Galerie d'Anatomie comparée

Sensory organs (display 94)

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The sensory organs

An animal's ability to perceive and interact with its natural environment is essential for survival. In vertebrates, we generally observe two types of sensory structures: physical receptors and chemical receptors. Physical receptors are sensitive to stimuli such as light and pressure; this category results in sight, hearing and touch. Chemical receptors or chemoreceptors are the basis for smell and taste.

Sensory organs are highly adapted to the environment of the animal, sometimes leading to amazing sensory abilities: think of elephants, for example, which are capable of estimating quantities of food simply by smell, or the piercing eyesight of a falcon flying high above a field in search of its prey.

The following four display cases are dedicated to the senses of smell, taste, touch, hearing and sight. They contain osteological preparations, specimens preserved in liquid, anatomical casts and sculptures.

Smell: anatomy and function

Numerous species rely on smell in their search for food, in their social interactions and for orientation. Olfactory detection begins with a movement of air or water through the nostrils, a process often linked to breathing, or through the mouth when food is being eaten. Charged with molecules called odorants, the air or water is directed towards the olfactory epithelium. The surface area of the latter is often increased by bony folds known as nasal conchae. Connections form between the odorous molecules and compatible proteinaceous receptors situated on the hairs of the olfactory neurons. These neurons regenerate themselves throughout the lifetime of the animal. The number of olfactory genes, which program the receptors to accept a certain range of odorous molecules, varies from one species to another. In human beings, around 390 genes make it possible to detect - but not always differentiate - millions of odorants.

The interaction between an odorant and its compatible receptor provokes the sending of electrical impulses towards the olfactory bulbs. The information then travels towards the cerebral cortex, which is in communication with the amygdala and the hippocampus. The processing of memories linked to a certain smell occurs here. As regards the level of olfactory stimulation, it depends on the concentration of odorants but also the exposure time. This allows a high sensitivity to new smells to be maintained.

The vomeronasal organ is a sensorial structure located between the oral and nasal cavities of certain vertebrates. Its development varies depending on the species. The sensory neurons of this organ are characterised by microvilli capable of detecting chemical compounds such as pheromones. The information acquired during this interaction is then transmitted to the accessory olfactory bulb, where it is processed and sent to other areas of the brain.

Orientation through smell

Situated between the oral and nasal cavities, a snake’s vomeronasal organ features two tubular cavities that open onto the palate.

Odorants are collected thanks to a forked tongue which retracts into the cavities. The sensory epithelium of the organ captures - in stereo - the different concentrations of chemical substances on each part of the tongue, thereby helping the animal track prey or find a mate.

Thus, by sticking out its tongue a snake can broaden its field of sensory perception.

The dog’s sense of smell

Certain breeds of dog can be trained to accomplish extraordinary feats of smell such as locating avalanche victims, finding truffles in a forest or detecting skin cancer.

There are a number of physiological reasons for these abilities:

  • A large olfactory epithelium that can attain 200 cm2 in dogs compared to 5 cm2 in human beings
  • A very high number of olfactory neurons, up to 220 million in dogs compared to 6-10 million in human beings
  • A significant variety of olfactory genes that allow more connections with different odorants