Question

olfactory receptor type
in order to initiate an action potential regarding olfaction, which must occur first?
cilia of the olfactory receptors must displace.
the olfactory bulbs must be activated.
the synaptic areas within the brain must be activated.
the molecules of the odorant must dissolve in the mucus that covers the nasal epithelium.

Explanation:

For an action potential regarding olfaction to be initiated, the odorant molecules must first dissolve in the mucus covering the nasal epithelium. This is the initial step in the olfactory process. Only after this dissolution can the cilia of olfactory receptors interact with the odorant molecules (displacement of cilia is a subsequent step). Activation of olfactory bulbs and synaptic areas in the brain occurs further along in the neural transmission pathway of the olfactory signal, after the initial interaction at the nasal epithelium - mucus - odorant molecule level.

Answer:

The molecules of the odorant must dissolve in the mucus that covers the nasal epithelium.