Unit 2-Nervous System

Front 1

When does primary neurulation occur

Back 1

weeks 3-4

Front 2

How many phases are there in Primary neurulation

Back 2

4

Front 3

Describe what occurs during phase 1 of Primary neurulation (Neural plate induction and formation)
(signaling, structures invovled, structures formed)

Back 3

Inductive signals from the primitive node (chordin, follistatin, noggint) decrease BMP4 expression which increases FGF expression. This causes the ectoderm cells to proliferate an dform the neuroplate (neuroepithelium).

Front 4

Describe the second stage of neurulation (shaping of the neural plate)

Back 4

The cranial end of the neural plate becomes expanded and will form the brain. the caudal end narrows and lengthens via convergent extension, it will form the spinal cord

Front 5

Describe the third stage of primary neurulation, the formation of the neural folds

Back 5

The lateral edges of the neural plate bend dorsally and become neural folds. The neuroepithelial cells above the notochord change shape and act a median hinge point. The furrow between the folds is the neural groove which contains neuropeithelium and surface ectoderm. The sufrace ectoderm an underlying mesoderm proliferate to elevate the folds.

Front 6

Describe the fourth phase of primary neurulation, the fusion of the neural folds

Back 6

The folds oppose each other and bend at the dorsolateral hinge point. Rearrangement forms an outer layer of surface ectoderm and an inner layer that forms the roof of the tube.

Front 7

What are neuropores?

Back 7

Temporary openings of the neural tube that remain after fold fusion. They allow access to amniotic fluid until the vessels can form

Front 8

When do the neural folds fuse

Back 8

day 22,
cranial neuropre closes 24-27, caudal 26-30

Front 9

How are the three primitive brain regions defined? What are they

Back 9

Prior to neural tube closure, folding in the saggital plane creates a ventral flxure in the area of the expanded crnail part of the neural plate. This fines the forebrain (cranial to the flexure), the midbrain (at the flexure) and hindbrain (caudal).

Front 10

Where do neural crest cells come from

Back 10

They are a population of neuroepithelial cells at the interface of the neuroepithleium and the surface ectoderm that undergo an epithelial-mesenchymal transformation. IN the head the cells leave prior to fold fusion, in the trunk they leave after.

Front 11

What is the purpose of seondary neurluation

Back 11

Process by which the spinal cord from S3-Coccyx forms.

Front 12

Describe how secondary neurulation occurs

Back 12

Phase 1-Neural cord formation, undiffernetiated mesenchyme in the tailbud form a solid neural cord
Phase 2-A lumen forms in the cord and becomes continous with the central canal of the spinal cord formed in the neural tube
Phase 3-Taild bud regression

Front 13

Give a genearl timeline of primary neurulation

Back 13

Phase 1 (neural plate formation) beins in week 3. The process extends into week 4 and fusion of the folds begins around day 22.

Front 14

When does secondary nerulation occur?

Back 14

weeks 4-8

Front 15

Errors of secondary nerulation result in which type of neural tube defects

Back 15

closed, the defect is covered so no neural tissue is exposed however the skin may be dysraphic. Includes lipomyelomeningocele, lipomeningocele and tethered cord

Front 16

Errors of primary neurluation result in which type of neural tube defects

Back 16

open or dysraphic.
They result from faulty closure of the neural folds and are therefore located dorsally and in the midline

Front 17

Which vitamin is important in preventing neural tube defects

Back 17

folic acid 400ug daily

Front 18

Describe anencephaly

Back 18

-absence of the calvaria
-rudimentary mass of forebrain and midbrain tissue exposed dorsally
-brainstem is present, normal eyes
-cleft palate, atrophy of adrenal cortex, polyhydramnios

Front 19

How can anenecephaly be Dx'ed

Back 19

-ultrasound
-alpha fetoprotein in materna serum

Front 20

Decribe Encephalocele (meningoencephalocele)

Back 20

-bifid cranium
-brain+meninges herniate through defect
associated with hydrocephalus, polydactyly, polycystic kidneys
-quadraplegia, incontinence

Front 21

Describe Cranial Meningocele

Back 21

-Small skull defect
-Herniation of meninges forming CSF filled sac
-brain does NOT herniate (differentiate from meningoencephalocele)

Front 22

Describe cranium bifidium

Back 22

-opening between skull bones, usually occiptal but sometimes frontal
-no herniation
-autosomal dominant inheritance
(clincally this term is used interchangeable with encephalocele however this is incorrect because there no herniation)

Front 23

Describe cranial meningocele

Back 23

Primary neurulation, open tube defect.
Defect in skull with herniation of meninges but NO brain tissue. Formation of CSF filled sac

Front 24

Describe Cranium Bifidum

Back 24

Primary nerulation, open tube defet. opening in skull bones but no herniations. Autosomal dominant.

Front 25

Describe myeloschisis

Back 25

primary neurulation open tube defect. Defect in fomration of the vertebral arch, neural plate open dorsally. NO cystic swelling.

Front 26

Describe meningomyelocele

Back 26

Primary neurulation, open tube defect. Defect in formation of vertebral arch w/ herniation of spinal cord and meninges into sac. Associated with hydrocephalus and club feet, incontinence, paraplegia.

Front 27

What is the spinal cord equivalent of encephalocele

Back 27

meningomyelocele
(They both invovled herniation of the structure and the meninges)

Front 28

Describ.e meningocele

Back 28

Primary nerulation-open tube defect. Defect in vertebral arch formation w/ herniation of meninges ONLY. 10% of spina bifida cystica cases

Front 29

The majority of spinal bifida cystica cases are the result of which neural tube defect

Back 29

90% are meningomyelocele with herniation of the spinal cord and meninges
10% are meningocele with herniation of just the meninges

Front 30

Describe spina bifida occulta

Back 30

10% of adult population, usually asymptomatic. Characterized by defect in the formation ofthe vertebral spinous process.May be associated with diastematomyelia, a bone spur in the spinal canal the can tether the spinal cord and prevent normal ascention.

Front 31

Proliferation and differntiation of which tissue type leads to formation of the grey and white areas of the spinal cord

Back 31

neuroepithelium

Front 32

How does the position of the neuroepithelial cell indicate it's progress through the cell cycle

Back 32

Close to neural tube surface=not dividing, S phase
close to neural tube lumen=dividing, M phase

Front 33

Differentiation of neuroepithelial cells occurs in a specific order. Which cells are foremd and when

Back 33

1. neuroblasts
2. Glioblasts forming macroglia and radial glia
3. ependymal cells formed but no migration occurs

Front 34

Explain how neuroblasts differentiate from the neuroepithelial cells

Back 34

These are the first cells to differntiate from the neuroepithelial cells of the neural tube wall. The leave the cell cycle and migrate toward the surface of the neural tube. After they migrate they differnetiate into neurons and form axons and dendrites

Front 35

Explain how glioblasts differnetiate from the neuroepithelial cells

Back 35

These are the second cells to differntiate after the neuroblasts have left. They migrate and differntiate into macroglia (astrocytes and oligodendrocytes) and Radial glia

Front 36

Where do microglia come from

Back 36

These are macrophages that develop from mesoderm. They migrate into the CNS through blood vessels

Front 37

How do ependymal cells form

Back 37

These are the last cells to form from the neuroepithelium after migration of the neuroblasts and glial cells. The cells do NOT migrate but rather remain at their orignal location. They become the epithelial cells that line the ventricles and spinal canal.

Front 38

Differntiation of the neuroepithelial cells results in a trilaminar spinal cord wall. What are the three layers? Where did they come from and what will they form?

Back 38

From inside out (lumen is inside_
1. Ventricular layer-the "left overs after neuroblasts and glial cells leave, become the ependymal cells
2. Intermediate/Mantel layer-where the neuroblasts/ glioblasts end up after leaving, this becomes the grey matter
3. Marginal layer-Axons from the neuroblasts in the intermediate layer form this layer, oligodendroglia reside where, becomes the white matter

Front 39

Explain the patterning the must occur in order to propertly position sensory neurons in the spinal cord

Back 39

In the dorsal half of the intermediate layer, expansions on either side of the midline form due to neuroblast and glioblast migration. This results in the formation of paired alar plates. Dorsalizing Signals (BMPs) from the roof plate lead to the formation of sensory neurons.

Front 40

Describe the signaling that occurs to form sensory neurons.

Back 40

Dorsalizing Signals (BMPs) from the roof plate instruct neuroblasts in the alar plate to form sensory neurons

Front 41

Explain the patterning that must occur in order to properly position motor neurons in the spinal cord.

Back 41

Expansion of the ventral half of the intermediate layer results in the formation of basal plates. Under the influence of ventralizing signals (SHH) from floor plates, neuroblasts differentiate into motor neurons.

Front 42

Explain the signaling the must occur to form motor neurons

Back 42

Ventralizing (SHH)from the floor plate signal neuroblasts in the Basal plates to form motor neurons

Front 43

Explain how sympathetic motor columns are formed

Back 43

Lateral extensions of the basal plates at T1-L2

Front 44

Explain how the parasympathetic motor columns are formed

Back 44

Lateral extensions of teh basal plates at S2-S4.

Front 45

What is the sulcus limitans

Back 45

A groove runing the entire length of the spinal cord between the alar and basal plates. It forms a boundry between the sensory an motor areas

Front 46

Describe how the spnial cord changes positions during development

Back 46

8weeks- entire length
24 weeks S1
Birth L3
Adult L1-L2
Filum terminale remains attached to sacrum

Front 47

Explain how the three flexures of the neural tube form.

Back 47

Folding in the sagittal plane causes a ventral flexure in the expanded cranial end of the neural plate. This becomes the mesencephalic flexure. A second ventral flexure, the cervical flexure forms at the juction of of the brain and the spinal cord. Rapid growth of the brain then leads to a dorsal Rhombencephalic Flexure in the area of the hindbrian.

Front 48

How does the brain fold back on itself

Back 48

Deepening of the rhombencephalic and midbrain flexures.

Front 49

During week 4 at the open neural fold stage, three brain regions are visible. What are they and how are they named.

Back 49

The regions are named in relation to the mesencephalic flexure
1. Prosencephalon-forebrain-before flexure
2. Mesencephalon-midbrain-at flexure
3. Rhombencephalon-hindbrain-after flexure

Front 50

During week 5 the three brain subdivisions divided further. What are the resulting regions.

Back 50

-the prosencephalon divides into the telencephalon and the diencephlaon.
-the Mesencephalon stays the same
-The rhombencephalon divides into the metencephalon and the myelencephalon
(so, from cranial to caudal: Te Di Mes, Met, My

Front 51

Describe the three signaling centers that form after the establishment of the 5 brain regions. Where are they, what do they do and what do they secrete?

Back 51

1. prosencephalic center=prechordal plate, organizes forebrain and midbrain with OTX2 and LIM1

2. Rhombencephalic=Notochord, organizes hingbrain, WNT3a, FGF, RA

3. Isthmus organizer, between other two, organizes midbrain and cerebellum

Front 52

What controls organization of the forebrain

Back 52

OTX2 and LIM1 secreted from the prosencephalic signaling center (prechordal plate)

Front 53

What controls the organization of the midbrain

Back 53

1. OTX2 and LIM1 secreted from the prosencephalic signaling center (prechordal plate)
2. Isthnus organizer

Front 54

What controls organization of the hindbrain

Back 54

1. Rhombencephalic signaling center (notochord) WNt3a, FGF< RA, control the nested expression of HOX genes

Front 55

What controls the organization of the crerebellum

Back 55

Isthmus organizer

Front 56

What are rhombomeres are how are they formed

Back 56

Temporary segements in the hingbrain that form as aresult of Hox gene expression (mediated by rhombencephalic center). These are important in cranial n. development.

Front 57

Describe Holoprosencephaly

Back 57

Reginalization of the prosencephalon is absent or incomplete. Associated with spectrum of CNS and facial malformations. Affects forebrain,
corpus callosum, olfactory tract, flax cerebri are often absent
single ventricle may be present
seizures, midface anomalies, developmental delay
chromosomal defect, alcohol

Front 58

Which of the 5 brain regions make up the wall of the neural tube in the brain stem

Back 58

myelencephalon, metencephalon, mesencephalon

Front 59

Which structures give rise to the motor and sensory cranial nuclei and cranial nerve tracts in the brainstem

Back 59

basal plates-motor
alar plates-sensory
marginal layer-tracts

Front 60

T/F alar and basal plates form in the forebrain

Back 60

false

Front 61

What structure gives rise to the brain ventricular system

Back 61

The lumen of the neural tube

Front 62

What structure gives rise to the commissures

Back 62

Develop at the site of cranial neuropores from comissural plate, part of the prosenceplaon at the cranial neuropore closure.

Front 63

From which brain region is the cerebellum derived

Back 63

Forms from bilateral dorsal outgrowths of the metencephalon, rhombic lips (part of the alar plate). The rhomibic lips fuse to form the cerebellar plate forming the Vermis. A hemisphere expands lateerally from each side of the vermis

Front 64

When does neuron migration peak

Back 64

3-5 months

Front 65

Describe Lissencephaly

Back 65

Error of neuron migration.Smooth brain, cortical surface with macrogyria or agryria, accompanie dby heterotopia (neurons in aberrant places), decreased lamation of cortex. Poor responsivness and feeding, seizures, decreased muslce tone, severe DD

Front 66

Describe Microgyria

Back 66

excessive sulcation of the cortex, only 4 layers due to insufficien neuroblast migration, severe DD, speach problems, seizures, hypotonia,

Front 67

The cerebellar cortex forms from the metencephalon rhombic lips which fuse to form the cerebellar plate. The Metencephalon has already been organized into three layers-ventricular, intermediate, and marginal. Explain how these layers rearragned to form the cerebellar cortex.

Back 67

1. Neuroblasts from the intermediate layer of the rhombic lips of the metencephalon migrate above the marginal layer to form the external granular layer just under the pia mater.
2. Additional neuroblasts from the intermediate layer migrate up into the marginal layer and form Purkinje cells.
3. The cells in the external granular layer then move inward under the Purkinje cells to form the granular layer.
4. The neuroblasts left over in the intermediate layer form the Deep cerebellar nuclei

Front 68

What is the progenitor of the cerebral hemispheres (telencephalic vesicles)

Back 68

lateral outgrowths of the telencephalon

Front 69

In which general direction does cortex formtion occur

Back 69

From deep to superficial

Front 70

Describe hydrocephalus
-cause
-characteristics
-types

Back 70

Enlarged ventricles due to blockage of CSF flow/absoprtion. Non-communicating (obstructive) CSF can't get into subarachnoid space. IN communicating it can't reach arachnoid granulations to be absorbed. Associated with Arnold-Chiaria Malformation and other herniations.

Front 71

Describe the Arnold-Chiari malformation

Back 71

Caudal displacement and herniation through the foramen magnum of ventrally located cerebellar structures.

Front 72

WHich periphernal nervous system structures arise from neural crest tissue

Back 72

primary sensosry neurons, schwann cells, postganglionic autonomic neurons, enteric neurons

Front 73

Which peripehral nervous system structures arise from ectodermal placodes

Back 73

Epipharyngeal placodes (sensory ganglia for CN 5,7,8,9,10)
olfactory placode
Otic Placode (CN8)

Front 74

Which peripheral nervous system structures arise from the spinal cord and brain

Back 74

Motor neuron axon, preganglionic sympathetic axons, parasypathetic axons

Front 75

What are ectodermal placodes

Back 75

-localized thickenings of surface ectoderm in head region
-located adjacent to developing forebrain, midbrain, hindbrain

Front 76

What structure gives rise to the primary somatic motor neurons in the ventral grey matter of the spinal cord

Back 76

Neuuroepithelium of the neural tube