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How can Caenorhabditis elegans respond to many chemicals with only a small number of chemosensory cells?

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A pine grosbeak with pink and gray plumage perches on a branch, eating red berries among autumn foliage. — Chemoreception Animals, such as this pine grosbeak, use chemoreception to respond to chemicals that can be tasted and smelled in their environments. Many of these chemicals affect behaviors such as food preference and defense.

The nematode Caenorhabditis elegans is able to detect a wide array of water-soluble and lipophilic chemicals despite possessing only 34 chemosensory cells because of its complex genetic and neural organization.

The organism utilizes a large repertoire of more than 700 genes to control the production of diverse receptor proteins. Because the number of sensory cells is limited, individual cells must express multiple types of these receptor proteins to expand the range of detectable stimuli.1

The specific behavioral response elicited by a chemical—such as attraction or repulsion—is determined by the connections the receptor cell makes with other components of the nervous system. This is evidenced by experiments showing that if a specific receptor protein is moved from one cell to another, the animal's behavioral response to the associated chemical can be reversed.1