4-7 Brainstem and III, IV and VI Flashcards
What are the 2 signalling systems that pattern the dorsoventral axis of the developing NS?
SHH - sonic hedgehog - motor, ventral
BMPs - bone morphogenic proteins - sensory, dorsal
What do the following embryological structures give rise to in the adult spinal cord:
marginal zone
mantle zone
ventricle zone
alar plate
sulcus limitans
basal plate
marginal zone - white matter
mantle zone - gray matter
ventricle zone - ependymal cell layer
alar plate - dorsal horns
sulcus limitans - coronal section/plane, between dorsal and ventral
(around this is lateral horns, visceral motor system)
basal plate - ventral horns
On the spinal cord, things are organized dorsally to ventral:
dorsal
GSA
GVA
GVE
GSE
ventral
How are these same modalities organized on a developing brainstem?
Imagine a line going across sulcus limitans, and rotating it 90 degrees:
Lateral GSA GVA GVE GSE medial
More complete:
SSA GSA GVA GVE SVE GSE | GSE SVE GVE GVA GSA SSA
In the developing brain stem, the following structures in the myelencephalon become what in the adult structure?
Roof plate
Alar plate
Basal plate
Myencephalon = precursor to medulla
Roof plate - choroid plexus
Alar plate - sensory nuclei for CN VII - X
Basal plate - motor nuclei for CN VII - XII
In the developing brain stem, the metencephalon is formed in 2 divisions. What are they?
Dorsal division
Ventral division
What does the dorsal division of the metencephalon form?
Alar plate forms cerebellum, develops from rhombic lip
Sensory cranial nerve nuclei (V)
What does the ventral division of the metencephalon form?
Basal pons with pontine nuclei
(doesn’t follow typical dorso-ventral patterning)
What does the mesencephalon give rise to in the adult brain? Where is the sulcus limitans?
Midbrain:
Tectum & tegmentum
Sulcus limitans at cerebral aqueduct
What does the alar plate of the mesencephalon give rise to?
Tectum of midbrain
- corpora quadrigemina
GSA of CN V
What does the basal plate of the mesencephalon give rise to?
GSE and GVE of CN III
GSE of CN IV
What are the GSE of the brainstem? Where are they, relatively, and what do they contain?
CN III, IV, VI, XII
Generally located in dorsomedial region
Contain cell bodies of LMNs
How are the nuclei for CN III, IV and VI connected? Where are they located, roughly? Why is this spatial relationship important?
CN III, IV and VI are located near medial aspect of brainstem, but at different levels
III is up in midbrain
IV in rostral pons
VI in caudal pons
MLF can connect all nuclei easily, since they are located almost on top of each other at different levels, a fiber tract can create vergence and coordination between the different nuclei
This allows for vestibuloocular reflex, saccades, tracking, etc.
What does control of eye movements allow you to?
Shift gaze, or direct image to fovea
What is quick phase eye movement generated by?
Quick phases of nystagmus generated during vestibular or optokinetic stimulation or as automatic resetting movements in the presence of spontaneous drift of eyes
What is the function of the omnipause neurons?
Keep eyes still, allow them to focus/fixate on things
Normally, these release glycine on the PPRF
What is the PPRF?
Parapontine reticular formation
activates ipsilateral abducens nucleus
Omnipause neurons release glycine on these neurons
Disinhibition supplied from superior colliculus, and allows for gaze to shift
How is saccades initiated?
Sudden burst of activity from midbrain, superior colliculus
Activates mesencephalic reticular formation (MRF)
Activated MRF will release GABA onto RIPOPN/omnipause neurons
RIPOPN neurons now turned off
Inhibition of PPRF burst neurons now off, these will now activate CN VI nucleus
What pathways converge on the superior colliculus?
Frontal eye fields
Supplementary eye fields
Parietal eye fields
Dorsolateral prefrontal cortex
What cortical areas control voluntary saccades to contralateral side?
FEF - area 8 and supplemental eye fields
What cortical areas control reflexive saccades?
parietal eye fields
What cortical area controls voluntary inhibition of reflexive saccades?
Dorsolateral prefrontal cortex
What is the pathway for voluntary saccades?
Voluntary command on right side for left moving saccades
Brodman’s area 8/FEF sends fiber to midbrain and superior colliculus to synapse there
Fibers will leave and travel to/decussates at contralateral MRF
Fibers will descend to pons
Fibers will inhibit RIPOPN neurons
PPRF now able to be active
PPRF activates ipsilateral CN VI/abducens
also activates contralateral CN III/medial rectus
(double check laterality on this, my notes from Vosko aren’t adding up that well)
What is the role of the basal ganglia in oculomotor movements?
Helps with tracing of familiar faces with eye movements
Needs input from SNPR
Both direct and indirect pathways involved
What is the pathway for basal ganglia involvment in eye tracking?
Parietal or FEF send activating projecting neuron to striatum
striatum = caudate + putamen, has GABA-ergic neurons
Striatum projects to SNPR and inhibits it
SNPR is normally inhibiting superior colliculus, VA/VL thalamus
BG is working
VA/VL and superior colliculus is disinhibited
Direct pathway shuts down SNPR, superior colliculus, and VA/VL thalamus
Activation of superior colliculus allows for gaze shift
What does cerebellar input to the eyes do?
Tells eyes how much to move, saccades to send eyes to correct position relative to your body
What is the path of afferent/efferent cerebellar input on eye tracking?
Neurons from FEF or parietal eye fields will descend to pons, synapse and decussate
Fibers will enter cerebellum via middle cerebellar peduncle
Fibers will head to fastigial nucleus in flocculonodular level
Synapse there
Fibers from fastigial nucleus will head out inferior cerebellar peduncle/juxtarestiform body to ipsilateral vestibular nucleus
From medial vestibular nucleus to ipsilateral abducens nucleus
PPRF will send fibers to lateral rectus and contralateral CN III nucleus
