Spinal Gray Matter

Gray Matter Function

I always recommend to students that they learn about the gray matterThe inner portion of the spinal cord composed mostly of neuron cell bodies and synapses. of the spinal cordThe central nervous system structure that relays signals between the brain and body.. They should do this before they learn about the white matterThe outer portion of the spinal cord made of myelinated nerve fibers that transmit signals.. This is because in general Gray matter is concerned with linking together Sensory input and motor output. It keeps the job simple in doing that. Spinal white matter is about sending that input to the brain or sending that input from the brain. Therefore white matter forces you to envision the entire spinal column. Whereas gray matter can allow you to focus and use examples at just one level.

The distinction between white matter and Gray matter is simply the presence of myelin. White matter contains those myelinated axons. Gray matter contains either cell bodies of neuronsThe functional cells of the nervous system that transmit signals. or unmyelinated axons. It can contain both of them. It doesn’t have to contain one or the other. Grey matter of the spinal cord provides an area where neurons can synapseThe junction between two neurons where communication occurs.. So we have Axon terminals that are releasing neurotransmittersChemicals released by neurons to transmit signals across a synapse. and dendritesBranch-like extensions from a neuron that receive signals from other neurons. of cell bodies that are receiving those neurotransmitters. These areas are unmyelinated and therefore are Gray matter.

Let’s draw a simple reflex arc over here on the right side of this transverse spinal section A cut or slice of the body or an organ for study.. I’m going to draw a unipolar sensory neuron that comes in the dorsalRelating to the back side of the body. ramus. It goes through the spinal nerve and passes the dorsal root ganglionA cluster of neuron cell bodies located in the peripheral nervous system (PNS).. Then, it travels through the dorsal root and enters into the Gray matter of the spinal cord at this level. I’m also going to draw that neuron synapsing with the cell bodyThe central part of a neuron containing the nucleus and organelles. of a multipolar neuronA neuron with one axon and multiple dendrites; the most common type in the CNS.. This neuron is going to leave through the ventralRelating to the front or belly side of the body. root. It passes through the spinal cord and enters the ventral ramis. It will ultimately go into one of those plexuses. This is a very simplistic reflex arc that shows you how neurons can use Gray matter for synapsing. Of course you know that it’s much more complex.

Gray Matter Anatomy

Let’s start by designating some anatomical terms. The points on this Gray matter of this transverse section of the spinal cord are called horns. Therefore this is the dorsal this is the lateralAway from the midline of the body. and this is the ventral horn. How did I know dorsal from ventral? And use the anterior median fissureA deep groove along the front of the spinal cord that divides it into two halves. to tell me where the ventral side of the spinal cord is. I can use the dorsal root ganglion to tell me what side the spinal cord is. So the points of this butterfly shaped Gray matter are called horns.

Gray Matter Anatomy

Let’s take a look at what’s over on the right hand side of this picture which is 2 pathways.  Each pathway contains 2 neurons and both of the neurons lead to whole bunch of skeletal muscle and neuromuscular junctions. You’ll see that the green neurons here have a cell body located in the brain. Then it descends the spinal cord.

If a multipolar neuron is outgoing, it is sending some information about visceral tissues. It will end right here and synapse with another neuron.

If a multipolar neuron is outgoing and sending some information about somatic tissues, it will end right here. Then, it will synapse with another neuron. 

A unipolar neuronA neuron with one process that splits into peripheral and central branches, common in sensory neuron may be incoming. It brings in some information about somatic tissues. It will end right here and synapse with another neuron. 

If a unipolar neuron is incoming and bringing in some information about visceral tissues, it will end right here. Then, it will synapse with another neuron.

Somatic on the outside and visceral on the inside.  Convenient.  How to remember motor and sensory you ask?  We always need to connect dorsal with sensory and ventral with motor.  How about this?  Polio is a virus that affects your ability to use skeletal muscles, making it hard to walk.  Polio is a virus that attacks ventral roots only.