the Mind of the Nematode
In this lengthy article, we will answer all of her questions
What is a nematode worm?
What is the nervous nematode system?
What is the function of the nervous system of nematodes?
And how does the neurotransmitter ready for nematode?
What are the types of neural structures of a nematode?
The hermaphrodite systema nervosum features a total complement of 302 neurons, which are arranged in an essentially invariant structure. Neurons with similar morphologies and connectivities are grouped into classes; there are 118 such classes. Neurons have simple morphologies with few, if any, branches. Processes from neurons run in defined positions within bundles of parallel processes, synaptic connections being made in passing. Process bundles are arranged longitudinally and circumferentially and are often adjacent to ridges of the hypodermis. Neurons are generally highly locally connected, making synaptic connections with many of their neighbors. Muscle cells have arms that run bent process bundles containing motoneuron axons. Here they take their synaptic input in specified regions onward the surface of the bundles, where motoneuron axons reside. Most of the morphologically identifiable synaptic connections during a typical animal are described. These contain about 5000 chemical synapses, 2000 neuromuscular junctions, and 600 gap junctions.
Introduction
The functional properties of a systema nervosum are largely determined by the characteristics of its component neurons and therefore the pattern of synaptic connections between them. Although great progress has been made this century in understanding the way during which information is coded within a neuron and therefore the process of data transmission between neurons via synapses, little is currently identified about the detailed connectivity of systems of neurons. the rationale for this is often simply that a systema nervosum is an enormously complex organ. within the vertebrate cerebellum alone, it's been estimated that there are quite 1010 neurons (Braitenberg & Atwood 1958) each making many thousands of synaptic contacts.
We have undertaken an entire reconstruction of a systema nervosum from electron micrographs of serial sections. we've been ready to do that by employing a very simple, small systema nervosum, that of the soil nematode Caenorhabditis elegans. The severity and consistency of the structure of the nematode's systema nervosum pulled the eye of many neuroanatomists at the turn of the century.
Goldschmidt and his contemporaries produced detailed and accurate descriptions of sensuality and knots, and thus methods of the method (Chitwood & Chitwood 1974), but the limited resolution of the sunlight microscope prevented them from unambiguously resolving individual processes within the beams. Goldschmidt was convinced that neuron processes anastomosed extensively in which nerve tissue was therefore a syncytial network.
He presented a group of intriguing diagrams representing the layout of processes within the Ascaris systema nervosum in support of his view of the structure of nerve tissue, a view that he vigorously defended (Goldschmidt 1908, 1909). the choice viewpoint considered that neurons are mononucleate branched structures that their processes don't anastomose. it's now clear that this alternative viewpoint, as espoused by his contemporary critics, like Cajal (1972), was correct. newer anatomical studies with the microscope have finally laid to rest the secularists' view of the systema nervosum. we've therefore not tried to interpret Goldschmidt's connectivity diagrams, although we've retained a number of the names, given to the sensilla and ganglia, that were employed by him and his contemporaries.
In recent years, C. elegans has become the subject of intense developmental and genetic study. The highly repeatable sequence of cell divisions occurring during the event of this organism allowed the identification of the entire cell line from enriched oils to mature adults (Sulston 1983; Sulston et al. 1983).
Each differentiated cell type that's produced at the terminal twigs on the lineage tree is now known. Laser ablation studies have given some insight into the degree of cell autonomy that's involved in determining the pattern of cell divisions and differentiation that occur. Generally, it seems that, in C. elegans, cells behave fairly autonomously during development, although there are several well-defined instances where regulative cell-cell interactions are demonstrated (Sulston & White 1980; Kimble 1981).
C. elegans was originally selected as an organism that deserves extensive developmental studies, partly because it's readily amenable to genetic analysis. Many mutants are isolated and mapped (Brenner 1974). The mutants that are isolated exhibit an honest kind of phenotypes: some are morphological, some affect various aspects of development, and much of exhibits aberrant behavior. a number of the behavioral mutants are shown to possess defects in muscles (Waterston et al.1980), but many probably have alterations within the systema nervosum (Lewis & Hodgkin 1977; Chalfie & Sulston 1981; Hedgecock et al. 1984). It is hoped that in-depth knowledge of the systemic neural structure of C. elegans will facilitate the interpretation of the changes taking place in these mutant neuron systems. This may shed some consecutive light on the genetic control of developmental processes that ultimately result in an interconnected group of interconnected neurons that make up a neuron.
The reconstructions that are presented during this paper describe the connectivity of all the neurons within the systema nervosum of the C. elegans hermaphrodite except those within the pharynx, which are described by Albertson & Thomson (1976). The detailed morphologies of the sensilla within the head are described by Ward et al. (1975), Ware et al. (1975), and Wright (1980); the structure of the ventral cord has been described by White. (1976) and an independent reconstruction of the tail ganglia has been described by Hall (1977). Together these papers provide a fairly complete description of the connectivity, topography, and ultrastructure of the systema nervosum within the hermaphrodite. The C. elegans male features a more extensive systema nervosum than that of the hermaphrodite; most of the 'extra' nerve tissue is situated within the tail. A partial reconstruction of the systema nervosum within the male tail has been described by Sulston et al. (1980).
The Ascaris abdominal cord structure is derived from the reconstructing of microscopic section images (Stretton et al. 1978). Despite the huge difference in size between these nematodes (10 cm vs. 1 mm for C. elegans), it was found that the neurons in the ventral cord were remarkably similar, and it was possible to identify equivalent motor neuron classes in two animals. The large size of Ascaris allows the use of electrophysiology techniques to study its nervous system. These studies identified inhibitory and stimulating classes of the motor nerve and showed that acetylcholine is the neurotransmitter used by the stimulating motor nerve (Johnson and Stretton 1980). The small size of C. elegans prevents such electrophysiological studies but, by analogy, these results may be related to the equivalent neurons in C. elegans and even provide evidence of their functional properties.
Although neural tissue reconstructions from electronic thumbnails can in principle identify all focal synaptic contacts, the obtained communication pattern is unlikely to represent exactly the functional synaptic connections between neurons. There is evidence that synaptic transmission by some peptide transmitters operates over a large range (Jan et al. 1983), indicating that these types of synapses may not be localized in separate focal points and therefore will not be seen in electronic thumbnails. There are other ways in which information can be transferred between neurons that do not appear from rebuilds. Muscular nerve transmission may be used to travel over long distances and where there may be many targets; A good candidate for a secretory neuron is found in the pharynx (Albertson & Thomson 1976). Short-range transmission may occur by electrical leakage currents or by capacitive coupling between processes that go hand in hand over long distances. However, despite these limitations, high-resolution reconstructions provide a wealth of information about synaptic connections between neurons. Thus, of all currently available technologies, these reconstructions may provide the most comprehensive picture of the synaptic circuits of a nervous system such as C. elegans.
Because of the vast amount of information involved in providing contact data, we have attempted to organize your presentation in a manner that facilitates quick access. The structure of the `` canonical '' nervous system is presented, which is actually a mosaic of many nervous systems. A general description is given for the first time to the structure of C. elegans and some salient features of the nervous system. This is followed by a detailed description of each neuron category in alphabetical order in Annex 1. These descriptions are somewhat self-contained and include morphological data in addition to synaptic data. There are several references in the first section of the illustrations in Appendix 1. These appear as the category name followed by a letter, for example, Bahr. The small letter indicates the graph indicated in the description of the ASE neuron class.
Materials and methods
All the reconstructed nerves described in this study are derived from Caenorhabditis elegans (var. Bristol) nematodes; These were cultivated in E. coli meadows that grew on the Petri agar plates (Brenner 1974).
Electron microscope
Worms were rinsed from Petri sheets and installed in 1% osmium tetroxide in 0.1 m sodium phosphate, pH 7.4 for one hour at 20 ° C. Pre-fixation of glutaraldehyde was not performed in this work because, although this method provides better conservation of the microstructure, we found that osmium alone gave better contrast to cell membranes, and this facilitated the resolution of the process outlines in dense neuron regions.
After fixation, the worms were spread over a thin layer of 1% agar and cut in half. The deadly worms were covered with a 1% molten agar droplet, and the agar blocks containing one-half worm were cut. It was dried by a graded chain from alcohol to propylene oxide, then to propylene oxide as well as Araldite (CY 212 resin, CIBA Ltd.) and then to Araldite at room temperature overnight. The next day they were transferred to fresh and polished Araldite in gelatin capsules overnight at 60 ° C.
LKB ultratome III with a diamond knife was used to cut transverse serial parts of approximately 50 nm thickness. Section bars were generally captured on 75 coated copper mesh Formvar mesh. The parts in the head region, where most of the nervous system is located, were captured on the meshes of the openings, where it was found necessary that each section is present in this region for successful reconstructions. The networks were stained with a 5% aqueous solution of uranyl acetate for 10 minutes at 60 ° C, then with lead citrate for 5 minutes at room temperature according to the Reynolds procedure (1963).
Sections were imaged on a truncated film using an AEI 6B or AEI 802 electron microscope. Most of the reconstructions were done directly from microscopic prints of the nervous tissue. In the neural ring region, quad montages were necessary. In other regions, individual publications were sufficient. Each section is imaged in the neural ring region and other areas of dense nerves: images of each third section are usually sufficient to pack the following process. Some computer-aided reconstruction system has been used by White (1974) and Stevens & White (1979), but most rebuilds have been done manually from a total of around 8,000 prints.
Small groups of operations were given arbitrary labels, which were written on the literature using Rotring pens. These stickers were moved through all the images for which the associated operations were present, and this action was repeated until all process profiles were tagged. The processes can then be linked to other processes in which the branches occurred, or ultimately they are assigned to specific neurons if their cellular bodies are within the scope of the reconstruction. When all tags were finished, each process was followed separately by each section that appeared in it, and a list of all the synoptic contacts she made was compiled. In this way, all synaptic contacts were recorded twice, once for each member in a pair of interacting processes. This provided a useful check on logging, as any networked contacts recorded only once were reassessed.
Rebuilt gradually with data from five overlapping chains. These were rated N2T, N2U, JSH, N2Y, and JSE (Figure A1, Appendix 1). The structure was found to be sufficiently stable for the equivalent processes and cellular objects to be identified in the interference region of two series. The N2T series was the first extended chain to be cut in the head; Reconstruction of the head sense described by Ward et al. (1975) based on this series.
Although this chain extended through the nerve ring to the abdominal cord, networked networks were used and it was found that the loss of the inevitable cross-section, by blocking it by the network rods, allowed the only limited reconstruction of these regions. The N2U series of Old Shemale presented good quality photos. It was divided into aperture networks through the neural ring and the anterior ventral cord and a complete reconstruction of this area were obtained. This series also covered more than half of the animal's body length and enabled the front and back dorsal cords to be rebuilt. The JSH animal was the fourth stage larva (L4), which was divided into the mesh of the apertures.
Complete reconstruction of the nervous system in the neural ring and anterior ventral cord was obtained from this animal.
This allowed the validation of the structure inferred from the N2U chain in these areas, which is more difficult to reconstruct because it contains a dense neurotransmitter with several processes approaching the level of the partition. Some significant differences in the structure were seen that could be related to age between N2U and JSH series. The tail nodes, some posterior abdominal cord, and back were covered in JSE reconstruction. The area between the front end of the JSE series and the back end of the N2U series in Shemale has not been reconstructed. A long intervening chain from both ends, called N2Y, was obtained from a male animal (Sulston et al. 1980, which is referred to as Series 4). Motor neurons in the abdominal cord and cells are reconstructed from the posterior lateral ganglion of this animal.
Motor neurons (with the exception of the sex-specific VCn class) mainly exhibited the same synaptic behavior as their frontal anal counterparts in a hermaphrodite. Since there is no reason to expect any gender differences in the cells of the posterior lateral nodes, this data has been combined to enable a complete reconstruction of the entire nervous system. The described structure is a compound derived from all series except JSH.
Reliability of data
The biggest problem encountered during the rebuilding work was the location of the errors. The errors are generally made in one of three ways. (1) Human error was the most common, which would have occurred when long process packets without distinctive features were followed which usually led to a change in process labels. (2) Many processes operate near the partition level near the nerve ring, which indirectly cuts the membranes of these processes and produces blurred images. This made identifying the process very difficult in such situations, resulting in the second source of errors. (3) Similar process identification errors also occurred in areas of poor image quality due to dirt on partitions or loss of partitions on network bars although this was the least common source of errors.
Errors are generally manifested in the emergence of an unlikely structure, such as a process that has been linked to more than one cell body or, on the contrary, has not been attached to anything at all. Much of the nervous system was found to be bilaterally symmetrical. Some sensory receptors in the head have higher levels of symmetry. Any deviations seen from the expected symmetries were considered suspicious. Errors were identified either by thorough research of each section containing the process involved or by looking at the reconstruction of interruptions in synaptic behavior, then closely examining the areas of the process in which the interruptions occurred. In this way, a complete and self-consistent structure is built. Structures in major neurological areas have been validated through separate reconstructions. JSH series in case of the neural ring and N2S series in case of the abdominal cord. Hall has independently rebuilt the tail nodes. The structure that he describes is basically the same structure that we describe here.
We are reasonably confident that the structure we provide is largely correct and provides a reasonable picture of the nervous system regulation in the C. elegans hermaphrodite model. It is possible that when creating a structure for this complexity some small errors have been crept into, but we feel that these errors may be very limited due to the amount of mutual verification performed. However, there are still a few minor mysteries, which require a lot of effort to get rid of it. These are described in Appendix 2.
Nomenclature
We have adopted a standardized system of nomenclature to designate neurons and cells associated with C. elegans. Unfortunately, it has not been possible to make such a system compatible with the various labels used to date. Annex 3 lists the equations between these systems and those used in this study. Neurons are given random names consisting of three capital letters. Alternatively, the last letter can be a number up to two numbers. Additional symmetry descriptors are added to the name in cases of groups of cells in the same class that is related to each other by simple engineering symmetry. These descriptors are D or V (dorsal or ventral) and L or R (left or right). A group of hexagonal symmetry cells, such as IL1, contains its members: IL1DL, IL1DR, IL1L, IL1R, IL1VL, and IL1VR. Members of the categories of the motor nerve of the abdominal cord do not have these symmetrical relationships with each other. In these cases, the third number of the class name is a number, representing the anterior or posterior location of neurons relative to fellow class members; For example, VA3 is the third motor nerve. The use of a three-letter name without descriptors refers to all class members if there is more than one letter. For motor neurons, the lowercase n is used to represent the general name of all class members (for example, VAn). A slight modification of this system is used to describe sensory-linked cells, i.e. sheath and socket cells. The sheath cell is designated by the "sh" and the "so" socket cell. Thus in the case of the vertical sensory in the lower right back, the neuron is referred to as the CEPDR, the sheath cell as the CEPshDR, and the socket cell as the CEPsoDR.
General description of C. elegans
Behavior
Animals undergo four larval stages before reaching adulthood: Ll, L2, L3, and L4. Each stage is finished by throwing. If food is scarce, animals can go through an alternative developmental sequence in which a resistant "dower" larvae is produced in L2 to L3. Dauers can survive extreme conditions (dehydration and food deficiency) for long periods until conditions improve and food becomes available, at which time they will melt and become normal adults (Cassada & Russell 1975; Riddle et al. 1981). Several structural changes occur upon entering the dauer stage, including modifications to the ends of some sensory receptors (Albert & Riddle 1983).
Elegans usually inhabit the separations between wet soil particles or in rotting plants. It lives in a film of water and is fixed to solid surfaces by surface tension. Movement is achieved through the dorsal fold of the body, which leads to the spread of the sinusoid wave along the body. This can either be in the front-to-back direction, which leads to the forward movement, or the front-to-forward direction, which gives movement to the back. The head has an additional degree of freedom, in that it can make lateral movements as well as central dorsal movements. Abdominal dorsal flexion (with the posterior sinus position of the body), along with superficial tension forces, restrain the animals from lying on their sides. The L1, gyrate, and adult stages contain longitudinal lateral hills of skin and algae, which may increase lateral friction and reduce lateral slipping. The thickness of the water film is crucial; Too thin or a water film does not result in animals becoming dehydrated and dying, while if the film is greater than its diameter, it is not installed on the surface and cannot make any progress. C. elegans can move well on the surface of agar although this should be completely different from its natural habitat. If there is no food available locally, it will move forward for very long periods with brief breaks from time to time to reflect. When he locates the food he starts eating and stops moving, except for short trips to find food forwards and backward. Eggs tend to lay only when bisexual people have an abundant food supply.
C. elegans responds in a systematic way to a number of sensory stimuli: chemical attraction will lead to a gradient from the chemical attractant or to the bottom gradient of the repellent (Ward 1973; Dusenbery 1974); You will avoid high-priority areas (Culotti & Russell 1978); She will actively maintain herself at an ideal temperature in the temperature gradient (Hedgecock & Russell 1975) and she will respond to a slight touch by moving away from the stimulus point (Chalfie & Sulston 1981). In addition to these responses, the worm is supposed to use its mechanical sensory system to move through the gaps between soil particles in its natural environment. Mating behavior is presented only by the male (Hodgkin 1983), who has additional neural circuits in the tail to control intercourse (Sulston et al. 1980).
Structure
The animal is surrounded by impermeable, rigid, elastic skin, which is placed by a system of underlying subcutaneous cells. The body cavity (the pseudo color) is maintained at a high hydrostatic pressure relative to the outside; This pressure, which works on elastic skin, gives the animal stiffness (the so-called hydrostatic skeleton (Crofton 1966).
There are four longitudinal ridges running inside the body cavity: two midges and two sides. These ridges consist of a chain from the adjacent subcutaneous to a group of neurological processes, the entire structure bordering the base plate. Four streaks of muscle cells in the body move between four of these longitudinal ridges. Muscle cells do not have clear attachment points on either end and may have subcutaneous attachments distributed along their length. It flexibly deforms the skin against the pressure from swelling pressure.
Food is pumped to the animal and treated with the prominent pharynx. This device is almost self-contained with its muscles, epithelium, and nervous system, and has been described in detail by Albertson & Thomson (1976). Pharynx may function as a largely independent unit, although there are two neurons that originate in and enter the central nervous system. These neurons (RIP) are exclusive after the synapse outside the throat and thus may mediate overall control of pharyngeal pumping from the central nervous system. The pharynx is used to ingest food (usually bacteria), concentrate it by filtering and then grinding it, and possibly also to secrete digestive enzymes from gland cells (Albertson & Thomson 1976). The treated food is pumped into the intestine, which contains a microvilli cavity. The intestine is associated with the anus. Defecation is controlled by three groups of specialized muscles (Figure 12).
There is an output system, consisting of a single channel cell arranged in an "H" configuration (Bird 1971). The Harms operate longitudinally down the sidelines. It is connected to a cross-bridge connected to the excretory duct on the ventral side; This opens outward from the animal through the excretory pores on the ventral midline. Two centrally located "glandular" cells have forward-directed processes, which merge and communicate with the lumen of the excretory duct near the follicles (Nelson et al. 1983). These processes continue to run forward on the ventral surface of the ventral nerve cord (Figure 16) until the nerve ring is reached, where it ends. The function of these glands is not yet known.
The adult sexual reproductive system consists of symmetrical pairs of the uterus, egg ducts, sperms, and ovaries, which are attached to the uterus and connected to the vulva. This is located on the ventral midline midway below the body (Hirsh et al. 1976). During development, sperms are produced before eggs and are stored for later use. The positioning of the oocytes mediates a group of sixteen muscle cells, eight of which act to press the contents of the uterus and eight to open the vulva opening (Figure 11).
The male's gonads join the rectum over the vas deferens to form a mantle in the tail (Sulston et al. 1980). The cloak is surrounded by a large fan-like pod, which is rich in sensual ends. These ends are derived from male neurons, which are created after the fetus with other male neurons. The male also has extra abdominal muscles and additional abdominal muscles that control the island particles (Solston et al. 1980).
Regulation of the nervous system and muscles
This number is fixed among animals. Each neuron has a unique mixture of properties, such as morphology, conduction, and positioning, so each neuron can be given a unique label. Only groups of neurons that differ from one another are designated in the positions of the groups. There are 118 classes performed using these criteria, and row sizes range from 1 to 13. Thus, elegans have a rich variety of neuron types although they only have a small, total group of neurons. This is in sharp contrast to structures such as the mammal cerebellum, which contains more than 1,010 neurons (Braitenberg & Atwood 1958) and still contains only five categories of component neurons (Eccles et al. 1967).
Sensory transduction
The largest part of the nervous system of C. elegans is located in the head and is rich in sensory receptors. These are arranged in groups of sensory organs, known as Sensilla. The arrangement and structure of Sensilla are described in detail (Ward et al. 1975; Ware et al. 1975; Wright 1980). Each sensor contains one or a number of ciliary nerve endings and two non-neuronal cells: the sheath cell and the socket cells. The receptor cell is an effective cell between the face that connects the senses under the skin. The glandular cell is a glial-like cell that encapsulates the ends of nerve cells. Its inner surface, adjacent to nerve dendrite, is widely spread and often a large number of secretory-like vesicles are found in the cytoplasm. In addition, the cells of the vertical sensory glanders contain flat plate-like processes that partially envelop the nerve of the nerve ring, and the front ends of the ventral cord (Figure 16). The function of the sheath cells is unknown, but it may create a specific extracellular environment for receptor ends.There are two large sensors, pamphlets, sideways, and have internal channels, consisting of sheath and socket cells, which open through the epidermis to the outside. Eight of the neurons have fringed ends in this channel; Another four are attached to the sheath cell. There are two identical structures, the phases of the phases, in the tail, but they are simpler in that they only have nerves that end up in the canal. Amphids and phases are generally considered the main chemically received organs in an animal because their structure allows a group of nerve endings to be exposed to the external environment of an animal.
The other sensory in the head is arranged in two concentric rings around the mouth (Figure 1). There is an inner ring of six, the inner oral sensory, each with two associated neurons (IL1 and IL2). The bifurcations of IL2 penetrate the epidermis out of the animal and thus can be chemical receptors. The other end (ILl) is in the skin. There is an outer ring composed of four sensors, the outer quadriceps (OLQ), and paired with another set of four, the vertical sensory (CEP). There are two side lateral recovery sensors (OLL) next to the amphibious channel openings. The only other sensual in the effeminate is a pair of lateral senses, degrees, located laterally in the anterior body (ADE) and the posterior body (PDE). These sensors have a morphology similar to the vertical sensory in the head (Ward et al. 1975)
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Figure 1. The sensory receptors in the head, as shown in an ideal section near the tip of the head. This region is rich in sensory receptors, which are organized in a delicate and complex arrangement. Most receptors are sensory components that have sheathed cells and a socket. Amphibious senses are found in the lateral blades and have open channels outside with entry to ADL, ADF, ASG, ASH, ASE, ASI, ASJ, and ASK. AWA, AWB, AWC, and AFD bind to alfalfa sheath cells. There is one inner oral sensory in each labe, containing IL1 and IL2 receptor neurons. These sensors also have channels outside, through which the IL2 project is performed. Dorsal labia and ventral labia each have one vertical sensation with a CEP receptor, and one external oral sensory with an OLQ receptor. Both side blades also have an external oral sensory but with an OLL receptor. FLP and BAG are free fringed receptors inside the head that are not part of the sensory. URX and URY are not threatened but have flat ends, which insinuate themselves around the inner and outer verbal senses. (See Figure 1 in color.)
In addition to sensory neurons, there are other classes of neurons, which, based on their connection and formation, may also serve the function of sensory conversion. The best-known neurons of this type are ALM, PLM, AVM, and PVM touch receptors. These have specialized processes full of microtubules, which operate in a position close to the skin (Chalfie & Sulston 1981).
Getting rid of cell bodies and nodes
Several nodes have been described and named in the nervous system of other nematodes (Chitwood & Chitwood 1974). We have retained these names, where applicable, for the contract in C. elegans. In many regions, cells are grouped together into well-defined nodes by arranging the basal plate in a false pseudomembrane. This sometimes divides adjacent cells into different nodes. The lateral and ventral ganglia are not clearly separated in Figure 2, for example, but in fact, the ventral ganglion cells are a well-defined group (Figure 3), separated from the adjacent lateral ganglia by two basal plates (Figure 13). The arrangement of the basal plate about a false pseudo will be discussed later; We will now describe the behavior of the various nodes.
Figure 3. View of the central node. Abdominal ganglion cells are bound by basal plates that separate them from the side ganglion cells although they are contiguous (Figure 2). The posterior region of the node is interrupted due to the presence of the excretory canal and excretory duct cells, which exclude the neuronal bodies from this region. VB2, AVFR, and SABVL are part of the retro liposome node and are separated from the abdominal ganglion cells by the basal plate. All abdominal ganglion cells are legitimate in the neural ring, and many cell categories also have members of lateral ganglia.
Most neurons in C. elegans have their own cell bodies located in the head around the pharynx (Figure 2). The pharynx consists of two prominent lamps that link them to the isthmus. A wide nervous region, the pharyngeal nerve ring, encircles the central region of the isthmus and the cells of the adjacent cells gather front and back. There are no clear subgroups of neuronal bodies in front of the annulus and thus are grouped together and indicated by the anterior node. The front node is mainly composed of a neuronal, casing, and sensory-cellular bodies located in the six labia majora (Figure 1). The relative locations of cell bodies within the ganglia are well preserved somewhat between animals in the same growth stage and genotype. However, there is a certain amount of `` slop ''; The extent of this can be seen by comparing the left and right sides shown in Figure 2. The most extreme cases of change arise in this region because the pharyngeal front bulb fits perfectly into the body cavity and excludes cell bodies from its maximum diameter region. This leads to some uncertainty in the positioning of some cell bodies in relation to the bulb; For example, in N2U reconstruction, OLQsoDL is located in front of the lamp, while its symmetrical partner, OLQsoDR, is located behind the lamp (Figure 2). In live animals, cells can sometimes be seen turning from one side of the headlight to the other side as the pharynx moves.
After the neural ring, the basal plate divides the cell bodies surrounding the annulus into four groups (Figure 13): a small dorsal knot, two side nodes, and an abdominal ganglion (Figure 3). All amphibian sensory neurons have their own cellular bodies in the lateral nodes, which also contain the inner motor and neuronal neuron bodies. The dorsal ganglion contains neurons with the dorsal sensory dorsal neurons. The abdominal ganglion contains motor neurons and motor neurons. The cellular bodies of the ventral node are separated into two groups (Figure 3) by mechanical infiltration, as well as the cells of the front node. In this case, it is the duct and the excretory channel that replace the cells.
The posterior ends of the ventral node overlap with the anterior segment of the dorsal node, which is located on the posterior ventral midline of the secreted pore (Figure 2); However, the two cell groups are distinct and are separated by the basal plate. One row of cell bodies extends to the ventral midline (Figure 4) from the retro vesicular node to the tail, where it ends in another node, the pre-anal node. There are three additional nodes in the tail: two laterally symmetrical cotton nodes and one small dorsal straight node (Figure 5). There is a pair of small lateral ganglia in the posterior body, posterior lateral ganglia, and there are some isolated cells along the body laterally (Figure 4).
Figure 4. Cellular body locations of all neurons and associated cells in the body appear on the left side (a), the right side (b), and the middle (c). These diagrams are derived from optical microscope observations (Sulston & Horvitz 1977). Asymmetry in SDQL / R, AVM, and PVM sites is the result of different relay patterns for two-way symmetric QL and QR precursor cells. The nerve cells of the ventral cord shown in (C) can be separated into those when hatching, which appears through the stickers on the right, and those that develop after the membrane, as shown on the stickers on the left. The anterior and posterior sequences of cell types in these two groups are always the same, but there is some slight difference in the way the two groups overlap, which gives some difference in the common adult sequence.
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