's up, Medite here! Let's continue the anatomy of the central nervous system. In this segment, we will cover the anatomy of the fourth ventricle, and then we're gonna cover the structures and the cranial nuclei of the rhomboid fossa. So remember, the central nervous system consists of two parts, the encephalon and the spinal cord. And the encephalon is then further subdivided into specific parts. We have the brainstem, which consists of the medulla, pons and the midbrain. the mesencephalon, we have the cerebellum back here, and then the diencephalon and the telencephalon. So our focus in this video is going to be the space between these three structures, called the 4th ventricle, and the base of the 4th ventricle, called the rhomboid fossa, which is here. So in this video, we're first going to go through all the ventricles in the brain, then we're going to cover the borders and the communications of the 4th ventricle, after that we're going to cover the topography of the rhomboid fossa, then cover the anatomical structure of the 4th ventricle, you see here on the rhomboid fossa, and then the cranial nuclei and the cranial nerves associated with the rhomboid fossa. Then I've made a little quiz at the end which might help you if you need to memorize. Alright, again the 4th ventricle is here, which lies between the Pons, medulla and cerebellum. Inferiorly, the 4th ventricle is going to continue as the central canal within the spinal cord. Superiorly, the 4th ventricle will continue upwards as the aqueduct of the midbrain. which is inside the mesencephalon. Let's now look at the whole ventricular system within the brain to understand what we're learning. So if you continue upwards above the aqueduct, we will find the third ventricle. And the third ventricle has communications upwards called the interventricular foramen, which communicates with the lateral ventricles. So if you now look at the whole ventricular system from an anterior perspective, it will look like this. So the lateral ventricles are here. and they're called lateral ventricles because they're located laterally. Then we have the third ventricle, which has three communications, two up here and one down here, which is the aqueduct. And the fourth ventricle, with the aqueduct up here, the central canal down here, and two apertures located on the lateral sides that go into the subarachnoid space. So these ventricles are spaces within the central nervous system that contains cerebrospinal fluid. which contains nutrients for the nerve tissue as well as removing waste products from them. The cerebrospinal fluid then flows through these apertures on the 4th ventricle into the subarachnoid space, and then the cerebrospinal fluid is filtrated into the venous system through the dural sinuses. So let's go through that again once we understand the structures of the 4th ventricle. So let's go back to this picture and zoom in. Now, the 4th ventricle consists of a roof, called the roof of the 4th ventricle, or tegmen ventricular quarti, and a base, which is called the rhomboid fossa. Let's go through the roof first, and then talk about the rhomboid fossa. So the upper part of the roof is formed by a plate of white matter that you will find between the superior cerebellar peduncles, called the superior medullari velum. So here is the posterior view of the brain. When we remove the cerebellum, you will see the base of the 4th ventricle, which is the rhomboid fossa. On either side of the rumbot fossa, you will see the cerebellar peduncles, which contains fibers that run between the cerebellum and all three parts of the brainstem. The inferior cerebellar peduncles contain fibers that go to the medulla, the middle cerebellar peduncle contain fibers that go to the pons, and the superior cerebellar peduncle contain fibers that go to the midbrain. So the superior medullar velum is located between the superior cerebellar peduncles, like this. So this is the superior part of the roof of the 4th ventricle, the superior medullar velum. It's a thin plate of white matter. Now the lower part of the roof is also formed by a thin plate of white matter called the inferior medullar velum, which is between the inferior cerebellar peduncles, as you see here. Now between the inferior and the superior medullar velum, there's a pointy roof called the fastigium, which is the apex of the 4th ventricle. Now, the lower part of the roof has a few more structures than the inferior medullaryvelum that we need to address. And to understand them, we need to repeat our three layers of the meninges. So the outermost layer is the dura mater. Underneath the dura mater, you will find the arachnoid mater. Then underneath that again, you will find a very thin and delicate layer covering the tissue of our central nervous system, called the pia mater. And between the pia mater and the arachnoid mater, is a space called the subarachnoid space which is filled with cerebrospinal fluid, which again delivers nutrition for the brain and spinal cord tissue as well as removing waste products. So where do you find the cerebrospinal fluid? You find them in the subarachnoid space and in the ventricles and canals of our central nervous system. At the 4th ventricle, there are apertures or openings at which the cerebrospondin fluid flows from the ventricular system into the subarachnoid space. And you see how the PMR terminates at this aperture and then continues above the aperture again? Once it terminates, the PMR forms a membrane which loops loops to the inside of the inferior medullar velum as you see here. This membrane is called Tela Choroidea. Another structure you will find here, and that's a structure you will see in all the ventricles of the CNS, and that is the Choroid Plexus. The Choroid Plexus is highly vascular and it produces the actual cerebrospinal fluid. So that was all the structures associated with the roof of the 4th ventricle. Now let's go through the communications of the 4th ventricle. And we'll do that by looking at the 4th ventricle from two perspectives. Remember, the 4th ventricle communicates with the 3rd ventricle through the aqueduct of the midbrain, and continues downwards as the central canal within the spinal cord. Laterally, we'll find two apertures called the lateral apertures, or foramina of Luschka, which opens into the subarachnoid space. Then there's an opening we looked at earlier, called the median aperture, or also referred to as the Foramen of Magendie. All of these apertures open into the subarachnoid space to provide a flow for the cerebrospinal fluid between the ventricles and the subarachnoid space. So that was all for the 4th ventricle, let's now open up the roof and focus on the base of the 4th ventricle, which is the rhomboid fossa. Now we're looking at the brainstem from the posterior perspective after removing the cerebellum, so we can see the PANS, the medulla, and the midbrain. And here is the rhomboid fossa. Now we divide the rhomboid fossa into two main regions. The upper region is Pons, and the lower region of the rhomboid fossa is the medulla oblongata. Now topographically, the rhomboid fossa is bordered by the peduncles. It's bordered by the superior cerebellar peduncle and the inferior cerebellar peduncle. Let's now isolate the posterior view of the brainstem and focus on the anatomical structures of the rhomboid fossa. So first off, there's a groove in the middle of the rhomboid fossa that divides the rhomboid fossa into two symmetrical halves, called the median sulcus. So the median sulcus goes all the way from the central canal of the spinal cord to the aqueduct of the midbrain. On either side of the median sulcus, there are elevations we call the medial eminence. The motor nuclei of the brainstem are usually situated underneath this eminence. Another thing you will see here in the rhomboid fossa is that the rhomboid fossa is crossed by myelinated nerve fibers called medullar stria, dividing the fossa into an upper part and a lower part. Usually the upper part is pons and the lower part is medulla. Above the medullar stria, you will find an elevation on either side of the median silcus called the facial colliculus. These are elevations made by fibers leaving the facial nucleus as they loop around the abducens nucleus. Below the medullaris rea, you will find the hypoglossal trigone, which is where the nucleus of the 12th cranial nerve is located, and the vagal trigone, which is the area where the vagal part of the nucleus ambiguus is located. I will show you this later in this video when we go through the nuclei of the cranial nerves in the rhomboid fossa. Alright, on the angle of the rhomboid fossa, you will find the vestibular area. This is where the vestibular nuclei are situated underneath. Meaning this place is responsible for balance from the vestibular system. Then a little more superiorly, you'll find the locus cellulareus, which are composed of cells that produce norepinephrine. And you'll learn more about the locus cellulareus and the norepinephrine system in the physiology, but this system is related to the sleep-wake cycle, along with attention and arousal and a few more things. So that was all the anatomical structures of the fourth ventricle. Take a mental picture of this for now. And let's continue with the cranial nuclei you will find in the rhomboid fossa. In the rhomboid fossa, you will find the cranial nuclei number 5 to 12, and we will find the trigeminal nerve, the abducent nerve, the facial nerve, the vestibulocochlear nerve, the glossopharyngeal nerve, the vagus nerve, the accessory nerve, and the hypoglossal nerve. Let's now go through all of the nuclei associated with each of these cranial nerves. starting with the trigeminal nerve. The trigeminal nerve has two roots of nerves, one motor and one sensory. The sensory part of the trigeminal nerve synapses with the mesencephalic nucleus of the trigeminal nerve. The trigeminal nerve is one of the biggest cranial nerves we have, and it's divided into three parts in the facial area. So the mesencephalic nucleus of the trigeminal nerve receives proprioceptive information from mainly the muscles of mastication, as well as from the memetic muscles and the extraocular muscles. The next nucleus of the trigeminal nerve is the principal nucleus of the trigeminal nerve. It receives information about touch and vibration and some proprioception as well. The spinal nucleus of the trigeminal nerve is in the medulla and the spinal cord, so it receives information about pain and temperature. The motor nucleus of the trigeminal nerve gives off fibers that innervate the muscles of mastication and the anterior belly of the gastricus, the myelohyoid and the tensor tympani muscles. So that was this nerve. Next we have the sixth cranial nerve, the abducent nerve. The abducent nerve consists of only one motor fiber, coming from only one nucleus in the rhombus fossa, and that is the nucleus of the abducent nerve. The abducent nerve is responsible for abduction movement of the eyeball, and it does that by innervating the lateral rectus muscles of the eyeball, so that is this one. Next we have the facial nerve. The facial nerve consists of two roots, One motor root innervates the facial muscles, and an intermediate nerve that carries parasympathetic and sensory fibers. The motor root of the facial nerve comes from the motor nucleus of the facial nerve. So fibers go from this nucleus to innervate all the facial muscles of facial expression, as well as some superficial muscles on the neck region as well. The intermediate nerve carries sensory fibers and parasympathetic fibers. The parasympathetic fibers come from the parasympathetic nucleus, called the superior salivatory nucleus, giving off parasympathetic innervation to glands in the facial regions, like the lacrimal gland, the submandibular and the sublingual glands. The sensory fibers of the intermediate nerve synapse with the nucleus of the solitary tract, which receives information about taste. So that is the facial nerve. Next we have the cranial nerve number 8, which is the vestibulocochlear nerve. The vestibulocochlear nerve consists of the vestibular nerve and the cochlear nerve, so if you put them together you'll get the vestibulocochlear nerve. So there are four sensory nuclei for the vestibular parts. These are the medial, lateral, superior and inferior vestibular nuclei. And there are two cochlear nerves, medial and lateral. Remember, the inner ear consists of two parts, the vestibulum for balance, and the cochlea for hearing. The vestibular nerve transmits information about balance, motion and acceleration. So inside the semicircular canals of the vestibulum, there are crystals that detect movement that stimulate the receptors of the vestibular nerve. This nerve will then go to the vestibular nuclei. The cochlear nerve transmits sound impulses from the organ of Corti by, you know, movements of the endolymphs. And then these fibers will go to the medial and lateral cochlear nuclei. So that was the vestibulocochlear nerve. Next is the ninth cranial nerve, the glossopharyngeal nerve. This nerve contains motor, sensory and parasympathetic fibers. The parasympathetic fibers come from the inferior salivatory nucleus that innervates salivary glands like the parietal glands. The motor fibers come from the nucleus ambiguous that innervates muscles of the pharynx and the soft palate. The sensory fibers synapse with the nucleus of the solitary tract, just like the facial nerve. so it contains sensory information of taste from the posterior third of the tongue. Next we have the tenth cranial nerve, the vagus nerve. The vagus nerve also contains three types of fibers, which are motor, sensory and parasympathetic fibers. The motor and the sensory part of this nerve are also associated with the nucleus ambiguous and the nucleus of the solitaire tract, so it innervates the muscles of the pharynx, soft palate and the larynx, as well as sensing taste from the posterior third of the tongue. The parasympathetic nerve fiber comes from the posterior nucleus of the vagus nerve, and this nerve is the only cranial nerve that actually leaves the cranium to innervate all the organs of the thorax and the abdomen. Remember, the parasympathetic innervation is rest and digest. So the vagus nerve reduces the heart rate, it increases the gastric motility and absorption, and all of those things related with the parasympathetic functions of the organs. Next, we have the 11th cranial nerve, the accessory nerve. And notice that I've added the spinal cord, because this cranial nerve is a little special. So the accessory nerve consists of two motor fibers. We have the cranial root, that comes from the part of the nucleus ambiguous, located in the posterior lateral sulcus of the medulla oblongata. And it contains a spinal root, that comes from the spinal nucleus of the accessory nerve. This nucleus appears on the posterior lateral sulcus of the spinal cord between C1 and C6 spinal segments. It then ascends along the spinal cord to then enter the cranial cavity through the foramen magnum and joins with the cranial roots, and then form the 11th cranial nerve, which is the accessor nerve. The accessor nerve is primarily a motor nerve that innervates the sternocleidomastoid muscle and the trapezius. It's called accessory nerve because it forms a kind of a mixed system with the vagus nerve and the glossopharyngeal nerve. So that's this one. The last nerve is the 12th cranial nerve, called the hypoglossal nerve. It's a motor neuron of which the fibers come from the nucleus of the hypoglossal nerve. These motor fibers go to the tongue and innervate all the muscles of the tongue. So that was the 12th cranial nerve. So here I've added all the nuclei of the rhomboid fossa, with the corresponding cranial nerves that synapses with them. And so this is where this video gets scary. I am going to make all of these cranial nerves disappear, and basically if you hit pause, could you go through from the beginning and list, you know, which cranial nerve go with number 1, which cranial nerve go with number 2, and what does number 3 do, and what does number 4 do. This is a little challenging, but you know, once you get it right, you then understand it. So that was a video about the 4th ventricle and the rhomboid fossa. If you found this video helpful, please put a like, share, comment, whatever you find convenient to you, and I hope this was helpful.

And the encephalon is then further subdivided into specific parts. We have the brainstem, which consists of the medulla, pons and the midbrain. the mesencephalon, we have the cerebellum back here, and then the diencephalon and the telencephalon.

So our focus in this video is going to be the space between these three structures, called the 4th ventricle, and the base of the 4th ventricle, called the rhomboid fossa, which is here. So in this video, we're first going to go through all the ventricles in the brain, then we're going to cover the borders and the communications of the 4th ventricle, after that we're going to cover the topography of the rhomboid fossa, then cover the anatomical structure of the 4th ventricle, you see here on the rhomboid fossa, and then the cranial nuclei and the cranial nerves associated with the rhomboid fossa. Then I've made a little quiz at the end which might help you if you need to memorize. Alright, again the 4th ventricle is here, which lies between the Pons, medulla and cerebellum.

Inferiorly, the 4th ventricle is going to continue as the central canal within the spinal cord. Superiorly, the 4th ventricle will continue upwards as the aqueduct of the midbrain. which is inside the mesencephalon. Let's now look at the whole ventricular system within the brain to understand what we're learning. So if you continue upwards above the aqueduct, we will find the third ventricle.

And the third ventricle has communications upwards called the interventricular foramen, which communicates with the lateral ventricles. So if you now look at the whole ventricular system from an anterior perspective, it will look like this. So the lateral ventricles are here. and they're called lateral ventricles because they're located laterally.

Then we have the third ventricle, which has three communications, two up here and one down here, which is the aqueduct. And the fourth ventricle, with the aqueduct up here, the central canal down here, and two apertures located on the lateral sides that go into the subarachnoid space. So these ventricles are spaces within the central nervous system that contains cerebrospinal fluid. which contains nutrients for the nerve tissue as well as removing waste products from them.

The cerebrospinal fluid then flows through these apertures on the 4th ventricle into the subarachnoid space, and then the cerebrospinal fluid is filtrated into the venous system through the dural sinuses. So let's go through that again once we understand the structures of the 4th ventricle. So let's go back to this picture and zoom in. Now, the 4th ventricle consists of a roof, called the roof of the 4th ventricle, or tegmen ventricular quarti, and a base, which is called the rhomboid fossa.

Let's go through the roof first, and then talk about the rhomboid fossa. So the upper part of the roof is formed by a plate of white matter that you will find between the superior cerebellar peduncles, called the superior medullari velum. So here is the posterior view of the brain. When we remove the cerebellum, you will see the base of the 4th ventricle, which is the rhomboid fossa.

On either side of the rumbot fossa, you will see the cerebellar peduncles, which contains fibers that run between the cerebellum and all three parts of the brainstem. The inferior cerebellar peduncles contain fibers that go to the medulla, the middle cerebellar peduncle contain fibers that go to the pons, and the superior cerebellar peduncle contain fibers that go to the midbrain. So the superior medullar velum is located between the superior cerebellar peduncles, like this.

So this is the superior part of the roof of the 4th ventricle, the superior medullar velum. It's a thin plate of white matter. Now the lower part of the roof is also formed by a thin plate of white matter called the inferior medullar velum, which is between the inferior cerebellar peduncles, as you see here. Now between the inferior and the superior medullar velum, there's a pointy roof called the fastigium, which is the apex of the 4th ventricle. Now, the lower part of the roof has a few more structures than the inferior medullaryvelum that we need to address.

And to understand them, we need to repeat our three layers of the meninges. So the outermost layer is the dura mater. Underneath the dura mater, you will find the arachnoid mater. Then underneath that again, you will find a very thin and delicate layer covering the tissue of our central nervous system, called the pia mater.

And between the pia mater and the arachnoid mater, is a space called the subarachnoid space which is filled with cerebrospinal fluid, which again delivers nutrition for the brain and spinal cord tissue as well as removing waste products. So where do you find the cerebrospinal fluid? You find them in the subarachnoid space and in the ventricles and canals of our central nervous system. At the 4th ventricle, there are apertures or openings at which the cerebrospondin fluid flows from the ventricular system into the subarachnoid space.

And you see how the PMR terminates at this aperture and then continues above the aperture again? Once it terminates, the PMR forms a membrane which loops loops to the inside of the inferior medullar velum as you see here. This membrane is called Tela Choroidea. Another structure you will find here, and that's a structure you will see in all the ventricles of the CNS, and that is the Choroid Plexus. The Choroid Plexus is highly vascular and it produces the actual cerebrospinal fluid.

So that was all the structures associated with the roof of the 4th ventricle. Now let's go through the communications of the 4th ventricle. And we'll do that by looking at the 4th ventricle from two perspectives.

Remember, the 4th ventricle communicates with the 3rd ventricle through the aqueduct of the midbrain, and continues downwards as the central canal within the spinal cord. Laterally, we'll find two apertures called the lateral apertures, or foramina of Luschka, which opens into the subarachnoid space. Then there's an opening we looked at earlier, called the median aperture, or also referred to as the Foramen of Magendie. All of these apertures open into the subarachnoid space to provide a flow for the cerebrospinal fluid between the ventricles and the subarachnoid space. So that was all for the 4th ventricle, let's now open up the roof and focus on the base of the 4th ventricle, which is the rhomboid fossa.

Now we're looking at the brainstem from the posterior perspective after removing the cerebellum, so we can see the PANS, the medulla, and the midbrain. And here is the rhomboid fossa. Now we divide the rhomboid fossa into two main regions. The upper region is Pons, and the lower region of the rhomboid fossa is the medulla oblongata. Now topographically, the rhomboid fossa is bordered by the peduncles.

It's bordered by the superior cerebellar peduncle and the inferior cerebellar peduncle. Let's now isolate the posterior view of the brainstem and focus on the anatomical structures of the rhomboid fossa. So first off, there's a groove in the middle of the rhomboid fossa that divides the rhomboid fossa into two symmetrical halves, called the median sulcus.

So the median sulcus goes all the way from the central canal of the spinal cord to the aqueduct of the midbrain. On either side of the median sulcus, there are elevations we call the medial eminence. The motor nuclei of the brainstem are usually situated underneath this eminence.

Another thing you will see here in the rhomboid fossa is that the rhomboid fossa is crossed by myelinated nerve fibers called medullar stria, dividing the fossa into an upper part and a lower part. Usually the upper part is pons and the lower part is medulla. Above the medullar stria, you will find an elevation on either side of the median silcus called the facial colliculus. These are elevations made by fibers leaving the facial nucleus as they loop around the abducens nucleus. Below the medullaris rea, you will find the hypoglossal trigone, which is where the nucleus of the 12th cranial nerve is located, and the vagal trigone, which is the area where the vagal part of the nucleus ambiguus is located.

I will show you this later in this video when we go through the nuclei of the cranial nerves in the rhomboid fossa. Alright, on the angle of the rhomboid fossa, you will find the vestibular area. This is where the vestibular nuclei are situated underneath.

Meaning this place is responsible for balance from the vestibular system. Then a little more superiorly, you'll find the locus cellulareus, which are composed of cells that produce norepinephrine. And you'll learn more about the locus cellulareus and the norepinephrine system in the physiology, but this system is related to the sleep-wake cycle, along with attention and arousal and a few more things. So that was all the anatomical structures of the fourth ventricle.

Take a mental picture of this for now. And let's continue with the cranial nuclei you will find in the rhomboid fossa. In the rhomboid fossa, you will find the cranial nuclei number 5 to 12, and we will find the trigeminal nerve, the abducent nerve, the facial nerve, the vestibulocochlear nerve, the glossopharyngeal nerve, the vagus nerve, the accessory nerve, and the hypoglossal nerve.

Let's now go through all of the nuclei associated with each of these cranial nerves. starting with the trigeminal nerve. The trigeminal nerve has two roots of nerves, one motor and one sensory. The sensory part of the trigeminal nerve synapses with the mesencephalic nucleus of the trigeminal nerve.

The trigeminal nerve is one of the biggest cranial nerves we have, and it's divided into three parts in the facial area. So the mesencephalic nucleus of the trigeminal nerve receives proprioceptive information from mainly the muscles of mastication, as well as from the memetic muscles and the extraocular muscles. The next nucleus of the trigeminal nerve is the principal nucleus of the trigeminal nerve.

It receives information about touch and vibration and some proprioception as well. The spinal nucleus of the trigeminal nerve is in the medulla and the spinal cord, so it receives information about pain and temperature. The motor nucleus of the trigeminal nerve gives off fibers that innervate the muscles of mastication and the anterior belly of the gastricus, the myelohyoid and the tensor tympani muscles. So that was this nerve.

Next we have the sixth cranial nerve, the abducent nerve. The abducent nerve consists of only one motor fiber, coming from only one nucleus in the rhombus fossa, and that is the nucleus of the abducent nerve. The abducent nerve is responsible for abduction movement of the eyeball, and it does that by innervating the lateral rectus muscles of the eyeball, so that is this one. Next we have the facial nerve.

The facial nerve consists of two roots, One motor root innervates the facial muscles, and an intermediate nerve that carries parasympathetic and sensory fibers. The motor root of the facial nerve comes from the motor nucleus of the facial nerve. So fibers go from this nucleus to innervate all the facial muscles of facial expression, as well as some superficial muscles on the neck region as well. The intermediate nerve carries sensory fibers and parasympathetic fibers. The parasympathetic fibers come from the parasympathetic nucleus, called the superior salivatory nucleus, giving off parasympathetic innervation to glands in the facial regions, like the lacrimal gland, the submandibular and the sublingual glands.

The sensory fibers of the intermediate nerve synapse with the nucleus of the solitary tract, which receives information about taste. So that is the facial nerve. Next we have the cranial nerve number 8, which is the vestibulocochlear nerve.

The vestibulocochlear nerve consists of the vestibular nerve and the cochlear nerve, so if you put them together you'll get the vestibulocochlear nerve. So there are four sensory nuclei for the vestibular parts. These are the medial, lateral, superior and inferior vestibular nuclei. And there are two cochlear nerves, medial and lateral.

Remember, the inner ear consists of two parts, the vestibulum for balance, and the cochlea for hearing. The vestibular nerve transmits information about balance, motion and acceleration. So inside the semicircular canals of the vestibulum, there are crystals that detect movement that stimulate the receptors of the vestibular nerve.

This nerve will then go to the vestibular nuclei. The cochlear nerve transmits sound impulses from the organ of Corti by, you know, movements of the endolymphs. And then these fibers will go to the medial and lateral cochlear nuclei. So that was the vestibulocochlear nerve. Next is the ninth cranial nerve, the glossopharyngeal nerve.

This nerve contains motor, sensory and parasympathetic fibers. The parasympathetic fibers come from the inferior salivatory nucleus that innervates salivary glands like the parietal glands. The motor fibers come from the nucleus ambiguous that innervates muscles of the pharynx and the soft palate.

The sensory fibers synapse with the nucleus of the solitary tract, just like the facial nerve. so it contains sensory information of taste from the posterior third of the tongue. Next we have the tenth cranial nerve, the vagus nerve.

The vagus nerve also contains three types of fibers, which are motor, sensory and parasympathetic fibers. The motor and the sensory part of this nerve are also associated with the nucleus ambiguous and the nucleus of the solitaire tract, so it innervates the muscles of the pharynx, soft palate and the larynx, as well as sensing taste from the posterior third of the tongue. The parasympathetic nerve fiber comes from the posterior nucleus of the vagus nerve, and this nerve is the only cranial nerve that actually leaves the cranium to innervate all the organs of the thorax and the abdomen.

Remember, the parasympathetic innervation is rest and digest. So the vagus nerve reduces the heart rate, it increases the gastric motility and absorption, and all of those things related with the parasympathetic functions of the organs. Next, we have the 11th cranial nerve, the accessory nerve.

And notice that I've added the spinal cord, because this cranial nerve is a little special. So the accessory nerve consists of two motor fibers. We have the cranial root, that comes from the part of the nucleus ambiguous, located in the posterior lateral sulcus of the medulla oblongata.

And it contains a spinal root, that comes from the spinal nucleus of the accessory nerve. This nucleus appears on the posterior lateral sulcus of the spinal cord between C1 and C6 spinal segments. It then ascends along the spinal cord to then enter the cranial cavity through the foramen magnum and joins with the cranial roots, and then form the 11th cranial nerve, which is the accessor nerve. The accessor nerve is primarily a motor nerve that innervates the sternocleidomastoid muscle and the trapezius. It's called accessory nerve because it forms a kind of a mixed system with the vagus nerve and the glossopharyngeal nerve.

So that's this one. The last nerve is the 12th cranial nerve, called the hypoglossal nerve. It's a motor neuron of which the fibers come from the nucleus of the hypoglossal nerve.

These motor fibers go to the tongue and innervate all the muscles of the tongue. So that was the 12th cranial nerve. So here I've added all the nuclei of the rhomboid fossa, with the corresponding cranial nerves that synapses with them.

And so this is where this video gets scary. I am going to make all of these cranial nerves disappear, and basically if you hit pause, could you go through from the beginning and list, you know, which cranial nerve go with number 1, which cranial nerve go with number 2, and what does number 3 do, and what does number 4 do. This is a little challenging, but you know, once you get it right, you then understand it.

So that was a video about the 4th ventricle and the rhomboid fossa. If you found this video helpful, please put a like, share, comment, whatever you find convenient to you, and I hope this was helpful.

Transcript for:Anatomy of Fourth Ventricle and Rhomboid Fossa

Transcript for:
Anatomy of Fourth Ventricle and Rhomboid Fossa