Protocerebrum

About 80% of the animal world belongs to the phylum Arthropod on planet earth. Arthropods are very diverse and complex since most body parts are segmented. Jointed limbs in segments, the presence of an exoskeleton (composed of chitin and sclerotin) are some of their unique features. The nervous system of the arthropods is divided into many compartments making it very complex. The nervous system of arthropods consists of neurons as present in other vertebrates’ nervous systems. Thus it seems that the nervous system of arthropods possesses many similar features to that of a vertebrate’s nervous system. Majorly the brain of the arthropods is divided into three different segments, which are named as follows: Protocerebrum, deutocerebrum, and tritocerebrum.

Nervous System in Arthropods

The structural and physiological development of the brains of the different species of arthropods subclasses has been investigated based on their homologies. The brain of an arthropod plays an essential function in the assimilation of sensory information to select the appropriate response, properly process it and mark it to the brain, and send it downstream. The head (dorsally) constitutes the brain of the arthropods. The head consists of three pairs of ganglia: the protocerebrum, the deutocerebrum, and the tritocerebrum.   

Let’s have a brief look at each of them:

1. Protocerebrum

• Protocerebrum is the brain segment located dorsally and anteriorly and immediately after the deutocerebrum segment of the brain of the Arthropoda. 

• There exists a dorsal bend near the oesophagus at the tritocerebrum in the central nervous system of the arthropods. 

• All three segments (protocerebrum, deutocerebrum, and tritocerebrum) form the cerebrum, which is the brain of the arthropods. 

• The location of the protocerebrum is immediately dorsal to the fused subesophageal section of the synganglion due to the dorsal bend. 

• In the case of Arthropoda, synganglion is formed by the neuromeres and four walking legs. The protocerebrum segment innervates structures such as the eyes. It controls the vision of arthropods. 

• The anterior part of the protocerebrum is mainly connected with the nerves of the eyes. 

• This segment also received nerves from the other organs, or neutrophils (controls anterior sense organs such as eyes and controls their movement), centres such as optic centres (other centres for managing the complex behaviours), and bodies (corpora pedunculata). 

• The ventral medial protocerebrum is located ventrally and innervates nerve cells in the brain segment’s medial region, which plays a vital function in controlling vision in the brain of the arthropods.  

2. Deutocerebrum

• The deutocerebrum segment in the brain of the arthropods gives rise to the nerves that innervate the structure that is antennae. 

• It controls the antennae signals, which control the chemosensation and tactile sensation in the brain. 

3. Tritocerebrum

• The tritocerebrum segment in the brain of the arthropods is similar to the vertebrate autonomic system since it integrates signals from the protocerebrum to the deutocerebrum. 

• It constitutes the stomatogastric system, which helps regulate the food intake and controls the gut movements, which are responsible for the digestion in the body of the arthropods. 

• Given this, it is apparent that the tritocerebrum innervates the nerves connected with the mouth and the digestive canal of the nervous system. 

Protocerebrum meaning: In general, there are different levels of the fusion of the ganglia in the nervous system in arthropods. Further, regarding the sensory receptors in the brain of the arthropods, there are various receptors such as cuticle hairs. At the base of the antennas, many sensory cells and organs are concentrated, e.g. statocyst.

In the nervous system of the anthropoids, the neurosecretory cells are developed to the highest degree. The protocerebrum segment of the brain of the arthropods is composed of these neurosecretory cells that innervate the structure, which is called corpora cardiaca, and this is situated posterior to the brain. These neurosecretory cells of the protocerebrum release a hormone named ecdysiotripin, or the brain hormone. This hormone is regulated by the nerve impulses that are generated from the brain to the nerve endings in the blood to the corpora cardiaca structure. It acts to stimulate the ecdysial gland. This is a non-endocrine gland and is situated in the thorax. 

Conclusion 

Given the detailed description, we may conclude that the nervous system of the arthropods, such as the grasshopper, is complex due to its division into different segments, which have different roles and functions to play. The brain is divided into specialised segments based on its controlling capacity. The protocerebrum is the segment that lies immediately after the deutocerebrum segment, and its important function is that it innervates the nerve cells which are involved in controlling vision in arthropods. The second segment is the deutocerebrum which innervates the nerve cells and helps in processing the signals coming from the antenna signals. Thirdly the tritocerebrum part involves the nerves that innervate from the mouth section and controls the mouthparts and the anterior digestive canal. It also constitutes the stomatogastric system which controls the digestive system in the arthropods.