Anatomy and Physiology of Nasal Cavity
The nasal cavity comprises of a bony cavity which is bounded by numerous bones such as the nasal bone, the ethmoid bone, the maxilla and a part of the sphenoid bone. The nasal cavity is lined by a mucous membrane and it produces some amount of sticky mucus to keep the cavity moist.
The nasal cavity starts at the nostril or external nares which are mainly bounded by membranes and cartilages but not bones. The nasal the external nares are guarded by cilia or hairs which serve to protect the nasal cavity from dust. Other irritant particles get stuck in the sticky mucus of the nasal cavity and hence the respiratory tract is protected from external agents in this manner.
The nasal mucosa contains olfactory nerve endings which protrude through the sieve like ethmoidal plate to reach the mucous membrane. These nerve endings play the role of monitors of smell as they are stimulated chemically by the volatile particles which enter with the air within the nostril. These chemicals give rise to unique signals in these nerve endings which ultimately results in the sensation of smell.
As we inhale the nasal mucosa with its olfactory nerve endings at the roof of the nasal cavity are affected and this stimulation is carried through the synapses of the receptors neurons and is conducted to the olfactory bulb and reaches the olfactory tract. This stimulation after this travels further into the brain and into the thalamus. Here the stimulation is interpreted and recognized. The interesting fact is that the eyes and ears also play a role in the interpretation of this stimulus.
The stimulus does not travel through any relay system but it is directly carried into the different parts of the brain. The stimulation of smell is associated not only with the higher functions of living but with sexual behavior and emotions as well.