Word Finder - ganglia

definition

An encapsulated collection of nerve-cell bodies, located outside the brain and spinal cord.

definition

Any of certain masses of gray matter in the brain, as the basal ganglia.

definition

(by extension) A centre of intellectual or industrial force, activity, etc.

definition

A cystic tumour on a tendon sheath or joint capsule; a ganglion cyst.

The eyes are indicated as black dots behind the cerebral ganglia.

In the region of the neck lateral strands pass through the transverse canal of the cervical vertebrae; but from the thoracic region onwards, where the cardiac branch to the heart is given off, each strand is double and the basal ganglia are successively connected with the next by a branch which runs ventrally over the capitulum of the rib, and by another which passes directly through the foramen or space formed between capitulum and tuberculum.

The nervous system is remarkably concentrated in some beetles, the abdominal ganglia showing a tendency to become shifted forward and crowded together, and in certain chafers all the thoracic and abdominal ganglia are fused into a single nervecentre situated in the thorax, - a degree of specialization only matched in the insectan class among the Hemiptera and some muscid flies.

In all Chaetopods this system consists of cerebral ganglia connected by a circumoesophageal commissure with a ventral ganglionated cord.

The cerebral ganglia constitute an archicerebrum for the most part, there being no evidence that, as in the Arthropoda, a movement forward of post-oral ganglia has taken place.

In the latter, the segmentally arranged ganglia are more sharply marked off from the connectives than in other Chaetopods, where nerve cells exist along the whole ventral chain, though more numerous in segmentally disposed swellings.

The nervous system is embedded in the epidermis, and the pairs of ganglia are separated as in Serpula, &c.; each pair has a longish commissure between its two ganglia.

The ganglia are crowded at the posterior end of the body as in leeches, and there is much tendency to the obliteration of the coelom as in that group. Pterodrilus and Cirrodrilus bear a few, or circles of, external processes which may be branchiae; Bdellodrilus and Astacobdella have none.

The most reliable test appears to be the nerve ganglia, which are more distinct from the intervening connectives than in other Annelids.

In the middle of the body, where the limits of the somites can be checked by a comparison with the arrangement of the nephridia and the gonads, and where the ganglia are quite distinct and separated by long connectives, each ganglion is seen to consist of six masses of cells enclosed by capsules and to give off three nerves on each side.

An teriorly and posteriorly separate ganglia have fused.

The brain con sists not only of a group of six capsules corre sponding to the archi cerebrum of the Oligo chaeta, but of a further mass of cells surrounding S S and existing below the alimentary canal, which can be analysed into five or six more separate ganglia.

So that a leech in which only twenty-seven segments are apparent by the enumeration of the annuli, separate ganglia, nephridia, lines of sensillae upon the body, really possesses an additional seven lying behind that which is apparently the last of the series and crowded together into a minute space.

Each renal organ is a sac lined with glandular epithelium (ciliated cell, with concretions) communicating with the exterior by its papilla, and by ce, Cerebral ganglia.

On the whole the ganglia are strongly individualized in the Pectinibranchia, nerve-cell tissue being concentrated in the ganglia and absent from the cords.

The euthyneurous visceral loop is long, and presents only one ganglion (in Aplysia camelus, but two distinct ganglia joined to one another in Aplysia hybrida of the English coast), placed at its extreme limit, representing both the right and left visceral ganglia and the third or abdominal ganglion, which are so often separately present.

Such special irregularities in the development of ganglia upon the visceral loop, and on one or more of the main nerves connected with it, are very frequent.

Our figure of the nervous system of Aplysia does not give the small pair of buccal ganglia which are, as in all glossophorous Molluscs, present upon the nerves passing from the cerebral region to the odontophore.

T h e buccal nerves and ganglia are omitted.

It flattens out short visceral " loop " with its three ganglia and disappears before is lightly-shaded.

The brain innervates the eyes and feelers, and must be regarded as a " syncerebrum " representing the ganglia of the three foremost limb-bearing somites united with the primitive cephalic lobes.

The legs, wings and other organs of the trunk receive their nerves from the thoracic and abdominal ganglia, and the fusion of several pairs of these ganglia may be regarded as corresponding to a centralization of individuality.

A The ganglia of the nervous _ Tre system offer some important evidence as to the morphology of the head, and are alluded to below.

The continuous layer of cells from which the nervous system is developed undergoes a segmentation analogous with that we have described as occurring in the ventral plate; there is thus formed a pair of contiguous ganglia for each segment of the body, but there is no ganglion for the telson.

The ganglia become greatly changed in position during the later life, and it is usually said that there are only ten pairs of abdominal ganglia even in the embryo.

But the protocerebrum contains the ganglia of the ocular segment in addition to those of the procephalic lobes.

There are other ganglia in addition to those of the ventral chain, and Janet supposes that the ganglia of the sympathetic system indicate the existence of three anterior head-segments; the remains of the segments themselves are, in accordance with this view, to be sought in the XIII.

There are large lacunae in the head in front of the ganglia.

Laterally, the sub-oesophageal ganglia give off (v.) nerves to the ventral mantle, and finally they supply (vi.) branches to the various muscles.

From each of these sub-oesophageal ganglia numerous nerves arise.

The cerebral mass is in Limulus more easily separated by dissection as a median lobe distinct from the laterally placed ganglia of the cheliceral somite than is the case in Scorpio, but the relations are practically the same in the two forms. Formerly it was supposed that in Limulus both the chelicerae and the next following pair of appendages were prosthomerous, as in Crustacea, but the dissections of Alphonse Milne-Edwards (6) demonstrated VI FIG.

The wide divarication of the lateral cords in the prosoma and their connexion by transverse commissures, together with the " attraction " of ganglia to the prosomatic ganglion group which properly belong to hinder segments, are very nearly identical in the two animals.

Lastly the nervous system is well developed and consists of a pair of well-marked and interconnected ganglia placed near the anterior end and dorsal to the oesophagus.

From these ganglia, nerve-tracts provided with ganglion-cells are given off.

The prey is sometimes stung in the neighbourhood of the nerve ganglia, so that it is paralysed but not killed, the grub of the fossorial wasp devouring its victim alive; but this instinct varies in perfection, and in many cases the larva flourishes equally whether its prey be killed or not.

No organs of circulation or respiration are known; but the nervous system is well developed, and consists of a pair of ganglia corresponding with the limbs and connected by longitudinal commissural chords.

Posteriorly beneath the posterior adductors, and covered only by a thin layer of elongated epidermal cells, are the visceral ganglia.

United with these ganglia on the outer sides are the osphradial ganglia, above which the epithelium is modified to form a pair of sense-organs, corresponding to the osphradia of other Molluscs.

In some Lamellibranchs the osphradial ganglia receive nerve-fibres, not from the visceral ganglia, but from the cerebral ganglia along the visceral commissure.

Formerly the posterior pair of ganglia were identified as simply the osphradial ganglia, and the anterior pair as the cerebral, pleural and visceral ganglia united into a single pair.

But it has since been discovered that in the Protobranchia the cerebral ganglia and the pleural are distinct, each giving origin to its own connective which runs to the pedal ganglion.

In them the foot has a flat ventral surface used for creeping, as in Gastropods, the byssus gland is but slightly developed, the pleural ganglia are distinct, there is a relic of the pharyngeal cavity, in some forms with a pair of glandular sacs, the gonads retain their primitive connexion with the renal cavities, and the otocysts are open.

Generally the system is differentiated into ganglia connected by nerve-cords consisting of nerve-fibres only.

At the point of the collar whence the nerve-cords arise are the cerebral ganglia; from these one pair of connectives passes to a pair of pedal ganglia, and another pair of connectives to a pair of pleural ganglia.

There are usually three small ganglia on the course of this visceral commissure, namely, the right and left visceral ganglia and the abdominal.

The perioesophageal nerve-ring of Chaetopoda and Arthropoda is represented, not by the collar first mentioned in the above description, but by the commissures connecting the cerebral and pedal ganglia.

The otocysts are invaginations of the epithelium of the foot, but are innervated from the cerebral ganglia, and the same innervation has been proved in some cases for the osphradia.

The foot has been developed into long processes which have extended in a circle round the mouth; all the ganglia, including the visceral, have been concentrated around the oesophagus.

Later in its action, the drug depresses the intra-cardiac motor ganglia, causing prolongation of diastole and finally arrest of the heart in dilatation.

The nervous system consists of a cerebral ganglion in the head, a conspicuous ventral ganglion in the trunk, and of lateral cornmissures uniting these ganglia on each side.