Kenyon cells are the intrinsic
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s of the
mushroom body,
a
neuropil
Neuropil (or "neuropile") is any area in the nervous system composed of mostly unmyelinated axons, dendrites and glial cell processes that forms a synaptically dense region containing a relatively low number of cell bodies. The most prevalent an ...
found in the brains of most
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s and some
annelids. They were first described by F. C. Kenyon in 1896. The number of Kenyon cells in an organism varies greatly between species. For example, in the fruit fly, ''
Drosophila melanogaster
''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...
,'' there are about 2,500 Kenyon cells per mushroom body, while in cockroaches there are about 230,000.
Structure
While the exact features of Kenyon cells can vary between species, there are enough similarities to define their general structure. Kenyon cells have
dendritic
Dendrite derives from the Greek word "dendron" meaning ( "tree-like"), and may refer to:
Biology
*Dendrite, a branched projection of a neuron
*Dendrite (non-neuronal), branching projections of certain skin cells and immune cells
Physical
* Dendr ...
branches that arborize in the calyx or calyces, cup-shaped regions of the mushroom body. At the base of the calyces, Kenyon cell
axon
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
s come together and form a bundle known as the pedunculus. At the end of the pedunculus, Kenyon cell axons bifurcate and extend branches into the vertical and medial lobes.
Kenyon cells are mainly
postsynaptic
Chemical synapses are biological junctions through which neurons' signals can be sent to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous syste ...
in the calyces, where their
synapses form microglomeruli. These microglomeruli are made up of Kenyon cell dendrites,
cholinergic
Cholinergic agents are compounds which mimic the action of acetylcholine and/or butyrylcholine. In general, the word " choline" describes the various quaternary ammonium salts containing the ''N'',''N'',''N''-trimethylethanolammonium cati ...
boutons, and
GABAergic terminals.
Antennal lobe projection neurons are the source of the cholinergic input, and the GABAergic input is from protocerebral neurons.
Kenyon cells are
presynaptic
In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell.
Synapses are essential to the transmission of nervous impulses from ...
to mushroom body output neurons in the lobes. However, the lobes are not only output regions; Kenyon cells are both pre and postsynaptic in these regions.
The cells are subdivided into subtypes; for example, those that have their cell bodies outside of the
calyx cup are called ''clawed Kenyon cells''.
Development
Kenyon cells are produced from precursors known as
neuroblasts. The number of neuroblasts varies greatly between species. In ''Drosophila melanogaster'', Kenyon cells are produced from only four neuroblasts, while in the honey bee they are the product of thousands of neuroblasts. Differences in neuroblast number between species are related to the final number of Kenyon cells in an adult.
The positioning of Kenyon cells depends on their birth order. The somata of early-born Kenyon cells are pushed outward as more Kenyon cells are created. This results in a concentric pattern of cell bodies, with the somata of the last-born cells in the center, where the neuroblast had been, and the somata of the first-born cells at the outermost margins of the cell body area.
Where a Kenyon cell sends its dendrites in the calyces and which lobes it projects its axons to varies based on its birth-order.
Distinct types of Kenyon cells form at specific times during development.
Function
Mushroom bodies are essential for
olfactory learning and memory. Odor information is represented by sparse combinations of Kenyon cells. Learning is facilitated by
dopamine-driven
plasticity of the odor response of Kenyon cells. The
cAMP
Camp may refer to:
Outdoor accommodation and recreation
* Campsite or campground, a recreational outdoor sleeping and eating site
* a temporary settlement for nomads
* Camp, a term used in New England, Northern Ontario and New Brunswick to descri ...
signaling cascade, especially
protein kinase A
In cell biology, protein kinase A (PKA) is a family of enzymes whose activity is dependent on cellular levels of cyclic AMP (cAMP). PKA is also known as cAMP-dependent protein kinase (). PKA has several functions in the cell, including regulatio ...
, must function properly in Kenyon cells for learning and memory to occur.
Information about odors may be encoded in the mushroom body by the identities of the responsive neurons as well as the timing of their spikes.
Experiments in locusts have shown that Kenyon cells have their activity synchronized to 20-Hz
neural oscillations
Neural oscillations, or brainwaves, are rhythmic or repetitive patterns of neural activity in the central nervous system. Neural tissue can generate oscillatory activity in many ways, driven either by mechanisms within individual neurons or by ...
and are particularly responsive to projection neuron spikes at specific phases of the oscillatory cycle.
References
{{reflist
External links
The mushroom bodies- with a description of the Kenyon cells.
Arthropod anatomy
Animal nervous system