So dear students today we are going to begin with the cranial nerves. We know there are 12 pairs of cranial nerves which arise from the brain. and these cranial nerves that is the first two cranial nerves are along with the neuroanatomy topics and the other cranial nerves that is the aclo motor and all we are going to deal today before going into this cranial nerves topic we have to know one basic thing that the cranial nerve nuclei which gives rise to this cranial nerves they are mainly of two types one is the motor type that is cranial nerves or motor nuclei The other variety is the sensory type. So let's classify this cranial nerve motor nuclei. So the classification of motor nerves are the first one is somatic efferent. So I am classifying motor nuclei. First one is the somatic efferent. So the motor nerves are called as efferent. So motor nuclei constitutes the somatic efferent which supply the skeletal muscles. And the second type is special visceral efferent. means the special special means they are the skeletal muscles which are derived from the pharyngeal arches so we know there are six pharyngeal arches and fifth one will disappear and degenerate and remaining five pharyngeal arches has got a muscular component that is the mesoderm of it gives rise to muscles so the skeletal muscles which are derived from the pharyngeal arches are supplied by special visceral efferent fibers muscles derived from. And third type of motor nuclei is general visceral efferent. So general visceral efferent are the fibers form the parasympathetic pathway to supply the glands, smooth and cardiac muscles of visceral organs and heart. So they supply the glands, smooth muscles of visceral organs and cardiac muscles of heart. So this is how we classify the motor nerve nuclei. Let's talk about the classification of sensory nerves which arise from the sensory nerve nuclei. So sensory nuclei, the first variety is general visceral afferent. Sensory we call them as afferent and motor as afferent. So here the general visceral afferent the sensory nerve fibers they carry the general sensations from the viscera which includes like pain and reflex sensations from the visceral organs. Reflex sensations like hunger reflex, micturition reflex, defecation reflex, bronchospasm that is a spasm in the bronchus. and peristaltic moments of the intestine vasoconstriction of the blood vessels so all such reflex responses are carried by general visceral afferent so general visceral afferent they carry the visceral senses like pain and reflexes Next variety is general somatic afferent. General somatic afferent carry the general sensations from the body wall somatic means body wall so they carry the general sensations from the body wall like parietal layers like parietal pericardium parietal layers of the pleura and parietal layer of the peritoneum and cutaneous receptors all this and they carry senses which are associated with touch pain temperature And even texture discrimination, two point discrimination. So all these are carried by general somatic afferent. General somatic afferent they mainly general sensations from where? From body wall. That is parietal layers. Next about the special somatic afferent, they carry the smell, vision, auditory and vestibular senses and also taste sensations. So all these the special senses they are carried by special somatic afferent. So olfaction, smell, that is smell and vision. Even auditory hearing, vestibular senses, taste sensation. brain sensation from the tongue and other parts of the oral cavity. So all these are the different varieties of motor nuclei and cranial nerve nuclei which gives rise to our 12 pairs of cranial nerves. Ok let's talk about the third cranial nerve that is the Achillomotor nerve. Achillomotor nerve it is the nerve which is responsible for the eye movements of the eyeball. So majority of the extraocular muscles which are present around the eyeball they are all supplied by the oculomotor nerve. It is not only supplying these extraocular muscles. Oculomotor nerve is also associated with the constriction of the pupil and accommodation reflexes. So let's talk about this Achillomotor nerve in detail. So to identify the Achillomotor nerve in the base of the brain, so here is the base of the brain. Achillomotor nerve is our third cranial nerve. So they are numbered from anterior to posterior. So this is the first one, olfactory optic. And let's see now the third which is of our today's topic interest. This is the third. Now we can see it is arising from the brain. It arises from the interpeduncular fossa. Along with the third cranial, fourth cranial nerve is also present which is a very thinnest or slender cranial nerve. So it is hard to discriminate both. But here we can identify this as the third cranial nerve on each side. So talking about the functional components of third cranial nerve, it has got general somatic efferent. General somatic efferent. efferent means motor so we know already somatic means they carry the efferent to the skeletal muscles so they arise from the chief nucleus of motor nerve supply all the extraocular muscles of the eye excluding three muscles which are present around the eyeball so those three muscles are levator palpebrae superiors supplies extraocular muscles except levator palpebrae superioris superior oblique we say SO4 because it is supplied by fourth cranial nerve then LR6 that is the lateral rectus which is supplied by the abducent nerve so except these three rest all the extraocular muscles are supplied by the oculomotor so origin of this is general somatic efferent the next variety of functional component is the general visceral efferent general visceral efferent arise from eddinger westphal nucleus which is a separate nucleus present along with the acryl motor nucleus called as eddinger westphal nucleus and in the West wall nucleus and the fibers from a component of this oculomotor nerve they form a component of oculomotor nerve to terminate in a ganglion which is a parasympathetic ganglion present within the orbit called as ciliary ganglion which I am going to discuss little more in detail later so the post ganglionic fibers from this ciliary ganglion they supply the ciliaris muscle and sphincter pupillae muscle So that is about the third cranial nerve functional components. Let's talk about the nuclei which give origin to the oculomotor nerve. Oculomotor nerve nuclear complex, it is located around the aqueduct of sylveus. So the cavity which is present in the midbrain is the aqueduct of sylveus. So this is a schematic representation of the cross section of the midbrain at the level of superior colliculus. We see the origin of Achillomotor nerve at the level of superior. and the colliculi of midbrain. So the cavity of the midbrain what we see this triangular like is here which is called as cerebral aqueduct or aqueduct of sylveus. So this is the aqueduct which contains a CSF. So around the aqueduct there is a grey matter which contains the nuclei called as periaqueductal grey matter. So what we see in blue colour here is So, periaqueductal gray matter. So, the oculomotor nuclear complex, it is present within this periaqueductal gray matter that is at the level of superior colliculus. And the components of the oculomotor nuclear complex, it is containing two. One is the motor nucleus of oculomotor. So, we can see this one which is darker. This is the motor nucleus. of Achillomotor that is the third cranial nerve and little laterally on each side there is a separate nucleus called as Edinger-Westphal nucleus. So this purple one what is laterally present is the So, eddinger-westphal nucleus which is present within the acrylomotor nuclear complex. So, if we see the nuclei here, the right and left motor nuclei, they are very closely associated, almost present near the midline. They are joined in the midline and the eddinger-westphal nucleus present on each side. And they both give rise to this nerve which is the acrylomotor nerve. So the oculomotor nerve it arises ventrally from the midbrain. So this part of the midbrain is called as crust cerebri. And each lower half except the tectum of the midbrain it is called as cerebral peduncle. So each half except the tectum is called as cerebral. peduncle. So what is the peduncle? It is like a stalk. Cerebral peduncle because the white matter which is descending from the brain they pass through this crust cerebrae that is a corticospinal tracts, corticonuclear tracts, corticopontine tracts. All these fibers they are bundled in the crust cerebrae which is otherwise called cerebral peduncle. So we can see here in this picture that The oculomotor nerve here it is arising medial to the criss cerebri, medial to the cerebral peduncle. So the gap here between the two criss cerebri, this gap is nothing but the interpeduncular fossa because it is between the two peduncles it is the interpeduncular fossa. And we can see the Achillomotor nerve arising from the midbrain and present within the interpeduncular fossa. So it is a content of the interpeduncular fossa. And this fossa it is associated with a cistern, subarachnoid cistern. So this fossa you know the whole brain is covered by the meninges. So the arachnoid matter is a layer of meninges and which covers the. So the gap between the arachnoid matter, suppose I am drawing an arachnoid matter here. So this gap which is between the arachnoid matter and pia matter is the subarachnoid space which is called as inter peduncular cistern. So this one is. So, interpeduncular cistern, why I am talking about this interpeduncular cistern because it contains important blood vessels present around it which is called as circle of villus. So, within the cistern there is a circle of villus which supply the most of the brain and this circle of villus it is often associated with some aneurysms, baryaneurysm. So, if there is a rupture of any blood vessel leading to hemorrhage. So the nerve which first gets affected is the Achillomotor nerve. So because the Achillomotor nerve we can see it is present as a content of interpedicular system present within the interpedicular fossa. So that is one of the clinical importance at its origin of the Achillomotor nerve. So let's talk about some nuclear connections of the Achillomotor nerve. A nuclei which are connected to this third cranial nerve, it is connected to the Brain stemmed by cortico-nuclear fibers. So the nuclei are connected to the cortico-nuclear fibers from the opposite cerebral cortex. And superior colic line from the oculomotor now there are connections to the superior colic line. This is the superior colic line and which is related to a nucleus present in front of the tectum called as pre-tectal nucleus. So, the pre-tectal nucleus is present in front on each side of the superior colliculi. So, the connections are to the pre-tectal nucleus also and there is a bundle called as medial longitudinal fasciculus. In short, we can say it as MLF. medial longitudinal fasciculus MLF which is a interconnecting bundle which connects the third that is the aculomotor nerve which we are studying now and the third to the other cranial nerves like fourth trochlear sixth abducent and also connects to the eighth vestibulocochlear nerves so these cranial nerve nuclei are interconnected by means of medial longitudinal fasciculus So, these are the nuclear connections of the Achillomotor nerve. Continuing with the course of the Achillomotor nerve, we can divide the course into intraneural course that is the course of the Achillomotor nerve within the midbrain and the course of the Achillomotor nerve within the cranium that is called intracranial course and further the Achillomotor nerve enters the superior orbital fissure to enter the orbit. So further we can consider as intraorbital course. So starting with intranural course, the course of the axons inside the midbrain. So after their origin from the nuclei passes ventrally. So we can see here the red color line is the oculomotor nerve and it crosses the nuclei which are called as red nucleus. So we can see on each side two red nuclei which is crossed by the oculomotor nerve and medial part of substantia nigra. So this green one represents the substantia nigra. So we can see it crosses the substantia nigra also. So medial part of the substantia nigra and further it emerges from the ventral part of the midbrain crossing the medial part of cerebral peduncle. So we can see here it emerges from the medial side of the midbrain within the interpeduncular fossa crossing the ventral side of the crass cerebri. So this is about the intranural course. So let's talk about the intracranial course. In the subarachnoid space, the aculomotor nerve lies between the posterior cerebral artery and superior cerebellar artery. As I discussed just now, the aculomotor nerve, it is present in the interpeduncular fossa. And within the interpeduncular system, there is circle of villus, right? So, the basilar artery which terminally divides into posterior cerebral artery which is a part of circle of villus. So, the oculomotor nerve, so here it is, this is the midbrain. So, the oculomotor nerve which is arising on the ventral side of the midbrain is the third cranial or oculomotor nerve. And as it comes out of the midbrain, running towards the superior orbital fissure, it enters through the cavernous sinus. So, I am just writing. So we see the oculomotor nerve arising from the midbrain. And further it runs anteriorly towards the superior orbital fissure, then it enters inside the cavernous sinus. So it is present within the lateral wall of cavernous sinus. So before entering into this cavernous sinus, it is related to posterior cerebral artery and superior cerebellar arteries. So on each side. So the nerve is between these two arteries. One is the posterior cerebral artery and this is the superior cerebellar artery. Posterior cerebral and superior cerebellar arteries they are the branches of basilar artery. So we know it is the circle of villus which is around it. So it is sandwiched between these two arteries which is in closely relation with the posterior communicating artery also. Further we can see it enters into the lateral wall of cavernous sinus. So as it is closely related to these arteries aneurysm of any of these related arteries may result in the compression of Achillomotor nerve. and it crosses the tentorial notch further if we see this aculomotor nerve it crosses the tentorial notch to enter the lateral wall of cavernous sinus and within the lateral wall of cavernous sinus it lies superior to the other cranial nerves that is the trochlear nerve ophthalmic maxillary nerve so one thing we have to note here whatever the nerves which are towards the superior orbital fissure we see them crossing this cavernous sinus which is a dural venous sinus present on each side of the spinoid bone. So the aculomotor nerve, this aculomotor nerve it crosses the lateral wall of cavernous sinus as it is a third it is it lies above to fourth cranial that is the trochlear. So it is related here to the trochlear and beneath the trochlear it is related to the ophthalmic division of trigeminal. and also maxillary division of trigeminal. So these are the nerves present within the cavernous sinus, lateral wall of cavernous sinus. So tentorial notch is the vulnerable site of the achillomotor nerve causing the compression due to cavernous thrombosis and herniation of the anchors. So that is a vulnerable site for the achillomotor nerve causing its compression because of cavernous thrombosis. because the cavernous sinus is there. So if there is any clot present in the cavernous sinus leads to cavernous thrombosis and herniation of the ancus. Ancus is present in the base of the brain on each side of the cerebral peduncle where the parahippocampal gyrus continues anteriorly as ancus. So if there is a herniation of ancus also there may be a chance of compression of this aculomotor nerve. So that is about the intracranial course. Talking about its exit from the cranium, we know that it enters through the superior orbital fissure. So the oculomotor nerve enters into the superior orbital fissure. Just before entering into the superior orbital fissure, the oculomotor nerve divides into two ramus. So superior orbital fissure if you see it is further divided into three parts. lateral, intermediate and medial part. So the oculomotor nerve enters into the intermediate part and where before entering itself it divides into two divisions that is the superior and inferior rami of akyelomotor nerve. So within the superior orbital fissure it splits to form superior and inferior rami and enclosed within a common tendinous ring. So intermediate part is enclosed within a common tendinous ring. or common tendinous ring of zinc it is called. So along with this achillomotor nerve there is there are other two nerves which are present within the common tendinous ring. The other two nerves are nasociliary nerve. So the other two nerves are nasociliary nerve. which is a branch of ophthalmic division of trigeminal nerve and the sixth cranial nerve that is the abducent nerve. So that is how it enters the superior orbital fissure. So let's see in this picture now. This is the midbrain. We have seen the acrylomotor nerve nuclear complexes here. This is the periaqueductal gray matter. This is the aqueduct of sylveus. And here is the periaqueductal gray matter containing the oculomotor nerve nuclear complex. And we can see the oculomotor nerve it arises from the ventral side of the midbrain and then it lies in the interpedicular fossa. And we can see an artery here that is the internal carotid artery which is present within the cavernous sinus. Oculomotor nerve is along the lateral wall of the cavernous sinus that we have to note here. So we can see here it is dividing into superior and inferior ramus. So this is the oculomotor nerve. This is the superior ramus. And the other one is the inferior ramus. inferior ramus. So superior ramus we can see it goes as the name suggests it goes superior to the eyeball and supplies two muscles which are present superior that is superior rectus muscle. So it is supplying the superior rectus. I am writing SR for superior rectus muscle. So it innervates the superior rectus muscle. So if we see its intraorbital course, the superior division runs lateral to the optic nerve to supply the superior rectus muscle and one more muscle which lies superior to the eyeball that is levator palpebrae superioris. So levator palpebrae superioris and superior rectus. muscle. These two muscles are supplied by the superior division that is the superior ramus of acromotor nerve and inferior division supplies the rest of the muscles that is except lateral rectus and superior oblique which are supplied by the other cranial nerves. So the inferior division divides further into three branches. One branch supplies to the medial rectus. So this is the cut part of medial rectus. And then it supplies to the inferior rectus muscle which goes down. This is inferior rectus. And then it also supplies to inferior oblique muscle. This is the inferior oblique. So if we see the inferior oblique muscle, the nerve to the inferior oblique muscle, it gives off a branch which relays in the ganglion here. So we are seeing this one, this is the ciliary ganglion and you can see a branch going there. and relaying in the ciliary ganglion. So ciliary ganglion is a parasympathetic ganglion where it gives rise to short ciliary nerves. So this parasympathetic component they arise from the eddinger-westphal nucleus which are part of a oculomotor nuclear complex. So this eddinger-westphal nucleus the axons from the eddinger-westphal nucleus they travel along with the rest of the oculomotor nerve. to reach its destination that is to reach its ciliary ganglia and further that is the postganglionic fibers they form the short ciliary nerves which supply the ciliary muscle and sphincter pupillae muscle. So the short ciliary nerves supply the ciliary and sphincter pupillae muscle. So next about this ciliary ganglion. Ciliary ganglion is the peripheral parasympathetic ganglion and it is located on the posterior side of the orbit. So we can see here this is here is the ciliary ganglion which is present on the posterior side of the orbit which is sandwiched between the medial wall and the optic nerve posteriorly. So posterior part of the orbit is called as the apex of the orbit so it is related to near the apex of the orbit. So ciliary ganglion if we see its parasympathetic pathway the nerve arises from eddinger westphal nucleus so eddinger westphal nucleus. So eddinger westphal nucleus gives rise to preganglionic fibers and preganglionic fibers run along with which nerve? Aculomotor nerve that is a third cranial nerve. Further the aculomotor nerve that is in the branch which goes to the inferior oblique so that relays in the ciliary ganglion so branch which goes to the inferior oblique branch to inferior oblique muscle. So branch to the inferior oblique will form a preganglionic fibers which relay in the ganglion called as ciliary ganglion. which is a parasympathetic ganglion here and which is a small pin shaped structure like almost the size of a head of a pin it will be. Then ciliary ganglion gives rise to postganglionic fibers. Postganglionic fibers are the short ciliary nerves And these short ciliary nerves they relay in the ciliary muscle, they supply the ciliary muscle. And also it supplies pink tur pupillae muscle. Dilator pupillae is supplied by the sympathetic which travel along the blood vessels whereas the sphincter pupillae is supplied by the parasympathetic which is supplied by the ciliary ganglion via the short ciliary nerves. So this is all about the ciliary ganglion parasympathetic pathway. Let's talk about the lesions of the achillomotor nerve. Achillomotor nerve can have unilateral and bilateral but unilateral lesions It produces ptosis drooping of the eyelid due to the paralysis of levator palpebrae superioris and it also supplies external strabismus that is the squint due to the unopposed action of lateral rectus and superior oblique muscle and protrusion of the eyeball due to the flaccid paralysis of most of the extraocular muscles and diplopia double vision. Loss of accommodation that is resulting a dilated and a fixed pupil. So these are the unilateral lesions that is features of the unilateral lesions of Achillomotor nerve.