Nervous system of gastropods

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The dissected central ring ganglia of Lymnaea stagnalis. Scale bar is 1 mm.
LBuG and RBuG: left and right buccal ganglia
LCeG and RCeG: left and right cerebral ganglia
LPeG and RPeG: left and right pedal ganglia
LPIG and RPIG: left and right pleural ganglia
LPaG and RPaG: left and right parietal ganglia
VG: visceral ganglion. Lymnaea stagnalis central ring ganglia.jpg
The dissected central ring ganglia of Lymnaea stagnalis . Scale bar is 1 mm.
LBuG and RBuG: left and right buccal ganglia
LCeG and RCeG: left and right cerebral ganglia
LPeG and RPeG: left and right pedal ganglia
LPIG and RPIG: left and right pleural ganglia
LPaG and RPaG: left and right parietal ganglia
VG: visceral ganglion.

The nervous system of gastropods consists of a series of paired ganglia connected by major nerve cords, and a number of smaller branching nerves. It is sometimes called ganglionic. [1]

Contents

General layout of the gastropod ganglia. In most species, the brain is fused into a single, six-lobed, organ Gastropod nervous system.gif
General layout of the gastropod ganglia. In most species, the brain is fused into a single, six-lobed, organ
Buccal ganglia of Aplysia californica. Aplysia californica buccal ganglia.jpg
Buccal ganglia of Aplysia californica .

Description

The brain of a gastropod consists of three pairs of ganglia, all located close to the oesophagus and forming a nerve ring around it. 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 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.

Main nerve cords

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.

In air-breathing freshwater snails of the genus Lymnaea Lamarck, 1799 goal-directed decision-making during the hunt for food is performed by just two neuron types. Through measuring the action potentials between neurons, just two neurons were able to come to a complicated form of decision making. One neuron in the brain tells the snail if food is nearby, the second neuron signals whether the snail is hungry or not. Such decision making helps the snail save energy by reducing complex brain activity when there is no food nearby and adapts its behavior in the absence of food. Thus the snail can switch between a low-use mode and a high-use mode depending on the decision. [2]

Neurons of Helix , Helix aspersa , are used for study of epileptogenesis, because they are sensistive to epileptogenic drugs including pentylenetetrazol. [3]

Related Research Articles

<span class="mw-page-title-main">Ganglion</span> Clusters of neurons in the peripheral nervous system

A ganglion 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 both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively.

<span class="mw-page-title-main">Nervous system</span> Part of an animal that coordinates actions and senses

In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body, then works in tandem with the endocrine system to respond to such events. Nervous tissue first arose in wormlike organisms about 550 to 600 million years ago. In vertebrates it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers, or axons, that connect the CNS to every other part of the body. Nerves that transmit signals from the brain are called motor nerves or efferent nerves, while those nerves that transmit information from the body to the CNS are called sensory nerves or afferent. Spinal nerves are mixed nerves that serve both functions. The PNS is divided into three separate subsystems, the somatic, autonomic, and enteric nervous systems. Somatic nerves mediate voluntary movement. The autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system. Both autonomic and enteric nervous systems function involuntarily. Nerves that exit from the cranium are called cranial nerves while those exiting from the spinal cord are called spinal nerves.

<span class="mw-page-title-main">Vagus nerve</span> Cranial nerve X, for visceral innervation

The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that carries sensory fibers that create a pathway that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right vagus nerves—but they are typically referred to collectively as a single subsystem. The vagus is the longest nerve of the autonomic nervous system in the human body and comprises both sensory and motor fibers. The sensory fibers originate from neurons of the nodose ganglion, whereas the motor fibers come from neurons of the dorsal motor nucleus of the vagus and the nucleus ambiguus. The vagus was also historically called the pneumogastric nerve.

<span class="mw-page-title-main">Autonomic nervous system</span> Division of the nervous system supplying internal organs, smooth muscle and glands

The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.

<span class="mw-page-title-main">Parasympathetic nervous system</span> Division of the autonomic nervous system

The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Sympathetic nervous system</span> Part of the autonomic nervous system which stimulates fight-or-flight responses

The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Edinger–Westphal nucleus</span> One of two nuclei of the oculomotor nerve

The Edinger–Westphal nucleus is one of two nuclei of the oculomotor nerve. It is located in the midbrain. It receives afferents from the both pretectal nuclei. It contains parasympathetic pre-ganglionic neuron cell bodies that synapse in the ciliary ganglion. It contributes the autonomic, parasympathetic component to the oculomotor nerve, ultimately providing innervation to the iris sphincter muscle and ciliary muscle to mediate the pupillary light reflex and accommodation, respectively.

<span class="mw-page-title-main">Ventral nerve cord</span>

The ventral nerve cord is a major structure of the invertebrate central nervous system. It is the functional equivalent of the vertebrate spinal cord. The ventral nerve cord coordinates neural signaling from the brain to the body and vice versa, integrating sensory input and locomotor output. Because arthropods have an open circulatory system, decapitated insects can still walk, groom, and mate—illustrating that the circuitry of the ventral nerve cord is sufficient to perform complex motor programs without brain input.

Each spinal nerve receives a branch called a gray ramus communicans from the adjacent paravertebral ganglion of the sympathetic trunk. The gray rami communicantes contain postganglionic nerve fibers of the sympathetic nervous system and are composed of largely unmyelinated neurons. This is in contrast to the white rami communicantes, in which heavily myelinated neurons give the rami their white appearance.

<span class="mw-page-title-main">Sympathetic ganglia</span> Ganglia of the sympathetic nervous system

The sympathetic ganglia, or paravertebral ganglia, are autonomic ganglia of the sympathetic nervous system. Ganglia are 20,000 to 30,000 afferent and efferent nerve cell bodies that run along on either side of the spinal cord. Afferent nerve cell bodies bring information from the body to the brain and spinal cord, while efferent nerve cell bodies bring information from the brain and spinal cord to the rest of the body. The cell bodies create long sympathetic chains that are on either side of the spinal cord. They also form para- or pre-vertebral ganglia of gross anatomy.

<span class="mw-page-title-main">Lateral grey column</span>

The lateral grey column is one of the three grey columns of the spinal cord ; the others being the anterior and posterior grey columns. The lateral grey column is primarily involved with activity in the sympathetic division of the autonomic motor system. It projects to the side as a triangular field in the thoracic and upper lumbar regions of the postero-lateral part of the anterior grey column.

<span class="mw-page-title-main">Suboesophageal ganglion</span>

The suboesophageal ganglion of arthropods and in particular insects is part of the arthropod central nervous system (CNS). As indicated by its name, it is located below theoesophagus, inside the head. As part of the ventral nerve cord, it is connected to the brain and to the first thoracic ganglion. Its nerves innervate the sensory organs and muscles of the mouthparts and the salivary glands. Neurons in the suboesophageal ganglion control movement of the head and neck as well.

<span class="mw-page-title-main">Lumbar ganglia</span>

The lumbar ganglia are paravertebral ganglia located in the inferior portion of the sympathetic trunk. The lumbar portion of the sympathetic trunk typically has 4 lumbar ganglia. The lumbar splanchnic nerves arise from the ganglia here, and contribute sympathetic efferent fibers to the nearby plexuses. The first two lumbar ganglia have both white and gray rami communicates.

<i>Pseudunela cornuta</i> Species of gastropod

Pseudunela cornuta is a species of minute sea slug, an acochlidian, a shell-less marine and temporarily brackish gastropod mollusk in the family Pseudunelidae. Adults are about 3 mm long and live in the spaces between sand grains.

The evolution of nervous systems dates back to the first development of nervous systems in animals. Neurons developed as specialized electrical signaling cells in multicellular animals, adapting the mechanism of action potentials present in motile single-celled and colonial eukaryotes. Primitive systems, like those found in protists, use chemical signalling for movement and sensitivity; data suggests these were precursors to modern neural cell types and their synapses. When some animals started living a mobile lifestyle and eating larger food particles externally, they developed ciliated epithelia, contractile muscles and coordinating & sensitive neurons for it in their outer layer.

Bathyacmaea nipponica is a species of very small, deep-sea limpet, a marine gastropod mollusk in the family Pectinodontidae.

FMRFamide, a neuropeptide involved in cardiac activity regulation, is found in Biomphalaria glabrata, a species of a freshwater snail best known for its role as the intermediate host for the human-infecting trematode parasite Schistosoma mansoni.

<span class="mw-page-title-main">Circumesophageal nerve ring</span>

A circumesophageal or circumpharyngeal nerve ring is an arrangement of nerve ganglia around the esophagus/ pharynx of an animal. It is a common feature of nematodes, molluscs, and many other invertebrate animals, though it is absent in all vertebrate animals and is not structurally possible in simpler ones such as water bears.

<i>Bathyhedyle boucheti</i> Species of gastropod

Bathyhedyle boucheti is a species of panpulmonate slug, a deep-sea dwelling gastropod native to the continental slope off the coast of Mozambique. It is the first ever such panpulmonate slug to be discovered at such depths. It is the only known member of its family group. Its radular formula is 1.1.2.

Fictive behavior is when an organism’s sensory input and/or motor output is silenced for physiological experiments.

References

  1. Shigeno S, Parnaik R, Albertin CB, Ragsdale CW (2015-09-07). "Evidence for a cordal, not ganglionic, pattern of cephalopod brain neurogenesis". Zoological Letters. 1 (1): 26. doi: 10.1186/s40851-015-0026-z . PMC   4657373 . PMID   26605071.
  2. Crossley M, Staras K, Kemenes G (June 2016). "A two-neuron system for adaptive goal-directed decision-making in Lymnaea". Nature Communications. 7: 11793. Bibcode:2016NatCo...711793C. doi:10.1038/ncomms11793. PMC   4895806 . PMID   27257106.
  3. Giachello CN, Premoselli F, Montarolo PG, Ghirardi M (2013). "Pentylenetetrazol-induced epileptiform activity affects basal synaptic transmission and short-term plasticity in monosynaptic connections". PLOS ONE. 8 (2): e56968. Bibcode:2013PLoSO...856968G. doi: 10.1371/journal.pone.0056968 . PMC   3577694 . PMID   23437283.

Further reading