Final answer:
The olfactory bulb is involved in the sense of smell, receiving signals from olfactory neurons and processes them before these signals reach various brain regions including the olfactory cortex, limbic system, and hypothalamus.
Step-by-step explanation:
The correct answer to the question, "The ________ is involved in smell," is A) olfactory bulb. Olfactory neurons project from the olfactory epithelium to the olfactory bulb as thin, unmyelinated axons. The olfactory bulb processes these incoming signals through neural clusters called glomeruli, where each glomerulus is specific to one odorant. From the olfactory bulb, signals travel directly to the olfactory cortex, as well as other brain regions like the limbic system and hypothalamus, which are involved in memory and emotional responses. Significantly, the olfactory system is unique among the senses in that it does not send its signals through the thalamus before they reach the cerebral cortex. This direct connection between the olfactory bulb and brain regions is why smells can often trigger strong memories and emotional responses.