sensory systems: the vestibular system dr. jonathan spindel csd and isat james madison university

Sensory Systems:

The Vestibular

System

Dr. Jonathan Spindel

CSD and ISATJames Madison University

Why?

Dizziness and balance problems ...

• 7 million patients annually

• #1 complaint of patients over age 70

• #3 complaint of all patients (after headache and lower back pain)

One in three people will have dizziness or balance dysfunction during their life.

(85% of these are due to inner ear involvement)

What is “dizziness?”

• vertigo

• disequilibrium

• lightheadedness

(also … fuzzy-headed,

blurred vision, off-kilter,

stumbly, drunk, not right …)

“the four legged stool”

vestibular

visual

proprioceptive

diffuse CNS

Balance & Motion Management

Balance & Motion Management

vestibular

visual

proprioceptive

auditory

other

CommonCentral

Processing

Individual CentralProcessing

EyeMovements

Posture

Adaptive Controller

The Vestibular System

Head Motion:Angular Acceleration

Head Motion:Linear Acceleration

Head Position:Gravity

SemicircularCanals

Saccule &Utricle

CentralNervous System

Other Inputs

Spinal Cord &Cerebellum:

Posture

Forebrain:Orientation

Oculomotor System:

Eye Movements

The Vestibular System

Head Motion:Angular Acceleration

Head Motion:Linear Acceleration

Head Position:Gravity

SemicircularCanals

Saccule &Utricle

CentralNervous System

Other Inputs

Spinal Cord &Cerebellum:

Posture

Forebrain:Orientation

Oculomotor System:

Eye Movements

The Vestibular Periphery

3 semi-circular canals(sense angular acceleration)

2 otolith organs (maculae);saccule and utricle

(sense linear acceleration)

The Sensory Element: Vestibular Hair Cells

Transducers converting

mechanical energy into

neuro-chemical signals

interpretated by the brain

as motion of the head or

head position

KEY POINT: Continuous activity with directional sensitivity.Excited by bundle deflection towards KC.

Inhibited by bundle deflection away from KC.

Hair Cells in Action

Otolith Organs: Saccule & Utricle

Function:

• Static tilt (gravity)

• Linear acceleration

Otolith Organs: Static Tilt and Linear Acceleration

Semicircular Canals

Function:

• Angular acceleration

• VOR

Semicircular Canals: Structure of the “Crista”

SCC System: Organization

Canals function in paired sets:

right anterior & left posteriorright posterior & left anterior

right horizontal & left horizontal

Motion inducing excitation of one canal induces inhibition of the other.

NOTE: Canals are not orthogonal (at right angles to) normal directions of body/head movement, therefore most regular motions

stimulate multiple canal sets.

The Vestibular System

Head Motion:Angular Acceleration

Head Motion:Linear Acceleration

Head Position:Gravity

SemicircularCanals

Saccule &Utricle

CentralNervous System

Other Inputs

Spinal Cord &Cerebellum:

Posture

Forebrain:Orientation

Oculomotor System:

Eye Movements

The Vestibulo-Ocular Reflex (Excitatory)“Three-Neuron Arc”

Vestibulo-Ocular Reflex (VOR)

Nystagmus

(In general, the objective of most vestibular testing is to look for nystagmus to be there when it should

be, and to not be there when it shouldn’t be.)

Normal vestibular nystagmus is a series of eye motions which reflexively keep center vision focused on the fovea of the eye during head motion.

The Vestibular System

Head Motion:Angular Acceleration

Head Motion:Linear Acceleration

Head Position:Gravity

SemicircularCanals

Saccule &Utricle

CentralNervous System

Other Inputs

Spinal Cord &Cerebellum:

Posture

Forebrain:Orientation

Oculomotor System:

Eye Movements

Brainstem: Vestibular Nucleus

Posterior“Phantom”

Aspect

Vestibular Nuclear Complex

• Lateral VN (LVN)- input from utricle and semicircular canals (maintenance of posture)

• Medial VN (MVN) & Superior VN (SVN)- input primarily from semicircular canals (primary participant in VOR)

• Descending (Inferior) VN (DVN)- input from semicircular canals, utricle and saccule, and vermis of the

cerebellum (integrate vestibular reflexes with other sensory/cerebellar input)

(First site of central sensory interaction integration. Misnomer since only a small number of VNC neurons receive input from vestibular periphery, most receive input from other sensory systems (visual, proprioceptive, auditory, etc.).

The Vestibular System

Head Motion:Angular Acceleration

Head Motion:Linear Acceleration

Head Position:Gravity

SemicircularCanals

Saccule &Utricle

CentralNervous System

Other Inputs

Spinal Cord &Cerebellum:

Posture

Forebrain:Orientation

Oculomotor System:

Eye Movements

Lateral Vestibulo-Spinal Tract

Control of head and neck, upper limb, trunk and lower limb movements in response to motion.

Medial Vestibulo-Spinal Tract

MVST fibers do not extend beyond the

thoracic spinal segments.

Primary participants in movements that control head and upper body response to motion.