Mauthner cell

[1] Mauthner cells first appear in lampreys (being absent in hagfish and lancelets),[2] and are present in virtually all teleost fish, as well as in amphibians (including postmetamorphic frogs and toads[3]).

[4] A C-start is a type of a very quick startle or escape reflex that is employed by fish and amphibians (including larval frogs and toads).

[1][4] In fish this forward propulsion does not require contraction of the antagonistic muscle, but results from the body stiffness and the hydrodynamic resistance of the tail.

In cases when an abrupt acoustic, tactile or visual stimulus elicits a single action potential in one M-cell, it always correlates with a contralateral C-start escape.

[6] An extremely quick mutual feedback inhibitory circuit then assures that only one M-cell reaches spiking threshold—as the C-start has to be unilateral by definition—and that only one action potential is fired.

In fish, water jet stimuli that activate these neurons elicit non-mauthner initiated C-starts of a longer latency, compared with M-cell associated ones.

This notion is supported by studies using in vivo calcium imaging in larval zebrafish which show that MiD2cm and MiD3cm are activated along with the M-cell when an offending stimulus is directed towards the head but not the tail, and are correlated with C-starts of a larger initial turn angle.

These neurons are electrically coupled with motoneurons which innervate extraocular, jaw and opercular muscles and mediate pectoral fin adduction in hatchetfish.

[11] In adult postmetamorphic anurans (frogs and toads) that do not have a tail, M-cells are nevertheless preserved[3] and their discharges are associated with rapid movement of legs during an escape.

[12] In addition, larval lampreys (eel-like jawless fish of superclass Cyclostomata) exhibit rapid withdrawal behavior that is correlated with Mauthner cell activity and involves bilateral, posture-dependent muscular contractions along the length of the body.

Sudden vibration activates both Mauthner neurons in the lamprey brainstem, which causes an accordion-like muscular contraction in the trunk and tail and pulls the head down into the burrow.

[17] The Inner ear afferents also terminate with electrical synapses on a population PHP inhibitory interneurons (see below) to provide an additional level of feed forward inhibition.

[1] Inputs from the optic tectum and the lateral line help control which way the C-startle bends by biasing the mauthner cells when there are obstacles in the vicinity.

Both these requirements are quite natural considering that the consequences of a single Mauthner cell discharge are so strong; a failure to comply with these two rules would not only prevent the animal from escaping, but could even physically damage it.

The fastest part of this negative feedback network, which is also the one closest to the Mauthner cell, is that of the so-called passive hyperpolarizing field potential or PHP neurons.

Because of its size, presence of a quick feedback network, and abundance of electrical and quasi-electrical (ephaptic) synapses, the Mauthner cell has a strong field potential of a very characteristic shape.