Development of nervous system Flashcards
The ___ gives rise to all of the elements of the nervous system
The ectoderm gives rise to all of the elements of the nervous system
Neurulation:
starts with the formation of the _X__. ___ cells intercalate with the ectoderm and release compounds that pattern the ectoderm to become the __ __.
what happens to the X with time? what happens if this doesn’t take place?
Notochord
Prenotochordal cells
Neural plate
Notochord usually disappears; very rarely it might stick around and become slow growth tumor (called a chordoma)
Neurulation:
Edges of the neural plate elevate to form __ __ that further bend and form __ points
Anything that is posterior(dorsal) to the hinge points is going to be __ and anything that is anterior(ventral) to the hinge points is going to be __
Neural folds
Hinge points
Sensory; Motor
Closure of the neural tube starts in the __ region and happens __ and ___. Closure happens at around Day 25 (~4 weeks)
Complete failure of neural tube closure is __ (fully exposed brain and spinal cord)
failure to close cranially is ___
failure to close caudally is ___
Cervical region
cranially and caudally
craniorachischisis
Spina bifida: failure to close caudally
Anencephaly: failure to close cranially
Spinal rachischisis
(what is it?)
Spinal rachischisis: exposed neural tissue due to complete failure of neural tube to close (elements of spinal cord are actually part of the skin)
Spina bifida classifciations (define them and state how they woud be treated)
Spina bifida occulta
which spina bifida is a fluid filled cyst bound by the meninges?
Spina bifida meningomyoelocele
What kind of imaging would you use for this?
Spina bifida occulta: muscle and skin closed over normally, but bony elements may not be fully closed; usually asymptomatic (no treatment necessary); physical features: tuft of hair at the base of the spinal column
Spina bifida meningocele; treatment is surgical removal of the cyst
Spina bifida meningomyelocele: elements of spinal cord are also pushed up into that fluid filled cyst; treatment: also surgical removal but you have to be careful to protect the elements of the spinal cord
**use MRI and not CT** because you don’t want to expose baby to all that radiation
Cranium bifida (encephalocele)
how is this different from spina bifida?
describe the following:
cranium bifida meningocele
cranium bifida meningoencephalocele
cranium bifida meningohydroencephalocele
Cranium bifida: essentially the same fluid-filled cyst/bulge that forms like in spina bifida except that this is in the brain
Craniobifida meningocele: only contains parts of the meninges and the fluid
Craniobifida meningocephalocele: contains parts of meninges, the fluid, and brain tissue
Meningohydroencephalocele: the brain tissue that’s in the cyst also involves the ventricles
Cranium bifida defects by ethnicity (european vs asiopacific descent)
European descent, majority are posterior (involve occipital bone)
Asiopacific descent, majority are anterior (involve frontal bone)
Which part of the nervous system comes from the neural crest cells?
Neural crest derived structures: basically everything that makes up the peripheral nervous system
2 molecules responsible for dorsal/ventral patterning
Who’s responsible for rostral/caudal patterning?
__ is responsible for lateralization
which cells are involved in radial patterning?
SHH in notochord/floorplate; BMP in roofplate
Hox genes (expressed in neural tube)
SHH in notochord/floorplate
Neuroepithelial cells (and radial glia)
what is the fate of the neural tube given the following BMP/SHH gradients?
High BMP, low SHH
Low BMP, high SHH
dorsal fate; sensory
ventral fate; motor
What is the sulcus limitans?
Anything dorsal to it (aka the __ plate) - developing __ domain
Anything ventral to it (aka the basal plate) - developing __ domain
That hinge point discussed earlier = Sulcus limitans (slight groove that runs from brain down to spinal cord)
everything dorsal to it = sensory (aka alar plate – developing sensory domain),
everything ventral to it = motor (aka basal plate – developing motor domain)
Location of sensory and motor areas (dorsolateral vs ventromedial)
Sensory area is more dorsolateral
motor area is ventromedial
Radial patterning description (what happens to the neuroepithelial cells?)
T/F: Microglia come from the neural tube as well
Radial patterning: how to get from inside of neural tube to outside
Neuroepithelial cells jump down to bottom of ventricular layer where they will differentiate into various progenitor cells
falsehood. microglia are part of the immune system and don’t come from the neural tube (come from monocytes)
Rostral/caudal patterning by HOX genes:
smaller number of HOX genes expressed __ to the brain end
higher number of HOX genes expressed __ from the brain
Closer to brain end, smaller number of HOX genes expressed
Further from the brain = higher number of HOX genes expressed
Lateralization:
High SHH: more ___ (medial/lateral)
Low SHH: more ___ (medial/lateral)
If laterilzation isn’t the same thing as left and right, when does left and right patterning occur?
High SHH: more medial elements;
Lower SHH: lateral components
**not the same thing as left and right, which is already decided at the time of the bilaminar embryo**
Holoprosencephaly
(what is it, what’s the cause, how is this different from cyclopia?)
Lack of both hemispheres due to failed lateralization
Cyclopia is the most severe form of holoprosencephaly
Brain formation:
Which genes/molecules are responsible for patterning the brain into 3 broad regions? (which are apparently also the primary brain vesiscles/swellings)
what are the 3 brain regions (common + scientific names)
HOX genes
Prosencephalon – forebrain
Mesencephalon – midbrain
Rhombencephalon – hindbrain
Role of the primary flexures (cervical and mesencephalic)
function of each flexure
The flexures basically help to shape the brain and the rest of the neural tube
Cervical flexure – bends the whole brain forward and makes the brain point anteriorly
Mesencephalic flexure – brings forebrain forward
secondary flexure (aka ___ flexure) function (what structure is tucked underneath the cerebellum through this process)
Pontine flexure
Pontine flexure: causes bend inside the developing pontine region (tucks the brainstem up and underneath the cerebellum)
Secondary vesicles:
The forebrain gives rise to the __ and __
the hindbrain gives rise to the __ and ___
what happens to the midbrain?
Forebrain then gives rise to telencephalon and diencephalon
Hindbrain gives rise to metencephalon and myelencephalon
Midbrain stays the same, and develops a ton of fiber tracts to basically allow for communication between forebrain and hindbrain
Telencephalon structures (CHO)
Cerebrum
Hippocampus
Olfactory lobes
Diencephalon structures (all of the thalami + the eye)
Retina
Epithalamus
Thalamus
Hypothalamus
Metencephalon structures
Myelencephalon structures
Cerebellum
Pons
Medulla
Formation of ventricles:
the forebrain gives rise to the __ ventricles, which communicate with each other via the interventricular foramen
the 3rd ventricle comes from the __
the 4th ventricle comes from the __
The 3rd and 4th ventricles are connected to each other via __
The __ contains the 4th ventricle
Lateral ventricles
Midbrain
Hindbrain
cerebral aqueduct
brainstem
why is the cerebral aqueduct considered a problem point?
Cerebral aqueduct = problem point because it’s a narrow, fluid filled opening: its prone to stenosis
Hydrocephalus
(what is it, what’s the cause)
Cause: cerebral aqueduct stenosis or some other kind of blockage leading to leading to high pressure in the lateral ventricles and expansion of the cerebral hemispheres (obstructive hydrocephalus)
What is it: Excessive cerebrospinal fluid buildup in the brain
Hydrocephalus treatments:
(describe them)
Cerebral shunt
Endoscopic third ventriculostomy
Cerebral shunt: you basically put a hole through the ventricle, and then you put another tube that drains that fluid out to some other location
Endoscopic third ventriculostomy: punch a hole through some part of the 3rd ventricle that has some tissue that we don’t really need to create an opening for the fluid to drain (into the ventral subarachnoid space)
Chiari malformation (types)
Hydrocephalus pushes brain stem through the foramen magnum
Also caused by spina bifida in which the brainstem is pulled through the foramen magnum
Axon guidance:
Role of filopodia and lamellipodia
Filopodia – finger like extensions that ‘sample’ the local environment abound the growth cone
Lamellipodium – the foot or base from which filopodia extensions protrude
Describe chemoattraction/repulsion vs contact attraction/repulsion
Which ones are long range cues vs short range cues?
Long range cues: chemoattraction/repulsion; usually diffusible molecules (axon turns towards an attractive molecule or turns away from a repulsive molecule)
Short range cues: contact attraction/repulsion (contact with other cells or proteins or something)
role of leader axon and follower axon in axon guidance
Pioneer axon samples the surrounding environmnent and makes the initial pathway
Follower axon tracks along the pioneer axon, resulting in a bundle of axons aka nerve/tract
How do the central tracts form?
They also use the pioneer and follower mechanism
The earliest pioneer axons establish the major brain white matter tracts, the initial axon scaffolding.
The initial axon scaffolding increases in size and additional tracts are formed throughout brain development.
Describe agenesis of the corpus callosum
Agenesis of corpus callosum: absence or partial absence of fiber tracts
(usually asymptomatic)
How do the cortical layers form? (basically how do you build the ventricles?) (hint: layer one forms the last)
what types of neurons are formed from this type of migration?
Cells get from ventricular side out into dorsal side (basically formed from the inside out)
So for e.g. layer 4 would migrate through layers 6, then 5, the it would stop there; layer 1 forms the last
Excitatory neurons are coming from this radial migration
The long migration pathway from one brain region to another is mediated by the ___ ___ ___
which regions are involved in this pathway?
what type neurons come from this pathway? (stimulatory or inhibitory?)
Median ganglionic eminence
Cortex
Olfactory bulb
Rhombic lip going to cerebellum/cerebellar nuclei
Inhibitory. All the inhibitory neurons come from the MGE.
how do gyri and sulci form?
difference between sulci and fissures
function of gyri and sulci
Continued neuronal migration and formation in the cerebral cortex forms the gyri and the sulci
Brain forms gyri and sulci to increase surface area for all those neurons
Deep sulci – fissures; those divide the brain into lobes
which sulci form first? which fissure determines where the temporal lobe is going to form?
Describe pachygyria and lissencephaly
the central sulcus and the lateral fissure
lateral fissure
Pachygyria: poorly formed gyri, not as many
Lissencephaly: absence of gyri, smooth brain surface (reduced surface area of brain leads to significant cognitive development)
