Nervous System

The nervous system of the cockroach is ventral in position (it runs along the underside of the body, opposite to the dorsal blood vessel), solid, and ganglionated — meaning it is organised as a chain of nerve-cell clusters called ganglia connected by nerve cords, rather than as a single continuous brain-and-spinal-cord as in vertebrates. It has three functional parts: the Central Nervous System (CNS), the Peripheral Nervous System (PNS) and the Autonomous Nervous System (ANS).

A. Central Nervous System (CNS). The CNS consists of a nerve ring in the head plus the ventral nerve cord running the length of the body.

The nerve ring is built from the supra-oesophageal ganglia, a connecting circum-oesophageal connective, and the sub-oesophageal ganglion. The paired supra-oesophageal (cerebral) ganglia lie above the oesophagus, between the bases of the antennae, and together they are known as the brain. Each cerebral ganglion is itself formed by the fusion of three smaller ganglia — the protocerebrum, deutocerebrum and tritocerebrum. Below the oesophagus lies the bilobed sub-oesophageal ganglion, likewise formed from the fusion of three pairs of smaller ganglia. A pair of lateral nerves called the circum-oesophageal connectives link the cerebral ganglia above to the sub-oesophageal ganglion below, effectively forming a ring around the oesophagus.

From the sub-oesophageal ganglion arises the ventral nerve cord (VNC), which runs along the mid-ventral line within the perineural sinus. It is a double cord made up of nine pairs of segmental ganglia in total. The first three pairs, one in each thoracic segment, are relatively large and are called the thoracic ganglia. The remaining six pairs lie in the abdomen; the sixth abdominal ganglion is the largest of all and sits in the seventh abdominal segment (there is no separate ganglion in the sixth segment itself, since some ganglia have fused during development).

B. Peripheral Nervous System (PNS). The PNS is made up of the nerves that branch outward from the various ganglia of the CNS to reach the sense organs and muscles. Six pairs of nerves leave the cerebral ganglia and travel to the eyes, antennae and labrum. Nerves leaving the sub-oesophageal ganglion go to the mandibles, maxillae and labium. Nerves from the thoracic ganglia supply the wings, legs and the internal organs of the thorax. Nerves from each abdominal ganglion supply the organs of that particular abdominal segment.

C. Autonomous Nervous System (ANS). This consists of four small ganglia together with a retrocerebral complex, regulating internal organs such as the gut somewhat independently of the main nerve cord:

1. Frontal ganglion — lies above the pharynx, in front of the brain.
2. Hypocerebral ganglion — lies on the front (anterior) part of the oesophagus.
3. Ingluvial ganglion (also called the visceral ganglion) — lies on the crop.
4. Ventricular ganglion — lies on the gizzard. …