Normal and abnormal development of the antennal lobes in M. sexta

Human Odor Sensing System

These figures are images of the human odor sensing system. The first panel shows a human head with the route that odor molecules take into the body - up the nose and into the nasal cavity. In addition it shows where the olfactory bulb is in relation to the nasal cavity and the brain. The second panel shows a close up of the olfactory bulb revealing some of it's characteristic structure. Note that the sensory cells in the nasal cavity actually travel through tiny holes in the bones of the skull in order to make their connections (synapses) with the central nervous system in the olfactory bulb. Also note that the sensory cells make their first contact with the brain in ball-shaped structures called glomeruli.

M.sexta Odor Sensing System

This image shows the "moth equivalent" of the information in Fig. 1A&B. The first panel shows a face on view of the head of the moth Manduca sexta with the front part of the head cut away to reveal the brain. In this diagram the central part of the brain, or protocerebrum (PR) lies in the center between the optic lobes (OL). The antennal nerves (AN) carrying sensory information from the moth's antenna (the antennae are the main organ of odor detection; i.e., the insect's noses) enter the head and join the brain at the antennal lobes (AL). The antennal lobe of an insect serves the same function as the olfactory bulb of human brains. The second panel shows a detailed view of the brains of male and female Manduca sexta (female on the left and male on the right). In these images the surface of the antennal lobes have been cut away to reveal the olfactory glomeruli. These glomeruli probably serve the same function in moths as they do in humans and are structurally very similar. Note that the antennal lobes of males possess a few special glomeruli (MGC) whose job is to decode information about the chemical signal that female moths release to attach males for mating, their sex-attractant pheromone. (Abbreviations: AL, antennal lobe; AN, antennal nerve; AMMC, antennal mechanosensory motor area; E, eye; F, flagellum of antenna; G, glomerulus; LC, lateral cell cluster of antennal lobe; MC, medial cell cluster of antennal lobe; MGC, macroglomerular cluster; OL, optic lobe of the eye; P, pedicel of antenna; PR, protocerebrum; S, scape of antenna; SEG, suboesophagial ganglion of the brain).

[Images from Scientific American by Roberto Osti (human) and courtesy of J.G. Hildebrand (moth).]

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