Figure 3. Modified sensory cilia.
The outer segment of photoreceptors (A), an elaborate array of membrane discs, in which light detection takes place is connected to the photoreceptor cell by a connecting cilium. The light detecting protein machinery must past through the connecting cilium on its way to the outer segment. (B) In the olfactory sensory neuron of vertebrates, a dendrite ends in a dendritic knob from which olfactory cilia originate. There are several cilia per neuron which protrude into the mucus layer where odorants bind to receptors. (C) Upon odorant receptor binding to the olfactory G-protein coupled receptor (receptor) the G-protein (Golf) is activated producing cAMP. The cAMP then causes the cyclic nucleotide gated ion channels to open and subsequently effect Cl− channels then potentiating a depolarization of the OSN.