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Vestibular System

Introduction

The vestibular system works to detect motion and gravity and initiates movement to maintain balance and orientation. It includes the part of the inner eyes and brain that process the sensory information involved in controlling eye movement and balance. Vestibular apparatuses are the small organs that lie within the temporal bone.  The sensory afferents are present that link to the vestibular nuclei within the brain stem.  The cerebellum and cortex influence the vestibular system’s activity to provide a high degree of adaptability. This system comprises several tracts and structures, but the system’s main components are present in the inner ear in the course of interconnected compartments called vestibular labyrinth. 

The vestibular nuclei in the system pass the information on to various targets, ranging from the eye’s muscles to the cerebral cortex. The system is essential for normal movement and equilibrium. Any injury or disease that damages these processing areas causes’ vestibular disorders. The severity of symptoms varies. People affected by the vestibular system’s symptoms may be perceived as lazy, overly anxious, or seeking attention.

Anatomy Of Vestibular System

The vestibular system, which is a system of balance, consists of five distinct end organs. The most important parts to consider in the vestibular system’s anatomy are the three semicircular canals and two otolith organs.  The central elements are composed of the conductive portion, vestibular nuclei in the brain stem, and cortical representation.

Labyrinth

The bony labyrinth is located in the temporal bone.

They are the balance center located in the inner ear. The membranous labyrinth of the vestibular system is in the middle of the bony labyrinth, resembling its small cavities. Helical formations act as shock absorbers that fix membranous labyrinth to the inner wall of the bony labyrinth. They serve both hearing and balance.

Also, the membranous labyrinth consists of the peripheral acoustic section of the cochlea, and it is where the auditory receptor organ of the Corti and even the peripheral component of the vestibular system. They consist of epithelial hair cells and are housed within an elaborately shaped chamber called the membranous labyrinth. The fluid contained in this labyrinth is called endolymph.

Peripheral Vestibular System  

The Peripheral vestibular system is situated behind the inner ear. It consists of a vestibular nuclear complex, which generates motor commands to drive the eyes and the body. The PVS is very accurate, and it is maintained and calibrated by the cerebellum.

Semicircular Canals

They are specialized mechanoreceptors to help access information regarding angular velocity. They are hollow passageways looping out from and back to the vestibule. The sensory input known as Vestibular Ocular Reflux generates an eye movement that matches the velocity of the head movement.

Otoliths

They are made of the Utricle( horizontal )and Saccule( vertical). They perform the job of giving us information about linear acceleration by triggering the brain’s action potential to detect head position. Otoconia are little calcium carbonate crystals, and they are embedded in the otolithic membrane. The correct formation and anchoring of otoconia are essential as they are essential for optimal vestibular function and maintain body balance.

Central Vestibular System

There are two main targets of the vestibular information from the primary input: the vestibular nuclear complex and the cerebellum.

Vestibular Nuclear Complex

This complex consists of four significant nuclei, superior, medial, lateral, and descending. This complex structure is located primarily within the pons, also extends caudally into the medulla. The superior and medial vestibular nuclei are the relays for the VOR, while the medial also coordinates head and eye movements that occur together.

Cerebellum

The cerebellum is one of the critical brain areas contributing to the coordination of movement and the motor cortex and basal ganglia. The cerebellum has input and output connections. It acts as a system that compensates errors by comparing intention with performance. 

Physiology Of Vestibular System 

The vestibular system is a complex set of structures and neural pathways that serve various functions and contribute to our senses of balance and equilibrium.

These functions include the sensation of orientation and acceleration of the head in any direction, and it offers compensation in eye movement and posture.

These reflexes are referred as vestibule–ocular and vestibulospinal reflexes.

Recent studies suggest that the vestibular system plays a role in consciousness, and dysfunctions of the system can cause cognitive deficits related to spatial memory, learning, and navigation.

Function 

This system functions to detect the head’s position and movement in space and allows coordination of eye movements and posture and coordination related to equilibrium.

The Utricle and the Saccule play an essential part in the tilting of the head. The three semicircular ducts oriented at right angles perform angular acceleration and head rotation in different planes.

In addition to the functions associated with the peripheral vestibular system, such as interpretation of the afferent signals is and output of efferent signals, Efferent signs include vestibule reflux. This reflux allows the eyes to remain fixed on an object while the head is moving. Cognitive functions that involve the central vestibular system depend on the neural pathways. The complex pathways and connections involved in the system play a functional role in self-motion, perception, spatial navigation, spatial memory, and object recognition memory.

Mechanism 

Acceleration of the endolymph within the various vestibular apparatus structures is involved in the peripheral vestibular system’s mechanism.

This acceleration results in head movement, and when the head stops accelerating, the hair cells return to their original position. The primary processor of vestibular signals is the vestibular nucleus complex. This complex extends from the rostral medulla to the caudal pons. The vestibular nucleus sends many calls to the thalamus, cortex, or cerebellum to either process and adjusts efferent signals to postural or ocular muscles. Apart from that, the hippocampus plays a vital role in spatial memory, including navigation and orientation functions.

Clinical Importance Of Vestibular System

Dysfunction of the vestibular system can show vertigo, vomiting, visual disturbance, hearing changes, and various cognitive defects. Many patients with vestibular defects exhibit impairment of spatial navigation, learning, memory, and object recognition. The balance system is activated whenever there is a concern about movement, and the vestibular system plays an integral part in balance and equilibrium. The majority of pathologies lie within the vestibule. Therefore, it is crucial to understand all the receptors involved in the system. The system’s primary function is to adjust the head, neck, and trunk position necessary to maintain balance. Your doctor performs several tests to examine the vestibular disorders. The tests include a hearing exam or vision exam. Some imaging tests are also conducted to diagnose vestibular disorders, along with blood tests. Look at your posture and movement using a structured exam called posturography.

If a disease or injury damages this system, it may result in vestibular disorder. You can also have problems with your hearing and vision. Along with that, dizziness is experienced by some patients with balance issues.

Benign paroxysmal positional vertigo ( BPPV)

BPPV is the most common cause of positional vertigo, and you feel like you are spinning or swaying. The tiny crystals in the ear travel to an area where they should not be. BPPV can be treated with head movements, and the crystals travel back to the right position.

Labyrinthitis 

Labyrinthitis is an inner ear infection. It happens when a fragile structure labyrinth gets swelled. Common symptoms include,

  • Problem with hearing and balance
  • Ear pain and pressure
  • In labyrinthitis, pus can come out from the ear.
  • Nausea 
  • High fever

In case of bacterial infections, doctors usually prescribe antibiotics to ease the symptoms. To reduce inflammation, doctors may recommend steroids. Antiemetics can help with dizziness and vomiting.

Vestibular Neuritis

A viral infection somewhere else in the open can cause imbalance and affect the nerve that sends sound and balance information from your inner ear to your brain. Common symptoms include

  • Nausea
  • Vomiting
  • Sudden dizziness
  • Trouble walking

Your doctor may prescribe antiviral to wipe out the virus.

Meniere’s disease 

Meniere’s disease may be caused by much fluid in the inner ear due to virus allergy or autoimmune reaction. Symptoms include,

  • Sudden attacks of vertigo
  • Tinnitus
  • Hearing loss
  •  There is a feeling of fullness in the affected ear due to excessive fluid in the ear.

Perilymphatic fistula (PLF)

PLF is the tear or defect between your middle ear and fluid-filled inner ear that can make you feel dizzy and cause some hearing loss.

Surgery can help repair the perilymph fistulas. The openings or tears due to PLF can be plugged with tissue taken from the outer part of your ear.

Acoustic Neuroma

The tumor in your ear can squeeze the nerves that control your hearing and balance. It is not cancerous and grows slowly. The symptoms include,

  • Hearing loss
  • Dizziness
  • Ringing in your ear
  • Compression of nerves causes the side of your face to feel numb.

Ototoxicity

Some drugs and chemicals cause damage to your inner ear and lead to ototoxicity. It can cause hearing loss. It gets better when you stop taking the medication, or it gets permanent.

Enlarged Vestibular aqueducts 

Vestibular aqueducts are the narrow, bony canals that go from your inner ear to the inside of your skull. Their enlargement can cause hearing loss. The cause is not exact, but specific genes you get from your parents can cause this problem .the best way to safeguard is to avoid contact sports or anything that can lead to head injury .avoid anything that causes pressure on your head.

Vestibular Migraine  

If your brain sends the wrong signals to your body’s balance system, it can lead to vestibular migraines. The common symptoms are,

  • Severe headache
  • Dizziness
  • Sensitivity to sound or light
  • Hearing loss
  • Ringing in your ears
  • Blurred vision.

Anti-depressants and calcium channel blockers may help.

Summary

The vestibular system plays an integral part in the space orientation both at rest and in movement. The vestibular and auditory sensory systems are responsible for various activities, postural control, emotion, and creative thought.

It allows rapid movements in response to both self-induced and externally generated forces. It consists of two structures of the bony labyrinth of the inner ear, the vestibule, semicircular canal, and membranous labyrinth forms. The Saccule and Utricle, the two membrane sacs of the vestibule, are known as otolith organs. They respond to gravitational forces and are therefore known as gravity receptors. The cerebellum is an integral part of the vestibular system. The system of cerebellum compensates the errors by comparing intention with the performance.

The vestibular system involves detecting the heads position and movement. Along, it provides coordination, which is related to equilibrium. They have a characteristic epithelium known as the macule. The vestibular system’s nerve is the vestibulocochlear nerve and is concerned with the sensations of position and equilibrium. The system consists of the central elements, the conductive part, and the vestibular nuclei present in the brain stem.  The blood supply is derived from the labyrinthine artery. The vestibular system also works to detect motion along with gravity. The primary function of the vestibular system is the maintenance of balance. The stimulation of the hair cells present in them keeps the brain informed about the head’s position. When the head suddenly rotates, the displacement of endolymph causes depolarization or hyperpolarization .the system is also responsible for the eyes’ movement. This function causes the eyes to turn in the direction of movement of the head.

Balance disorders can strike at any age, especially in older age. Dizziness and vertigo are the most common symptoms of the vestibular system imbalance. The dysfunction is mostly caused by head injury, aging, and viral infection; genetic and environmental factors also play an essential role I the vestibular system dysfunction. Disequilibrium may lead to unsteadiness, imbalance, and spatial disorientation. The vestibular system’s common disorders include vestibular migraine, labyrinthitis, Meniere’s disease, age-related dizziness and imbalance, perilymph fistula. The treatment takes several weeks to recover a person .anti virals and antibiotics are helpful entirely. Some exercises such as head movements, slow marching in a straight line, yoga ) performing gentle stretches, especially the neck and back, can help with imbalance problems.

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