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Day #186: Know your spinal cord – The spino-olivary tract

Spinal cord slice

Spinal cord anatomy

Day twenty-nine, wow does time fly! We have over four weeks worth of fun spinal knowledge for you to tap into, all in reverse chronological order in our handy neuroanatomy category! If you read the title, you know we’re back on tract (see what I did there?). Today we’re talking the spino-olivary tract, or is it the olivospinal tract? Keep reading to find out!

The spino-olivary tract is a smaller tract, but has an important function. Before we get into exactly what the tract does we need to talk about the olives. This requires us to go back to the medulla! The olives or olivary bodies are named after the shape (isn’t everything in the body named that way?). They are located on the anterior surface of the medulla lateral to the medullary pyramids.

The olives consist of two main parts, the first would be the inferior olivary complex. This is mainly involved in cerebellar motor-learning and function. So we already can tell that the tract we are talking about may have something to do with motor function. However, there is a second part of the olive called the superior olivary nucleus. While this is considered part of the pons (a portion of the brainstem) it is part of the auditory system and aids in the processing of sound. Below is an image showing us the location of the olives in relation to the medullary pyramids.

olivary bodies

The olives are just above the decussation of pyramids and have an olive like shape, hence the name.

We might be able to guess that since we are dealing with the spinal cord, we are dealing with the inferior olivary complex when we talk about the spino-olivary tract and you would be correct! Now, the inferior olivary complex can be subdivided into three parts, since we are focused more on the spinal cord than the brainstem, we won’t cover them in detail, but know that this is the case and if you’re interested you can google or maybe we will cover brain structures sometime too, who knows!

Now, the spino-olivary tract is located in the anterior funiculus of the spinal cord. Since it is a smaller tract, there isn’t a very clear image showing it’s location so I’ve created an image to make it easier to see below.. It has a role in unconscious proprioception and is involved in helping us maintain our balance. More specifically the tract carries proprioceptive information from the muscles and tendons to the olivary bodies. This isn’t the only tract that has this job. If you recall the spinocerebellar tract also plays a role in balance.

spino-olivary tract location

When the internet won’t provide you a good image of the spino-olivary tract, you make your own. Above you can see the location of the spino-olivary tract. Recall that the spinal cord is symmetric so this tract exists on both sides, but only showing it on the one side makes it more clear.

Compared to some of the tracts we’ve covered, it is a fairly tiny tract. Now let’s talk about its odd path to the brain! The problem here is that we don’t exactly know how it travels (it’s hard to track smaller tracts). We do know that the axons enter from the dorsal root ganglion (like all sensory tracts do) and synapse on a second-order neuron in the grey matter. We are not sure exactly where in the grey matter it synapses though. We do know that from there, it decussates (crosses the midline) at the level it enters . From there it ascends as the spino-olivary tract where it then synapses on a third-order neuron in the inferior olivary complex. From here, the third-order neuron decussates a second time (we’ve seen this happen before!) then enters the cerebellum through the inferior cerebellar peduncle.

Now one last thing. I mentioned at the top that there may be a tract called the olivospinal tract, don’t confuse the two. One way to remember this is that the spino-olivary tract is a sensory tract, (traveling from the spine to the olives), while the olivospinal tract is a motor tract going from the olives to the spinal cord. An even easier way to remember this, we don’t think the olivospinal tract even exists anymore… oops. So you shouldn’t confuse the two and when in doubt google will remind you the olivospinal tract probably isn’t a thing.

That about wraps up the spino-olivary tract, a small but mighty tract with a somewhat important role of making sure you’re balance is at it’s best. Next up we will talk about the anterior white commissure since we’ve been talking about it indirectly, but haven’t formally covered what exactly that is.

Until next time, don’t stop learning!

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