Nervous system

Definition

The integrated network of neurons, ganglia, and nerves that coordinates sensory input, motor output, and internal physiological regulation in an organism. In arthropods, the nervous system is organized as a ventral nerve cord with segmental ganglia rather than a dorsal spinal cord; the brain (supraesophageal ganglion) and subesophageal ganglion integrate information from compound eyes, ocelli, antennae, mechanoreceptors, and chemoreceptors to control locomotion, feeding, and escape responses. The system works in concert with neurosecretory cells and the endocrine system to mediate rapid behavioral and developmental changes.

Etymology

Latin nervus (sinew, tendon, nerve) + systema (organized whole)

Example

In the American cockroach (Periplaneta americana), the ventral nerve cord contains a chain of thoracic and abdominal ganglia that allow rapid escape responses: a wind stimulus detected by cercal hairs activates giant interneurons that synapse directly on leg motor neurons, producing a startle turn in 20–50 milliseconds without brain involvement.

Related Terms

• ganglion
• Ventral nerve cord
• supraesophageal ganglion
• compound eye
• mechanoreceptor
• Chemoreceptor
• neurosecretory cell
• blood-brain barrier
• Synapse
• Axon

Usage Notes

Arthropod nervous systems differ markedly from vertebrate architecture: they lack myelin sheaths, rely more heavily on graded synaptic transmission, and exhibit extensive local processing in segmental ganglia that permits reflexes independent of the brain. 'Central nervous system' in insects typically refers to the brain and ventral nerve cord together, while 'peripheral nervous system' encompasses sensory neurons and motor nerves extending to muscles and sensory structures. The stomatogastric nervous system (including the frontal, hypocerebral, and ingluvial ganglia) controls foregut and midgut function and is sometimes treated separately from the main central system. When describing neurotoxic insecticides, specificity matters: pyrethroids target voltage-gated sodium channels throughout the nervous system, while neonicotinoids act selectively on nicotinic acetylcholine receptors concentrated in the brain and ganglia.