Video Transcript
The diagram provided shows a basic outline of a cross section of the spinal cord. Which letter indicates the area that mostly contains neuronal cell bodies, dendrites,
and unmyelinated axons? (A) X, (B) Y.
To answer this question, we must recall what we know about the spinal cord and its
organization when viewed in a cross section. The spinal cord is one of the two components of the central nervous system. The major function of the spinal cord is to relay messages from the body to the brain
and back again. To carry out this major function, nerve impulses are conducted through the thick
bundle of nerve fibers and nervous tissue that make up the spinal cord. The bundle of nerve fibers contains two types of neurons: unmyelinated and myelinated
neurons. These two types of neurons are easiest to see and differentiate when viewing the
spinal cord in cross section.
When looking at a cross section of the spinal cord, there’s a distinctive letter-H
shape found at its core. The H-shaped core is typically gray in color because it’s mainly composed of
unmyelinated neurons, dendrites, and cell bodies. Many of the unmyelinated neurons are intermediate neurons, which help relay
information between sensory neurons or motor neurons and the brain. The gray-matter core of the spinal cord is surrounded by white matter, which is
composed of the myelinated neuron axons.
The myelinated axons form the nerve tracts that allow signals to ascend to and
descend from the brain. Importantly, the myelin found on these axons helps increase the speed of conductance
of the nerve signals between the spinal cord and the brain. Since myelin is a lipid-rich substance that is white in color, it causes these
tissues around the gray-matter core to appear white as well.
After reviewing the types of nervous tissue found in the spinal cord when viewed in
cross section, we’re able to answer the question correctly. The letter that indicates the area that mostly contains neuronal cell bodies,
dendrites, and unmyelinated axons is the letter X.
