Vestibular System: Functions, Components, and Clinical Significance

What is the primary function of the vestibular system?

To help maintain balance, stabilize vision, and allow spatial orientation.

What are the main components of the vestibular system?

The maculae (utricle and saccule) and the crista ampullaris within the semicircular canals.

How does the vestibular system contribute to balance?

It integrates vestibular, visual, and somatosensory inputs within the central nervous system.

What role does proprioception play in the vestibular system?

It informs the brain about body part position, stretch, and pressure.

How does the vestibular system detect angular acceleration?

Through the semicircular canals.

What are the otolith organs, and what do they detect?

The saccule and utricle; they detect static tilt and linear acceleration.

What is the orientation of the utricle?

It is oriented horizontally with a 30° upward tilt toward the anterior.

What is the orientation of the saccule?

It is oriented vertically in the sagittal plane.

What are otoconia, and what is their significance?

Calcium carbonate crystals that increase specific gravity, aiding in the detection of gravitational pull and linear acceleration.

What condition can occur due to displaced otoconia?

Benign Paroxysmal Positional Vertigo (BPPV).

What happens during BPPV?

Dislodged otoconia enter a semicircular canal, causing vertigo and nystagmus when the head changes position.

What is the striola in the otolith organs?

A dividing line that allows for multidirectional sensitivity of hair cells.

How do hair cells in the utricle and saccule respond to movement?

Movement of otoliths deflects the cilia of hair cells, triggering neural impulses sent to the brain.

What is the role of the vestibular nerve?

To transmit signals from hair cells to the brain regarding head position and movement.

What is the primary sensor for head orientation relative to gravity?

The utricle.

What is the primary sensor for vertical movement?

The saccule.

What is the function of the cristae in the semicircular canals?

To detect angular acceleration during head rotation.

What fluid fills the membranous labyrinth of the vestibular system?

Endolymph.

What is the anatomical arrangement of hair cells in the utricle?

Hair cells are oriented with kinocilia facing the striola.

What is the anatomical arrangement of hair cells in the saccule?

Hair cells are oriented with kinocilia facing away from the striola.

What is the significance of the vestibular system in daily activities?

It plays a major role in maintaining postural stability and balance.

What happens to the vestibular system's input when environmental conditions vary?

Different sensory inputs dominate depending on stability: somatosensory on stable surfaces, visual on unreliable surfaces, and vestibular when both are compromised.

How does the vestibular system interact with visual and somatosensory inputs?

It integrates these inputs to maintain balance and spatial orientation.

What is the effect of head movement on the otolith organs?

The weight and movement of the otoliths deflect the cilia of hair cells, enabling the brain to detect gravity and linear deceleration.

What is the primary function of the saccule?

is most sensitive to vertical linear acceleration and contributes to maintaining postural stability.

How are the kinocilia oriented in the saccule compared to the utricle?

In the saccule, the kinocilia face away from the striola, opposite to the arrangement in the utricle.

What are the three orientations of the semicircular canals?

The three orientations are horizontal (lateral), posterior (inferior), and superior (anterior).

What is the role of the ampulla in the semicircular canals?

Each canal terminates in the ampulla, which contains the sensory organ called the crista ampullaris.

How do the semicircular canals function in pairs?

Each movement induces excitation on one side and inhibition on the other, forming a push-pull system for detecting angular acceleration.

What types of movements do the semicircular canals detect?

They detect yaw (shaking head 'no'), pitch (nodding 'yes'), and roll (tilting head sideways).

What is the vestibulo-ocular reflex (VOR)?

is a reflex where head movements cause eye movements that keep a target in view.

What is nystagmus?

is an involuntary rhythmic eye movement characterized by slow movement in one direction and rapid jerking in the opposite direction.

What triggers the fast compensatory movements in nystagmus?

Fast compensatory movements, known as saccades, are triggered by the position of the eye within the orbit.

What is the role of endolymph in the semicircular canals?

Endolymph flow is opposite to the direction of angular acceleration, providing information about head rotation.

What are the two principal pathways of the vestibulo-spinal reflex?

the Lateral Vestibulospinal Tract (LVST) and the Medial Vestibulospinal Tract (MVST).

What is the function of the lateral vestibulospinal tract?

The LVST extends throughout the spinal cord and is involved in controlling head, neck, trunk, and leg movements.

What is the function of the medial vestibulospinal tract?

extends only through the thoracic segments and is involved in controlling upper body and head movements.

What is the purpose of the Sensory Organization Test?

The test assesses balance and sensory interaction under various conditions, such as eyes open/closed and on different surfaces.

What does the Fukuda Stepping Test measure?

measures the ability to march in place with eyes closed, assessing vestibular function.

What is the crista ampullaris?

the sensory organ within the ampulla of the semicircular canals, containing hair cells.

How are hair cells oriented in the crista ampullaris?

in the same direction as defined by the kinocilia, with specific orientations for vertical and horizontal canals.

What is the significance of the cupula in the crista ampullaris?

The cupula is a gelatinous structure that hair cells project into, allowing them to respond to endolymph flow.

What happens to the firing rate in the vestibular system during head movements?

The firing rate increases in one canal and decreases in the paired canal during head movements.

What is the vestibulo-spinal reflex (VSR)?

a reflex that creates body movement to maintain posture and stabilize the body in response to vestibular system activation.

What is the role of Scarpa's ganglion in the vestibular system?

contains the cell bodies of sensory neurons that transmit information from the vestibular system.

What is the relationship between angular acceleration and endolymph flow?

Endolymph flow lags behind the motion of the canal, producing a deflection of the cupula opposite to the direction of head movement.

What is the clinical significance of nystagmus in vestibular testing?

Nystagmus is assessed to determine vestibular function; it should be present when expected and absent when not.