Final answer:
Olfactory fibers from the nasal cavity directly enter the olfactory bulbs, which are neural structures in the cerebrum responsible for processing olfactory signals.
Step-by-step explanation:
When olfactory fibers pass through the roof of the nose, they directly enter the olfactory bulbs. These bulbs are neural structures located on the ventral surface of the frontal lobe in the cerebrum, which receives signals from olfactory receptors. The olfactory system begins with the olfactory epithelium in the nasal cavity, where the receptor neurons are located. These olfactory neurons extend axons through the cribriform plate of the ethmoid bone to meet the olfactory bulbs.
From there, the axons form the olfactory tract and project to various brain regions. Notably, unlike other senses, olfactory signals do not pass through the thalamus before reaching the cerebral cortex. Instead, they have direct access to areas associated with memory and emotion, such as the temporal lobe and limbic system structures, making smell a strong trigger for memories and emotional responses.