Visual Pathway Overview

Hello and welcome to Insight of Thermology. I am Dr. Amrit and today we are going to discuss about the anatomy of visual pathway. Each eyeball acts as a camera and it perceives the image and relay this information finally to the visual cortex through a pathway and this pathway is called the visual pathway. So our visual pathway comprises of the retina that is the eyeball then the optic nerve, the optic chiasms, the optic tract, lateral geniculate body optic radiations and finally ending into the visual cortex. Now let us imagine this to be us who are looking at this video. So if we pass an imaginary line imaginary plane passing through the center of the nose this is our right eye and this is our left eye right. So the right eye will see the right side of the field of vision and the left eye will see the left sided field of vision okay. That field of vision again will be divided into the nasal half of field of vision and the temporal half of field of vision. The nasal half is the one which is present towards the nose and the temporal half is the one which is present away from the nose. OK, so this is what is represented here in this diagram. Let us talk about the representation of visual fields in the visual pathway. So over here, I have drawn the right visual field of the right eye and the left visual field that is which is coming from the left eye. Right. The right sided parts of the visual fields of each eye I have drawn in red color, as can be seen here. okay and the left-sided visual field of both eyes I have drawn in a purple color right so let us see how this right-sided visual field and how this left-sided visual field is actually represented in the visual pathway now if you carefully observe in this pathway let us first label the diagram so the first part is our retina and from the retina the nerves are then going into the optic nerve the optic nerves are getting merged with each other and they are forming the optic piazza. now from the optic chiasm they will form the optic tract and then these optic tracts are going into the lateral geniculate body then we have the optic radiations and finally they are reaching the visual cortex okay yeah so if you uh would carefully see here that the visual cortex of the left hand side is all red in color not just that even the lateral geniculate body of the left hand side is red in color. and the optic tract is also red in color of the left hand side but if you see over here the left sided the red the red part of the visual field as can be seen here is actually on the right side right and the same way if you compare this with the left sided field of vision the left side of field of vision is drawn in purple and you can see that the left optic track the left deniculate body the left optic radiation and the left visual cortex are all purple in color right So we can say that what we can say from this is that there is a contralateral representation of the fields. There is a contralateral representation of the field. What I mean to say is that the right side of the visual field, which is represented in red color is present on the left side of the visual pathway and the left side of the visual field, which is represented in purple color is present on the right side of the visual pathway. Right. So this is the first point that I want you to know. let us see how this happens now if you know that you should know that in retina the nasal retina is going to carry information from the temporal part of the field and the temporal retina is going to carry information from the nasal part of the field that means if this is our nasal part of the field of the left eye it will go on to the temporal retina okay and therefore it is represented in red similarly this red color of the right side of the field that is is the temporal field is going to go where on to the nasal part of the right eye. therefore this is represented in red color now similarly coming to the other side of the fields here in the left eye if you can see this is the temporal part of the field therefore it will go on the nasal part of the retina and in the right side since this is the nasal part of the field it will go on to the temporal retina and hence you can see the corresponding colors next they will travel just in the same manner in the optic nerve but the twist will come when they reach the optic chiasm now in the optic chiasm only the nasal fibers are going to cross each other. That means the nasal fiber of the right eye and the nasal fibers of the left eye, they are going to get converged to each other and they will cross ahead in the optic chiasm. But this will not happen. to the temporal fibers the temporal fibers will just be traveling on their way just like that uncrossed okay so only the nasal fibers are getting crossed and the temporal fibers will not get crossed from the optic chiasm what comes out is the optic tract and let us see what happens in the optic tract so just have a look at these at this optic tract of the left hand side so what are the fibers which are present in the left optic tract as you can see this will it is consisting of the uncrossed temporal fibers. Okay. So the first fibers which are present in the left optic trap are the uncrossed temporal fibers. And I'm writing it in red so that it is clear that these are the fibers from the right side of the visual field. And what are the other fibers which are coming? The crossed one. These crossed ones are the nasal fibers, right? So it consists of the crossed nasal fibers of the contralateral side. and the uncrossed temporal fibers of the ipsilateral side so these two fibers are together forming the left optic tract now what about the right optic tract okay the right optic tract also will be formed in the similar manner they are consisting of the uncrossed temporal fibers of the same side that is ipsilateral side and second they are consisting of these crossed fibers right the consisting of the crossed fibers which are the nasal fibers coming from the contralateral side and if you see if you observe here they're all of the same color that means they are coming from the left side of the field of vision right so this is the representation starting from the optic tract and it goes on from lateral geniculate body optic radiation and also to the visual cortex this representation is the same that is the left side of the visual pathway is taking the information of the right side of the visual field and the right side of the visual pathway is getting information of the left side of of the visual field. doesn't matter you if you want to remember you can remember how this crossing in all occurs but what you should remember is that there is a contralateral representation now let us talk about all of this in detail the anatomy of each part in detail i have already explained the anatomy of our optic nerve therefore i'm going to start with the optic chiasms in optic chiasm as i already told you that it is only the nasal fibers which are going to cross and the temporal fibers are just passing uncrossed and this crossing is what is called optic chiasm okay so this diagram over here represents in detail how the crossing of the fibers occurs but this i will be explaining you in the video on the lesions of the visual pathway right so let us talk about where exactly this optic chiasm is actually present so have a look at this diagram of the base of the skull base of the skull and we can see a wing-like bone over here which is the sphenoid bone right so if we take out this bone in detail you can see this bone in this diagram So, in this bone, there is a depression in the center and this depression is called a cellar tersica and this cellar tersica is the place where our pituitary gland will actually be sitting. In front of the cellar tersica, there is a projection of the bone that you can see here and this is called the dorsum cellae and behind also there is a projection of the bone and that is called tuberculum cellae. So, these three structures I want you to know in relation to the optic chiasm because in cellar triskel we have the pituitary gland and somewhere above the cellar tercica only we have our optic chiasm located right so this diagram over here actually represents the uh it actually represents the location of the pituitary gland and the optic chiasm so you can see how the this is exactly this is actually our optic nerve over here and this optic nerve is crossing and forming the optic chiasm and you can see this optic chiasm is actually present right above the cellar tercica and that cellar tercica is actually having the pituitary gland okay so this is a very important relation that our pituitary gland is actually located just below the optic chiasm now location of the optic chiasm over the cella tersica we have three types of chiasm the normal chiasm which is the central chiasm the prefixed chiasm and the post fixed chiasm so let us look at them one by one so in a normal chiasm as i already told you that the optic chiasm is present right in right above the cella tersica or right above the pituitary gland. So in such a case what happens is whenever the tumor of the pituitary gland this will go and affect the optic chiasm directly okay and this is called a normal chiasm and also called a central chiasm right now in certain cases we have a prefixed chiasm in a prefixed chiasm the optic chiasm is actually located somewhat anterior to the cellulose not exactly above but somewhat anterior to the cellulose so in such a case what happens is whenever the pituitary gland will expand or because of a tumor it will go and affect the structure which is present behind the optic chiasm and what is that structure it is the optic tracts right so now you can easily guess what is meant by a post fixed chiasm a post fixed chiasm is nothing but the chiasm is actually located more posteriorly over the dorsum cell it is present so it is present more posteriorly so in such a case what will happen when the pituitary gland is going to expand before because of the tumor it will go and affect our optic nerves okay so i hope this is clear and this was about the anatomy of the optic chiasm in line in the visual pathway are the optic tracts that you can see over here that they are coming after the optic chiasm and then the knob like structures which in which the optic tracts are ending and these are called. the lgb or the lateral geniculate body so the lateral geniculate body are nothing but it's a part of the thalamus okay and the thalamus is present over the brain stem right roughly it is like if this is our brain stem okay above these brain stem we have these two round areas which are called the thalamus and above that thalamus we have our cerebral hemispheres okay so that is how a thalamus is present so behind the thalamus over here there will be two structures okay and these two structures are very important in relation to two sensations in our body these two structures are the medial geniculate nucleus and the lateral geniculate nucleus the lateral geniculate nucleus is important to us because it is associated with the light pathway or it is associated with the visual sensation and the medial geniculate nucleus is associated with the auditory pathway that means it is associated with hearing Okay, and how do you remember? So for easy remembrance, let me tell you a very simple mnemonic. That is, how can we see with both our eyes, we can see with both our eyes because of light, okay. And light pathway and light, it all starts from the letter L. And our lateral geniculate body also starts with the letter L. So you can remember that lateral geniculate body is associated with the light pathway or the visual pathway and the medial geniculate nucleus associated with the auditory pathway or the hearing Between the two optic tracts, as you can see, there is a structure which is present. This is nothing but our midbrain. And the posterior part of the midbrain has two round structures and these are called a superior colliculus. So what I want you to know is that from the optic tract, some of the fibers will deroute and they will actually not go to the lateral geniculate body. Instead, they will go into this superior colliculus. And these fibers which deroute and go towards the superior colliculus of the midbrain, they are the fibers associated with our pupillary. reflex okay and what is pupillary reflex pupillary reflex is a simple reflex that whenever we shine light into an eye the pupils will actually constrict okay so the pupil will constrict in response to the light and this is what is called the pupillary reflex okay so some of the fibers are taking the d root from the optic tract and going towards the superior right the pupillary it is basically the pupillary fibers but is also showing the fibers which are taking deroot from the optic tract. they are going into the superior colliculus okay next what we have is the optic radiations okay the optic radiations are also called the geniculo calcarine pathway okay they also call the geniculo calcarine pathway and why are they called geniculo calcarine pathway because they are starting from the lateral geniculate nucleus or the lateral geniculate body and they are looping around. our brain and finally they are reaching the visual cortex okay and specifically they are reaching the calcane fissure where our primary visual areas and secondary visual areas are located and because they are going from the geniculate nucleus to the calcane fissure it is also called the geniclo calcane pathway right so as you can see from this area of thalamus where the later geniculate nucleus is present some of the fibers are going to come out like this right so these fibers are coming out and they will arch near the temporal horn of the lateral ventricle. So the structure over here is a lateral ventricle and you can see this part of the lateral ventricle which is called the temporal horn because it is present in the temporal lobe also it is called the inferior horn. So some of the fibers are going to arch towards this inferior horn of the lateral ventricle and then they are going to travel in the temporal lobe and finally they are going to reach the visual cortex. Fibers are traveling in the inferior lobe that is the temporal lobe. these fibers are called the inferior fibers of the optic radiation and they're also called the mayor's loop okay it's also called the mayor's loop and i as i told you that at every point almost there's a counter lateral representation of the visual field therefore the inferior fibers of the optic radiation are carrying the impulses from the superior visual field apart from this mayor's loop some of the fibers from the geniculate uh from the geniculate body will be traveling straight or away posteriorly into the visual cortex traveling in the parietal lobe okay and these fibers are located superiorly therefore they are called the superior fibers of the optic radiation and i already told you that there is counter lateral representation that means the superior fibers are carrying the information from the inferior field of view okay and they're traveling in the parietal lobe and going straight away to the visual cortex and they are called the bohm's loop okay so just like we have a mayors loop for the representation of the inferior optic radiation fibers the superior optic radiation fibers which are traveling in the parietal lobe they are called the bohm's finally let us talk about the visual cortex okay so the visual cortex actually consists of an important visual center which is the primary visual cortex and this primary visual center is also called the broadman's area it is called the broadman's Area number 17. Okay. So this Brodmann's area number 17 is actually located on the medial side of the occipital lobe on the either side of the calcane fissure. So this is a calcane fissure. And on the either side of it, we have the area number 17. And a part of it also extends onto the lateral side of the occipital lobe. So this is our mainly the Brodmann's area 17, which is a primary visual cortex. and then we have the secondary visual cortex that is area number 18 and 19 which are located basically on the either side of the primary visually visual cortex okay so in the old classification we have the area number 17 18 and 19 and now the newer classification has classified these three areas only into v1 v2 v3 v4 and v5 right yeah so let us see what exactly happens in this visual cortex so this purple one is our primary visual cortex and the green one is the secondary visual cortex area. right so these areas will send information in two streams okay so let me tell you what does it mean so the area which is present here is the red area and it is present in our temporal lobe right so it is called the inferior temporal area and this visual cortex areas will send information to this temporal area okay this information which is relayed in the temporal area from the visual cortex the primary visual cortex is called the ventral stream okay so what is the function of this ventral stream the ventral stream will tell us about the what of the vision okay the water the vision is means that what are we looking at so it will tell us about the shape of the object it will tell us about the color of the object and basically it will tell you about the identification of the object so if we see an apple we are able to tell that it is an apple by the ventral stream we're able to tell that it is red in color because of this presence of ventral stream similarly this cortex will also send information dorsally into the area of the the bridal lobe. and this is called the dorsal stream of information and this dorsal stream of information will answer the question where that means if we see an apple where is the apple present probably it is present on the tree or it is present on the table or is it present beneath the table so the questions of where do we see an object its orientation in space that would be answered by the dorsal stream finally in the end i would like to talk about the order of neurons which is present in our visual pathway, right? So basically what is happening is that the information is coming from the rods and cones and then from the rods and cones, it is going to the bipolar cells and from the bipolar cells, it goes to the ganglion cells and the ganglion cells will finally form the nerve fiber layer, the nerves, the optic nerve, optic chiasm and so on and so forth. And finally, they're going to reach where? The lateral geniculate body. Why I have only written these important cells and the lateral geniculate body is because I'm going to talk about the important relay stations of the neurons, right? So where is the first order neuron present in the visual pathway now there is a lot of controversy regarding the first order neuron in visual pathway but so there are two schools of thoughts which talk about this the first school of thought which mostly the ophthalmological books talk is that the rods and cones are considered to be the first order neuron so everything after that will follow mathematically so the bipolar cells will become the second order neurons and the ganglion cells will become the third order neurons and the later geniculate body will become the fourth order neuron however the proper physiological books like the ganons and guidance they say that the rods and cones actually are the sensory receptors and receptors are not actually neurons so they say that the first order neuron is actually the bipolar cells and then the ganglion cells will form the second order neuron and then the lateral geniculate body forms the third order neuron right so it's just a controversy between the physiologist and the ophthalmologist and so based on what the person studies in the order of neurons will actually change so i wanted you to know both the ways so i hope this video was helpful to you in the next video we are going to talk about the visual pathway lesions which will become very easy hopefully after this video so thank you and have a nice day any doubts are welcomed in the comment section

So if we pass an imaginary line imaginary plane passing through the center of the nose this is our right eye and this is our left eye right. So the right eye will see the right side of the field of vision and the left eye will see the left sided field of vision okay. That field of vision again will be divided into the nasal half of field of vision and the temporal half of field of vision. The nasal half is the one which is present towards the nose and the temporal half is the one which is present away from the nose. OK, so this is what is represented here in this diagram.

Let us talk about the representation of visual fields in the visual pathway. So over here, I have drawn the right visual field of the right eye and the left visual field that is which is coming from the left eye. Right. The right sided parts of the visual fields of each eye I have drawn in red color, as can be seen here.

okay and the left-sided visual field of both eyes I have drawn in a purple color right so let us see how this right-sided visual field and how this left-sided visual field is actually represented in the visual pathway now if you carefully observe in this pathway let us first label the diagram so the first part is our retina and from the retina the nerves are then going into the optic nerve the optic nerves are getting merged with each other and they are forming the optic piazza. now from the optic chiasm they will form the optic tract and then these optic tracts are going into the lateral geniculate body then we have the optic radiations and finally they are reaching the visual cortex okay yeah so if you uh would carefully see here that the visual cortex of the left hand side is all red in color not just that even the lateral geniculate body of the left hand side is red in color. and the optic tract is also red in color of the left hand side but if you see over here the left sided the red the red part of the visual field as can be seen here is actually on the right side right and the same way if you compare this with the left sided field of vision the left side of field of vision is drawn in purple and you can see that the left optic track the left deniculate body the left optic radiation and the left visual cortex are all purple in color right So we can say that what we can say from this is that there is a contralateral representation of the fields.

There is a contralateral representation of the field. What I mean to say is that the right side of the visual field, which is represented in red color is present on the left side of the visual pathway and the left side of the visual field, which is represented in purple color is present on the right side of the visual pathway. Right.

So this is the first point that I want you to know. let us see how this happens now if you know that you should know that in retina the nasal retina is going to carry information from the temporal part of the field and the temporal retina is going to carry information from the nasal part of the field that means if this is our nasal part of the field of the left eye it will go on to the temporal retina okay and therefore it is represented in red similarly this red color of the right side of the field that is is the temporal field is going to go where on to the nasal part of the right eye. therefore this is represented in red color now similarly coming to the other side of the fields here in the left eye if you can see this is the temporal part of the field therefore it will go on the nasal part of the retina and in the right side since this is the nasal part of the field it will go on to the temporal retina and hence you can see the corresponding colors next they will travel just in the same manner in the optic nerve but the twist will come when they reach the optic chiasm now in the optic chiasm only the nasal fibers are going to cross each other.

That means the nasal fiber of the right eye and the nasal fibers of the left eye, they are going to get converged to each other and they will cross ahead in the optic chiasm. But this will not happen. to the temporal fibers the temporal fibers will just be traveling on their way just like that uncrossed okay so only the nasal fibers are getting crossed and the temporal fibers will not get crossed from the optic chiasm what comes out is the optic tract and let us see what happens in the optic tract so just have a look at these at this optic tract of the left hand side so what are the fibers which are present in the left optic tract as you can see this will it is consisting of the uncrossed temporal fibers.

Okay. So the first fibers which are present in the left optic trap are the uncrossed temporal fibers. And I'm writing it in red so that it is clear that these are the fibers from the right side of the visual field.

And what are the other fibers which are coming? The crossed one. These crossed ones are the nasal fibers, right?

So it consists of the crossed nasal fibers of the contralateral side. and the uncrossed temporal fibers of the ipsilateral side so these two fibers are together forming the left optic tract now what about the right optic tract okay the right optic tract also will be formed in the similar manner they are consisting of the uncrossed temporal fibers of the same side that is ipsilateral side and second they are consisting of these crossed fibers right the consisting of the crossed fibers which are the nasal fibers coming from the contralateral side and if you see if you observe here they're all of the same color that means they are coming from the left side of the field of vision right so this is the representation starting from the optic tract and it goes on from lateral geniculate body optic radiation and also to the visual cortex this representation is the same that is the left side of the visual pathway is taking the information of the right side of the visual field and the right side of the visual pathway is getting information of the left side of of the visual field. doesn't matter you if you want to remember you can remember how this crossing in all occurs but what you should remember is that there is a contralateral representation now let us talk about all of this in detail the anatomy of each part in detail i have already explained the anatomy of our optic nerve therefore i'm going to start with the optic chiasms in optic chiasm as i already told you that it is only the nasal fibers which are going to cross and the temporal fibers are just passing uncrossed and this crossing is what is called optic chiasm okay so this diagram over here represents in detail how the crossing of the fibers occurs but this i will be explaining you in the video on the lesions of the visual pathway right so let us talk about where exactly this optic chiasm is actually present so have a look at this diagram of the base of the skull base of the skull and we can see a wing-like bone over here which is the sphenoid bone right so if we take out this bone in detail you can see this bone in this diagram So, in this bone, there is a depression in the center and this depression is called a cellar tersica and this cellar tersica is the place where our pituitary gland will actually be sitting.

In front of the cellar tersica, there is a projection of the bone that you can see here and this is called the dorsum cellae and behind also there is a projection of the bone and that is called tuberculum cellae. So, these three structures I want you to know in relation to the optic chiasm because in cellar triskel we have the pituitary gland and somewhere above the cellar tercica only we have our optic chiasm located right so this diagram over here actually represents the uh it actually represents the location of the pituitary gland and the optic chiasm so you can see how the this is exactly this is actually our optic nerve over here and this optic nerve is crossing and forming the optic chiasm and you can see this optic chiasm is actually present right above the cellar tercica and that cellar tercica is actually having the pituitary gland okay so this is a very important relation that our pituitary gland is actually located just below the optic chiasm now location of the optic chiasm over the cella tersica we have three types of chiasm the normal chiasm which is the central chiasm the prefixed chiasm and the post fixed chiasm so let us look at them one by one so in a normal chiasm as i already told you that the optic chiasm is present right in right above the cella tersica or right above the pituitary gland. So in such a case what happens is whenever the tumor of the pituitary gland this will go and affect the optic chiasm directly okay and this is called a normal chiasm and also called a central chiasm right now in certain cases we have a prefixed chiasm in a prefixed chiasm the optic chiasm is actually located somewhat anterior to the cellulose not exactly above but somewhat anterior to the cellulose so in such a case what happens is whenever the pituitary gland will expand or because of a tumor it will go and affect the structure which is present behind the optic chiasm and what is that structure it is the optic tracts right so now you can easily guess what is meant by a post fixed chiasm a post fixed chiasm is nothing but the chiasm is actually located more posteriorly over the dorsum cell it is present so it is present more posteriorly so in such a case what will happen when the pituitary gland is going to expand before because of the tumor it will go and affect our optic nerves okay so i hope this is clear and this was about the anatomy of the optic chiasm in line in the visual pathway are the optic tracts that you can see over here that they are coming after the optic chiasm and then the knob like structures which in which the optic tracts are ending and these are called. the lgb or the lateral geniculate body so the lateral geniculate body are nothing but it's a part of the thalamus okay and the thalamus is present over the brain stem right roughly it is like if this is our brain stem okay above these brain stem we have these two round areas which are called the thalamus and above that thalamus we have our cerebral hemispheres okay so that is how a thalamus is present so behind the thalamus over here there will be two structures okay and these two structures are very important in relation to two sensations in our body these two structures are the medial geniculate nucleus and the lateral geniculate nucleus the lateral geniculate nucleus is important to us because it is associated with the light pathway or it is associated with the visual sensation and the medial geniculate nucleus is associated with the auditory pathway that means it is associated with hearing Okay, and how do you remember?

So for easy remembrance, let me tell you a very simple mnemonic. That is, how can we see with both our eyes, we can see with both our eyes because of light, okay. And light pathway and light, it all starts from the letter L.

And our lateral geniculate body also starts with the letter L. So you can remember that lateral geniculate body is associated with the light pathway or the visual pathway and the medial geniculate nucleus associated with the auditory pathway or the hearing Between the two optic tracts, as you can see, there is a structure which is present. This is nothing but our midbrain.

And the posterior part of the midbrain has two round structures and these are called a superior colliculus. So what I want you to know is that from the optic tract, some of the fibers will deroute and they will actually not go to the lateral geniculate body. Instead, they will go into this superior colliculus. And these fibers which deroute and go towards the superior colliculus of the midbrain, they are the fibers associated with our pupillary.

reflex okay and what is pupillary reflex pupillary reflex is a simple reflex that whenever we shine light into an eye the pupils will actually constrict okay so the pupil will constrict in response to the light and this is what is called the pupillary reflex okay so some of the fibers are taking the d root from the optic tract and going towards the superior right the pupillary it is basically the pupillary fibers but is also showing the fibers which are taking deroot from the optic tract. they are going into the superior colliculus okay next what we have is the optic radiations okay the optic radiations are also called the geniculo calcarine pathway okay they also call the geniculo calcarine pathway and why are they called geniculo calcarine pathway because they are starting from the lateral geniculate nucleus or the lateral geniculate body and they are looping around. our brain and finally they are reaching the visual cortex okay and specifically they are reaching the calcane fissure where our primary visual areas and secondary visual areas are located and because they are going from the geniculate nucleus to the calcane fissure it is also called the geniclo calcane pathway right so as you can see from this area of thalamus where the later geniculate nucleus is present some of the fibers are going to come out like this right so these fibers are coming out and they will arch near the temporal horn of the lateral ventricle. So the structure over here is a lateral ventricle and you can see this part of the lateral ventricle which is called the temporal horn because it is present in the temporal lobe also it is called the inferior horn.

So some of the fibers are going to arch towards this inferior horn of the lateral ventricle and then they are going to travel in the temporal lobe and finally they are going to reach the visual cortex. Fibers are traveling in the inferior lobe that is the temporal lobe. these fibers are called the inferior fibers of the optic radiation and they're also called the mayor's loop okay it's also called the mayor's loop and i as i told you that at every point almost there's a counter lateral representation of the visual field therefore the inferior fibers of the optic radiation are carrying the impulses from the superior visual field apart from this mayor's loop some of the fibers from the geniculate uh from the geniculate body will be traveling straight or away posteriorly into the visual cortex traveling in the parietal lobe okay and these fibers are located superiorly therefore they are called the superior fibers of the optic radiation and i already told you that there is counter lateral representation that means the superior fibers are carrying the information from the inferior field of view okay and they're traveling in the parietal lobe and going straight away to the visual cortex and they are called the bohm's loop okay so just like we have a mayors loop for the representation of the inferior optic radiation fibers the superior optic radiation fibers which are traveling in the parietal lobe they are called the bohm's finally let us talk about the visual cortex okay so the visual cortex actually consists of an important visual center which is the primary visual cortex and this primary visual center is also called the broadman's area it is called the broadman's Area number 17. Okay. So this Brodmann's area number 17 is actually located on the medial side of the occipital lobe on the either side of the calcane fissure. So this is a calcane fissure.

And on the either side of it, we have the area number 17. And a part of it also extends onto the lateral side of the occipital lobe. So this is our mainly the Brodmann's area 17, which is a primary visual cortex. and then we have the secondary visual cortex that is area number 18 and 19 which are located basically on the either side of the primary visually visual cortex okay so in the old classification we have the area number 17 18 and 19 and now the newer classification has classified these three areas only into v1 v2 v3 v4 and v5 right yeah so let us see what exactly happens in this visual cortex so this purple one is our primary visual cortex and the green one is the secondary visual cortex area.

right so these areas will send information in two streams okay so let me tell you what does it mean so the area which is present here is the red area and it is present in our temporal lobe right so it is called the inferior temporal area and this visual cortex areas will send information to this temporal area okay this information which is relayed in the temporal area from the visual cortex the primary visual cortex is called the ventral stream okay so what is the function of this ventral stream the ventral stream will tell us about the what of the vision okay the water the vision is means that what are we looking at so it will tell us about the shape of the object it will tell us about the color of the object and basically it will tell you about the identification of the object so if we see an apple we are able to tell that it is an apple by the ventral stream we're able to tell that it is red in color because of this presence of ventral stream similarly this cortex will also send information dorsally into the area of the the bridal lobe. and this is called the dorsal stream of information and this dorsal stream of information will answer the question where that means if we see an apple where is the apple present probably it is present on the tree or it is present on the table or is it present beneath the table so the questions of where do we see an object its orientation in space that would be answered by the dorsal stream finally in the end i would like to talk about the order of neurons which is present in our visual pathway, right? So basically what is happening is that the information is coming from the rods and cones and then from the rods and cones, it is going to the bipolar cells and from the bipolar cells, it goes to the ganglion cells and the ganglion cells will finally form the nerve fiber layer, the nerves, the optic nerve, optic chiasm and so on and so forth.

And finally, they're going to reach where? The lateral geniculate body. Why I have only written these important cells and the lateral geniculate body is because I'm going to talk about the important relay stations of the neurons, right? So where is the first order neuron present in the visual pathway now there is a lot of controversy regarding the first order neuron in visual pathway but so there are two schools of thoughts which talk about this the first school of thought which mostly the ophthalmological books talk is that the rods and cones are considered to be the first order neuron so everything after that will follow mathematically so the bipolar cells will become the second order neurons and the ganglion cells will become the third order neurons and the later geniculate body will become the fourth order neuron however the proper physiological books like the ganons and guidance they say that the rods and cones actually are the sensory receptors and receptors are not actually neurons so they say that the first order neuron is actually the bipolar cells and then the ganglion cells will form the second order neuron and then the lateral geniculate body forms the third order neuron right so it's just a controversy between the physiologist and the ophthalmologist and so based on what the person studies in the order of neurons will actually change so i wanted you to know both the ways so i hope this video was helpful to you in the next video we are going to talk about the visual pathway lesions which will become very easy hopefully after this video so thank you and have a nice day any doubts are welcomed in the comment section

Transcript for:Visual Pathway Overview

Transcript for:
Visual Pathway Overview