39 - NeuroScience - Vestibular & Occulomotor Systems Flashcards
2 Components of the vestibular system in the inner ear
Saccule & Utricle
Semicircular Canals
Saccule & Utricle
Linear Acceleration
Semicircular Canals
Angular Acceleration (3D) Activated by specific movements of the head with respect to the rest of the body.
Saccule, Utricle & Semicircular Canals
Activate peripheral projections of the vestibular ganglia
Hair Cells synapse on
Peripheral Dendrites of ganglion cells
Central projection of ganglion cells project to
Vestibular nuclei in Medulla & Pons (via CN VIII)
Afferents in CN VIII project to
Vestibular Nuclei
Cerebellum (Flocculus/Nodulus)
What makes the Trochlear Nerve so unique?!
Exits brainstem on dorsal surface
Crossed, Right CN IV controls Left Superior Oblique
Vestibular Nucleus
Complex
Collection of 4 nuclei:
Each is indistinguishable from a standard view of the brainstem, but connectivity is different.
Located in rostral medulla through middle-pons
Location of Occulomotor Nuclei
Midbrain (Occulomotor & Trochlear)
Pons (Abducens)
Vestibular System - 2 Descending Components
Lateral Vestibulospinal Tract (LVST)
Medial Vestibulospinal Tract (MVST)
Descending Vestibular System - Lateral Vestibulospinal Tract (ACTUALLY ONE OF THE MEDIAL DESCENDING SYSTEMS)
Emerges from projection neurons in Lateral Vestibular Nucleus (LVN)
Regulates activity of motor neurons to ipsilateral antigravity muscles
In spinal cord, its projections are in the Ventral Medial aspects of the white matter.
Descending Vestibular System - Medial Vestibulospinal Tract
Originates in Medial Vestibular Nucleus (MVN)
Only goes to cervical portion of the spinal cord
Stabliizes head position & coordinates head/eye movements
Vestibular System - 3 Ascending Components
Medial Longitudinal Fasciculus (MLF)
Projection to VPN of Thalamus
Projection to Cerebellum
Ascending Vestibular System - Medial Longitudinal Fasciculus (MLF)
Arises from Medial Superior & Inferior Nuclei
Coordinates eye movements via inputs to CN III, CN IV, CN VI
Ascending Vestibular System - Projection to Ventral Posterior Nucleus (VPN) of the Thalamus
At the level of the VPL and VPM
Allows conscious perception of head position, orientation & balance. (Proprioception)
Ascending Vestibular System - Projection to the Cerebellum
Projects to Vermis, Floculus/Nodulus through juxtarestiform body (medial portion of cerebellar peduncle)
Balance & control of eye movements
Broca’s Area 3a
Head Position
Broca’s Area 2v (posterior postcentral gyrus)
Posterior Insular Cortex
Balance and body orientation
Posterior Parietal Cortex
Eye Position
Areas that receive information about position from VPN in the thalamus and provide cortex with perceptions of these behaviors
Broca’s Areas:
3a (Head position
2v (Balance & Body Orientation)
Posterior IC (Balance & Body Orientation)
PPC (Eye Position)
Brainstem Structures Controlling Eye Movement
Motor Nuclei:
III
IV
VI
Mesencephalic Gaze Center Paramedian Pontine Reticular Formation Pontine Nuclei Superior Colliculus Cerebellum Vestibular Nuclei
Conjugate Vertical Eye Movements are regulated by
Mesencephalic Gaze Center
Must integrate its connectivity with III and IV
Location of the Mesencephalic Gaze Center
Midbrain
Location of the Paramedian Pontine Reticular Formation (PPRF)
Medial Pons
Horizontal Gaze is regulated by
Paramedian Pontine Reticular Formation
Smooth pursuit is regulated by
Pontine Nuclei
Superior Colliculus
Cerebellum
Superior Colliculus is important for
Saccadic Movement
Smooth Pursuit
Cerebellum is good for
Maintaining Eye Position
Smooth Pursuit
Vestibular Nuclei & Nucleus Prepositus Hypoglossi - Location
Medial portion of the Medulla, just rostral to the hypoglossal nucleus
Vestibular Nuclei & Nucleus Prepositus Hypoglossi - Function
Eye position & movement
Vestibulo-Ocular Reflex - Pathway
Head moves to the right
Vestibular Complex on the right is activated by inputs from CN VII
Vestibular Complex projects to the contralateral (left) side to the Abducens Nucleus.
Left lateral rectus is activated.
The internuncial cells of that abducens nucleus project through the MLF to the contralateral Nucleus of III.
Right medial rectus is activated.
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