Difference Between Notochord and Nerve Cord

Main Difference – Notochord vs Nerve Cord

Notochord and nerve cord are two characteristic features of chordates. Both notochord and nerve cord is from the neck to the tail in the dorsal part of the body. Notochord is a skeletal rod, and nerve cord is a solid strand of nervous tissue. The main difference between notochord and nerve cord is that notochord belongs to the skeleton whereas nerve cord belongs to the central nervous system of chordates. Notochord occurs between the nerve cord and the central nervous system. Nerve cord occurs below the notochord. Notochord provides sites for the attachment of the skeletal muscles. Nerve cord coordinates the functions of the body.

Key Areas Covered

1. What is Notochord
      – Definition, Characteristics, Formation
2. What is Nerve Cord
      – Definition, Characteristics, Formation
3. What are the Similarities Between Notochord and Nerve Cord
      – Outline of Common Features
4. What is the Difference Between Notochord and Nerve Cord
      – Comparison of Key Differences

Key Terms: Brain, Central Nervous System, Dorsal Nerve Cord, Ectoderm, Mesoderm, Notochord, Spinal Cord, Ventral Nerve Cord

What is Notochord

Notochord refers to a longitudinal flexible rod of chordates which supports the body. It also occurs in the early embryonic stages of the vertebrates. In adult vertebrates, the notochord becomes a part of the vertebral column, which surrounds the nerve cord. Notochord extends from the head to the tail near the dorsal surface of the body. It is a cartilaginous structure and contains cells derived from the mesoderm. The major function of the notochord in chordates is to provide axial support to the animal. Notochord also provides sites for the attachment of skeletal muscles. The notochord and the spinal cord of a vertebrate animal are shown in figure 1.

Difference Between Notochord and Nerve Cord

Figure 1: Notochord and Spinal Cord in a Vertebrate

During gastrulation, when the blastula develops into the gastrula, notochord develops with the formation of the neural plate. The cells in the mesoderm become rigid and condense to form the notochord. Throughout embryonic development, notochord aids the elongation of the embryo.

What is Nerve Cord

Nerve cord refers to the major cord of nerve fibers which develops into the brain and the spinal cord of vertebrates. Two nerve cord types can be found in animals: dorsal nerve cord and ventral nerve cord. In chordates, nerve cord is a hollow cord dorsal to the notochord. In non-chordate animals such as bilaterians, the nerve cord is ventral in the body. Segments of ganglia are connected through nerve fibers to form the ventral nerve cord. The ventral nerve cord of an earthworm is shown in figure 2.

Main Difference - Notochord vs Nerve Cord

Figure 2: Ventral Nerve Cord

Nerve cord forms from the ectoderm. The nerve cord of vertebrates develops into the central nervous system, which is composed of the brain and the spinal cord.

Similarities Between Notochord and Nerve Cord

Both notochord and nerve cord are characteristics features of chordates.
Both notochord and nerve cord lie from neck to the tail in the dorsal part of the body.
Both notochord and nerve cord are rod-like structures.

Definition

Notochord: Notochord refers to a longitudinal flexible rod of chordates which supports the body.

Nerve Cord: Nerve cord refers to the major cord of nerve fibers which develops into the brain and the spinal cord of vertebrates.

Structure

Notochord: Notochord is a rod-like structure, which is made up of vacuolated cells.

Nerve Cord: Nerve cord is a chain of ganglia.

Origin

Notochord: Notochord originates from the mesoderm.

Nerve Cord: Nerve cord originates from the ectoderm.

Occurrence

Notochord: Notochord occurs in chordates.

Nerve Cord: Nerve cord occurs in both invertebrates and vertebrates.

Function

Notochord: Notochord provides structural support and the sites for the attachment of skeletal muscles.

Nerve Cord: Nerve cord coordinates nerve impulses which arrive from the peripheral nervous system.

In Vertebrates

Notochord: Notochord forms the axial skeleton of vertebrates.

Nerve Cord: Nerve cord forms major parts of the central nervous system: brain and the spinal cord.

Conclusion

Notochord and nerve cord are two characteristic features of chordates. Both notochord and nerve cord occur dorsally in chordates. Nerve cord occurs in both invertebrate and vertebrate animals. The nerve cord of invertebrates is ventral. Notochord of vertebrates develops into the vertebral column. The nerve cord of vertebrates develops into the brain and the spinal cord. This means notochord provides support and nerve cord performs a nervous function in animals. Therefore, the main difference between notochord and nerve cord is the function of each structure in the animal body.

Reference:

1. “What is Notochord? – Definition, Formation & Function.” Study.com, Available here.
2. “Dorsal nerve cord.” Wikipedia, Wikimedia Foundation, 5 Sept. 2017, Available here.
3. “Ventral nerve cord.” Wikipedia, Wikimedia Foundation, 22 May 2017, Available here.

Image Courtesy:

1. “Lamprey larva labelled” By Tracyanne – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Earthworm nervous system” By image created by user: Looie496; scanned from figure 12 (p. 86) of the book The mental and physical life of school children by Peter Sandiford, published by Longmans, Green and compay, 1913 (Public Domain) via Commons Wikimedia