The antennal lobe is the primary (first order) olfactory brain area in

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s. The antennal lobe is a sphere-shaped deutocerebral neuropil in the brain that receives input from the olfactory sensory neurons in the antennae and mouthparts. Functionally, it shares some similarities with the

olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...

vertebrates Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

. The anatomy and physiology function of the insect brain can be studied by dissecting open the insect brain and imaging or carrying ou
''in vivo'' electrophysiological recordings
from it.

Structure

In insects, the

olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

pathway starts at the antennae (though in some insects like ''

Drosophila ''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or p ...

'' there are olfactory sensory neurons in other parts of the body) from where the sensory neurons carry the information about the

odor An odor (American English) or odour ( Commonwealth English; see spelling differences) is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive ...

ant molecules impinging on the antenna to the antennal lobe. The antennal lobe is composed of densely packed neuropils, termed glomeruli, where the sensory neurons

synapse In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...

with the two other kinds of neurons, the postsynaptic principal neurons (termed projection neurons) and local interneurons. Each olfactory sensory neuron expresses a single odorant receptor type and targets the same glomeruli as other olfactory sensory neurons expressing that receptor type, such that each glomerulus houses all or the majority of sensory neurons of a given receptor type. The number and identities of glomeruli are species specific; most species contain 40 to 160 individually identifiable glomeruli within the antennal lobe. For instance, there are 32 glomeruli in

mosquito Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...

, 43 glomeruli in the fruit fly antennal lobe, and 203 glomeruli in

cockroach Cockroaches (or roaches) are insects belonging to the Order (biology), order Blattodea (Blattaria). About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known Pest (organism), pests. Modern cockro ...

. The local neurons, which are primarily inhibitory, have their neurites restricted to the antennal lobe. Projection neurons, which generally receive information from a single glomerulus, project to higher brain centers such as the mushroom body and the lateral horn. The interaction between the

olfactory receptor neuron An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a sensory neuron within the olfactory system. Structure Humans have between 10 and 20 million olfactory receptor neurons (ORNs). In vertebrates, ORNs are Bi ...

s, local neurons and projection neurons reformats the information input from the sensory neurons into a spatio-temporal code before it is sent to higher brain centers.

Structure

References

Further reading

Reviews of antennal lobe anatomy