Nervous system of gastropods
Encyclopedia
The nervous system of gastropods consists of a series of paired ganglia
connected by major nerve cords, and a number of smaller branching peripheral nerves.
The brain
of a gastropod consists of three pairs of ganglia, all located close to the oesophagus. In some primitive forms, these ganglia are relatively discrete, but in most species they have become so closely bound together as to effectively form separate lobes of a single structure.
The cerebral ganglia are located above the oesophagus and supply peripheral nerves to the eyes, tentacles, and other sensory organs in the head. Beneath the oesophagus, at the forward part of the foot, lie the pedal ganglia. As their name implies, these supply nerves to the foot muscles.
The third pair of ganglia within the brain lie slightly behind and below the cerebral ganglia. These are the pleural ganglia, and supply nerves to the mantle cavity. Bundles of nerves connect the cerebral, pedal, and pleural ganglia together, as well as running above and below the oesophagus to connect the right and left cerebral and pedal ganglia to each other.
In most gastropods, a short pair of nerve cords passes forward from the cerebral ganglia to a pair of buccal ganglia located above the back of the mouth. These supply nerves to the radula
and other parts of the mouth.
The main nerve cords of the central nervous system
run through the length of the body from the pleural ganglia. In the ancestral gastropod, these would presumably have run down either side of the animal, but because of the torsion
of the visceral mass found in many modern forms, they now cross over each other. However, a number of species have undergone de-torsion, restoring their original bilateral symmetry.
A pair of parietal ganglia lie along the length of the main nerve cords, supplying nerves to the gill
and associated olfactory organ
. Because of the torsion of the nerve cords, one parietal ganglion is typically higher in the body than the other. Finally, the nerve cords terminate in a linked pair of visceral ganglia, which supply nerves to the remaining organs of the visceral mass.
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
connected by major nerve cords, and a number of smaller branching peripheral nerves.
The brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
of a gastropod consists of three pairs of ganglia, all located close to the oesophagus. In some primitive forms, these ganglia are relatively discrete, but in most species they have become so closely bound together as to effectively form separate lobes of a single structure.
The cerebral ganglia are located above the oesophagus and supply peripheral nerves to the eyes, tentacles, and other sensory organs in the head. Beneath the oesophagus, at the forward part of the foot, lie the pedal ganglia. As their name implies, these supply nerves to the foot muscles.
The third pair of ganglia within the brain lie slightly behind and below the cerebral ganglia. These are the pleural ganglia, and supply nerves to the mantle cavity. Bundles of nerves connect the cerebral, pedal, and pleural ganglia together, as well as running above and below the oesophagus to connect the right and left cerebral and pedal ganglia to each other.
In most gastropods, a short pair of nerve cords passes forward from the cerebral ganglia to a pair of buccal ganglia located above the back of the mouth. These supply nerves to the radula
Radula
The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...
and other parts of the mouth.
The main nerve cords of the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
run through the length of the body from the pleural ganglia. In the ancestral gastropod, these would presumably have run down either side of the animal, but because of the torsion
Torsion (gastropod)
Torsion is an anatomical event which takes place during the very early part of the life of snails and slugs of all kinds. In other words, torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle and shell 180˚...
of the visceral mass found in many modern forms, they now cross over each other. However, a number of species have undergone de-torsion, restoring their original bilateral symmetry.
A pair of parietal ganglia lie along the length of the main nerve cords, supplying nerves to the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
and associated olfactory organ
Osphradium
The osphradium is the olfactory organ in certain molluscs, linked with the respiration organ.The main function of this is to test incoming water for silt and other possible food particles.It is used by all members of the Genus Conus....
. Because of the torsion of the nerve cords, one parietal ganglion is typically higher in the body than the other. Finally, the nerve cords terminate in a linked pair of visceral ganglia, which supply nerves to the remaining organs of the visceral mass.
Further reading
- Benjamin P. R., Kemenes G. & Kemenes I. (2008) "Non-synaptic Neuronal Mechanisms Of Learning And Memory In Gastropod Molluscs". Frontiers In BioscienceFrontiers in BioscienceFrontiers in Bioscience is a peer reviewed academic journal.It is indexed in PubMed, INDEX Medius, MEDLINE, Research Alert, Current Web Content, and CrossRef....
13: 4051-4057. doi:10.2741/2993, abstract, - Chase R., Antkowiak T., Geoffroy E. & Weatherill D. (2004). "Why the ovotestis of Helix aspersaHelix aspersaHelix aspersa, known by the common name garden snail, is a species of land snail, a pulmonate gastropod that is one of the best-known of all terrestrial molluscs. The species has been placed in the genus Helix, in all sources between 1774 and 1988 and in most sources until recently...
is innervated". Acta Biologica Hungarica 55(1-4): 239-249. doi:10.1556/ABiol.55.2004.1-4.29. .