The Ventral Nerve Cord

The kingdom Animalia developed from the phylum Porifera, which involves sponges. The nervous system is not differentiated in such a manner in invertebrates. Invertebrates include the phylum Porifera to the phylum Echinodermata. Invertebrates possess the ventral nerve cord. The ventral nerve cord has two ganglia connected to the brain to coordinate neural signals. The ventral cervical cord is part of the nerve cord in the cervical region. Some features fundamentally characterize animals that are included in chordates. These features are the presence of a dorsal hollow nerve cord and notochord, pharyngeal gill slits. 

The Ventral Nerve Cord

The ventral nerve cord is in the central region of the body and runs throughout the ventral plane of the body. There are different ascending neurons present to import stimuli to the brain in the form of information. In the same way, different descending neurons are also present to impart or convey the message or the responses from the brain to the body.

Three different types of such neurons are mentioned below: 

• Sensory neuron: It receives and imports the information to the brain from the body, environment, or stimuli.

• Motor neuron: It imparts response of that stimulus from the brain.

• Interneurons: This type of neuron maintains coordination between the sensory and motor neuron.

Where Is The Ventral Nerve Cord Present?

The ventral nerve cord is found in invertebrates as there is no dorsal nerve cord present. The dorsal nerve cord is present in higher animals, hemichordates also possess a nerve cord, but it is a stomochord.

Hemichordata (Half chordate) are thought to be chordates as they have a rod-like structure that looks like a notochord. But, later, it was found that this rod is not solid but rather hollow and not mesodermal, rather ectodermal, which means it is not notochord. Rather, it is a stomochord, not an invertebrate or vertebrate. It is excluded from Chordata and put into non-chordate as a separate species. Yet Invertebrates first develop the nervous system; the brain is represented by one pair of cerebral ganglia, which looks ladder-shaped.

Anatomy Of The Ventral Nerve Cord 

The neural system consists of an excitable cell that can detect, receive and transmit the stimuli (change in environment) but can’t produce stimuli.

The neural system has two divisions

CNS (central nervous system): It includes the brain and spinal cord. These are the sites for information processing and control.

PNS (Peripheral nervous system): It includes all the body’s nerves associated with CNS, which are the cranial nerve + spinal nerve. 

The nerve fibre of the peripheral nervous system are of two types:

• Sensory or afferent nerve fibres

• Motor or different nerve fibres

Sensory nerve fibres are which bring sensory impulses from organs to CNS. Motor nerve fibres are which take motor impulses from CNS to different organs.

PNS have further two divisions

Somatic neural system (SNS): It controls and regulates the functions of voluntary organs (skeletal muscle).

Autonomic neural system (ANS): It controls and regulates the function of involuntary organs or involuntary muscles. 

This ANS is further divided into sympathetic and parasympathetic. The sympathetic & parasympathetic nervous systems both have three components: 

• Sympathetic chain

• Postganglionic nerve fiber

• Preganglionic nerve fiber

Both the nervous system has some differences in these three components.

The ventral nerve cord in the head region includes subesophageal ganglion. Through circumesophageal connectives, it is connected to the brain. A pair of circumesophageal connectives links the head and the subesophageal ganglion, and connectives lie between adjacent ganglia.

The ventral nerve cord in earthworm

The nervous system of earthworm (Annelida) has one pair, solid the ventral nerve cord with segments arranged ganglia.

In the fourth segment near the ventral cervical cord, the nerve cord is bifurcated and joins above the third segment with cerebral ganglia or supra pharyngeal ganglia. It forms a ring around the pharynx.

The ventral nerve cord in cockroach 

Having one pair of solid, the ventral nerve cord with segments arranged ganglia are nine in number. Three of them are thoracic, and six of them are in the abdominal region. Supraesophageal ganglia are called BRAIN. It gives nerve to the antenna and the compound eye. A very little part of the central nervous system is present in the head region, and that’s why cockroaches can survive for a week even after cutting the head. The head comprising a little part of it makes him sustainable, with the rest present in the thoracic and abdominal region.

Conclusion

Here in this article, you learned about the ventral nerve cord. The ventral cervical cord is part of the nerve cord in the neck region. After concluding the scientific fact and the anatomy of the nervous system, a very clear-cut configuration comes out that the ventral nerve cord is part of the invertebrate nervous system with less specialization. In contrast, the dorsal spinal cord is characteristic of vertebrates, with the specialized brain in the case of chordate (Mammalia).