The stomatogastric ganglion (STG) is a much-studied

ganglion A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there are ...

(collection of

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s) found in

arthropods Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

and studied extensively in

decapod The Decapoda or decapods, from Ancient Greek δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfish, shrimp, and p ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s. It is part of the stomatogastric nervous system.

Anatomy

The neurons comprising the stomatogastric ganglion have

cell bodies In cellular neuroscience, the soma (: somata or somas; ), neurocyton, or cell body is the bulbous, non-process portion of a neuron or other brain cell type, containing the cell nucleus. Although it is often used to refer to neurons, it can also ...

located dorsal to the

stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

within the lumen of the opthalmic artery. Most are

motor neurons A motor neuron (or motoneuron), also known as efferent neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or ...

, with

neurites A neurite or neuronal process refers to any projection from the cell body of a neuron. This projection can be either an axon or a dendrite. The term is frequently used when speaking of immature or developing neurons, especially of cells in cultur ...

that exit through motor

nerves A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called ...

and innervate the muscles of the

gastric mill The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including archosaurs (birds and other dinosaurs, crocodiles, alligators, pterosaurs), earthworms, some gastro ...

and

pylorus The pylorus ( or ) connects the stomach to the duodenum. The pylorus is considered as having two parts, the ''pyloric antrum'' (opening to the body of the stomach) and the ''pyloric canal'' (opening to the duodenum). The ''pyloric canal'' ends a ...

. These STG motor neurons also form direct synaptic connections with one another. In crabs and lobsters, in which it has been well-studied, the stomatogastric ganglion is a collection of approximately 25-30 neurons. The circuit varies slightly between different crustacean species and between individuals of the same species, but most of the neurons are conserved, and most stomatogastric muscles are innervated by just one motor neuron. The

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

and chemical synaptic connections between all of the STG neurons have been fully mapped and characterized, forming a complete wiring diagram (also called a

connectome A connectome () is a comprehensive map of neural connections in the brain, and may be thought of as its " wiring diagram". These maps are available in varying levels of detail. A functional connectome shows connections between various brain ...

Function

Neural activity in the stomatogastric ganglion produces rhythmic movements of the gastric mill and pyloric region of the digestive system. Neural circuits within the STG are prominent examples of

central pattern generators Central pattern generators (CPGs) are self-organizing biological neural circuits that produce rhythmic outputs in the absence of rhythmic input. They are the source of the tightly-coupled patterns of neural activity that drive rhythmic and stereo ...

, and their rhythm-generating properties have been studied in detail. The characteristic gastric mill rhythm and pyloric rhythm arise from the intrinsic

electrophysiological Electrophysiology (from ee the Electron#Etymology, etymology of "electron" ; and ) is the branch of physiology that studies the electrical properties of biological cell (biology), cells and tissues. It involves measurements of voltage change ...

properties of the neurons and from the strength of synaptic connections between neurons. The stomatogastric ganglion also receives many modulatory inputs. These

neuromodulators Neuromodulation is the physiology, physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic receptor, metabotropic, G protein-coupled rece ...

, such as

serotonin Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. It is an amine synthesized ...

proctolin Proctolin is a neuropeptide present in insects and crustaceans. It was first found in '' Periplaneta americana'', a species of cockroach in 1975. Proctolin was extracted from 125,000 cockroaches and the Edman degradation was carried out on the sa ...

, FLRFamide-like peptides, and red pigment-concentrating hormone (RPCH) can change the speed and form of the rhythmic activity.

References

{{Reflist Crustacean anatomy

Anatomy

Function

See also

References