Final answer:
The highly vascularized area directly above the vestibule is the olfactory epithelium, which contains the olfactory receptor neurons that project to the olfactory bulb.
Step-by-step explanation:
The highly vascularized area directly above the vestibule that is responsible for the sense of smell is known as the olfactory epithelium. This region contains the olfactory receptor neurons, which are bipolar sensory neurons that have dendrites extending into the mucus lining of the cavity.
The olfactory bulb is the neural structure that receives signals from the olfactory receptors. The axons of these olfactory sensory neurons make up the first cranial nerve, which projects through the cribriform plate of the ethmoid bone to synapse with neurons in the olfactory bulb.