Taste Receptor Cells
Olfaction (or the sense of smell) involves detecting the chemical composition of inhaled air. These chemicals are referred to as odorants. Odorants bind to olfactory receptor cells in the nasal cavity. These receptors have hairlike extensions, called cilia, that extend into the mucus covering the surface of the nasal cavity. There are many different types of olfactory receptor cells, and each type binds only to specific odorants. The olfactory receptor cells send neural signals to the olfactory bulb. The olfactory bulb is a part of the brain made up of many different types of neurons. The olfactory nerve carries smell information to other regions of the brain and is formed by the axons of neurons in the olfactory bulb. A specific smell is perceived due to the combination of activation from a range of different olfactory receptor cells.The nose and the mouth are connected via the retronasal passage, meaning that the sense of smell is closely linked to taste perception. Unlike information related to vision, hearing, taste, and touch, olfactory information is not carried directly to the thalamus, which serves as the sensory relay of the brain. Instead, olfactory information is sent directly to regions of the brain involved in memory, learning, and emotions, such as the hippocampus and the amygdala. These connections have an evolutionary, or adaptive, function. Upon eating rotten or poisonous foods, which are typically bitter, olfactory information about this experience can help elicit emotions of disgust and create a vivid memory of which foods to avoid in the future.