Dizziness / Balance
Do you have symptoms of dizziness, vertigo, disorientation, disequilibrium or imbalance?
You may be having problems with the parts of your brain responsible for balance and orientation. This part of the brain is called the vestibular system, and it is responsible for detecting head motion and answering the question of “where am I in relation to my environment?”
There are many descriptive words for vestibular (inner-ear balance function) symptoms, yet each term has its own definition and cause. It is important to decipher exactly what is causing your individual set of symptoms.
The vestibular system
As can be seen in the picture below, the ear is made of an outer ear (A), the middle ear (B) and the inner ear (C). The inner ear houses part of the vestibular system, called the vestibular apparatus, which detects motion of the head, and then transfers the information to the brain via the vestibular portion of the nerve (shown in the diagram as blue). This nerve also transfers sound information to the brain, and therefore gives us the ability to hear.
We call the vestibular apparatus and nerve the “peripheral” vestibular system, and we call the region of the brain that interprets vestibular information the “central” vestibular system.
The vestibular apparatus is approximately 1cm. It is an extraordinary design, allowing us the ability to detect various types of head motion, including rotational motion, as well as horizontal and vertical acceleration.
The way that it detects motion is via the semi-circular canals and the utricle and saccule. In the picture below, you may see the semi-circular canals represented as the anterior, posterior and horizontal canals.
Movement of the head creates movement of fluid inside these regions of the vestibular apparatus, stimulating the nerves which transfer information to the brain. The brain receives information from both the left and right ear, so it can know where the head is in relation to gravity.
The brain receives information about head motion in a part of the brain called the brainstem. At the level of the brainstem, the brain is able to integrate information from the eyes (visual input) and the spine (somatosensory input), so that it can correlate and cross-check it with the vestibular input.
A brain which is functioning well will agree that the information from the inner ear, eyes and spine are all telling it the same thing. In a person with symptoms such as vertigo, dizziness or imbalance, the brain may be receiving information that is confusing or contrasting. That is to say, the left inner ear may be sending information that does not match the information from the eyes and spine.
Two very important features of the vestibular system are the vestibulo-ocular reflex (VOR) and vestibulo-spinal reflex (VSR) .
The VOR is the connection of the inner ear to the eyes. It is an important connection because when the head is in motion, the eyes must be able to react so that they can stay focussed on a target. Imagine if you were trying to focus on reading your phone whilst walking and your eyes were bouncing up and down with every step! The image would be too unsteady to read. The VOR gives information to the eyes about which way the head moves, so the eyes can stay relatively still, enabling them to stay focused on a target.
The VSR is a similar reflex to the VOR, but instead it connects the vestibular system to the muscular system, enabling the muscles to respond to movement. For example, if the vestibular system detects a fall or a tip to the right, the VSR will enable the appropriate muscles in the body to engage and therefore correct the motion, bringing us back towards the centre of gravity to prevent falling.
Both the VOR and VSR are essential reflexes for normal everyday living, such as standing walking and scanning our environment. It allows us to know where we are in our environment and where our environment is in relation to our body. The vestibular system is established very early in the developing fetus and much the of the brains function relies on the vestibular system working well.
