The outer region of the spinal cord, composed primarily of myelinated axons, is called the:
A gray matter
B lateral horns
C white matter
D gray commisure
The correct answer and explanation is:
Correct Answer: C) White matter
The spinal cord is a vital part of the central nervous system that serves as a communication highway between the brain and the rest of the body. It consists of two major types of tissue: gray matter and white matter. The outer region of the spinal cord is made primarily of white matter, while the inner region contains gray matter.
White matter is made up mostly of myelinated axons. Myelin is a fatty substance that wraps around nerve fibers (axons), providing insulation and greatly increasing the speed at which electrical impulses (nerve signals) are conducted. These myelinated axons in the white matter form ascending tracts, which carry sensory information to the brain, and descending tracts, which carry motor commands from the brain to the rest of the body.
In contrast, gray matter consists mainly of neuronal cell bodies, dendrites, and unmyelinated axons. It is involved in processing and integrating information. In the spinal cord, gray matter is arranged in a butterfly or H-shaped region in the center.
Other options given are incorrect for the following reasons:
- A) Gray matter is located centrally in the spinal cord and does not form the outer region.
- B) Lateral horns are part of the gray matter and are found only in certain segments of the spinal cord, particularly in the thoracic and upper lumbar regions. They are not located in the outer region.
- D) Gray commissure is the thin strip of gray matter that connects the two sides of the spinal cord’s gray matter.
In summary, the outer region of the spinal cord that contains myelinated axons is called white matter. This white matter is responsible for the fast transmission of nerve signals to and from the brain.