PMC

Schematic of the olfactory pathway to the brain with four different scenarios how the SARS-CoV-2 virus may cause anosmia or hyposmia. (A) Normal pathway: odorant molecules bind to the olfactory receptor neuron (ORN), the ORN transmits the smell sensation through the cribriform plate (bone) to the mitral cell (MC) in the olfactory bulb of the brain. Olfactory epithelium also contains support cells (sustentacular cells, SuC) and stem cells (SC) that can regenerate SuCs and ORNs. (B) Odors may not reach the ORNs, because of nasal obstruction/congestion by increased mucus. (C) The transmission of odor sensation may be blocked because of damage and/or death of ORNs. (D) The sensation of smell may be compromised because the virus affects neurons in the brain. (E) The transmission of odor sensation may be compromised, because the SuC (which assists the ORN with odor processing) is damaged by the virus.

Correlation between sensitivity of smell sensation in olfactory and trigeminal nerve and differentiation capacity of smell sensation in olfactory and trigeminal nerves.

A representative case (in Patient #17 of ) of an olfactory perception experienced during radiation therapy. The upper column indicates when the patient experienced the sensation. The lower column shows the beam positions that overlapped the sagittal views of treatment-planning CT. Red lines indicate the start and end of the sensation. Yellow lines indicate the start and end of the full treatment session. The yellow area indicates the olfactory epithelium.

A-B) show the retraction of whiskers induced by air-puffing toward the right side (A) and left side (B) of whiskers two seconds after air-puffing, in which the retractions are pointed by yellow arrows. C) shows the retraction duration of right-side whiskers (an opposite side of olfactory deprivation, gray bar) and of left-side (white) after air-puffing (n = 15, p<0.001, ***). D) shows the frequency of free-air whisking from right-side whiskers (gray) and left-side (white, n = 23, p<0.01, **).