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

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s. The antennal lobe is a sphere-shaped deutocerebral neuropil in the brain that receives input from the

olfactory sensory neurons 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 ...

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 ( ...

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

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

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...

'' there are olfactory sensory neurons in other parts of the body) from where the sensory neurons carry the information about the odorant molecules impinging on the antenna to the antennal lobe. The antennal lobe is composed of densely packed neuropils, termed

glomeruli ''Glomerulus'' () is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn". ''Glomerulus'' may refer to: * the filter ...

, where the

sensory neurons Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The ...

synapse with the two other kinds of neurons, the postsynaptic principle 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 glomeruli 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 (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...

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

cockroach Cockroaches (or roaches) are a Paraphyly, paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are we ...

. 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 b ...

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