Olfaction in animals

Olfaction in the other alive kingdoms
The importance and sensitivity of smell varies among different organisms: most mammals have a good sense of smell, whereas most birds do not, with the exceptions being the tubenoses (i.e. petrels and albatrosses) and the kiwis. Among mammals it is well developed in the carnivores and ungulates, who must always be aware of each other, and in those, such as moles, who smell for their food. It is less well developed in the catarrhine primates (Catarrhini), and nonexistent in cetaceans, who in compensation have a sensitive and well-developed sense of taste. The lack of olfaction is called anosmia. In many species olfaction is highly tuned to pheromones; a male silkworm moth, for example, can smell a single molecule of bombykol.

Insects
Insects primarily use their antennae for olfaction. Sensory neurons in the antenna generate odor-specific electrical signals called spikes in response to odour. They process these signals from the sensory neurons in the antennal lobe followed by the mushroom bodies and lateral horn of the brain. The antennae have the sensory neurons in the sensilla and they have their axons terminating in the antennal lobes where they synapse with other neurons there in semidelineated (with membrane boundaries) called glomeruli. These antennal lobes have two kinds of neurons, projection neurons (excitatory) and local neurons (inhibitory). The projection neurons send their axon terminals to mushroom body and lateral horn (both of which are part of the protocerebrum of the insects) and local neurons have no axons. Recordings from projection neurons show in some insects strong specialization and discrimination for the odors presented (especially for the projection neurons of the macroglomeruli, a specialized complex of glomeruli responsible for the pheromones detection). Processing beyond this level is not exactly known though some preliminary results are available.

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