Download Anatomy and Physiology of Balance

Anatomy and
Physiology of
Balance
Vestibular Hair Cells
• Type I
(aka inner)
• Type II
(aka outer)
With
Kinocilium
The Semicircular Canals
• posterior canal
shares plane with
contralateral
anterior canal.
• horizontal canals
share plane.
Stimulated by Angular Acceleration
• greatest when fulcrum
is within head
• induces relative motion
of endolymph
• crista is displaced by
fluid motion
Responses of the Cristae
• All kinocilia are
oriented in the
same direction
• Crista in each pair
of canals respond
inversely to each
other
The
Otolithic
Organs
Saccule: roughly
vertical orientation,
responds to acceleration components within saggital
plane
Utricle: horizontal (+ 30 deg.) orientation
Excitation Patterns in the Utricle
STRIOLA
Anterior
Posterior
Medial
Cranial Nerve VIII
Vestibular Portion of C.N. VIII
superior division: utricle, anterior part of
saccule, and horiz & anterior canals
inferior division: posterior part of saccule,
and posterior canal
• to vestibular nuclei
• to cerebellum
Vestibulocochlear Nerve
• Exits temporal bone
near its medial edge.
• Enters lateral face of
brainstem at the level
of the lower pons.
• Synapsing in
(Cochlear and)
Vestibular Nuclei
Responses of Vestibular Neurons:
• To changes in acceleration, but onset
and fade slowly
• For most normal head movements
firing rates are in phase with head
VELOCITY.
Other inputs to vestibular nuclei:
•
•
•
•
Cerebellum: primarily inhibitory
Spinal cord
Pontine reticular formation
Contralateral vestibular nuclei
From the Vestibular Nuclei:
• Vestibulo-Oculomotor Pathways:
– Direct: to oculomotor nuclei.
– Indirect: via reticular formation to
oculomotor nuclei (III IV and VI)
• Vestibulo-Spinal Pathways:
– Lateral V-S-throughout spinal cord
– Medial V-S-cervical & thoracic
– Reticulospinal tract-via brainstem reticular
formation
Median Longitudinal Fasciculus
• A tract linking Vest. Nuclei to
nuclei of CN III, IV, & VI;
• Supports conjugate eye
movement during movement of
the head.
• Continuous with the medial
vestibulospinal tract.
• The mlf runs near midline
ventral to ventricle IV and the
periaqueductal gray matter of
the midbrain
In the brainstem
• Vestibular inputs undergo integration
• Integrated signal is combined with
original (velocity driven) signal
• Processing to reset spatial map for eye
musculature
Integration & “Leaky” Integration
The VOR
Central Nervous System Will
Adapt to Peripheral Damage
Eye Movements
•
•
•
•
•
Saccades—rapid shift in gaze
Pursuit—stabilize image of moving object
Fixation—stabilize image of still object
VOR—stabilize image during head motion
OKN—backup for when VOR decays to
cont’d head rotation
• Vergent movements—change depth of focus
Saccades
Pause cells inhibit
Burst Neurons
which stimulate:
III & VI (horizontal)
or
III & IV (vertical)
Compare, Select
& Combine Senses
Visual
System
Vestibular
System
SomatoSensation
SENSORY INPUTS
Vision
Vestibular
Somatosensory
SOMATOSENSORY
RECEPTORS Compare, Select
& Combine Senses
SomatoSensation
Joints
Position
Kinesthesia
Muscles
Length
Tension
Skin
Touch
Pressure
VISUAL
RECEPTORS
Compare, Select
& Combine Senses
Visual
System
Central
Orientation
Navigation
Peripheral
Motion-sensitive
Body-sway
VESTIBULAR RECEPTORS
Compare, Select
& Combine Senses
Vestibular
System
Semi-circular canals
Orientation
Navigation
Utricle & Saccule
Horizontal & vertical
acceleration & deceleration
SENSORY ORGANIZATION
Determination of Body
Position
Compare, Select
& Combine Senses
Visual

Vestibular
Somatosensory
Processing of inputs from the periphery
Selection based on
Availability Accuracy
Value for the task at hand
Functional
Balance:
Navigating in
our
Environment
A Quiz
Vestibular Pathways Quiz