Vestibular System Physiology and Anatomy

Comprehensive vocabulary flashcards covering the anatomy, physiology, pathways, reflexes, and clinical concepts of the vestibular system based on the lecture notes.

Primary Functions of the Vestibular System

Gaze stability, postural stability, and orientation to gravity.

Vestibulo-Ocular Reflex (VOR)

A reflex that moves the eyes equal and opposite to head movement to keep a visual target stable on the retina.

Three-Neuron Arc of the VOR

The pathway consisting of vestibular afferent to vestibular nucleus, vestibular nucleus to ocular motor nucleus, and ocular motor neuron to the extraocular muscle.

Eye Movement in Rightward Head Turn VOR

The eyes move left through the VOR during a normal rightward head turn to maintain fixation on the target.

Vestibulospinal Reflex

Vestibular activation of spinal motor pathways that helps maintain posture, equilibrium, and antigravity muscle activity.

Vestibulocollic Reflex

A reflex that activates neck muscles to stabilize the head relative to gravity and body movement.

Cervico-Ocular Reflex

A reflex using cervical proprioceptive input to help stabilize gaze during trunk or neck movement.

Otolith Organs

The utricle and saccule, which primarily provide orientation to gravity.

Three Sensory Systems of Balance

The vestibular, visual, and somatosensory/proprioceptive systems, which contribute most directly to maintaining balance.

Bony Labyrinth

The rigid outer structure of the inner ear formed by the semicircular canals, vestibule, and cochlea.

Membranous Vestibular Labyrinth

The internal system composed of the semicircular ducts, utricle, and saccule.

Perilymph

The fluid that fills the bony labyrinth around the membranous labyrinth.

Endolymph

The fluid that fills the membranous labyrinth.

Vestibule

The central portion of the bony labyrinth that contains the utricle and saccule.

Semicircular Canals

The anterior (superior), posterior, and horizontal (lateral) canals that detect angular or rotational acceleration of the head.

Ampulla

The widened portion of each semicircular duct that contains the sensory receptor for angular acceleration.

Crista Ampullaris

The sensory epithelium within the ampulla that contains vestibular hair cells.

Cupula

A gelatinous structure over the crista ampullaris that bends with endolymph movement and deflects hair cells.

Vestibular Hair Cells

Sensory cells that convert mechanical deflection caused by head movement into changes in vestibular nerve firing.

Stereocilia

Graded hair-like projections on vestibular hair cells that bend during mechanical stimulation.

Kinocilium

The tallest polarized projection on a vestibular hair cell that determines whether deflection excites or inhibits the cell.

Hair Bundle Deflection Toward Kinocilium

Deflection pattern that causes the vestibular hair cell to depolarize and increases vestibular afferent firing.

Hair Bundle Deflection Away From Kinocilium

Deflection pattern that causes the vestibular hair cell to hyperpolarize and decreases vestibular afferent firing.

Tonic Vestibular Nerve Firing

The baseline or resting firing rate of the vestibular nerve that allows head movement to be encoded through either an increase or a decrease in firing rate.

Semicircular Canal Orientation

The arrangement of the semicircular canals in approximately perpendicular planes to detect rotations in three dimensions.

Horizontal Semicircular Canal Angle

The orientation of the horizontal semicircular canal relative to true horizontal, which is tilted upward approximately $30$\text{ degrees} when the head is upright.

Coplanar Pairs

Functional pairs of semicircular canals consisting of the right anterior with left posterior, left anterior with right posterior, and the two horizontal canals with each other.

Vestibular Push-Pull System

A functional mechanism where head rotation excites a canal on one side while inhibiting its coplanar partner on the opposite side.

Superior Vestibular Nerve

The nerve branch that mainly innervates the anterior canal, horizontal canal, and utricle.

Inferior Vestibular Nerve

The nerve branch that mainly innervates the posterior canal and saccule.

Scarpa's Ganglion

The vestibular ganglion containing the cell bodies of primary vestibular afferent neurons.

Vestibular Nuclei

Central nervous system nuclei located primarily in the pons and medulla of the brainstem.

Central Connections of Vestibular Nuclei

Major projections from the vestibular nuclei to the ocular motor nuclei, cerebellum, spinal cord, thalamus/cortex, and autonomic centers.

Medial Longitudinal Fasciculus (MLF)

A brainstem pathway that links vestibular nuclei with ocular motor nuclei to coordinate conjugate eye movement.

Cochlea

An inner ear structure responsible for converting sound vibration into neural signals for hearing.

Labyrinthine Artery

The artery directly supplying the inner ear, which most commonly arises from the anterior inferior cerebellar artery (AICA).

AICA-Territory Event Presentation

Acute vertigo paired with new unilateral hearing loss, occurring because the AICA commonly supplies both central vestibular structures and the labyrinthine artery serving the inner ear.

Sensory Reweighting

The central nervous system's adjustment of how much it relies on vestibular, visual, and somatosensory information for balance.

Visual Compensation in Balance

The increased reliance on visual input for balance when vestibular or somatosensory information is impaired and the environment provides a stable visual reference.

Vestibular Reliance Conditions

Situations such as darkness, unstable surfaces, or rapid head movement where vestibular input becomes critical because vision or somatosensation is unreliable.

Vestibular Loss with Peripheral Neuropathy in Darkness

A clinical situation causing extreme instability because darkness removes visual compensation while vestibular and somatosensory inputs are already impaired.

Benign Paroxysmal Positional Vertigo (BPPV)

A condition occurring when otoconia, usually displaced from the utricle, enter a semicircular canal or attach to a cupula and make the canal abnormally gravity-sensitive.