The term accessory olfactory sensory neuron (OSNa) refers to one of two types of olfactory sensory neuron in the rat ( Swanson-2004 ) and mouse ( Hof-2000 ). The other is the main olfactory sensory neuron (OSNm). For more information on OSNa's, see accessory olfactory receptor neuron (OLRa). Final 17 Jan 2025.