Vestibular System Overview

Superior Vestibular Nucleus

• Coordinates eye movements in response to head movements.

Lateral Vestibular Nucleus

• Controls muscle activity for posture and balance.

Largest Nucleus

• The lateral vestibular nucleus has the largest cell volume.

Ovoid Otocyst

• The ventral part of the ovoid otocyst develops into the saccule and cochlea.

Checkered Appearance

• The medial vestibular nucleus has a distinctive checkered appearance.

Medial Vestibular Nucleus

• The medial vestibular nucleus receives vestibular information from the semicircular canals and otoliths.

Bony Labyrinth

• Perilymph is the primary fluid found in the bony labyrinth.

Peripheral Vestibular System

• The peripheral vestibular system includes the semicircular canals, otoliths, and vestibular nerve.

Endolymphatic and Semicircular Ducts

• The endolymphatic and semicircular ducts become well represented during the 6th week of fetal development.

Vestibular Reflex

• The patellar reflex is NOT associated with the vestibular system.

Membranous Labyrinth

• The perilymphatic space suspends the membranous labyrinth within the bony labyrinth.

Perilymph and Cerebrospinal Fluid

• There is communication between perilymphatic fluid and cerebrospinal fluid through the cochlear aqueduct.

Semicircular Canals

• Semicircular canals are oriented in three planes: horizontal, anterior, and posterior.

Medial Vestibulo-spinal Tract

• The medial vestibulo-spinal tract (MVST) plays a primary role in stabilizing the head.

Lateral Vestibulo-spinal Tract

• The lateral vestibulo-spinal tract (LVST) enhances extensor muscle activity, supporting posture and balance.

Neck Muscles

• The cervico-ocular reflex stabilizes vision using input from neck muscles.

LVST

• One of the key functions of the LVST is to maintain posture by influencing muscle activity in the limbs and trunk.

MVST Neurons

• MVST neurons regulate neck muscle activity to ensure head stability.

Lateral Vestibulo-spinal Tract

• The lateral vestibulo-spinal tract primarily operates on the ipsilateral side of the body.

MVST Neuron Input

• Besides vestibular information, the spinal trigeminal tract provides input to MVST neurons.

Cervico-ocular Reflex

• The cervico-ocular reflex (COR) is distinguished from the vestibulo-ocular reflex (VOR) by the use of neck proprioception to stabilize vision.

Vestibulo-ocular Reflex

• The vestibulo-ocular reflex (VOR) primarily functions to stabilize vision during head movements.

Vestibulo-ocular Reflex Dysfunction

• If the vestibulo-ocular reflex is not functioning properly, vision will appear blurry during head movements.

Vestibular System and Posture

• The vestibulospinal reflex is responsible for adjusting muscle tone and maintaining body posture in response to head position changes.

Horizontal Eye Movements

• The horizontal semicircular canals and the medial vestibular nucleus are responsible for controlling horizontal eye movements.

Vestibular Nystagmus

• Eye movements during vestibular nystagmus are characterized by a slow drift in one direction and a rapid flick in the opposite direction.

Vestibular System & Balance

• The vestibular system works alongside other systems, like the visual and proprioceptive systems, to maintain balance.

Head Turning Movements

• The vestibulo-ocular reflex is crucial for head turning movements.

Vestibulo-ocular Reflex Response

• The vestibulo-ocular reflex responds to head movements by generating compensatory eye movements in the opposite direction.

Golgi Tendon Organs

• Golgi Tendon Organs sense muscle tension and provide information to the central nervous system.

Proprioceptive Feedback

• Proprioceptive feedback contributes to body awareness by informing the central nervous system about joint position and muscle length.

Visual Consistency

• The inflow theory explains how individuals maintain visual consistency despite eye movements through sensory feedback.

Muscle Spindles

• Muscle spindles play a critical role in proprioception by sensing muscle length and rate of change in length.

Proprioception & Balance Control

• Proprioception is essential for balance control, providing the central nervous system with information about body position and movement.

Proprioceptive Signals

• Proprioceptive signals inform the central nervous system about muscle length, joint angles, and limb movement.

Inflow and Outflow Theories of Stability

• The inflow and outflow theories of stability primarily deal with the role of sensory feedback in controlling movement.

Stance Maintenance

• Individuals primarily rely on proprioceptive input for maintaining a normal stance.