Anatomy of Smell

At the other end, next to the olfactory bulb, they contain synapses which connect electrochemically to the nerve cells of the olfactory bulb. The latter is part of the brain and this is where signal processing starts. Each receptor cell fires spontaneously at a rate of between 3 and 60 impulses per second. The rate of firing increases when an odorant is present. The neurons from the epithelium converge on areas of the olfactory bulb 

About 60% of odorants also trigger receptors in the trigeminal nerve fibres, which run around the entire surface of the nasal cavity. The interaction between the olfactory and trigeminal senses will be discussed later under the section Signal Processing . 

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