 taste pathway like other pathway consists of three neurons. So there will be first order neuron, second order neuron and third order neuron. Now you see that there are different nerves which are carrying the information. One is the facial nerve. So here you see seventh nerve is there. It carries the information from the anterior to third part of the tongue. So basically these exons are supplying the tastes which are present in the anterior to third part of the tongue. Then we have the ninth cranial nerve that is the glossopharyngeal nerve and it is supplying the area that is from the posterior part of the tongue that is the circumvalid papilla. From there the information is going via the ninth nerve, okay. And again behind the posterior most part actually these taste buds I have missed before these taste buds are also present on the pharynx. They are present on the tonsillar pillars which are present there also. Then even in the epiglottis, okay. They are present and in the soft palate as well. So from these areas it is the tenth cranial nerve which is carrying the taste sensation. So three nerves are involved. Seventh cranial nerve from anterior to third part. Ninth cranial nerve glossopharyngeal nerve from the posterior one third part of the tongue and the tenth cranial nerve from the posterior most part, right. And all of these reach the NPS in the brain stem, nucleus tractus solitarius and they go and synapse there. So you see here synapse is shown. So what is the first order neuron? From the tastes the cranial nerves carrying information to the nucleus tractus solitarius. So all these are forming the first order neuron. Now from nucleus tractus solitarius the information is going to the thalamus and the nucleus here is ventropostero medial nucleus of the thalamus. So this is the second order neuron and you see one specialty here that it is on the ipsilateral side that is there is no crossing over. So in the taste pathway there is no crossing over. It goes to the posterior medial nucleus of the thalamus and synapses there. Then from posterior medial nucleus of the thalamus it goes to the gastiatric cortex which is basically present in the parietal cortex but little deep, right. So it goes into the gyri of the parietal cortex in the anterior insula and frontal operculum anterior insula and frontal operculum in the parietal cortex. So that is the third order neuron which forms a taste pathway. Olfactory pathway is the exception in the sensations where it directly reaches to certain areas of the cortex without passing through the thalamus. So here if you see that the axons from the mitral cell and tufted cell reach via the olfactory tract. Olfactory tract is nothing but the axons of the mitral cells and tufted cells from the olfactory tract and olfactory nerve is basically this. The axons of the bipolar olfactory sensory neurons all together form the olfactory nerve, okay. So then the axons of mitral cells and tufted cells from the olfactory tract which reaches to various areas in the cortex. So one is the primitive area, primitive olfactory system and that is responsible for the basic olfactory reflexes which reaches basically to the hypothalamus and that is actually a direct connection to the hypothalamus and like basic reflexes licking of the lips, salivation. These are innate reflexes not learned reflexes, okay and that is the most primitive olfactory pathway and that does not pass via the thalamus. It is that the pathway also goes to the pyreform cortex and amygdala and from there to the hypothalamus and that is responsible for liking and disliking of the food aversion to the food which foods we don't like which foods we like. So this is learning depending on the experience and that is happening because of the passage of information first to the areas of the cortex pyreform cortex then cortical portion of the amygdala and from there information reaching to the hypothalamus. So this is also a primitive pathway but it is less primitive than that of the basic innate reflex pathway and finally there is a newer pathway which passes through anterior olfactory nucleus or factory tubercle via the thalamus it reaches to orbital frontal cortex or directly reaches to frontal cortex okay. So this newer pathway is actually passing via the thalamus the dorsomedial thalamic nucleus and this is important for conscious perception of the order and analysis of the order that what is the type of the order what is the strength of the order that is by this newer pathway which reaches to the orbital frontal cortex and to the frontal cortex via the thalamus then the information from olfactory pathway also reaches to the memory area that is via the entorhinal cortex to the hippocampus and that is important for the memory of the order. So that I was talking talking about the liking and disliking of food so from hippocampus information is reaching to the hypothalamus only when memory is there then only we can remember that this order is linked to a particular food and whether we like it or don't like it. So that was about the olfactory pathway. Auditory pathway starts from hair cells which are present in cochlea. These hair cells are of two types that is the outer hair cells and there are inner hair cells and both of them receive the efferent and efferent. However, major efferents come from inner hair cells and the major efferents go to the outer hair cells but both have the efferents and the efferents. Now the efferents from these outer and inner hair cells form the auditory component of the vestibulocochlear nerve and these are basically the dendrites of the bipolar neurons which are present in the spiral ganglion. These are bipolar neurons because they have a long dendrite process and then there is axon which goes to the medulla. So these efferents form the auditory component of the vestibulocochlear nerve. Now this spiral ganglion is also present in the cochlea where it is present, it is present in the modulus of cochlea. Fine. Now at medulla they actually synapse all the fibers of this axon synapse and they synapse in nuclei in the medulla known as ventral and dorsal cochlear nuclei. Ventral and dorsal cochlear nuclei. So first synapse is occurring in the cochlear nuclei. From ventral and dorsal cochlear nuclei there is diversion of the pathways and the auditory pathway goes in four directions. So this is the ventral and dorsal cochlear nuclei. From here most of the pathways actually go and synapse on the nuclei present in the medulla and this is the superior olivary nuclei. Again superior olivary nuclei add to there is medial and lateral superior olivary nuclei. So most of the fibers go synapse on the opposite side. So suppose this is the midline okay and I am drawing pathway of only one side remember. So there will be ventral and dorsal cochlear nuclei this side also. For simplicity I am drawing only one side. So remember most of the pathways travel on the contralateral side going to the superior olivary nuclei. Then some fibers also go to the ipsilateral superior olivary nuclei so that is the second pathway. Third from here some of the fibers directly go to the nucleus of the lateral leminescus nucleus of the lateral leminescus and here it forms the bundle of fibers forms a lateral leminescus. So that is the third pathway and also some of the fibers go to the reticular formation reticular formation in the pons. So all these group of fibers have different processing going on remember that is why there is so much diversion of the pathways. From superior olivary nuclei then again the fibers ascend and they reach to another nucleus of the midbrain that is the inferior colliculus. Again from here they reach to the inferior colliculus okay and here also nucleus the fibers which have synapse in the lateral leminescus they also reach to the inferior colliculus. So these fibers which reach to the inferior colliculus they are third order neurons okay. First order neurons synapse in the ventral and dorsal cochlear nuclei second order neuron mostly the synapses is occurring in the superior olivary nucleus and from there the third order neuron it is reaching to the inferior colliculus. From inferior colliculus these fibers reach to the thalamus and there is nucleus medial geniculate body. So there again there is synapsing of the neurons and from medial geniculate body there are auditory radiations okay auditory radiations and then from there they reach to the auditory cortex and where is this auditory cortex present? It is present in the superior temporal gyrus superior temporal gyrus okay. Thanks for watching the video if you liked it do press the like button please share the video with others and don't forget to subscribe to the channel Physiology Open. Thank you.