Anatomy and Physiology
By Rich Higgins
The coyote’s olfactory system is comprised of two components, detection and analysis. Detection occurs in the rostrum and analysis takes place in the brain. To understand the complete process of detection it is necessary to understand the anatomy and the physiology of the snout, the players involved and how they all function together. Prepare to marvel at one of nature’s wonders. The rhinarium, or nose pad is located at the anterior of the rostrum. The outside contains teardrop shaped openings called nares, or nostrils, which transition into slots that extend down and rearward. The inside of the nares contains a flap called the alar fold that can close off the nostril. The nares open into the nasal cavity, which is divided in two halves by a bone and cartilaginous structure called the nasal septum. These cavities contain the ethmoturbinate bones, which form a scroll like structure of moveable cartilage and porous bone, the paranasal sinuses and, at the posterior wall, the subethmoidal shelf which is another porous bony structure. All of these structures are covered with a mucus membrane called the epithelial mucosa. This membrane, also called the epithelium, contains as many as 250 million olfactory receptor cells located in clumps on the knobs of cilial cells imbedded in the mucus membrane. The cilia are connected to tiny nerves called dendrites which connect into axons which form into larger olfactory nerves which extend through the ethmoid into the olfactory bulb and on into the frontal cortex. Additionally, the Jacobson’s organ is located in the nasal cavity and opens into the roof of the mouth between the canine teeth. This organ provides a separate but parallel system of olfactory detection. The organ primarily detects pheromones and the sensory nerves do not communicate with the olfactory bulb and the cortex but with the hypothalamus, which regulates sexual and social issues. I know this all sounds complex and many of you will simply read over the polysyllabic words, but at the very least you will be able to tie all of the parts together when I explain how they all work
To detect a scent coyotes use a sniffing process, a series of rapid, short inhalations and exhalations. The nares are mobile, the coyote can aim them in the direction it wants to examine and change the size and shape to accommodate a greater airflow or to restrict the entrance of debris and particulates. The inspired air is forced into the nasal cavity and through the turbinates, which warm and humidifies the air. The mucus membrane that covers everything filters bacteria and particulates, traps and dissolves scent molecules and passes them over the scent receptor cells. As the air continues through the ethmoidal shelf it is forced into the olfactory epithelium in the shelf’s nasal pocket where the scent molecules that are not recognizable in a single sniff accumulate. This pocket prevents washout of the scent molecules during the aspiration of the air. During aspiration, as the air is forced out, the alar fold closes and forces the air down and back through the slots on the side of the nares so that it doesn’t interfere with the scent molecules still in the air or on the ground in front of the coyote. As the process is repeated the hair like cilia cells move the mucous containing the scent molecules across the olfactory receptors until the interaction generates nerve impulses that are transmitted into the olfactory lobe and then into the frontal cortex for analysis. This incredible system essentially dissolves scent molecules in a mucous membrane, moves them across 250 million scent receptors that are imbedded in every part of the nasal cavity including the sinuses while accumulating enough for recognition and then firing off an electrical signal to different parts of the brain for analysis. The system is so efficient that it is estimated that the coyote’s nose can detect scent molecules in parts per trillion. One trillion pennies laid out on the ground would cover an area 10 miles by 14 miles, 140 square miles. Detection is a done deal. It is going to happen, plain and simple, but fortunately detection is only half of the equation. Analysis is the other half and it takes place in the brain. This is something we can influence. This is something we can screw with.