Human sense of smell

Odorant molecules excite a sensory neuron when they bind to chemoreceptors in its plasma membrane.

1. Inhaled odorant molecules bind to receptor proteins on chemoreceptive sensory neurons in the nasalcavity. A receptor protein binds only one type of odorant molecule, and each cell has only one type ofreceptor. This art shows three types of receptor cells (coded red, green, and blue), but there are hundreds.

2. An odorant molecule binds to a receptorprotein on a sensory neuron, initiating anaction potential that travels along the neuron’saxon to the olfactory bulb in the brain.

3. In the olfactory bulb, axons of sensoryneurons synapse on interneurons. Eachinterneuron receives signals only from cellswith the same type of receptor.

4. Interneurons in the olfactory lobe relaysignals from sensory neurons to other regionsof the brain, including the limbic system andcerebral cortex.