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Squid giant axon
 
 
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The squid giant axon is the very large (up to 1 mm in diameter; typically around 0.5 mm) axon
Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
 that controls part of the water jet propulsion system in squid
Squid

Squid are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, Symmetry #Bilateral_symmetry, a mantle , and cephalopod arms....
. Squid use this system primarily for making brief but very fast movements through the water.

Between the tentacles of a squid is a siphon
Siphon

A siphon is a continuous tube that allows liquid to drain from a reservoir through an intermediate point that is higher, or lower, than the reservoir, the flow being driven only by the difference in hydrostatic pressure without any need for pumping....
 through which water can be rapidly expelled by the fast contractions of the body wall muscles of the animal. This contraction is initiated by action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
s in the giant axon. Action potentials travel faster in a larger axon than a smaller one, and squid have evolved the giant axon to improve the speed of their escape response
Escape response

Escape response, escape reaction, or escape behaviour is a possible reaction in response to stimulus indicative of danger, in particular, it initiates an escape motion of an animal....
.

In their Nobel Prize
Nobel Prize

The Nobel Prize , established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Nobel Prize in Physics, Nobel Prize in Chemistry, Nobel Prize in Physiology or Medicine, Nobel Prize in Literature, and Nobel Peace Prize in 1901....
-winning work uncovering ionic mechanism of action potentials, Alan Hodgkin
Alan Lloyd Hodgkin

Sir Alan Lloyd Hodgkin, Order of Merit, Order of the British Empire, Fellow of the Royal Society was a United Kingdom physiology and biophysics, who won the 1963 Nobel Prize in Physiology or Medicine....
 and Andrew Huxley
Andrew Huxley

Sir Andrew Fielding Huxley, Order of Merit , Royal Society is an England physiology and biophysics, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Alan Lloyd Hodgkin on the basis of nerve action potentials, the electrical impulses that enable the activity of an organism to be coordinated by a central nervous system....
 performed experiments on the squid giant axon.






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The squid giant axon is the very large (up to 1 mm in diameter; typically around 0.5 mm) axon
Axon

An axon or nerve fiber is a long, slender projectionof a nerve cell, or neuron, that conducts action potentialaway from the neuron's cell body or soma....
 that controls part of the water jet propulsion system in squid
Squid

Squid are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, Symmetry #Bilateral_symmetry, a mantle , and cephalopod arms....
. Squid use this system primarily for making brief but very fast movements through the water.

Between the tentacles of a squid is a siphon
Siphon

A siphon is a continuous tube that allows liquid to drain from a reservoir through an intermediate point that is higher, or lower, than the reservoir, the flow being driven only by the difference in hydrostatic pressure without any need for pumping....
 through which water can be rapidly expelled by the fast contractions of the body wall muscles of the animal. This contraction is initiated by action potential
Action potential

An action potential is a self-regenerating wave of electrochemical activity that allows nerve cells to carry a signal over a distance. It is the primary electrical signal generated by nerve cells, and arises from changes in the permeability of the nerve cell's axonal Cell membranes to specific ions....
s in the giant axon. Action potentials travel faster in a larger axon than a smaller one, and squid have evolved the giant axon to improve the speed of their escape response
Escape response

Escape response, escape reaction, or escape behaviour is a possible reaction in response to stimulus indicative of danger, in particular, it initiates an escape motion of an animal....
.

In their Nobel Prize
Nobel Prize

The Nobel Prize , established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Nobel Prize in Physics, Nobel Prize in Chemistry, Nobel Prize in Physiology or Medicine, Nobel Prize in Literature, and Nobel Peace Prize in 1901....
-winning work uncovering ionic mechanism of action potentials, Alan Hodgkin
Alan Lloyd Hodgkin

Sir Alan Lloyd Hodgkin, Order of Merit, Order of the British Empire, Fellow of the Royal Society was a United Kingdom physiology and biophysics, who won the 1963 Nobel Prize in Physiology or Medicine....
 and Andrew Huxley
Andrew Huxley

Sir Andrew Fielding Huxley, Order of Merit , Royal Society is an England physiology and biophysics, who won the 1963 Nobel Prize in Physiology or Medicine for his work with Alan Lloyd Hodgkin on the basis of nerve action potentials, the electrical impulses that enable the activity of an organism to be coordinated by a central nervous system....
 performed experiments on the squid giant axon. The large diameter of the axon provided a great experimental advantage for Hodgkin and Huxley as it allowed them to insert voltage clamp electrodes
Electrophysiology

Electrophysiology is the study of the electrical properties of biological cell s and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart....
 inside the lumen of the axon.

While the squid axon is very large in diameter it is unmyelinated
Myelin

Myelin is an electrically-insulating dielectric material that forms a layer, the myelin sheath. Usually, myelin surrounds only the axon of a neuron....
 which decreases the conduction velocity potential substantially. The conduction velocity of a typical 0.5 mm squid axon is about 25 m/s. The sodium gain per impulse is 4 pm/cm2 (picomole per square centimeter) and the potassium gain is also 4pm/cm2.

See also

  • Lateral giant neuron
    Lateral giant neuron

    The lateral giant neuron 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....