The sense of smell, also known as olfactics is the sense deputy to the perception of fragrant stimuli. This sense is mediated by specialized sensory cells of the nasal cavity. To obtain the perception of odors it is essential that the interaction between the nose (whose mucosa is able to transpose olfactory stimuli), and the cells responsible for the transport of these stimuli to the brain, which can decoded the stimuli and thus transforms them into a perception. Smell depends on airborne chemicals, which the sensory receptors then respond to. These chemoreceptors are located in the olfactory epithelium, a passage of tissue located high in the naval cavity. Olfactory epithelium is made up of three types of cells: sensory neurons (each with a primary cilium), supporting cells between them, and the basal cells that divide regularly and hence producing a fresh crop of sensory neurons to replace those that die. Odorant receptors represent one family of many types of G-protein coupled receptors or GPCRs for short. A couple of examples of GPCRs are: receptors of peptide hormones, taste receptors, the light receptor rhodopsin, GABA receptors at certain synapses in the brain. Each olfactory neuron expresses only a single type of receptor.
What is smell?
Smell is one of the five senses, which allows humans to perceive fragrant stimuli. The chemoreceptors are special cells which are responsible for the reception of odors, and are able to react to the chemical characteristics of the odorous substances, they are located in a particular area of the nasal mucosa, known as the olfactory mucosa and are characterized by a yellowish pigmentation. These neurons are highly specialized with a tuft of cilia and their bases are prolonged in nerve fibers, through the ethmoid bone (the bone that forms the roof of the nasal cavity), reaching the olfactory bulbs; from here other neurons that reach the brain trigger the perception of odor. Within the olfactory mucosa, odorous molecules are made soluble before settling on the eyelashes of neurons. This is the phenomenon that triggers the nervous stimulus and sends a message that there is a fragrant. They pass through the olfactory bulbs, and finally reaching the brain.
The pathologies of smell can be of two types, quantitative and qualitative. The former is represented by hyposmia or partial reduction of the sense of smell, and anosmia, or the total reduction of the sense of smell. In the case of reductions in quality of the sense of smell, we speak of parosmia, a disorder that is characterized by alteration of the sense of smell in a human body. The underlying causes of these disorders can vary: rhinitis, sinusitis, cancer, mucosal lesions of various origins (viral, traumatic or inflammatory). Disturbances of smell can inevitably also influence the sense of taste.
What function does the sense of smell serve?
Smell is the deputy sense in the perception of fragrant stimuli, which allows us to identify certain objects or chemicals around us. Humans can discriminate between hundreds and thousands of different odorant molecules, each with its own specific structure.
