Human Anatomy, Part 2 - K. A. Dubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2008

Special Part
Sensory organs, organa sensuum
Olfactory organ

The Olfactory Organ, organum olfactorium, is the peripheral part of the chemical exteroceptive distant-action analyzer. Odorous substances dissolve in the Water vapor of the Nasal cavity and the secretion of the nasal glands, thereby stimulating the olfactory neurosensory Cells, cellulae neurosensoriae olfactoriae, in the nasal cavity. The latter are part of both the main olfactory organ and the accessory or vomeronasal organ.

The main olfactory organ is represented by a restricted area (up to 500 mm²) of the mucous membrane covering the superior and middle nasal conchae and the superior nasal meatus, namely the olfactory region, regio olfactoria.

The vomeronasal organ consists of a pair of epithelial tubules located within the Connective Tissue of the mucosa that covers the nasal septum at the junction of its cartilaginous part and the Vomer. These epithelial tubules are blind-ended at one end and open into the nasal cavity at the other. The Functions of the vomeronasal Olfactory sensory system are associated with reproductive processes (Regulation of the estrous/Menstrual cycle and Sexual Behavior) as well as emotional spheres.

The neurosensory Cells of the main olfactory organ (the first neuron of the olfactory pathway) possess a short peripheral process—a dendrite—which terminates in a characteristic enlargement known as the olfactory vesicle, clava olfactoria. The rounded apex of this vesicle bears 10–12 motile olfactory cilia, which act as specialized antennae for odorant molecules. The long central processes, or axons, form 20–40 olfactory filaments, fila olfactoria, which pass through the openings of the lamina cribrosa into the cranial cavity and terminate in the olfactory bulbs, bulbus olfactorius. Here lie The Cell bodies of the second-order Neurons, known as mitral cells. Each mitral cell forms synaptic contacts with thousands of axons from the neurosensory cells of both the ipsilateral and contralateral sides. The processes of the mitral cells form the olfactory tracts and terminate in the primary olfactory centers: the trigonum olfactorium, substantia perforata anterior, and septum pellucidum. Fibers of the third-order neurons extend from the primary olfactory centers to the secondary olfactory centers, including the gyrus hippocampi, uncus, and gyrus dentatus.

Structurally, the neurosensory cells of the vomeronasal organ closely resemble those of the main olfactory organ. The primary difference is that the olfactory vesicles of the former bear non-motile microvilli instead of cilia on their surface. The axons of the vomeronasal neurosensory cells (the first neuron of the pathway) form small nerve bundles which, much like the axons of the main olfactory neurosensory cells, pass through the openings of the lamina cribrosa and terminate in the accessory olfactory bulb. The latter is located in the dorsomedial part of the main olfactory bulb and shares a similar structural Organization. The exact pathway of the second- and third-order neurons from the vomeronasal organ in humans remains unclear; however, studies in animals have proven that the vomeronasal organ has central representation in the medial preoptic Nucleus and several other hypothalamic nuclei.