- Structure 1.1
- Functions 1.2
- Crustaceans 2
- Cellular antennae 3
- References 4
Antennae are the primary olfactory sensors of insects and are accordingly well-equipped with a wide variety of sensilla (singular: sensillum). Paired, mobile, and segmented, they are located between the eyes on the forehead. Embryologically, they represent the appendages of the second head segment.
The three basic segments of the typical insect antenna are the scape (base), the pedicel (stem), and finally the flagellum, which often comprises many units known as flagellomeres. The pedicel (the second segment) contains the Johnston's organ which is a collection of sensory cells.
The number of flagellomeres can vary greatly, and is often of diagnostic importance. True flagellomeres have a membranous articulation between them, but, in many insects, especially the more primitive groups, the flagellum is entirely or partially composed of a flexible series of small annuli, which are not true flagellomeres.
In many beetles and in the chalcidoid wasps, the apical flagellomeres form a club, and the collective term for the segments between the club and the antennal base is the funicle; for traditional reasons, in beetles it is the segments between the club and the scape, but, in wasps, it is the segments between the club and the pedicel.
In the groups with more uniform antennae (for example: Diplopoda), all segments are called antennomeres. Some groups have a simple or variously modified apical or subapical bristle called an arista (this may be especially well-developed in various Diptera).
Olfactory receptors on the antennae bind to free-floating molecules, such as water vapour, and odours including pheromones. The neurons that possess these receptors signal this binding by sending action potentials down their axons to the antennal lobe in the brain. From there, neurons in the antennal lobes connect to mushroom bodies that identify the odour. The sum of the electrical potentials of the antenna to a given odour can be measured using an electroantennogram.
In the case of the Monarch butterfly, it has been shown that antennae are necessary for proper time-compensated solar compass orientation during migration, that antennal clocks exist in monarchs, and that they are likely to provide the primary timing mechanism for Sun compass orientation.
nauplius larva for swimming. In some groups of crustaceans, such as the spiny lobsters and slipper lobsters, the second antennae are enlarged, while, in others, such as crabs, the antennae are reduced in size.
Within the 
"Almost every vertebrate cell has a specialized cell surface projection called a primary cilium. …primary cilia are key participants in intercellular signaling. This new appreciation of primary cilia as cellular antennae that sense a wide variety of signals could help explain why ciliary defects underlie such a wide range of human disorders, including retinal degeneration, polycystic kidney disease, Bardet-Biedl syndrome, and neural tube defects."
- Darby, Gene (1958). What is a butterfly?. Chicago:
- Gullan, Penny J.; Cranston, Peter S. (2005). The Insects: an Outline of Entomology (3rd ed.). Oxford, UK:
- Chapman, Reginald Frederick (1998). The Insects: Structure and Function (4th ed.). New York:
- Thomas A. Keil (1999). "Morphology and development of the peripheral olfactory organs". In Hansson, Bill S. Insect Olfaction (1st ed.).
- Lawrence, Eleanor, ed. (2005). Henderson's Dictionary of Biological Terms (13th ed.).
- "Electroantennography (EAG)".
- Merlin, Christine; Gegear, Robert J.; Reppert, Steven M. (September 2009). "Antennal circadian clocks coordinate sun compass orientation in migratory monarch butterflies".
- "Superphylum Arthropoda".
- Satir, Peter; Christensen, Søren T. (June 2008). "Structure and function of mammalian cilia".
- Singla, Veena; Reiter, Jeremy F. (August 2006). "The primary cilium as the cell's antenna: signaling at a sensory organelle".