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Vestibular System

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Have you ever wondered how the sense of balance works in our body? When do we say that our body is in a balanced condition? Is there any special organ that is involved in the balance? What is the vestibular apparatus function?

To Answer All the Mentioned Questions Let Us Go Through an Important Concept. 

Balance is the capability of maintaining the center of mass of a body to its base that provides supports. If a system is said to balance properly, then it should work constantly. These works include clear vision even in case of motion, can make automatic adjustments to the postures, can determine the speed, can identify the things, and has stability in activities and several conditions. It can be achieved by a complex set of control systems that include sensory input required for the vision, proprioception for the touch, and the vestibular system for several senses such as equilibrium, motion, and spatial orientation. The deeper portion of the ear, that's the inner ear, is present just below the brain, where one part of it does the job of hearing and the other part is called the vestibular system. Let us learn more about it.


Vestibular System Anatomy

The vestibular meaning is as follows, it is a sensory system found in invertebrates that contributes to the sense of balance and for the spatial orientation of the body. As the movements consist of rotations and translations, this system consists of two components as otoliths and semicircular canals. These systems send signals to the neural structures that can control the movement of the eye, this signal is a vestibulo-ocular reflex. The signals are also sent to the muscles that help to maintain an upright posture. The signals are sent to the brain with the help of that and from the proprioception helps the individual to understand the kinematics and dynamics of the body. 


Semicircular Canal System: It helps in the detection of rotational movements. In each labyrinth, the vestibular system consists of three semicircular canals. These are present orthogonally to each other. These are known as horizontal canals, anterior semicircular canals, and posterior semicircular canals. These anterior and posterior semicircular canals collectively known as vertical semicircular canals. 


The rotation of the head around the vertical axis is correspondent to the movement of the fluid present in the horizontal semicircular canal. The rotation of the head in the sagittal plane and the frontal plane is detected by anterior and posterior semicircular canals. These two canals are oriented about 45 degrees approximately to the frontal and the sagittal planes. This movement of the fluid helps to push the specialized structure called the cupula. This cupula consists of hair cells that help in the transmission of mechanical movements to electrical signals. 


These canals are arranged in such a way that the canal present on the left side is in parallel with the canal present to the outside. These canals are worked in a push-pull manner. If one canal is said to be stimulated the other parallel counter one will be inhibited. This specialized system helps to sense in all the possible directions. When the right horizontal canal gets stimulated by the rotation of the head to the right side of the body, the left horizontal canal gets inhibited to the left due to the head rotation.


The images on the retina are stabilized during the head movement due to the reflex eye movement or vestibulo-ocular reflex (VOR). It happens by preserving the image in the centre of the visual field when the movement of the eye is in the opposite direction to that of the head. To stabilize the vision, VOR is important. VOR does not work on the principle of the visual input instead it can work even in the case of closed eyes or in darkness. In patients whose VOR is said to be impaired, they often find it difficult to read as they cannot stabilize their eyes. 


The principle of the push-pull system acts as a basis for the Halmagyi-Curthoys test or Rapid head impulse test. 

Otolithic Organs: 

It is another type of vestibular organ. These organs can sense linear accelerations. On each of their sides, the human has an otolithic organ. One organ is called the utricle and the other is called the saccule. These utricles consist of hair cells and the supporting cells are known as the macula. These organs are found in the saccule as well. Each of the cells of a macula has one true cilium called the kinocilium and approximately 40 to 70 stereocilia. The otolithic membrane is present on the tips of the cilia these membranes are made of protein calcium carbonate granules called otoconia. These membranes help to increase the sense of motion and gravity. The stimulation in the form of a combination of these two organs results from the orientation of the head. The head orientation is interrupted by the brain as it starts comparing the inputs to each other. These include the inputs from the eyes and the receptors that are responsible for stretching the neck. By comparing these results the brain detects if the head is tilted or the whole body is tipping. These organs can sense quickly depending on the motion to the left or right or up or down or forward or backward. 

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Nerve, Ganglion, and Nuclei

  1. Vestibular Nerve: It helps to transmit the equilibrium signals from the vestibular apparatus. It enters the posterior cranial fossa through the internal auditory meatus from the inner ear. It synapses in the brain stem with the vestibular nuclei. These are the only cranial nerves that make their first-order neurons synapse with the cerebellum directly. This feature makes this nerve unique. 

  2. Vestibular Ganglion: The vestibular ganglion also known as the ganglion of Scarpa is found lying in between the internal auditory meatus. The bipolar sensory neurons are known as the first-order neurons of the vestibular pathway. The peripheral process of these ganglions consists of the nerve fibres that help to receive the stimuli from the hair cells present in the semicircular canals and the otolithic organs. The central processes of ganglion consist of the nerve fibres that are a portion of the vestibulocochlear nerve. 

  3. Vestibular Nuclei: The four nuclei are combined known as vestibular nuclei. It lies in the brainstem within the rhomboid fossa. These contain second-order neurons that synapse in the vestibulocochlear nerve. These nuclei include:

  • Superior vestibular nucleus

  • Lateral vestibular nuclei

  • Inferior vestibular nuclei

  • Medial vestibular nuclei

The inputs from the cristae ampullary present in the semicircular canals are received by superior and medial vestibular nuclei. The remaining fibres in the semicircular canal, utriculate, and saccule are sent to lateral and inferior nuclei. 


Mechanism of the Balance System

The body balances the work by providing complete and continuous assistance through the processes such as feedback, detection of position, and communication between the eyes, ears, muscles, brain, and joints. 

  • Brain’s Movement Control Centre: The small portion of the brain that is present at the back of the head where it meets the spinal cord is the cerebellum. It receives signals from the ear, eyes, joints, and muscles about the position of the body. In return, it sends signals to the muscles to make the adjustments that are required to maintain the body’s balance.

  • Position Feedback from Ear: The vestibular system present in each of the ear three semicircular canals and two otolith organs. These canals and organs combined to provide feedback to the cerebellum about the movement of the head. There are different types of orientation in order to detect the movements. The fluid is present inside the canals, which is responsible for the stimulation of the hair cells which sends the messages to the cerebellum through the vestibular nerve or the balance nerve. The otolithic organs send signals to the brain in a straight line about the body movement and the relation of the head to the gravity that is the head is tilted, or lying down or leaning. 

  • Position Feedback from Eyes, Joints, Muscles, and Skin: The balance mechanism works with the visual system in order to prevent the blurring of the objects when the head rotates. It also provides awareness of the position while running, walking, or riding a vehicle. Along with the visual system the sensors present in the skin, muscles, joints provide information about the movement to the brain. The position is known in relation to the other body parts and with the environment. By utilizing this feedback the signals are sent to the muscles in order to move or make the required adjustments to maintain the balance and the coordination of the body. 

Vestibular Disorders

If any disease or injury to the processing areas then vestibular disorders occur, it can occur from environmental conditions or by genetic conditions, it not only can occur but can be worsened. The problems that are related to vestibular dysfunction include the complications that occur due to autoimmune disorders, ageing, and allergies.

  1. Acoustic Neuroma: It is also called a vestibular schwannoma. It is a nonmalignant but serious tumor that appears on the sheath of the vestibulocochlear nerve of the inner ear. The vestibulocochlear nerve is also called an acoustic nerve, and since the disease is associated with it leads to the name. The effects of this disease are loss of hearing, dizziness, or loss of balance.

  2. Age-Related Dizziness and Imbalance: The dizziness found in elder people is due to problems that occur with the vision system, related to the brain or vestibular system. Approximately 50% of older people are associated with dizziness due to these reasons.

  3. Autoimmune Inner Ear Disease (AIED): The immunity system can attack the whole body or some particular systems. If it attacks the inner ear then it is called AIED.

  4. Benign Paroxysmal Positional Vertigo (BPPV): It is a common disorder that can cause dizziness or other symptoms due to the debris, this debris is known as otoconia that include small crystals of calcium carbonate. This otoconium is displaced and sends false signals to the brain.

  5. Bilateral Vestibular Hypofunction: The loss of functioning of the vestibular system bilaterally results in difficulty in maintaining a balance of the body. This maintaining of balance is especially due to walking on uneven surfaces or in dark. 

  6. CANVAS Syndrome: The CANVAS is an acronym for cerebellar ataxia, neuropathy, and vestibular areflexia. The patients who get affected by this disease are very rare. It is a combination of two different clinical findings, cerebellar ataxia, and vestibular areflexia and the common one is peripheral neuropathy. As each of these systems contributes to the balance malfunctioning of all these at the same time can worsen the balance of the body.

  7. Cervicogenic Dizziness: The neck pain is accompanied by dizziness, but it is difficult to tell if the neck pain and dizziness are coincidental or related. True spinning vertigo is rarely associated with the syndrome thus Cervicogenic Dizziness is the suitable name. There are no tests to confirm the cause of the disease.


  1. Cholesteatoma: The abnormal growth of the skin that is found in the inner ear is called Cholesteatoma. It is usually caused by an infection that occurs repeatedly which can take the form of a cyst or a pouch where the old skin layer sheds inside the ear. It can increase the size and is able to destroy the surrounding bones present in the middle ear. This results in the loss of hearing, paralysis of facial muscles, and dizziness. 

Vestibular Rehabilitation

The symptoms that occur due to vestibular disorders can destroy the quality of life. They can contribute to emotional problems such as depression and anxiety. People with vestibular disorders often find the problems that are related to vertigo, visual disturbance, dizziness, and imbalance. There are some other secondary disorders that are related to vestibular are vomiting, nausea, fatigue, or reduction in concentration or focus. Hence, vestibular rehabilitation therapy (VRT) can help to overcome these symptoms. 


VRT is a specialized type of therapy that is used to treat both the primary and secondary related problems associated with the vestibular system. It is an exercise-based program that is designed to reduce dizziness, falls, or imbalance and gazes instability. For the people who are affected by VRT the ability to recover is difficult. After the damage of the vestibular system, the brain learns to use other senses in order to substitute for the damage.


In some people, the symptoms will reduce naturally, in case there is no recovery then VRT can help the people to promote the compensation by suggesting some exercises to address the specific problems. Habituation exercise is used to reduce dizziness through specific movements or visual stimuli. Gaze stabilization exercises are used to improve vision by improving the control of eye movements. The balance training exercises are advised to improve balance and steadiness. These balance exercises are used to reduce the barriers that are present in the environment and avoid the risk of falling sick. It increases the posture of bending, standing, turning, reaching, walking, and other activities. It is important to establish exercises that can be performed easily at home.


There are some factors that can limit the recovery of the diseases, those factors include lifestyle such as being inactive. The people will sometimes restrict the exercise movements or the level of activity to reduce the pain. Emotional concerns, decompensation, usage of other medications, or presence of other medical conditions. 


Conclusion

According to vestibular meaning, it helps to maintain the posture. It helps to coordinate with the eye and head movements, it also enables visual fixation. It is the sensory system present in the ear that is responsible for maintaining balance in the body. This system is present in the inner ear, which is located just below the brain. It is present exactly in the system of bony tubules, and the petrous part of the temporal bone which is considered as a part of the skull. Thus the vestibular system plays an important role but it gets weakened as a person gets aged.

FAQ (Frequently Asked Questions)

1. What is the Vestibular Labyrinth?

Ans: The vestibular labyrinth is the organ that is present in the temporal bone that sends signals directly to the cerebellar cortex and nuclei. These signals are the primary afferent projections. It is responsible for providing information to the brain about the position of the head, motion, and spatial orientation. It also performs some of the motor functions to keep and maintain balance, to stabilize the body and the head movement by maintaining the correct posture.

2. What are the Two Types of Hair Cells in the Vestibular Apparatus?

Ans: The vestibular hair cells are divided into two types:

  • Type I, these are thinner and goblet in shape. 

  • Type II, these are columnar types.

The hair cells are the primary sensory receptors present in the ear that converts mechanical stimuli into electrical signals. Both types of hair cells are present in the central and peripheral zones of all the five organs of the vestibular system. The semicircular canals use these hair cells to detect the movement of fluids along with the stereocilia.