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Jenna Week 3 & 4: Implications of the Vagus Nerve

It has been another incredible couple of weeks of learning and discovery with Jenna. I dedicated these past two weeks primarily to increasing her movement tolerance and hoof rehabilitation as well as addressing the cranial and cervical issues that presented during the initial assessment. In therapy sessions, my main focus was assessing and working on the vagus nerve.

Movement Tolerance

Jenna’s exercise routine has progressed to three walk/runs per week with us reaching a new personal best at completing just over 5km! This is a huge improvement from the 1-2km of strictly walking that we started with. She is now able to do 1-2min of sustained trotting alternated with 1-2min of walking for up to one hour without showing signs of discomfort or fatigue. This little gal is still bursting with energy on the way home which is affirmation to me that we are definitely on the right track. On alternate days we are doing approximately one hour of long slow walking to continue increasing endurance but also giving rest to her joints from so much impact. These sessions are referred to as “active rest” days – a term commonly used in athletic training wherein the body is still moving to produce circulatory benefits but there is no stress or strain on the joints. For humans, the equivalent would be light cardio and a stretching/mobility session. Such training days are successfully used to promote circulation and aid in the removal of connective tissue bi-products produced during exercise.

Hoof Rehabilitation

In an effort to improve movement tolerance on varied terrain, I have given Jenna free access to the other two paddocks on my property. As fate would have it each paddock has different footing and slight elevation changes. There is some sand in the upper paddock, gravel in the middle one, and soft dirt in her own paddock. I am thrilled that she is able to tolerate movement on these various footings as it will play a huge role in stimulating the internal and external structures of her feet. As discussed last week, having the ability to stimulate her feet with various surfaces promotes proprioception and new growth in the tissues. Since we are ideally wanting her foot to grow new hoof as fast as nature will allow this is an ideal set up for her now that she can handle moving on these other surfaces without pain.

I watched her for about 3 hours the first day I opened it up and recorded her going up and down the small hill about 30x as well as back and forth from top of paddocks back down to the stall – meaning she’s getting loads of stimulation, not to mention a little bit of up and down workout for her hind end!

Cranial and Cervical Treatments

Jenna’s initial assessment showed moderate to severe tenderness around the C0-C1 joint (the poll) as well as in the C1-C2 and C5-C6 joints respectively. Upon further assessment, I discovered that Jenna’s TMJ on the left is restricted when compared to the right, and there is a palpable compaction on the left C0-C1. A bony compaction can wreak havoc on the blood vessels and nerves travelling through the area and cause local muscles to contract as a protection mechanism. Specifically, bony compactions at C0-C1 can directly influence the TMJ as these structure share muscle fibres and work together. This means that dysfunction in one joint is usually paired with dysfunction in the other. Bony compactions can arise for a variety of reasons, such as repetitive strain, a severe muscle imbalance, or an acute trauma to the area.

The Vagus Nerve

Based on Jenna’s organ flinch test sensitivity and the compaction I found at C0-C1 (near the exit point of the vagus nerve), I was particularly interested in further assessing the vagus nerve tone and tenderness.

For those of you that aren’t familiar with the incredible anatomy of the the vagus nerve, let me explain. It is often referred to as the ‘wandering nerve’ because it is the only cranial nerve that exits the brain and travels past the neck of the horse innervating multiple structures very distal to its origin site. It exits the cranium at the jugular foramen (right next to where Jenna’s compaction was palpated), and travels down the neck innervating the throat (esophagus, larynx, trachea), where it then pierces through and innervates the heart and lungs, continuing down the body and terminating in most of the organs of digestion. For one nerve that’s a heck of a distance to travel and a ton of structures being innervated along the way….

In studying the anatomy, it is no wonder how dysfunction in this one nerve could cause such widespread effects. The other key importance of the vagus nerve is that it innervates the parasympathetic branch of all these structures listed. The nervous system houses both a sympathetic nervous system and a parasympathetic nervous system. The parasympathetic system is responsible for telling the organs to “rest and digest” while the sympathetic nervous system is responsible for the “fight or flight” response. If an animal stays in a sustained sympathetic state (due to stress, medication, or injury) the vagus nerve is unable to balance the system back to a resting state. This causes a buildup of the epinephrine and adrenalin which are produced during fight or flight mode. The excess of these neurotransmitters then causes a spike in cortisol which can only be sustained for a certain amount of time before output drops and leads to the pathology referred to as adrenal fatigue. An analogy would be envisioning an old fashioned balance scale wherein these two systems are in a continuous state of balancing each other out (or trying to).

The benefit of the far-reaching capacity of the vagus nerve is that we can positively influence it from a distance and have a soothing effect on the entire chain of structures. Recent research on the vagus nerve has also shown that stimulation of it is seen to directly reduce inflammation and/or inhibit it altogether! It is well know for being the longest autonomic nerve in the body and the only direct link from the brain to the heart and gut. If you are as fascinated as I am by this nerve I encourage you to do a bit of research yourself. There are many studies being conducted right now on this one nerve and its wide ranging capacities.

In my opinion, the vagus nerve is of utmost importance to assess when treating a horse on medications or who has had a traumatic injury – both of which Jenna has. As already discussed in Week 1, medications can cause the organs to contract at a higher frequency and intensity while trying to process and metabolize what the body perceives to be a foreign substance. As well, a head trauma could easily cause a compaction of bone in or around the vagus nerve exit point. It has therefore been my goal this week to release any bony obstructions and restore vagal tone because the effects of this could be recognized across her entire digestive system. Upon palpation I discovered sensitivity around C0-C1 which are captured in the video below.

Cervical Treatment

Jenna’s C5-C6 flinch test with referral points to either phrenic nerve impingement, brachial plexus impingement, or potentially both. Upon palpation, I felt that her C5 was left rotated, meaning the vertebral body is positioned to the left causing the right transverse process to protrude to the right. In layman’s terms, this means that you can feel her C5 sticking out more on the right because the shape of the vertebrae is like a pair of wings that is torsioned to the left from the centre of its axis.

C5 rotation can impact all of the nerves exiting at this point. The phrenic nerve exits between C3-C5 and innervates the diaphragm. An entrapment or compression of this nerve can cause difficulty with cardio-respiratory function (breathing) if it is compromised and could show up with decreased ability to lift through the thoracic spine (ie. difficulty rounding the back). The brachial plexus on the other hand, innervates the entire forearm which would show up as shortened or choppy stride with regards to movement. Remember back to where I got that huge nerve entrapment release in last week’s video. The pieces of the puzzle are slowly starting to reveal themselves and I am completely committed to the process of uncovering them one at a time on my search to determine the root cause of Jenna’s presentation. I proceeded to treat both her C0-C1 compaction as well as her C5-C6 rotations and am very excited to share the footage. While not all that exciting at first glance, if you watch very closely you will see a little bit of magic unfold!

Goals for week 5 & 6 include delving deeper into her cranial assessment and of course continuing with the new movement program.


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