Smell is caused by the detection of volatilised chemical compounds (evaporated molecules) in the atmosphere, either organic or non-organic, by neurons located in the olfactory epithelium, a small patch of tissue located at the back of human nasal cavities. The olfactory epithelium’s receptor neurons act as sensory signalling cells, initialising electric signals when odour is detected. When a threshold of stimulus is reached, the signals send that information to the olfactory bulb and cortex – part of the human limbic system (a set of brain structures that form the inner border of the brain cortex) – for processing. The odour is then deciphered, storing and matching the information of the volatilised chemical compounds with other known odours and past experiences.
Although it’s easy to forget, air molecules all weigh something, and their combined weight pressing down is what causes this pressure