Know your spinal cord – The spinoreticular tract

We’ve arrived at day thirty-seven in the spinal cord series and we’re still covering new ground. You can find all of our sweet spinal cord action in the neuroanatomy category, which at this point is pretty extensive for a high-level look. Yesterday we talked about the reticulospinal tracts so today we are talking about the sister tract, the spinoreticular tract. Are they related, or is it all just in the name?

As we’ve seen time and time again, there is a lot of information in the way the spinal tracts are named. The first half of the name (typically) tells you where it originates, the second half (again, typically) tells you where it ends. So when we talked about the reticulospinal tracts, we knew they originated at the reticular formation and ended in the spinal cord (somewhere, names aren’t everything), making the tracts efferent.

Today we are talking about the spinoreticular tract, so we know it originates in the spine (somewhere, we will get to that) and ends somewhere at the reticular formation. However, that doesn’t mean that the reticulospinal tracts and the spinoreticular tract are related, it could be by name only. That being said, the spinoreticular tract is a pain tract.

More specifically the spinoreticular tract is thought to be responsible for automatic responses to pain. Technically the function isn’t quite as clear as some of the other pain tracts. The key word here being automatic, which is why the tract ends at the brainstem and not the somatosensory cortex*. This route, while slower than the spinal reflexes, is still much faster.

• The tract does eventually make its way there, but go with me for a minute because the route is a bit muddled.

Unlike most of the tracts we’ve looked at that consists of two or three neurons, the spinoreticular tract has four. In this tract our first-order neuron (which passes through the dorsal root ganglion like all afferent pathways) synapse with a second-order neuron in the posterior horn of the spinal column on the ipsilateral side (same side) it enters. The second-order neuron decussates (crosses the midline), where it then travels up the spinal column. It “ends” at the brainstem, specifically at the medullary-pontine reticular formation. Below is an image showing the full pathway.

But wait, we said it was a four neuron tract and we only listed two neurons! Well this is because the neurons do synapse with a third-order neuron, which travels to the ventral posterolateral nucleus, located in the thalamus (shown below). There it synapses again with its fourth-order neuron which takes the information to the somatosensory cortex. At this point you become consciously aware of the pain. It is believed that spinoreticular tract also plays a role in the memory and in the affective (emotional) component of pain.

The spinoreticular tract is one of three tracts that make up the anterolateral system, the system responsible for… PAIN! The other two are the spinothalamic tract and the spinotectal tract, which we briefly discussed at the end of our tectospinal tract post. Interestingly they all follow a similar pathway, they just make different stops along the way. Maybe we can go into detail about the spinotectal tract next since we haven’t really covered it.

In any case, that is your introduction to the spinoreticular tract. Now you know where it starts, ends, how it gets there, and most importantly what it does! Things are still looking busy for me so I haven’t had a chance to plan out tomorrow’s post yet, but that spinotectal tract is looking pretty good right about now, so we may go over that next.

Until next time, don’t stop learning!