Vestibular system

<languages /><translate> The vestibular system are located in the labyrinth in the inner ear and are the balance organs.

Vestibular System

Anatomy

The vestibular system, which is key to our senses of balance, motion, and body position, is comprised of three semicircular canals connected to two membranous sacs called the saccule and utricle.

Otolith organs

The saccule and utricle are often referred to as the otolith organs. The otolith organs allow us to sense the direction and speed of linear acceleration and the position (tilt) of the head.

Semicircular canals

The semicircular canals allow us to sense the direction and speed of angular acceleration. The semicircular canals are oriented along three planes of movement with each plane at right angles to the other two. Pilots and astronauts call these three planes of rotation pitch

Fixed gaze

The vestibular system also helps you maintain a fixed gaze on a stationary or moving external object while you are undergoing complex head and body movements.

Vestibular Physiology

Inner ear. Cochlea and vestibular system from MRI data.

The Semicircular Canals

• The semicircular canals are a set of three membranous tubes embedded within a bony structure of the same shape.
• The central cavity of each canal is filled with a fluid called endolymph.
• Each endolymph-filled canal has an enlarged area near its base called an ampulla.
• Parts of the vestibular nerve penetrate the base of each ampulla and terminate in a tuft of specialized sensory hair cells.
• The hair cells are arranged in a mound-like structure called the ampullary crest.
• Rising above the ampullary crest is the cupula, consisting of the hair-like extensions of the hair cells surrounded by a gelatinous material arranged into a wedge-shaped structure.
• This structure consisting of the ampullary crest and the cupula is called a crista.
• When the endolymph moves (or the cupula moves and the fluid remains stationary), the gelatinous tip of the cupula and the hair cell extensions embedded within it are displaced to one side or the other.
• When the embedded hair cells bend, they send a signal via the vestibular nerve to the brain where the information is evaluated and appropriate action is initiated.
• The mechanics of how the semicircular canals actually function to "sense" angular acceleration may be more easily understood by reviewing the physics of inertia.
• The Law of Inertia states that "a body at rest remains at rest unless acted upon by an unbalanced force."
• This is important because angular acceleration and deceleration primarily affect the semicircular canals and entirely depend on the relative movement of endolymph with respect to the cupula.

Vestibular implant

Saccule and Utricle

• The saccule and utricle are referred to collectively as "the otolith organs".
• They sense linear acceleration and are affected by gravity.
• They also provide you with information concerning changes in head position (tilt).
• Because of the way they are situated within the vestibular apparatus, the saccule is more sensitive to vertical acceleration (like riding in an elevator) and the utricle is more sensitive to horizontal acceleration (riding in a car).
• Both the saccule and the utricle contain a thickened patch of specialized cells called a macula that consists of sensory hair cells interspersed with "supporting" cells.
• The free hair-like tufts extending from the hair cells are embedded in a gelatinous otolithic membrane which supports small piles of calcium carbonate crystals on its surface.
• Collectively, these calcium carbonate crystals are called otoliths.
• The otoliths increase the mass of the otolithic membrane and give it more inertia.
• When the head is tilted to the left or right, forward or back, the otoliths tend to move along the gravity gradient (downwards).
• Even a slight movement of the otolithic membrane is enough to bend hair cells and send sensory information to the brain. A similar inertia and gravity-dependent process occurs when you accelerate linearly -- up or down, forward or backward.
• The underlying physiology and functioning of the otolith organs are remarkably similar to those of the semicircular canals.
• Both systems depend upon inertia and the mechanical deflection of hair cells to initiate nerve impulses that are sent to the brain and interpreted as body movement.
• The brain then reflexively initiates appropriate "corrective" actions within the nervous, visual, and muscular systems to ensure that situational awareness and balance are maintained.

Vestibular Sense

Otolith organ of vestibular system

• Humans sense position and motion in three-dimensional space through the interaction of a variety of body proprioceptors, including muscles, tendons, joints, vision, touch, pressure, hearing, and the vestibular system.
• Feedback from these systems is interpreted by the brain as position and motion data. Our vestibular system enables us to determine body orientation, senses the direction and speed at which we are moving, and helps us maintain balance.
• When there is no visual input as is common in many flight situations, we rely more heavily on our vestibular sense for this information.

GLOSSARY

• Ampulla - (pl = ampullae) expanded area within each semicircular canal which contains a crista; used to detect angular acceleration.

• Angular acceleration - a simultaneous change in velocity and direction (as in spinning); sensed by the semicircular canals.

• Crista - (pl = cristae) within ampullary region of semicircular canal; name given to structure composed of ampullary crest (hair cells) combined with the cupula.

• Cupula - One component of a crista; sits atop ampullary crest and is composed of hair-like extensions of sensory hair cells embedded within a gelatinous mass.

• Endolymph - fluid within semicircular canals which, when it moves, deflects the cupula and initiates the sensation of angular acceleration.

• Hair cells - common name given to sensory cells located within the ampullary crest of semicircular canals and the macular region of saccule and utricle (otolith organs).

• Inertia - the fundamental property of inert material tending to resist changes in its state of motion. Macula (pl = maculae) thickened area within saccule and utricle consisting of hair cells and supporting cells. In both the saccule and utricle, the macula is covered by the gelatinous otolithic membrane containing otoliths.

• Linear acceleration - a change in velocity without a change in direction (up and down or side to side); sensed by the otolith organs.

Vestibular balance system

• Macula - thickened area within saccule and utricle consisting of hair cells and supporting cells. In both the saccule and utricle, the macula is covered by the gelatinous otolithic membrane containing otoliths.

• Momentum - tendency of a body in motion to resist a change in that motion.

• Nystagmus - repeated rapid eye movements.

• Otoliths - calcium carbonate crystals adhering to and embedded within otolithic membrane of saccule and utricle (otolith organs).

• Otolith organs - saccule and utricle, primarily responsible for sensing linear acceleration as well as head position (tilt).

• Pitch - rotational motion carried out along a front to back vertical plane.

• Roll - rotational motion carried out along a lateral vertical plane.

• Saccule - one of the two types of otolith organs of the vestibular system; used to sense linear acceleration and the position (tilt) of the head.

• Semicircular canals - three fluid filled circular tubular structures within each inner ear which are arranged at right angles to each other and are responsible for sensing angular acceleration.

• Sensory hair cells - common name given to sensory cells located within the ampullary crest of semicircular canals and the macular region of saccule and utricle (otolith organs).

• Somatosensory - integrated sensory system which combines individual inputs from skin, muscles, tendons and stretch receptors throughout the body.

• Vestibular system - the semicircular canals and the otolith organs (Responsible for sensing angular and linear acceleration, respectively.)

• Yaw - rotational motion carried out along a horizontal plane.

Vestibular system Resources
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