Transcript 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
In the brainstem
• Vestibular inputs undergo integration
• Integrated signal is combined with
original (velocity driven) signal
• Processing to reset spatial map for eye
musculature
Ocular
Musculature
Superior Rectus (SR)
Inferior Rectus (IR)
Lateral Rectus (LR)
Medial Rectus (MR)
Superior Oblique (SO)
Inferior Oblique (IO)
Superior Rectus
Superior Oblique
Midline
Medial Rectus
Inferior Rectus
Lateral
Rectus
Inferior Oblique
The Oculomotor Cranial Nerves
• III the oculomotor
• IV the trochlear
• VI the abducens
III (Oculomotor) innervates:
1) Medial rectus
2) Superior rectus
3) Inferior rectus
4) Inferior oblique
Levator palpebrae sup
Pupillary sphincter
Ciliary muscle
IV (Trochlear) innervates:
• Superior oblique
VI (Abducens) innervates
• Lateral rectus.
Proprioceptive info from eye muscles
• comes through
Trigeminal nerve.
Vestibulo-Ocular Reflex
Horizontal/Lateral Canal VOR
Anterior/Superior Canal VOR
Posterior Canal 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