Spinal Meninges

Spinal Meninges

There are three layers called meninges(singular: meninx) – Protective membranes surrounding the spinal cord and brain. that surround the spinal cordThe central nervous system structure that relays signals between the brain and body..  These layers are continuous with the layers of the same name that surround the brain.  Let’s go from superficialNear the surface of the body. to deepAway from the surface of the body., as we would if we were to cut into a spinal cord

Deep to the epidural spaceThe space between the dura mater and vertebrae, filled with fat and blood vessels. is the dura materThe thick, outermost layer of the meninges that protects the spinal cord. or the first layer of the spinal meninges.  The name of this layer means “tough mother”.  The second spinal meningeal layer is called the arachnoid materThe middle layer of the meninges, located between the dura and pia mater.. The arachnoid mater gets its name from the many collagenA structural protein in the dermis that provides strength and elasticity. fibers. These fibers separate it from the 3rd and final spinal meningitis that surrounds the spinal cord itself. These collagen fibers create something of a cobweb like appearance. The space deep to the arachnoid mater is called the sub arachnoid space. This space is held open by those collagen fibers and is filled with cerebrospinal fluid(CSF) – A fluid that cushions and nourishes the brain and spinal cord.. This fluid, which is basically filtered blood, runs through the arachnoid space. It surrounds the entire spinal cord. This space is continuous with a similar space surrounding the brain.

The 3rd and deepest spinal menini is called the pia materThe thin, innermost layer of the meninges that closely adheres to the spinal cord.. The word pia means soft. The pia mater clings to the spinal cord tissue much like a stocking. You can see here that the purple-colored pia mater dips into the anteriorThe front of the body or toward the front when standing in the anatomical position. fissureA deep groove in the brain’s surface.. It also dips into the posterior median sulcusA shallow groove along the back of the spinal cord.. Remember that the fissure and the sulcus are crucial. They allow us to determine that the top of this picture is the dorsalRelating to the back side of the body. side of the spinal cord. The bottom of this picture is the ventralRelating to the front or belly side of the body. side of the spinal cord.

Epidurals

The vertebral foramenCentral hole in each vertebra where the spinal cord passes through. contains the epidural space. This space is located between the first meningeal layer and the bone itself. It is mostly filled with adipose tissue.  This area is a great injection site for nonpolar lipid-based medications such as regional anesthetics.  The medications are able to spread out from the injection site because they are nonpolar. The adipose connective tissue that fills it is also nonpolar.  Sooooo….if you are unsure if your patient needs an epidural at L4/L5 or L3/L4, it doesn’t matter.  Inject them at the more superiorAbove or toward the upper part of the body. spinal level and let gravity do the rest.  Seriously. 

When someone says they are getting an epidural, that just indicates the area of the injection.  What they are injecting usually includes steroid medications to reduce inflammation. They might also use anesthetic medications to reduce the sensations received by the spinal cord in that area.

Spinal Taps

Epidural injection is usually putting some medication into the epidural space. A spinal tapA procedure to collect cerebrospinal fluid from the subarachnoid space. involves withdrawing some fluid from the spinal cord. The fluid filling the subarachnoid space circulates around the spinal cord and the brain. This cerebrospinal fluid although made from blood is distinctly different from blood. There are things in blood that you’re nervous tissue can never be exposed to. Those things are not in cerebrospinal fluid. For example, there are these little nonpolar substances called ketone bodies that are created in times of starvation. Ketone bodies change the pHA measure of hydrogen ion concentration in a solution. of your cerebrospinal fluid and affect the functioning of your central nervous systemComposed of the brain and spinal cord; integrates and processes information. . To confirm if these ketone bodies are entering your cerebrospinal fluid, withdraw some of that fluid. When we withdraw repo spinal fluid from the subarachnoid space this is what is called a spinal tap.  Therefor a l tap allows us to sample that selectively filtered cerebrospinal fluid. 

What is meningitis?  Short and sweet definition, it’s the inflammation of these meningeal layers.  This usually occurs from infection due to a bacterium or due to a virus.  If it’s a virus, you will be sick, but you will get better.  If it is a bacterium, you may die.  This is because we don’t have antibiotics that can cross what is called the blood-brain barrierA selective barrier that prevents harmful substances from entering the brain..  The blood-brain barrier should be called the blood-brain-spinal cord- barrier.  So….good luck.