Fundamentals of Entomology

ANATOMY: NERVOUS SYSTEM

NERVOUS SYSTEM

 
• To view the ventral nerve cord, examine the ventral region of the roach’s body cavity (or specimen you performed the dorsal dissection on) for something that resembles a railroad track running from the head posteriorly to the abdominal region. The “railroad track” is made up of two nerve cords (connectives) that run longitudinally with a series of node-like ganglia.
• The anterior most region of the ventral nerve cord is called the subesophageal ganglion. Just dorsal to that structure is the insect “brain” (or supraesophageal ganglion).

• The basic component in the nervous system is the nerve cell or neuron, composed of a cell body with two projections (fibers) the dendrites that receive stimuli and the axon that transmits information, either to another neuron or to an effector organ such as a muscle. Axon may have lateral branches called Collateral and terminal arborization and synapse. Insect neurons release a variety of chemicals at synapses either to stimulate or to inhibit effector neurons or muscles. Acetylcholine and catecholamines such as dopamine are the important neurotransmitters involved in the impulse conduction. Neurons are of following types based on structure and function.
A. On structural basis
Monopolar: neuron with a single axon
Bipolar: neuron with a proximal axon and a long distal dendrite.
Multipolar: neuron with a proximal axon and many distal dendrites.
B. Functional basis
Sensory neuron: It conducts impulse from sense organs to central nervous system (CNS).
Motor neuron: It conducts impulse from CNS to effector organs
Inter neuron (association neuron): It inter-links sensory and motor neurons.
• The cell bodies of inter neurons and motor neurons are aggregated with the fibers inter connecting all types of nerve cells to form nerve centers called ganglia.

Nervous system