Development of nervous system

Question 1

The ___ gives rise to all of the elements of the nervous system

Answer 1

The ectoderm gives rise to all of the elements of the nervous system

Question 2

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?

Answer 2

Notochord

Prenotochordal cells

Neural plate

Notochord usually disappears; very rarely it might stick around and become slow growth tumor (called a chordoma)

Question 3

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 __

Answer 3

Neural folds

Hinge points

Sensory; Motor

Question 4

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 ___

Answer 4

Cervical region

cranially and caudally

craniorachischisis

Spina bifida: failure to close caudally

Anencephaly: failure to close cranially

Question 5

Spinal rachischisis

(what is it?)

Answer 5

Spinal rachischisis: exposed neural tissue due to complete failure of neural tube to close (elements of spinal cord are actually part of the skin)

Question 6

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?

Answer 6

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

Question 7

Cranium bifida (encephalocele)

how is this different from spina bifida?

describe the following:

cranium bifida meningocele

cranium bifida meningoencephalocele

cranium bifida meningohydroencephalocele

Answer 7

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

Question 8

Cranium bifida defects by ethnicity (european vs asiopacific descent)

Answer 8

European descent, majority are posterior (involve occipital bone)
Asiopacific descent, majority are anterior (involve frontal bone)

Question 9

Which part of the nervous system comes from the neural crest cells?

Answer 9

Neural crest derived structures: basically everything that makes up the peripheral nervous system

Question 10

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?

Answer 10

SHH in notochord/floorplate; BMP in roofplate

Hox genes (expressed in neural tube)

SHH in notochord/floorplate

Neuroepithelial cells (and radial glia)

Question 11

what is the fate of the neural tube given the following BMP/SHH gradients?

High BMP, low SHH

Low BMP, high SHH

Answer 11

dorsal fate; sensory

ventral fate; motor

Question 12

What is the sulcus limitans?

Anything dorsal to it (aka the __ plate) - developing __ domain

Anything ventral to it (aka the basal plate) - developing __ domain

Answer 12

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)

Question 13

Location of sensory and motor areas (dorsolateral vs ventromedial)

Answer 13

Sensory area is more dorsolateral

motor area is ventromedial

Question 14

Radial patterning description (what happens to the neuroepithelial cells?)

T/F: Microglia come from the neural tube as well

Answer 14

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)

Question 15

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

Answer 15

Closer to brain end, smaller number of HOX genes expressed

Further from the brain = higher number of HOX genes expressed

Question 16

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?

Answer 16

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**

Question 17

Holoprosencephaly

(what is it, what’s the cause, how is this different from cyclopia?)

Answer 17

Lack of both hemispheres due to failed lateralization

Cyclopia is the most severe form of holoprosencephaly

Question 18

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)

Answer 18

HOX genes

Prosencephalon – forebrain

Mesencephalon – midbrain

Rhombencephalon – hindbrain

Question 19

Role of the primary flexures (cervical and mesencephalic)

function of each flexure

Answer 19

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

Question 20

secondary flexure (aka ___ flexure) function (what structure is tucked underneath the cerebellum through this process)

Answer 20

Pontine flexure

Pontine flexure: causes bend inside the developing pontine region (tucks the brainstem up and underneath the cerebellum)

Question 21

Secondary vesicles:

The forebrain gives rise to the __ and __

the hindbrain gives rise to the __ and ___

what happens to the midbrain?

Answer 21

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

Question 22

Telencephalon structures (CHO)

Answer 22

Cerebrum

Hippocampus

Olfactory lobes

Question 23

Diencephalon structures (all of the thalami + the eye)

Answer 23

Retina

Epithalamus

Thalamus

Hypothalamus

Question 24

Metencephalon structures

Myelencephalon structures

Answer 24

Cerebellum

Pons

Medulla

Question 25

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

Answer 25

Lateral ventricles

Midbrain

Hindbrain

cerebral aqueduct

brainstem

Question 26

why is the cerebral aqueduct considered a problem point?

Answer 26

Cerebral aqueduct = problem point because it’s a narrow, fluid filled opening: its prone to stenosis

Question 27

Hydrocephalus

(what is it, what’s the cause)

Answer 27

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

Question 28

Hydrocephalus treatments:

(describe them)

Cerebral shunt

Endoscopic third ventriculostomy

Answer 28

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)

Question 29

Chiari malformation (types)

Answer 29

Hydrocephalus pushes brain stem through the foramen magnum

Also caused by spina bifida in which the brainstem is pulled through the foramen magnum

Question 30

Axon guidance:

Role of filopodia and lamellipodia

Answer 30

Filopodia – finger like extensions that ‘sample’ the local environment abound the growth cone

Lamellipodium – the foot or base from which filopodia extensions protrude

Question 31

Describe chemoattraction/repulsion vs contact attraction/repulsion

Which ones are long range cues vs short range cues?

Answer 31

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)

Question 32

role of leader axon and follower axon in axon guidance

Answer 32

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

Question 33

How do the central tracts form?

Answer 33

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.

Question 34

Describe agenesis of the corpus callosum

Answer 34

Agenesis of corpus callosum: absence or partial absence of fiber tracts

(usually asymptomatic)

Question 35

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?

Answer 35

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

Question 36

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?)

Answer 36

Median ganglionic eminence

Cortex

Olfactory bulb

Rhombic lip going to cerebellum/cerebellar nuclei

Inhibitory. All the inhibitory neurons come from the MGE.

Question 37

how do gyri and sulci form?

difference between sulci and fissures

function of gyri and sulci

Answer 37

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

Question 38

which sulci form first? which fissure determines where the temporal lobe is going to form?

Describe pachygyria and lissencephaly

Answer 38

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)