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Understanding the vestibular system – part one

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In this 3 part series, you will learn about what the vestibular system actually is, what questions are important to ask during assessment and lastly how you actually recover from it.

Over a lifetime, dizziness can be similar to back pain. Coming and going at various points without rhyme or reason, and even moderate levels of dizziness can be hugely debilitating, affecting quality of life and ability to work. Dizziness is a problematic presentation both from an assessment and management perspective. This is because many conditions have symptoms that include dizziness, and reporting of symptoms can be inconsistent or vague and can change with emotion, mental state and fatigue.

What is the vestibular system?

The vestibular system partly comprises a tightly packed set of bones, membraines, hairs and circular canals called vestibular apparatus that sit in our inner ear and calibrate constantly to our environment, almost like our internal spirit level.

We have 5 sensory organs on each side in our vestibular apparatus:

3 semicircular canals

We have the horizontal, posterior and anterior canals. They are organised at 90 degrees to each other that detect angular acceleration and rotation, such as the full effect of a roller coaster. There is one canal for every plane of motion. Each canal contains a fluid (endolymph) which beats against hair cells, detecting motion in that plane.

They are arranged like so:

http://www.humanneurophysiology.com/vestibularsystem.htm

2 otolith organs

And then we have the saccule and utricle which sit next to our semicircular canals. They contain hair cells called maculae which detect vertical and horizontal movement, taking into account of gravity, such as going up a lift or during walking. The maculae is covered by a layer of calcium carbonate crystals, called otoconia.

In healthy individuals, these sensory organs stay in harmonious conversation with our visual (sight), auditory (hearing) and somatosensory (touch) systems that feed into the our brainstem and cerebellum as our sensing systems.

Once received, the brain will be able to provide an appropriate amount of output as postural activity to ensure:

  •     that we do not fall over
  •     that we can quickly correct our balance when moving unexpectedly (like on a bus)
  •     that we have a stable reference point on which to direct our vision, head position and attend to purposeful activity

This continually occurs in a feedback (reactive) and feedforward (anticipatory) fashion and is one of the fastest neurological tracts in our healthy individuals.

Motion sickness is a symptom of an challenged vestibular system, especially when the movement is slow and occurs in two directions (think of being on a boat). Nausea is partly related to the autonomic system, but also to vision because of conflicting information. That is why it can help sometimes to focus on a stable object or close one’s eyes, as does sleeping to dampen overstimulation or mismatch of vestibular and visual information.

In fact, some people like dancers and circus performers have more conditioned vestibular system and feedback systems, which is why they can perform spins and stunts without being affected by nausea, dizziness and imbalance.

Next week, we will discuss key things you should know when assessing your vestibular problem and asking the right questions.

Resources:

Baloh, R and Kreber K (2011) Clinical Neurophysiology of the Vestibular System (4th ed) Oxford University Press

Herdman, S (2007) Vestibular Physiotherapy (3rd ed) Philadelphia: FA Davis Co.


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