The medial giant interneuron (MG) is an interneuron

Interneuron

An interneuron is a multipolar neuron which connects afferent neurons and efferent neurons in neural pathways...

 in the abdominal nerve

Nerve

A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...

 cord of crayfish

Crayfish

Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...

. It is part of the system that controls the caridoid escape reaction

Caridoid escape reaction

The Caridoid Escape Reaction, also known as lobstering or tail-flipping, refers to an innate escape mechanism in marine and freshwater crustaceans such as lobsters, krill, shrimp and crayfish....

 of crayfish, clawed lobster

Lobster

Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...

s, and other decapod crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s. Crayfish have a pair of medial giants running the length of the entire animal, and are the largest neurons in the animal.

When a crayfish is given a sudden visual or tactile stimulus to the front part of the animal, the MG activates fast flexor motor neuron

Motor neuron

In vertebrates, the term motor neuron classically applies to neurons located in the central nervous system that project their axons outside the CNS and directly or indirectly control muscles...

s that cause the abdomen

Abdomen

In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...

 to flex, resulting in the crayfish moving directly backward, away from the source of the stimulation. This connection was first demonstrated by C. A. G. Wiersma in the red swamp crayfish, Procambarus clarkii

Procambarus clarkii

Procambarus clarkii is a freshwater crayfish species, native to the Southeastern United States, but found also on other continents, where it is often an invasive pest. It is known variously as the red swamp crawfish, red swamp crayfish, Louisiana crawfish, Louisiana crayfish or mudbug.-Range and...

.

The medial giant interneurons are less well studied than the lateral giant neuron

Lateral giant neuron

The lateral giant interneuron is an interneuron in the abdominal nerve cord of crayfish. It is part of the system that controls a special kind of escape reflex of crayfish....

s, which trigger a similar escape behavior.