Download Vestibular Pathways

Vestibular System
Dr. G.R. Leichnetz
What does the vestibular system do?
It informs the brain of movement of the head and body:
angular movement- semicircular canals
linear movement- otolith organs (saccule & utricle)
When the head and/or body moves, the vestibular system:
1. Adjusts eye movements, compensating for head
movement to maintain fixation, stabilize visual image
(medial longitudinal fasciculus, ascending MLF, to
extraocular motor nuclei).
2. Adjusts head position for “gaze” and balance
(medial vestibulospinal tract, descending MLF, to cervical cord)
3. Adjusts posture for balance, equilibrium (lateral
vestibulospinal tract)
There is also vestibular input to the cerebellum,
because the cerebellum coordinates the size and
velocity of movements appropriate for the above
circumstances. (vestibulocerebellar & cerebellovestibular fibers)
What is the Difference Between
Proprioception and Vestibular Sense?
Proprioception- position sensitivity- thru somatosensory
receptors; position of the limbs, body in space
Muscle spindles- stretch
Pacinian corpuscles- pressure
Meissner’s corpuscles- touch
Vestibular Sense- movement sensitivity- thru vestibular
receptors; change of head position, sense of balance,
equilibrium
Angular movement- semicircular canals
Linear movement- otolith organs (saccule & utricle)
The semicircular canals are part of the membranous
labyrinth located within the petrous portion of the
temporal bone, situated in the three planes of
orientation (anterior, posterior, horizontal canals).
Vestibular Receptors: The vestibular end organs sense
changes in the position and movement of the head in the
three dimensions of space.
Semicircular canals- crista ampullaris in ampullae
angular movement
Otolith organs- maculae of the saccule and utricle
gravitation, linear movement
Semicircular
canals
Otolith
organs
Netter
Cochlea
Vestibular Receptors
Semicircular canals: Crista ampullaris containing hair
cells with kinocilium, stereocilia, covered by cupula
(gelatinous cap)
Otolith organs: Saccule & Utricle
The maculae containing hair cells covered with
gelatinous mass with otoconia
Crista ampullaris of
the ampullae of the
semicircular canals
Maculae of the
saccule and utricle
Netter
Crista Ampullaris, Semicircular Canals- detects angular
movements
Ampulla
Hair cells
Planum Semilunatumproduces endolymph
Maculae in Saccule &Utricle
Hair cells, macula of utricle, cat
Otoconia, macula utricle, cat
Otoconia
Hair Cells
When the stereocilia are displaced toward the
kinocilium the hair cell is depolarized (excitation),
and when displaced away from the kinocilium the
hair cell is hyperpolarized (inhibition).
Primary vestibular afferents
end on hair cells
Crista Ampullaris of the Semi-Circular Canals
Ampulla At Rest
Ampulla During Movement
Kandel, et al., The Principles of Neural Science
Primary vestibular fibers have their bipolar cell bodies
of origin in the vestibular (Scarpa’s) ganglion and
travel in the vestibular division of C.N. VIII to
terminate in all subdivisions of the vestibular complex,
and the flocculonodular lobe of the cerebellum.
Flocculonodular lobe
Vestibular
complex
Vestibular ganglion
Vestibular receptors
The vestibulocochlear nerve (C.N. VIII) emerges with
the facial nerve (VII) from the cerebellopontine angle
next to the flocculus (hemispheric portion of the
flocculonodular lobe).
Facial
nerve (VII)
Vestibulocochlear
nerve (VIII)
Flocculus
(flocculonodular
lobe)
Cerebellopontine
angle
Vestibular signals are transmitted via the vestibular
division of the vestibulocochlear nerve (C.N. VIII) to
the vestibular complex.
Lateral Recess
of 4th ventricle
Vestibular Complex
ICP
Flocculus
Vestibular
Complex
ICP
Vestibulocochlear
Nerve (VIII)
The vestibular complex contains four subnuclei:
superior, medial, lateral, and inferior vestibular nuclei
INF
DCN
Inferior
cerbellar
peduncle
Vestibulocochlear
nerve (VIII)
MED
Vestibular
complex
Vestibular
Ganglion
Netter
The primary vestibular
neurons have their bipolar
cell bodies in the vestibular
ganglion.
Their peripheral processes
end on the hair cells in the
crista ampullaris or
maculae of saccule &
utricle.
Their central processes
travel in the vestibular
division of the vestibulocochlear nerve (C.N. VIII)
and terminate in all
subnuclei of the vestibular
complex. Some primary
afferents go to the
flocculonodular lobe of the
cerebellum.
Second-order
vestibular fibers
originate from the
vestibular complex
and ascend in the
medial longitudinal
fasciculus (MLF) to
the extraocular motor
nuclei (III, IV, and VI)
to coordinate the
vestibulo-ocular
reflex.
III
IV
Medial
longitudinal
fasciculus
VI
Vestibular
complex
The VOR produces
eye movements to
compensate for head
movements, keeping
the visual image on
the fovea of the retina
(maintaining fixation).
From Spencer in:
Conn, Neuroscience in Medicine
Second-order
vestibular fibers
originate primarily
from the medial and
superior vestibular
nuclei to ascend thru
the medial longitudinal
fasciculus to the
extraocular motor
nuclei.
These fibers
coordinate the
vestibulo-ocular reflex.
Canal-specific
projections target
oculomotor cell groups
to orchestrate
appropriate
compensatory eye
movements.
Vestibulospinal System
The medial vestibulospinal
tract (descending MLF)
originates primarily in the
medial vestibular nucleus
and descends to the
cervical spinal cord
(vestibulo-colic reflex).
Medial
vestibulospinal
tract (MLF)
Lateral
vestibulospinal
tract
The lateral vestibulospinal
tract originates from the
lateral vestibular nucleus
and descends ipsilaterally
in the anterior funiculus
through the entire length
of the spinal cord to
terminate in the medial
part of the ventral horn
(vestibular influence on
posture and equilibrium).
Medial vestibulospinal
tract (MLF) to cervical
cord to terminate on
neck muscle
motoneurons
(vestibulocolic reflex).
Adjustments in head
position.
Medial
vestibulospinal
tract (MLF)
ends in the
cervical spinal
cord
Lateral
vestibulospinal
tract extends
to entire length
of the spinal
cord
Lateral Vestbulospinal
tract is excitatory to
motor neurons in the
medial part of the
ventral horn of the
spinal cord,
innervating axial and
proximal limb
musculature which
affect posture and
equilibrium.
VESTIBULAR CONNECTIONS
WITH THE VESTIBULAR PARTS
OF THE CEREBELLUM:
FLOCCULONODULAR LOBE
AND FASTIGIAL NUCLEUS
The cerebellum receives proprioceptive and vestibular
input and uses this sensory information to coordinate
the appropriate size and velocity of movements.
For example, in the VOR there must be a compensatory
eye movement that precisely matches the head
movement, but in the opposite direction.
What parts of the cerebellum are associated with
vestibular function?
The flocculonodular lobe (flocculus + nodule) is the
vestibular part of the cerebellum, which is phylogenetically
the oldest part of the cerebellum (archicerebellum).
Flocculonodular lobe
The flocculus is the
hemispheric part of the
flocculonodular lobe of the
cerebellum.
Vestibulocerebellum
The nodule is the
vermal part of the
flocculonodular lobe.
The vestibular portion of the cerebellum
(flocculonodular lobe) receives some direct primary
vestibular afferents.
Flocculonodular lobe
Vestibular
complex
Vestibular
ganglion
Primary and secondary vestibulocerebellar fibers enter the
cerebellum through the inferior cerebellar peduncle
(juxtarestiform body) to terminate primarily in the
flocculonodular lobe, the vestibular part of the cerebellum.
Flocculonodular
lobe
Vestibular nerve
& ganglion
Primary and
secondary
vestibulocerebellar
afferents
CEREBELLAR
CORTEX
Vestibulocerebellar
fibers enter the
cerebellum thru the
inferior cerebellar
peduncle (JRB) and
end on granule cells in
the cerebellar cortex
(flocculonodular lobe),
which project in turn
to Purkinje cells.
Purkinje cells of the
flocculonodular cortex
project to the fastigial
nuclei
Primary
vestibular
afferents
terminate on
granule cells of
the F-N cortex,
which project
in turn to
Purkinje cells
Fastigial
nucleus
Purkinje cells of the
cerebellar cortex
project their axons to
the fastigial nucleus,
the vestibular-related
deep cerebellar
nucleus.
The fastigial nuclei are the medialmost of the deep
cerebellar nuclei located in the subcortical white matter
of the cerebellum in the roof of the fourth ventricle.
These nuclei have reciprocal connections with the
vestibular complex through the inferior cerebellar
peduncle (juxtarestiform body).
Fastigial nuclei
G
E
The fastigial
nucleus, the
medialmost of the
deep cerebellar
nuclei, has
reciprocal
connections with
the vestibular
complex thru the
juxtarestiform
body (part of inferior
F
D
ICP
VC
cerebellar peduncle).
Juxtarestiform body- part
of the ICP that carries
vestibulocerebellar and
cerebellovestibular fibers
F
Dentate
While most primary vestibular fibers go to the vestibular complex,
some go directly to the flocculonodular lobe of the cerebellum
(vestibulo-cerebellum), which projects to the fastigial nucleus. The
fastigial nucleus also has reciprocal connections with the vestibular
complex.
Fastigial nuclei
Vestibulocerebellar and
cerebellovestibular fibers
traverse the juxtarestiform body
Feedback Projections
from the Flocculonodular
Lobe and Fastigial
Nucleus to the Vestibular
Complex
Cerebellovestibular fibers
traverse the juxtarestiform
body.
What Clinical Signs Are Observed With
Lesions of the Vestibular System?
(eg. vestibular division of C.N. VIII, vestibular complex,
MLF, flocculonodular lobe of cerebellum)
1. Vertigo- disruption of vestibular interaction with the
visual system, resulting in a feeling that the room is
spinning; dizziness.
2. Nystagmus- pathological nystagmus; rhythmic
involuntary oscillation of the eyes; the eyes move
slowly in one direction, and then jerk quickly back
to the opposite side.
3. Loss of Balance, Equilibrium
Typically a benign
tumor (proliferation of
Schwann cells) that
grows on the vestibular
division of the
vestibulocochlear nerve
(C.N. VIII) in the
cerebellopontine angle.
A vestibular
schwannoma can
compress the
vestibulocochlear
nerve (C.N. VIII)
with partial or
complete deafness,
tinnitis, vertigo,
nystagmus, or facial
nerve (C.N. VII)
with weakness in
ipsilateral face.