Having a feeling of dizziness or being off balance is unsettling. Did you know a central control room in your body affects your balance, movement, and coordination? This control room is called the vestibular system, and it's fascinating.
The vestibular system sits inside the inner ear and comprises complex structures. The apparatus comprises the bony labyrinth in the inner ear, the semicircle canals and vestibule, and the membranous labyrinth structures inside them. The vestibular neuroreceptors are next to the auditory cochlea.
Imagine the feeling of being on a swing, and as you swing up, you drop your head back on the down stroke. That feeling you get is similar to vertigo. It soon disappeared after you got off, but people with a vestibular disturbance live with that feeling every day. Let's have a look at this important part of the inner ear.
What Is The Vestibular System?
The vestibular system is comprised of physical structures and neural pathways. These structures contribute to our sense of equilibrium and proprioception. The vestibular system functions include head movement in any direction, body orientation and acceleration, posture, and change in eye movement.
The reflexes of the vestibular system are referred to as vestibulospinal and vestibulo-ocular reflex. The vestibular system is centrally located in the inner ear and is connected to the brain through neural pathways. The brain responds to input from the peripheral vestibular system and makes these reflexes possible.
It is believed that the vestibular system plays a role in human consciousness. Any vestibular system dysfunction can disrupt learning, navigating spatial memory, and cognitive behavior.
The physical part of the vestibular system is made up of the following.
- The Bony labyrinth in the inner ear.
- The semicircle canals and vestibule.
- The membraneous labyrinth structures inside.
- The utricle and saccule inside the vestibule.
What Is The Function Of The Vestibular System?
The main function of the vestibular system is to detect the movement and position of the head in space. This allows for proper eye movement, equilibrium, and body posture.
The vestibular system and apparatus accomplish this task inside the inner ear by sending nerve signals through all individual components. The saccule and utricle inside the vestibule are responsible for sensing head tilting, gravitational forces in case of tripping and falling, and linear acceleration when the person runs.
Inside the saccule and utricle is the neuroepithelium. This is the macula, providing neural feedback regarding vertical motion from the saccule and horizontal motion from the utricle.
The macula has an otolithic membrane embedded with small calcium carbonate crystals. These crystals are known as otoliths and help the hair cells respond to signals. The three semicircular ducts sense whenever the head rotates or picks up angular acceleration.
The semicircular ducts are dilated close to the opening of the utricle. The dilation is known as the ampulla. The ampulla contains a new row epithelial structure known as the crista ampullaris or the sensory organ of rotation.
There are no otoliths in the crista ampullaris. It is coated by a gelatinous substance known as the cupula. The substance holds the hair cells in place. The central vestibular system controls the interpretation of different afferent signals and the output of efferent signals.
The vestibular ocular reflex is an efferent signal. This allows the eyes to remain fixed on an object while the head is tilting or moving. This coordinated movement between both eyes involves the para pontine reticular formation. There are outputs to various extraocular eye muscles, abundance - and ocular motor nerves.
What Is The Mechanism Of The Vestibular System?
So how exactly does the vestibular system work? What mechanics are in place when the body is in motion, and how does it simultaneously keep the head stable and the eyes fixed on a specific object?
This intricate system accelerates the endolymph within the various vestibular structures and apparatus. The endolymph is accelerated when the head moves in various directions. This acceleration stimulates the hair cell stereocilia. As soon as the head stops moving, the hair cells return to their original position.
This instant repositioning allows them to react to any changes in the acceleration of the endolymph. Due to the acceleration and depending on its direction, the inertial drag of the endolymph will either push or pull the stereocilia to or from the fixed kinocilium.
Any movement towards the kinocilium opens the cation channel, and movements away from the kinocilium close the cation channel. There is a polarization or depolarization that takes place. Depolarization opens up the calcium channels.
When a calcium channel is opened, neurotransmitters are released across the synaptic cleft. This nerve transmission leads into the vestibular ganglion. Inside the vestibular ganglion, these nerve signals have to pass through 20,000 bipolar neurons And exit along the vestibular nerve.
The cochlear and vestibular nerves enter the brain stem at the pontomedullary junction. The vestibular nucleus complex processes most vestibular signals. Other signals are sent from the vestibular nucleus to the cortex, cerebellum, or thalamus. From here, many postural or ocular muscles are adjusted through various signals.
Along with the vestibular system, the hippocampus is crucial n functions of navigation, orientation, and spatial memory.
When Does The Vestibular System Start Developing?
The vestibular system develops through the surface ectoderm during the third week of gestation. The primary development is the otic placodes. In the fourth week of gestation, the otic placards are surrounded by embryonic mesoderm and turn into otic pits.
From there, the otic pits develop and form the otic vesicles, and the upper part of the otic vesicle becomes the vestibular apparatus. Through the lengthening of the optic vesicle, a division between the ventral circular portion and dorsal utricular portion starts to form.
Later in development, the ventral circular portion becomes the cochlear duct and adult saccule. The dorsal utricle portion becomes the utricle and semicircular canals. At 19 weeks of gestation, the ossification of the system begins. The vestibular system reaches adult size at 25 weeks of gestation.
The exception is the internal aperture of the vestibular aqueduct that continues to develop until the baby is born. The otoconia and hair cells develop at the 7th week of gestation. Type one and two hair cells become visible between 11 and 13 weeks of gestation.
How Do You Know The Vestibular System Is Functioning?
Several medical tests can be performed to determine if the vestibular system is functioning properly. Some tests can be performed in a GP’s room, while others need to be performed by specialists using imaging and advanced sound equipment.
The following are the most common tests that can be performed on various patients –
The oculocephalic reflex – This test is typically used in comatose patients by triggering the vestibular system's reflexes to determine if the patient's brain stem is intact. This is done by rotating the patient's head horizontally. This should activate the vestibular system on the ipsilateral side of rotation.
If the patient's eyes deviate to the side opposite of the head movement, it indicates the brainstem being intact. If the brain stem is not intact, the eyes will follow the rotation of the head.
Caloric testing - This test uses temperature fluctuations to diagnose potential damage to acoustic nerves. Cold air or water is delivered into the ear in small amounts to trigger nystagmus. This is the involuntary movement of the eyes away from the affected ear and slowly turning back. After the cold water and air is deposited, warm water is used, but now the eyes will turn toward the affected ear and then slowly back to the front.
Videonystagnometry – One of the more common tests using a three-part vestibular function approach. These include caloric testing, ocular motor, and positional testing. Further, VHIT - video head impulse testing – and rotation tests can be added to the diagnostics to monitor head rotation at different angles and eye movement as a response. These tests check the integrity of the reflexes.
What Are Common Signs Of Vestibular System Disorders?
There are a few common symptoms of vestibular dysfunction, and it can manifest in the following manners –
- Visual disturbances
- Vertigo
- Nausea
- Changes in hearing or hearing loss/tinnitus
- Cognitive deficits
- Restlessness
Although some of these symptoms can be related to other diseases or conditions, if there are no significant results in blood tests, the diagnostic modalities should positively point to a vestibular disorder.
The link between cognition and the vestibular system is still mysterious. There seems to be a link between a vestibular disturbance and diminishing learning abilities, spatial navigation, object recognition, and memory capacity.
In the physiopathological study of vertigo, there are two types: central vertigo and peripheral vertigo. The more common of the two is peripheral vertigo. The most common causalities are –
- Meniere's disease
- Viral labyrinthitis
- BPPV or Benign Paroxysmal Positional Vertigo
Meniere’s Disease -
Caused by unknown factors, Meniere’s is diagnosed when there is an excess of fluid in the inner ear. The endolymph volume expands inside the membranous labyrinth, and that fluid volume impacts the cochlea and vestibular apparatus.
Vertigo triggered by Meniere’s can last for hours, causing nausea and dizziness and resulting in tinnitus and loss of hearing. There isn't currently a cure for Meniere's disease, but it is typically treated symptomatically with diuretics, anti-vertigo medication, surgical decompression of the endolymphatic sac, and a low sodium eating plan.
Viral Labyrinthitis / Vestibular Neuritis-
Viral neuritis causes peripheral vertigo as a result of an inflamed vestibular nerve. The other cause can be a viral infection in the inner ear, causing the vestibular nerve to be affected. The presenting symptoms are loss of balance and hearing simultaneously.
These distressing symptoms can last from a few days to several weeks. Because it is usually a viral infection, antibiotics are not readily prescribed, and treatments are symptomatic. These treatments include anti-inflammatory and pain medication, anti-vertigo medication, and sometimes a walking aid such as a crutch or a cane.
A walking aide is usually suggested for older patients due to the risk of falling and injury.
BPVV – Benign Paroxyxmal Positional Vertigo –
The most common and short-lived peripheral vertigo presentation is the BPVV lasting a few seconds to minutes. It is believed it is due to otoconia being displaced inside the posterior semicircular canal.
It creates a feeling of swaying, dizziness, and movement for a few seconds or minutes. The most successful treatment for BPPV is the Epley maneuver which an ENT Specialist or a Chiropractor can perform. The Dix-Hallpike test can be used to diagnose BPPV.
The Epley maneuver is performed by rotating and tilting the head sequentially to reposition the otoconia. In severe cases, anti-vertigo medication can be prescribed.
Aspirin Toxicity or Salicylate Poisoning -
Aspirin poisoning is ototoxic and can be a life-threatening condition. One of the results of aspirin poisoning is hearing damage, but fortunately, it is reversible. Symptoms of aspirin poisoning are disorientation, nausea, vomiting, metabolic acidosis, and tinnitus.
Treatment is with sodium bicarbonate and dextrose.
What Can Cause Vestibular Balance Disorders?
A vestibular balance disorder can affect anyone at any time and have numerous causes. Because the inner ear is so delicate and nerve-rich, it presents rapidly. The following causes are the most common –
- Bacterial or viral ear infections.
- Over 200 ototoxic medicines like aspirin and quinine.
- Poor blood circulation in the inner ear
- Traumatic brain injury
- Excess calcium deposits in the semicircular canals
Common Symptoms Of Vestibular Balance Disorders
The most common symptoms of vestibular balance disorders present as follows –
- Blurred vision
- Sudden loss of balance
- Dizziness and being off balance
- Feel like you're on the ocean swaying side to side
- Disorientation
- Falling
- Nausea
- Vomiting
- Fainting
- Anxiety attack
- Rapid heart rate
How Is Vestibular Balance Disorder Diagnosed?
If going to your regular GP does not result in a favorable diagnosis, they may refer you to a specialist called an ENT or Ear, Nose, and Throat specialist. These physicians specifically diagnose and treat related conditions.
The following tests or examinations can be expected from the ENT –
- General examination
- A detailed examination of the ears, nose, and throat
- Blood tests
- Hearing test
- Eye test
- Occupational tests to determine the patient’s balance
- A posturography scrutinizing movement and posture
- CAT scan or an MRI scan
- Doppler imaging
How Is Vestibular Balance Disorder Treated?
Depending on the diagnosis of the cause, the ENT specialist will prescribe the treatment best suited to the patient but can include the following –
Lifestyle changes – Many times, a lifestyle change such as quitting smoking and alcohol or a dietary change like cutting out sugar is all that is needed to promote healing.
Epley Maneuver – Used effectively to reposition the calcium particles in the semicircular canals.
Treatment for the underlying root cause – Antibiotics for bacterial infections or antifungal medications may be prescribed alongside anti-inflammatory and pain medications.
Surgical intervention – Used only when all other treatment methods have failed.
Rehabilitation – After surgery, you may need to undergo rehabilitation for a period. Vestibular rehabilitation is fairly specialized, and the therapists will help you with the following areas -
- Using a walking aide like a cane, walker, or crutches
- Walking outside on uneven surfaces
- Driving if possible
- Climbing stairs
- Bathing and going to the bathroom
- How to dress safely
- Securing your home and identifying hazards
- Adding rails in designated areas such as the shower
Conclusion
The vestibular system is critical to the body in terms of balance and mobility. A vestibular disturbance or disorder can be devastating and create permanent changes in daily functions.
If you experience sudden onset vertigo, it’s a good idea to have it looked at to determine the root cause and get early treatment.
Resources
https://www.ncbi.nlm.nih.gov/books/NBK557380/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916785/
https://en.wikipedia.org/wiki/Vestibular_system
https://www.britannica.com/science/ear/The-physiology-of-balance-vestibular-function
https://www.webmd.com/brain/vestibular-disorders-facts
