We Love The Vestibular System

Small and mighty, the vestibular system is a powerhouse of the balance system.  It continues to fascinate us as we are still learning more about its function and connections throughout the body.  The vestibular system plays a key role in the sensation of dizziness, imbalance, and motion.  When there are problems with the vestibular system, a huge variety of symptoms can develop including blurred vision, vertigo, and imbalance.  Because of its complexity and importance in our day-to-day function, we love helping people who have problems because of a dysfunction involving the vestibular system.  Understanding all of the things the vestibular system can do is fascinating.  Let’s explore how this system works together!

Purpose of the Vestibular System

Our balance system depends on us always knowing where we are at in space.  We orient ourselves in space based upon where the ground is at.  Our perception of the ground is greatly influenced by the pull of gravity.  We are aware of this gravitational force because of our vestibular system.  The vestibular system is responsible for coordinating movement of our posture and eyes in response to the direction of gravity and the position of our head.  

Think about an airplane pilot flying at night, through the clouds.  Without the instrument panel, the pilot would not know much information about the orientation of the plane in space.  The instrument panel provides information about the altitude and pitch of the aircraft.  This is much like the function of the vestibular system.  It provides information about how we are oriented in space, much like the instrument panel of an airplane.

The vestibular system is one third of our balance system.  The information that it provides is correlated with sensory information from our body and visual input from our eyes to give our brain an accurate picture of where our body is at in space at all times.  When the vestibular system is not working properly, we can feel disoriented and imbalanced. 

The Anatomy of the Vestibular System

The vestibular system itself is divided into two parts – central and peripheral.  The central vestibular system is located in the brain.  The peripheral vestibular system is located in the inner ear.  The central vestibular system focuses around the vestibular nuclei, found in the brainstem.  Input from the peripheral system comes into these nuclei and then gets distributed to the cerebellum (back of the brain responsible for subconscious balance and coordination), eye muscles, and spinal cord.  There is also a central connection between the vestibular system and the autonomic nervous system (our “fight or flight” and “rest and digest” responses to our environment).

The peripheral vestibular system, located behind the eardrum in the inner ear, shares space and a cranial nerve (vestibulocochelar nerve) with the cochlea (part of the hearing system).  There are matching systems in each ear.  Each peripheral system is made up of 5 small organs that are protected by a thin bony layer.  Two of the organs (utricle & saccule) sense vertical and horizontal movement.  The other three organs, semicircular canals, are full of fluid that help detect angular movement of the head.  Combined, the five organs are about the size of a dime.

There are tiny hairs in the utricle and saccule that have a sticky substance on top of them (the macula).  On top of the sticky substance are calcium carbonate crystals, called otoconia.  When your head moves horizontally or vertically, the otoconia help weigh down the hair cells and bend them.  Each hair cell is attached to a small branch of a nerve that provides information to the brain about linear movement.

Fluid, called endolymph, fills the semicircular canals.  When your head rotates and pitches in different directions (up/down, right/left, side-to-side) the endolymph moves around in the canal.  Pressure from the fluid causes movement in a membrane at the end of each canal (the ampulla).  The ampulla is attached to the nerves that send information about rotational movement to your brain.  Depending on the direction of the fluid’s movement, the ampulla either sends a message to the brain about the rotational movement, or not.  The semicircular canals in your right ear are paired together.  If a canal in your right ear sends a signal about right rotation, for example, the paired semicircular canal in the left ear has an inhibitory response.  This duplicate system prevents the brain from getting conflicting signals from the peripheral vestibular system.  It also gives us a bit of a backup system in case a problem occurs with one (or more) of the peripheral vestibular organs.

It’s All About Reflexes

When we think about reflexes, most of us would think about a doctor tapping our knee and our lower leg kicking.  That is one example of a reflex in our body – a movement that happens automatically without us consciously thinking about it.  There are a lot of reflexes in our body, and our vestibular system is key in several of them.  Here is how the vestibular system helps us with everyday function through reflexes:

1. Vestibulo-Ocular Reflex (VOR):  The VOR is a connection between the peripheral vestibular system and our eyes.  When the vestibular system detects movement of our head, signals go to the muscles of our eyes to ensure that we are able to keep our gaze stable with whatever we are looking at.  Without this reflex, everything would be blurry as soon as we move our head.  Think about how difficult it would be to do everyday things like grocery shop, drive, and even walk through your home if this reflex were not working properly.
2. Vestibulo-Spinal Reflex (VSR):  The VSR is a connection between the peripheral vestibular system and the spinal cord (and muscles around it!).  When our head moves, and when we sense a change in the orientation of our body, the VSR is important at keeping us upright!  This powerful connection activates muscles along our back in order to help us maintain our balance and posture in response to changes of our position in space.
3. Vestibulo-Collic Reflex (VCR):  The VCR is a communication from the peripheral vestibular system to the neck (cervical spine).  It triggers muscle contractions to keep the head and neck stable while the head is in motion.
4. Vestibulo-Sympathetic Reflex:  Surprisingly, the vestibular system plays a crucial role in regulating our blood pressure as our bodies change position via the Vestibulo-sympathetic reflex.  In a healthy system, it helps to prevent the development of orthostatic hypotension.  Orthostatic hypotension is a drop in blood pressure when we change positions against-gravity (such as going from sitting to standing) that can make us feel faint or lightheaded.  Problems with the otolith organs in the peripheral vestibular system as well as conditions such as BPPV can disrupt this reflex and produce additional dizziness symptoms due to dysregulated blood pressure with position changes.

So What Could Go Wrong?

There is a lot going on in such a small space!  A problem in the brain, vestibulocochlear nerve, bony layer protecting the peripheral organs, volume of endolymph in the system, breakdown of otoconia, infections, and benign tumors are just some examples of what we can find wrong with the vestibular system.  Most commonly, we see people who have:

• BPPV – Benign Paroxysmal Positional Vertigo (short bursts of spinning due to the otoconia moving out of the utricle and into a semicircular canal)
• Vestibular Migraine (a type of migraine that produces vertigo lasting hours in length, not necessarily with a headache)
• Vestibular neuritis (an infection of the vestibulocochlear nerve)
• PPPD (Persistent Postural Perceptual Dizzinesss – a constant sensation of movement and visual vertigo lasting more than 3 months after another vestibular “event”)

How Do I Get Help?

Remember that there are so many things that can cause dizziness symptoms.  The vestibular system is just one of the reasons you can experience feeling dizzy.  But, if the dizziness is due to a vestibular disorder, a physical therapist who has specialized training in vestibular rehabilitation can help you to reduce symptoms and get back to feeling like yourself again!