Spinal White Matter

Special Characteristics of Spinal White Matter

Spinal white matterThe outer portion of the spinal cord made of myelinated nerve fibers that transmit signals. just looks like a bowl of pudding. However, there are some very special characteristics that differentiate spinal white matter from Gray matter. Of course, the first thought you may have is that the white matter consists of myelinated neuronsThe functional cells of the nervous system that transmit signals. and axons. You would be correct. However the axons are running superiorAbove or toward the upper part of the body. to inferiorBelow or toward the lower part of the body. through the white matter. Therefore, looking at a transverse section A cut or slice of the body or an organ for study. of the spinal cordThe central nervous system structure that relays signals between the brain and body. makes it very difficult to see this clearly. The white matter is like a multi lane highway running up and down the spinal cord. There are exits getting off at each spinal nerve. Try really hard to keep that vision in mind as we look at spinal white matter.

I am from New Jersey. We have something called the Garden State Parkway. Which is the main roadway that runs between northern and southern New Jersey. Once you get on the Parkway, you reach a certain point. At this point, you can choose between going in the express lanes or in the local lanes. The local lanes have exits whereas the express lane doesn’t. When I was younger, you made the choice and were stuck in it for about 50 miles. Today, there are places where you can get off the express and onto the local or vice versa. The same thing happens the spinal white matter. There’s a phenomenon called decussationThe crossing of nerve fibers from one side of the CNS to the other.. In it, an Axon crosses from left to right or right to left. It uses one of the connoisseurs that we identified in a previous mini lecture.

We can define that spinal white matter is perfectly symmetrical with the idea of decussation in mind. Spinal Gray matter is also perfectly symmetrical. Spinal white matter axons have very specific and precise locations to each other period this is called somatotropin. Even though it looks like pudding there are very specific arrangements of the axons in portions of the white matter. Most of the pathways that use an Axon running up or down in spinal matter is a relay. This means that there are two to three neurons that serve the purpose of moving information. In skeletal motor neuronsNeurons that carry outgoing information from the CNS to effector organs., one multipolar neuronA neuron with one axon and multiple dendrites; the most common type in the CNS. originates in the brain. It descends the spinal cord and moves out to the neuromuscular junctionThe connection between a motor neuron and a muscle fiber..

White Matter Function

Within these larger designations of columns are smaller groupings of axons that have similar destinations. We call these groups of axons pathways. Even more specifically within one pathway there can be many individual tractsBundles of nerve fibers in the CNS that carry signals between brain regions. which are just axons with more specific destinations. Pathways or groupings of axons destined for similar locations exist within these larger columns of white matter. Pathways can run in three directions up down and side to side. But we can’t call them that. There are transverse pathways which are just axons that move from left to right using the anteriorThe front of the body or toward the front when standing in the anatomical position. posterior commissure. There are ascending pathways that are bringing action potentials to the brain.

These pathways are called afferent and carry sensory information into the central nervous systemComposed of the brain and spinal cord; integrates and processes information.  from peripheral tissues. There are also descending pathways or groupings of axons with similar destinations. These pathways are efferent. They carry information coming out of the central nervous systemThe organ system that controls body functions using electrical and chemical signals.. This information is headed for the neuromuscular junction of skeletal muscle or a connection with smooth muscle and glands. We have to visualize these pathways running inferior and superior as a highway. Each tract should be seen as a separate lane of traffic.

White Matter Anatomy

Of course let’s start with just some anatomical naming. There are two white matter structures columns and connoisseurs. We have previously looked at the connoisseurs these are areas where myelinated axons crossover from the left to the right. The anterior commissure is between the central canalA hollow canal in an osteon containing blood vessels and nerves. and the anterior median fissureA deep groove along the front of the spinal cord that divides it into two halves.. The posterior commissure is between the central canal and the posterior median sulcusA shallow groove along the back of the spinal cord.. Using our basicA solution with a pH above 7, having a lower concentration of H⁺ ions. drawing here with the Gray matter of a lumbar type section simplifies the process. It allows us to clearly see the individual columns of white matter.

The dorsalRelating to the back side of the body. column of white matter is this large area up here. It is, of course, close to the posterior median sulcus. The anterior column is similar and contains the anterior fissureA deep groove in the brain’s surface.. The lateralAway from the midline of the body. column can be more or less obvious. It depends on the level of the spineProminent ridge on the posterior scapula dividing it into supraspinous and infraspinous fossae. and the distribution of the Gray matter. The lateral column runs between the dorsal and ventralRelating to the front or belly side of the body. roots.