Vestibulospinal System

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Vestibulospinal System
Vestibular Classics March 02, 2007 Zakir Mridha
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• The function of Vestibulospinal Syestem is to
  control of proper body posture
• and movement.
• Specially, human upright vertical position is
  unstable.
• A continuous activation of postural muscles is
  therefore required to
• avoid falling.

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• The function of Vestibulospinal Syestem is to
  control of proper body posture
• and movement.
• Specially, human upright vertical position is
  unstable.
• A continuous activation of postural muscles is
  therefore required to
• avoid falling.
• The problem is complicated by the reduced
  dimension of the support
• base (the feet) and by the articulated
  structure of the human skeleton.

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• The function of Vestibulospinal Syestem is to
  control of proper body posture
• and movement.
• Specially, human upright vertical position is
  unstable.
• A continuous activation of postural muscles is
  therefore required to
• avoid falling.
• The problem is complicated by the reduced
  dimension of the support
• base (the feet)and by the articulated
  structure of the human skeleton.
• But surprisingly, upright posture is a
  capability, which is learnt in the
• first year of life.

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Normal steady position of the head is maintained
by powerful set of reflexes that is known as
vestibulocollic reflex
Peripheral sensory signals (angular and/or
linear accelerations)
detected by vestibular receptors
processed in the vestibular nuclei
LVST MVST
relayed to the spinal cord
Modulates activity in muscles that rotate the
head and upper torso and modulate adjustments
pertinent to limb and body orientation in the
gravitational field.
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• gt20 pairs of muscles that control reflex
  movements of the head neck.
• 3 major groups a) Neck Extensors
• b) Neck
  Flexors
• c) Neck
  Rotators
• Neck motoneurons are located
• mainly in C1, C2 and C3 segments
• Pathways of axons in the spinal cord
• 
  a) i-LVST
• 
  b) MVST and
• 
  c) c-LVST

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• gt20 pairs of muscles that control reflex
  movements of the head neck.
• 3 major groups a) Neck Extensors
• b) Neck
  Flexors
• c) Neck
  Rotators
• Neck motoneurons are located
• mainly in C1, C2 and C3 segments
• Pathways of axons in the spinal cord
• 
  a) i-LVST
• 
  b) MVST and
• 
  c) c-LVST

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• Location of the Vestibulo-spinal Neurons in
  Vestibular Nuclei
• Type of HC nerve-activated Neurons
• Axonal pathways
• Projection level
• Conduction velocity

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Experimental Arrangements
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Experimental Arrangements
Orthodromic Propagation of an impulse along an
axon in normal direction. Antidromic Performing
a nerve conduction study in such a manner that
the nerve impulses is being propagated in
a direction opposite to that in which the nerve
fiber ordinarily conducts.
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Experimental Arrangements
Orthodromic Propagation of an impulse along an
axon in normal direction. Antidromic Performing
a nerve conduction study in such a manner that
the nerve impulses is being propagated in
a direction opposite to that in which the nerve
fiber ordinarily conducts.
Three types of Neurons
VS neurons Send axon to spinal cord but not to
the OMN. VO neurons Send axon to OMN but not
to the spinal cord. VOS neurons Send axon to
both Spinal cord and OMN.
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Example of orthdromic and antidromic spikes

• Axonal projection of the HC-activated
• Vestibular neurons to the spinal cord were
• examined using a collision test between
• orthodromic andantidromic responses.
• Antidromic response was confirmed by its
• fixed latency at a stimulus intensuty
• near the threshold, and by consistent
• responses during high-frequency stimulation.
• The antidromic spike evoked by spinal cord
• stimulus were blocked by a preceding spike
• evoked by HC stimulation when the timing
• of the HC stimulation was close to that
• of the spinal cord stimulation.

C1/2
C3
OMN
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Projection levels in the spinal cord
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Axonal Pathways of HC nerve-activated
Vestibulospinal Neurons
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Locations of HC nerve activated vestibular
neurons
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HC nerve-activated vestibulospinal neurons
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Saccular nerve-activated vestibulospinal neurons
Sato et al. 1997
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Axonal pathways projection levels of SAC
UT-activated vestibulospinal neurons
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Sato et al. 1997
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• Neural connections and pathways underlying
  sacculocollic reflexes were studied by
• intracellular recording from neck extensor
  and flexor motorneurons.
• Extensor muscle Biventer Cervicis and Complexus
  Muscle Motoneuron located at
• C2 and C3 levels.
• Flexor Muscle Longus Capitis Muscle Motoneuron
  located at C2 levels

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Methods a) Selective electrical stimulation of
Saccular nerves. b) Action potentials recorded
from antidromically identified neck motoneurons
c) Pathways were determined by making
transection of VST
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Stimulus-response curves of N1 Potential
(Inset Typical field potential)
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Synaptic Potential in Neck Motoneurons following
Saccular Nerve stimulation
Excitatory Post Synaptic Potential (EPSP) is a
temporary increase in postsynaptic membrane
potential caused by the flow of positively
charged ions into the postsynaptic cell. They are
the opposite of Inhibitory Post Synaptic
Potential (IPSP), which usually result from the
flow of negative ions into the cell.
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Latency of Synaptic Potential in Extensors and
flexors motoneurons
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Diagram of disynaptic and trisynaptic
sacculo-collic motoneuron connections
Flexors
Extensors
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Diagram of the Utriculo-neck motoneuron
conections
Ikegami et al. 1994
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• Sternocleidomastoid muscle
•   origin, sternal head-manubrium, clavicular
  head-clavicle
• insertion, mastoid process and superior nuchal
  line of occipital bone
• innervation, accessory nerve and cervical
  plexus
• action, flexes vertebral column, rotates head.

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Effect of Saccular nerve stimulation on ipsi- and
contrlateral SCM motoneurons
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Effect of Utricular nerve stimulation on ipsi-
and contrlateral SCM motoneurons
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Results from transecting experiments
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Schematic diagram of the Sacculo- and
Utriculo-sternocleidomastoid pathways
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• Longissimus Muscle Group action, lateral flexion
• Obliqus Capitis superior Muscle (OCS)
• Splenius Muscle (SPL)
• Longissimus Muscle (LONG)
•  
• Semispinalis Muscle Group action, extends,
  rotates vertebral column
• Biventer Cervicis Muscle (BIV)
• Complexus Muscle (COMP)

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Predominant Connections from Otolith Canal to
neck motoneurons
Red LVST Green MVST n.t. Not Tested O No
Effect
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Red LVST Green MVST Black Unknown n.t.
Not Tested O No Effect
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