In humans the olfactory bulb is on the underside of the brain: one on each side, lying with the olfactory tract in the olfactory sulcus on the bottom (orbital) surface of each frontal lobe, on the cribriform plate of the ethmoid bone above the nose. [1][2]
Not a separate shape in this atlas; lit: the part that holds it. Lit: the whole orbitofrontal cortex, on both sides. The bulb itself is not modelled in this atlas; it lies against the underside of the orbitofrontal cortex, in the olfactory sulcus between the gyrus rectus and the medial orbital gyrus. Nothing is drawn at a guessed point. [2][3]
The 3D brain needs JavaScript. The text below still says where the olfactory bulb is and what it does.
Slice
Opens cut by a front (coronal) slice through the orbitofrontal cortex, which holds the olfactory bulb. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Lit here: the orbitofrontal cortex, the part that holds the olfactory bulb — see it on its own page.
Where it is
In most vertebrates the olfactory bulb is the most forward part of the brain; in humans it is on the inferior (bottom) side. [1]
It is supported and protected by the cribriform plate of the ethmoid bone, which separates it from the olfactory epithelium in the nose and is perforated by olfactory nerve axons. [1]
It and the olfactory tract lie in the olfactory sulcus, a sulcus formed by the medial orbital gyrus on the inferior surface of each frontal lobe, running close and parallel to the midline. [2]
The olfactory tract runs back from it as a narrow white band, triangular in a section from the front; behind, it splits into medial, intermediate and lateral striae at the olfactory trigone. [2]
What it does
It is involved in olfaction, the sense of smell: it passes smell information from the nose to other brain regions, including the amygdala, the orbitofrontal cortex and the hippocampus, where it contributes to emotion, memory and learning. [1]
Its glomerular layer is the first stage of synaptic processing; the glomeruli form a spatial map of odours arranged by chemical structure, such as functional group and carbon-chain length. [1]
Proposed jobs: telling odours apart, making odour detection more sensitive, filtering out background odours, and letting brain areas for arousal and attention adjust what is detected. It is still unclear which of these, if any, the bulb performs on its own. [1]
Connections
One input, the axons of roughly ten million olfactory receptor neurons in the nasal mucosa, and one output, the axons of its mitral cells. [1]
It also receives top-down input from the olfactory cortex, the amygdala, the neocortex, the hippocampus, the locus coeruleus and the substantia nigra. [1]
The olfactory tract carries the fibres of its mitral and tufted cells to targets including the piriform cortex, the amygdala and the entorhinal cortex. [2]
Inside it
The main olfactory bulb has five layers, from surface to centre: glomerular, external plexiform, mitral cell, internal plexiform and granule cell layers. [1]
There is a main and an accessory olfactory bulb; the accessory bulb sits on the upper back of the main bulb and forms a parallel pathway. [1]
Other names
Latin: bulbus olfactorius. Its stalk, the olfactory tract, is also called the olfactory peduncle or olfactory stalk. [1][2]
Size
The model has no shape for the olfactory bulb itself, so it is not measured here. The left orbitofrontal cortex that holds it measures about 67 mm front to back, 30 mm top to bottom and 40 mm side to side on this model (the box it fits in, not its volume). [4]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.