The olfactory tract carries smell from the bulb straight to the cortex: the piriform and entorhinal cortex and the amygdala. Only then does it reach the thalamus (mediodorsal nucleus); both routes end in the orbitofrontal cortex. [1][2][3]
The olfactory bulb and tract are not a separate shape in this atlas: step 1 lights the orbitofrontal cortex they lie against, in the olfactory sulcus below it; then lit: the parts it runs through, in order.
The 3D brain needs JavaScript. The steps below still say where the olfactory pathway runs, in order.
The brain starts seen from low on the left and a little from the front, so the underside of the frontal lobe, where the olfactory bulbs lie, and the front of the temporal lobe both show. Step through lights one step at a time, about 1.2 s each, from the bulb to the smell cortex, then through the thalamus to the orbitofrontal cortex; tap a step below to light it. The lit step is in the bright highlight colour, the steps before it stay lit in a paler tint of it and the steps still ahead are grey. Drag to turn, pinch or scroll to zoom. Step through is off because your device asks for reduced motion; tap each step instead.
The atlas has no shape for the olfactory bulb and tract, the piriform or entorhinal cortex or the mediodorsal nucleus, so those steps light the part they lie against or that holds them: the orbitofrontal cortex, the parahippocampal gyrus (lit whole, though both cortices cover only its front end, by the uncus) and the whole thalamus. [4][5][6]
The route, in 6 steps
Receptor axons from the nose pass up through the holes of the cribriform plate into the olfactory bulb, where they gather in small bundles, the glomeruli, and meet its mitral cells. The axons of the mitral and tufted cells leave as the olfactory tract, running back in the olfactory sulcus close to the midline. Not a separate shape in this atlas; lit: the part they lie against, the orbitofrontal cortex. [3][7][1]Where is the olfactory bulb?
Along the lateral olfactory stria the tract ends directly in the piriform cortex, the largest part of the primary olfactory cortex, on the front of the parahippocampal gyrus by the uncus. It has no border of its own in this atlas; lit: the parahippocampal gyrus that holds it. [1][5]Where is the piriform cortex?
The tract also reaches the entorhinal cortex, just behind the piriform cortex on the same gyrus and the main link between the hippocampus and the rest of the cortex. The atlas draws no border for it, so this step lights nothing new: the parahippocampal gyrus stays lit. [1][6]Where is the entorhinal cortex?
The tract ends directly in the amygdala too, deep in the front of the temporal lobe. Its cortical part is counted as part of the piriform cortex, and its cortical and medial nuclei pass smell on to the hypothalamus. [1][8][5]Where is the amygdala?
Only now does smell reach the thalamus, as a second route: the piriform cortex projects to the mediodorsal (medial dorsal) nucleus, which relays input from the olfactory cortex and the amygdala on to the prefrontal cortex. Not a separate shape in this atlas; lit: the part that holds it, the thalamus. [3][9]Where is the thalamus?
The orbitofrontal cortex, on the underside of the frontal lobes just above the bulbs, takes smell both straight from the primary olfactory cortex and through the mediodorsal nucleus. It is thought to represent smells, tastes and their reward value, and its neurons answer tastes and the sight of food as well as smells. [10][3][11]Where is the orbitofrontal cortex?
More about the olfactory pathway
Other names: smell pathway, lateral olfactory tract [3][1]
Smell is the one sense that reaches the cortex before any relay in the thalamus: the olfactory tract runs straight from the bulb to the piriform cortex, entorhinal cortex and amygdala. Sight, hearing, touch and taste each relay in the thalamus on the way up. [2][3]
The receptor axons gather in the outer layer of the bulb into glomeruli, small bundles about 50 micrometres across, where they meet the mitral cells; the mitral cells in turn send the tract on to five main regions of the cerebrum. [3]
There is one bulb and one tract on each side, lying in the sulci that run close to and parallel with the midline on the underside of the frontal lobes, on the cribriform plate above the nose. [1][7]
Besides the cortex, olfactory tract fibres also reach the limbic system and the hypothalamus. [2]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); it has no shape for tracts, so a pathway is shown by the parts it runs through.