In this article we will discuss about the central, peripheral and sympathetic nervous system of cockroach.
Central Nervous System of Cockroach:
The central nervous system consists of the supra-oesophageal ganglion or brain, sub- oesophageal ganglion and the nerve cord.
The supra-oesophageal ganglion or cerebral ganglion is a bilobed structure situated in the head in front of oesophagus, above the tentorium and almost between the bases of the antennae. It is formed by the fusion of three pairs of ganglia. It represents the brain and is concerned chiefly with sensory function.
From the supra-oesophageal ganglia arise two circumoesophageal connectives which encircle round the oesophagus and meet below it with the sub-oesophageal ganglion. The sub-oesophageal ganglion is also situated in the head and formed by the fusion of 3 pairs of ganglia.
Thus, the supra-oesophageal ganglion, circumoesophageal connectives and sub- oesophageal ganglion together constitute the nerve ring round the oesophagus in the head capsule. The sub-oesophageal ganglion is the principal motor centre and controls the movements of muscles, mouth parts, wings and legs.
From the sub-oesophageal ganglion arises a double nerve cord which travels through the thorax and abdomen below the alimentary canal on the ventral side up to the posterior end of the body. The nerve-cord has three large ganglia in the thorax, one each for pro-, meso-and metathoracic segments, therefore, they are called prothoracic, mesothoracic and metathoracic ganglia.
Further the nerve cord has six ganglia in the abdomen which lie in the 1st, 2nd, 3rd, 4th, 5th and 7th segments.
Each ganglion of the nerve cord is formed by the fusion of two ganglia except the ganglion in the 7th segment. The ganglion in the 7th abdominal segment is the largest of all the abdominal ganglia and probably formed by the fusion of 3 pairs of ganglia. Both the nerve cords run parallel and very close to each other but unlike earthworm they are not enclosedin a common sheath.
But they are fused only at the place of the presence of ganglion and they are solid.
Peripheral Nervous System of Cockroach:
The nerves originating from the nerve ring and ventral nerve cord to innervate different parts of the body constitute the peripheral nervous system.
Three pairs of nerves originate from the supra-oesophageal ganglion—optic, antennary and labrofrontal nerves. The first two innervate the eyes and antennae but the third one divides into labral nerve supplying to the labrum and the frontal nerve which runs forwards to join the sympathetic nervous system.
Similarly, three pairs of nerves originate from the sub-oesophageal ganglion—mandibular, maxillary and labial to innervate the mandibles, maxillae and labium respectively. Several pairs of nerves arise from each thoracic ganglion to supply the different parts of their own segment.
A pair of nerves, however, from metathoracic ganglion innervates the 1st abdominal segment. The nerves originating from first five abdominal ganglia innervate the 2nd, 3rd, 4th, 5th and 6th abdominal segments. From the last abdominal ganglion three pairs of nerves are given off to supply the 7th, 8th, and 9th segments. It also gives a branch to innervate the cercus and other associated structures.
Sympathetic Nervous System:
The autonomic or stomogastric or sympathetic or visceral nervous system of cockroach consists of some ganglia and their connectives. It includes the frontal, occipital, visceral or ingluvial and pre-ventricular ganglia. The nerves from these ganglia are connected with the supra-oesophageal ganglion.
The frontal ganglion is a small ganglion situated on the oesophagus in front of the supra-oesophageal ganglion. A pair of frontal connectives from the frontal ganglion is connected with the supra-oesophageal ganglion, a median recurrent nerve passes backward from it and connects the occipital or hypo cerebral ganglion behind the supra-oesophageal ganglion.
Three nerves, two lateral and one median originate from the occipital ganglion; the lateral nerves are connected with the corpora cardiaca and corpora allata which are endocrine glands, while the median nerve runs backwards over the oesophagus and joins the visceral ganglion situated on the crop.
From the visceral ganglion a pair supply the alimentary canal, one of them is connected with the pro-ventricular ganglion situated on the gizzard (Fig. 73.27).