Over the past days, I have been writing on the sense organs, starting with the Ear, to the Eye, and in my last post, I wrote about the tongue. While writing all these posts, and so many previous posts, it is no doubt that words like Cranial nerves kept showing, for instance;
The cranial nerves responsible for transmiting signals from the tongue to the brain are the Cranial Nerve VII, Cranial Nerve IX, and Cranial Nerve X. - source The Anatomy of the Tongue and Gustation Process
The Ganglion Cells connect with the Bipolar cells, and with connective axons at the end that forms the optic nerve (Cranial Nerve 2). - source Explaining Phototransduction in the Eye
The Superior Rectus muscle is located around the eye orbit, and connected to the sclera. It is innervated by the 3rd cranial nerve (ocularmotor nerve). - source Anatomy and Physiology of the Eye
The Stapedius Muscle is controlled by the parasympathetic fibers, and the facial nerve also known as the Seventh Cranial nerve. - source The Anatomy, and Physiology of the Ear
You see, if I will continue with the sense organ, for understanding, it is important that I explain the Cranial nerves, as it is important for everything that sends signal to the brain. It is important to know that there are 12 cranial nerves, which are the; Olfactory nerve (Cranial nerve 1), Optic Nerve (Cranial Nerve 2), Oculomotor Nerve (Cranial Nerve 3), Trochlear Nerve (Cranial Nerve 4), Trigeminal Nerve (Cranial Nerve 5), Abducens Nerve (Cranial Nerve 6), Facial Nerve (Cranial Nerve 7), Vestibulocochlear Nerve (Cranial Nerve 8), Glossopharyngeal Nerve (Facial Nerve 9), Vagus Nerve (Cranial Nerve 10), Accessory Nerve (Cranial Nerve 11), and Hypoglossal Nerve (Cranial Nerve 12). And I will be picking them one after the other in this post, and I will ensure I do justice at my best, to break down every complex terminology, and explain everything you need to know about them.
The Olfactory nerve (Cranial Nerve 1) Explained
As the name, you would expect that it has to do with smell. The olfactory nerve is the sensory nerve that conveys the sense of smell, and in the case of taste. You should know that taste has to do with smell as well. The olfactory nerve is the shortest cranial nerve, which does not converge from the brainstem. To understand the Olfactory nerve, let me explain the process of smell. When you produce gas from your colon (flatus/flatulence) which is usually composed of oxygen (O2), nitrogen (N2), carbon dioxide (CO2), hydrogen (H2), and methane (CH4), it goes into the nostrils and the nasal cavity. At the extreme end of the nasal cavity is the nose mucosa, which is below the cribiform plate of the Ethmoid bone, which directly below the olfactory bulb. The nose mucosa produces mucus which is responsible for humidifying, cleaning the air, warming the air, and trapping odor.. The mucus membrane is made up of epithelium, basement membrane, and lamina propria..
You started again, what is the meaning of colon gas? You should call it what we all understand. You know, those generic names that people give to that awful smell can be fun to hear. Instead of calling it Colon gas, you can call it names like Anus Applause, Break Wind, Booty Bomb, Air Biscuit, Crap call, Butt Trumpet, Cut of Cheese, Fart, Free Speech, Rectal Turbulence, Roar from the Rear, Mess from the Anus, Thunder from down under, Trouser Trumpet. Oh! I forgot we were creating a post, but you can tell us in the comment section what you call the colon gas in your own word. You should know that your colon gas is flammable. That said, let's get back to serious business
Since the mucus traps odor particles by dissolving it, the odor is picked by the dendrite extension of the olfactory receptor neurons, which is a bipolar neuron. The Axons of several Olfactory receptor neuron in the nose combine to form the olfactory nerve, which goes in through the Ethmoid bone into the olfactory bulb. You should understand that there are many olfactory receptor neurons in the nose, and they several olfactory receptor neurons, express each type of receptor protein, but it should be clear that each olfactory receptor neurons do not share receptor protein with another..
When the Olfactory Receptor Neuron receives the smell, it passes neurotransmitter to the glomerulus in the olfactory bulb. The glomerulus in the olfactory bulb is the place where the axons coming from the olfactory sensory neuron in the mucus lining of the nose meets with the dendrite extension of mitral cells.. The neurotransmitter activates the mitral cells, which will send action potentials to the axon in which forms the olfactory tract. Still in the Glomerulus is the granule cells which produces Gamma-Aminobutyric Acid (GABA) which inhibits the Mitral cells from perceiving everything, rather it discriminates odor impulses, and selects the most excitatory (relevant) odor to the Mitral cells to send to the Central nervous system., .
The olfactory tract splits at the Anterior perforated substance/ventral striatopallidal region into the Lateral Olfactory stria, and the Medial Olfactory stria. The Lateral Olfactory Stria takes the fiber to the innermost part of the temporal lobe called the Uncus, to the piriform olfactory cortex, hippocampal gyrus, the amygdaloid complex, and the Entorhinal complex of the temporal lobe, which is referred to as the Primary Olfactory Cortex that allows perceiving olfaction. , The medial olfactory stria takes fiber to the paraolfactory area in the subcollosal gyrus at the orbital frontal cortex which is associated with interpreting and placing reward for the smell or odor.
Conclusion
The Olfactory Nerve (cranial nerve 1) is responsible for Smell, where the Olfactory receptor neuron takes the odor particle which is trapped in the mucus line to into glomerulus in the olfactory bulb, where neurotransmitter are sent to the Mitral cells. Not forgetting GABA, which is produced by granule cells in the glomerulus to help regulate the odor that gets in (so you do not keep perceiving different odor randomly which aren't necessary). The Axons form the olfactory tract, which sends the signal to the cerebral cortex where the olfact is perceived, interpreted and rewarded depending on the type of olfact. Finally, there is an inability to perceive odor, and it is called Anosmia which could be from a nasal infection or Sinus infection.
Image Referencing
Image 1 || Wikimedia Commons || Head Olfactory Nerve Labeled