Typical feature of olfactory sensation is?

The olfactory sensory neurons are located in a specialized por- tion of the nasal mucosa, the yellowish pigmented olfactory epi- thelium. In dogs and other animals in which the sense of smell is highly developed (macrosmatic animals), the area covered by this membrane is large; in microsmatic animals, such as humans, it is small. In humans, it covers an area of 5 cm2 in the roof of the nasal cavity near the septum (Figure 14-1). The human olfactory epi- thelium contains 10 to 20 million bipolar olfactory sensory neurons interspersed with glia-like suppoing (sustentacular) cells and basal stem cells. The olfactory epithelium is said to be the place in the body where the nervous system is closest to the external world. Each neuron has a sho, thick dendrite that projects into the nasal cavity where it terminates in a knob containing 10 to 20 cilia (Figure 14-2). The cilia are unmyelinated processes about 2 mm long and 0.1 mm in diameter and contain specific receptors for odorants (odorant receptors). The axons of the olfactory sensory neurons pass through the cribriform plate of the ethmoid bone and enter the olfactory bulbs (Figure 14-1). New olfactory sensory neurons are generated by basal stem cells as needed to replace those damaged by exposure to the environment. The olfactory renewal process is carefully regulated, and there is evidence that in this situation a bone morphogenic protein (BMP) exes an inhibitory effect. BMPs are a large family of growth factors originally described as promoters of bone growth but now known to act on most tissues in the body during development, including many types of nerve cells.Ref: Ganon pg.no219