How Does Smell Convey Information

Follow a simplified olfactory pathway from an odor molecule’s interaction with sensory receptors to bulb output and selected receiving brain networks.

Where smell begins

Olfactory sensory neurons are cells in the lining high inside the nose. Receptors on these cells interact with odor molecules. We’ll follow how that interaction becomes a signal traveling toward the olfactory bulb.

Receiving an odor and carrying a signal A schematic sensory neuron. Odor molecules sit near receptor markers on cilia at the left. A dendrite connects this end to the cell body. An axon extends right toward the olfactory bulb. Structures and molecules are not drawn to scale. Odor molecules Cilia + receptors Dendrite Cell body Axon Toward the bulb →

Where the signal reaches another neuron

A connection inside a glomerulus A sensory axon ends inside a glomerulus, near the dendritic branches of a bulb neuron. The dendrite connects to that neuron's cell body outside the glomerulus. This schematic shows only selected parts of the circuit. Glomerulus Sensory axon Dendrite Bulb neuron Output axon Toward receiving regions →

Select the button to trace the pathway between two neurons.

The dashed circle marks a region containing many connections, not a cell membrane. The enlarged gap indicates a synaptic connection between different neurons. Local circuits and most branches are omitted.

Following a projection

Direct projection from the olfactory bulb to piriform cortex A schematic bulb output neuron sends its axon along a curved path into piriform cortex, where the axon forms terminal branches. Olfactory bulb Axon pathway Piriform cortex

Follow a bulb output neuron's axon into a receiving region.

This selected pathway illustrates a direct anatomical projection. The real pathway contains many neurons and branching axons; their activity is not represented by this single line.

Where bulb output travels

Selected direct and onward olfactory pathways Blue routes show selected direct projections from the olfactory bulb to piriform cortex, cortical amygdala, and lateral entorhinal cortex. Copper routes continue from those receiving regions toward orbitofrontal, hypothalamic and autonomic, and hippocampal networks. Piriform cortex Cortical amygdala selected areas Lateral entorhinal cortex Orbitofrontal cortex Hypothalamic + autonomic networks Hippocampal networks Olfactory bulb

Choose a destination to inspect its route.

Blue routes represent selected direct projections from bulb neurons. Copper routes represent selected onward connections beginning in regions that have already received olfactory input. These pathways are simplified: additional routes, intermediate regions, feedback connections, and direct bulb targets are omitted.