Almost all responses to odorants in
olfactory sensory neurons (OSNs) are facilitated by CNG channels. When an
odorant binds to its specific receptor in the chemosenstive
cilia membrane, it activates a
G protein, which causes a downstream reaction activating the enzyme
adenylyl cyclase (AC). This enzyme is responsible for an increase in cAMP concentration within the OSN. cAMP binds to the CNG channels in the OSN membrane, opening them, and making the cell highly permeable to
Ca2+. Calcium ions flow into the cell causing a
depolarization.