Peripheral and Central Anatomy and Physiology

Anatomy and physiology of the peripheral vestibular system

The vestibular system allows us to maintain optimal balance and posture.

  • 1st taught as a sensory system by Charles Darwin’s father

    • when someone moves, the vision system responds to that movement

  • more heavily considered as a system in the 1800s

The vestibular system works in tandem with the vision system and the proprioceptive system.

  • The triad

    • vestibular

    • vision

    • proprioception

The cochlea is anterior and medial to the vestibular system

The purpose of the vestibular system is to maintain balance to protect our bodies and ensure we do not fall and get hurt

Amniotes (not water bodied creatures) -

Relationship between rate of movement and involved system

  • At lower rates of movement → vision system dominates

  • At higher rate of movement → the vestibular system takes over

Rigid Body Motion

  • any rigid body can move in 6 different directions:

    • up and down

    • side to side

    • rotation (yaw)

    • tothe front or back (pitch)

    • rotation from

Otolith organs help records linear accelerations

  • utricle → front and back / horizontal

  • saccule → up and down /vertical

    *Utricle and saccule both play a role in linear/translational movement

Semicircular canals (All 90 degrees to each other)

  • Horizontal/lateral semicircular canal → side to side/lateral movement

  • Superior/anterior/vertical semicircular canal

  • Posterior/ inferior semicircular canal →

    The tail of the semicircular canals are connected to the utricle

Codes movements into electrical energy

Ampulla are sensory structures that are kinda like a barrier between the semicircular canals and the utricle

3, 4, and 6 are critical in vestibular awareness

  • responsible for ocular movements

Vestibular ocular pathway: helps to maintain stable vision

Vestibularospinal pathway: helps to maintain stable posterior

Structure of the Vestibular apparatus

semicircular canal’s sensory structure → crista (singular) cristae (plural)

  • cupula is a gelatinous mass that the hair bundles of the crista attach to

  • the density of the cupula and endolymph is the same at rest

otolith organs sensory structures → macula

  • type 1 cells are rounder than type 2 cells

    • there are more type 1 cells in the otolith organs

  • otoconia: calcium carbonate crystals are embedded on the otolithic membrane

    • the movement of the otoconia pulls the otolithic membrane, which causes hyperpolarization or depolarization

oval window opens on the saccular wall

Type 1 and type 2 hair cells

  • Type 1

    • have a calyx terminal - allows for a very fast transmission of signals

    • there is a need for faster transmission

    • important for sudden, transient, jerk-related motion

    • higher concentration in otolith

    • more centrally located in the otolith

    • have shorter kinocillium which is just in the gel layer of the otolithic membrane which makes them more sensitive to movement

  • Type 2

    • code ongoing movement/signals

    • farther away from the striola (midline of the otolith organ and where kinocilium orientation changes)

    • taller kinocillium that is embedded in the mesh-layer

Mechanoreceptors: a sense organ or cell that responds to mechanical stimuli such as touch or sound.

The tallest hair cell is the kinocilium

Excitation versus inhibition in each plane

Resting firing rate (70-100 spikes/second) and the there is an excitation the firing rate goes up (400 spikes/second) and the opposite corresponding canal firing rate decreases (to 0 spikes/second)

the anterior or one and posterior of the other function together

They function in conjunction!

Dr. Raghav Jha

RALP (right anterior, left posterior)

LARP (left anterior, right posterior)

  • when one is excited the other is inhibited

the direction of movement is typically the side of excitation

Ewald’s Law

Stimulation of the semicircular canal generate eye movements in the place of the canal

excitation creates larger movement then inhibition (why?)

1) when the fluid moves the kinocilllium to the stereocillia

the plane of eye movement is the same as the plane of

ampullopetal flow causes depolarization of the semicircular canals

Every direction of movement must be encoded by the vestibular system

How are angular and linear movements encoded

Angular movements are coded in pairs

linear movements are coded in the same structure

Vestibular afferents

Regular

  • at the level of the type 2 hair cells

Irregular

  • found with type 1 hair cells

Otoliths vs. SCC VESITBULAR

Blood supply Related Disorders

  • vertebro-basiliar insufficiency

  • posteroinferior cerebellar

  • Anterior cerebellular artery

  • TIA of isolated cochlear artery

    • sudden SNHL

  • TIA isolated vestibular artery lesions

Central Vestibular Structures

Vestibular nucleus

  • SVN

  • IVN

  • LVN

  • MVN

Parteoinsular vestibular cortex