Nerve cord

Definition

A longitudinal bundle of nerve fibers running along the body axis, serving as the central nervous system trunk in bilaterian animals. In arthropods and most other protostome invertebrates, it is a ventral nerve cord (paired or fused) with segmental ganglia; in chordates, it is a dorsal, hollow nerve cord that develops into the spinal cord.

Etymology

From Latin nervus (sinew, nerve) and chorda (cord, string).

Example

In a grasshopper, the ventral nerve cord runs beneath the gut and connects a chain of segmental ganglia; the brain in the head sends descending signals through this cord to coordinate walking and jumping.

Related Terms

• Ventral nerve cord
• dorsal nerve cord
• ganglion
• Central nervous system
• connective
• commissure
• neuroanatomy

Usage Notes

The position—ventral versus dorsal—is phylogenetically diagnostic: ventral nerve cords characterize protostomes (including insects, arachnids, crustaceans, and annelids), while dorsal nerve cords characterize deuterostomes (including vertebrates). Arthropod nerve cords are typically paired and linked by transverse commissures, often appearing fused in higher insects. The term is sometimes used loosely for any major longitudinal nerve tract, but specialists reserve it for the primary central axis.