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Nervous System I > Embryology > Flashcards

Embryology Flashcards

1
Q

Periventricular Heterotopia (PH)

A

Caused by mutation in FLNA gene, which codes for an actin binding protein; inability of neurons to migrate past the ventricular zone results in inappropriate “pile up” of cells

X-linked dominant inheritance; affected males do not survive to term, females present with epilepsy

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2
Q

Type 1 Lissencephaly

A

Caused by mutation in Lis1 gene, which encodes a protein that aides in microtubule polymerization; causes lack of layer specificity, neurons derail from radial glia at inappropriate positions

Affected individuals are heterozygous

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3
Q

Double Cortex Syndrome

A

Caused by mutation in DCX gene (X-linked), which encodes a protein that aides in microtubule polymerization; causes lack of layer specificity, neurons derail from radial glia at inappropriate positions (defect of ongoing migration)

In females, characterized by mild mental retardation and epilepsy

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4
Q

Cajal-Retzius Cells

A

Secrete reelin protein, which is the “stop” signal for neuronal migration; responsible for guiding the “inside-out” development of the cortical layers

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5
Q

Lissencephaly with Cerebellar Hypoplasia (LCH)

A

Caused by mutations in reelin gene; results in inversion of the normal inside-out pattern of cortical development

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6
Q

Radial migration

A

Describes the migration of cerebral cortex cells beginning from the ventricular zone and moving outward toward the superficial cortex along radial glia scaffold; gives rise to excitatory glutamatergic neurons

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7
Q

Band heterotopia

A

Phenotype found in females with Double Cortex Syndrome (DCX gene mutation); neurons with the normal DCX gene are able to migrate normally (inside-out) but neurons with the mutated copy migrate inappropriately, forming a “band” of improperly developed cerebral cortex below the subcortical plate

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8
Q

Chain migration

A

Neurons migrate from the ventricular zone to the olfactory bulb via chain migration

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9
Q

Tangential migration

A

Cells from the lateral and medial ganglionic eminences (secondary zones) migrate tangentially into the cortex and disperse throughout the tissue; gives rise to inhibitory GABA-ergic neurons

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10
Q

Neural crest cells

A

Arise from the border between neuroepithelium and ectoderm; during neurulation, neural crest cells constitute a mass of cells along the dorsal aspect of the neural tube; gives rise to PNS

Neural crest cells express integrin proteins that serve as receptors for ECM laminin and fibronectin proteins, which act as “permissive factors” for neuronal migration

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11
Q

Neural crest migration - Dorsal (lateral) stream

A

Gives rise to pigment cells

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12
Q

Neural crest migration - Medial (ventral) stream

A

Gives rise to PNS neurons and Schwann cells

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13
Q

NGF - What’s the receptor?

A

TrKA

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14
Q

BDNF - What’s the receptor?

A

TrkB

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15
Q

NT-3 - What’s the receptor?

A

TrkC

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16
Q

How do neurotrophic growth factors work?

A

Neurotrophic growth factors are secreted by target organs; they bind tropomyosin-related kinase (Trk) family receptors on growing axons; ligand-binding leads to receptor dimerization and generation of secondary, intracellular signaling molecules which promote axon growth

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17
Q

Long range guidance molecules - Attractive

A

Netrins

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18
Q

Long range guidance molecules - Repulsive

A

Semaphorins

Netrins

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19
Q

Short range guidance molecules

A

Cell surface: Cadherins, CAMs

ECM: Collagen, laminin, fibronectin, proteoglycan

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20
Q

Cranioraschisis Totalis

A

Most severe form of neural tube defect, caused by a complete failure of primary neurulation

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21
Q

Anencephaly

A

Failure of the rostral neuropore to close; the forebrain neurectoderm fails to separate from the cutaneous ectoderm; a cerebrovasculosa is seen where the skull cap should have developed

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22
Q

Encephalocele

A

Defect in the skull with protrusion of the meninges and/or brain; distinguished from anencephaly because there is an epidermal covering over the cranial neural tube closure defect

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23
Q

Myelomeningocele

A

Failure of the posterior neuropore to close (80% in the lumbar area, which is the last area of the neural tube to close); spinal cord and meninges bulge through the vertebrae in the back

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24
Q

Meningocele

A

A skin-covered, CSF-filled mass that is continuous with the CSF in the spinal canal; the meninges and CSF bulge through the vertebrae into the back

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25
Q

Lipomyelocele / Lipomyelomingocele

A

Occurs when a lipoma extends from the subcutaneous tissues to the dorsal aspect of the cord, tethering the cord inferiorly; reflects premature separation of the cutaneous ectoderm during the process of neurulation which allows mesenchyme to enter the unclosed neural tube and differentiate into fat

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26
Q

Dorsal dermal-sinus tract

A

An ectoderm-lined tract that can transgress the dura and allow communication between the skin and CSF; may also cause tethering of the spinal cord

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27
Q

Spina bifida occulta

A

Failure of the bony laminar arch to completely envelop the meningeal sac; usually occurs at L5-S1 levels

Usually asymptomatic, incidental clinical finding not requiring further work-up

28
Q

Chiari Type I malformation

A

Chronic herniation of cerebellar tonsils into the foramen magnum; blocks flow of CSF from central canal into subarachnoid space

Mesodermal disorder of the development of occipital somites and bony posterior fossa; NOT related to NTD or folate deficiency

Elongated cerebral tonsils are pushed downward through the foramen magnum, blocking the normal flow of CSF

29
Q

Hydromyelia

A

Accumulation of CSF within the central canal

Common complication of Chiari Type I malformation

30
Q

Syringomyelia

A

Formation of a CSF-filled cyst that breaks out of the central canal and dissects into the substance of the cord

Common complication of Chiari Type I malformation

31
Q

Type I Chiari Malformation - 3 complications

A
  1. Hydromyelia - accumulation of CSF within the central canal, caused by blockage of the operature which allows CSF to exit the central canal into the sub-arachnoid space
  2. Syringomyelia - formation and rupture of a CSF-filled cyst which can dissect into the substance of the spinal cord b
  3. Hydrocephalus - accumulation of CSF within the 4th ventricle, caused by impeded flow of CSF from 4th ventricle to subarachnoid space
32
Q

With what other disorder is Chiari Type II malformation

always seen with? Why?

A

Failure of neural folds to completely close leaves a dorsal defect (Thoraco-lumbar myelomeningocele) through which CSF can leak out, causing collapse of the ventricular system and “sagging” of the cerebellar vermis through the foramen magnum

33
Q

Features of Chiari Type II malformation

A

Elongation of the cerebellar vermis causing cerebral tonsils to protrude through the foramen magnum and block CSF flow

Abnormalities in the brainstem

Abnormalities of the dural venous sinus

34
Q

What causes Chiari II malformation?

A

Failure of the neural folds to completely close, leaving a dorsal defect which permits CSF to leak through the central canal into the amniotic fluid; this creates collapse/underdevelopment of the ventricular system and posterior fossa, as well as a failure of neuronal migration

35
Q

Holoprosencephaly

A

Failure of differentiation of the prosencephalon into two telencephalic vesicles; usually occurs during 5th week of fetal development

Due to sonic hedgehog mutation (Shh)

36
Q

Alobar holoprosencephaly

A

NO evidence of division of cerebral cortex; i.e. a single forebrain with a single ventricle

37
Q

Semilobar holoprosencephaly

A

Partial cleavage of the cerebral cortex; cerebral hemispheres are fused anteriorly and there is a single ventricle with a horse-shoe shaped appearance

38
Q

Lobar holoprosencephaly

A

Cerebral hemispheres are separated anteriorly and posteriorly; some degree of fusion of structures

39
Q

Dandy Walker Malformation

A

Cerebellar hypoplasia; characterized by partial or complete absence of formation of the cerebellar vermis, cystic dilation of the fourth ventricle that fills up an enlarged posterior fossa, and upward displacement of the tentorium

Sporadic; NOT associated with NTD

40
Q

Where is the conus medullaris found at different stages of development?

A

In the newborn: L3
3 months: Not below the lower margin of L2
Adult: L1-L2

41
Q

Major causes of perinatal stroke - full term vs. pre term

A

Full term - birth trauma resulting in stretching of carotid arteries and subsequent vascular insufficiency

Pre-term (<35 weeks): insufficient auto-regulation of blood flow leads to hemorrhage within the germinal matrix (GMH); most frequent cause of cerebral palsy

42
Q

Ulegyria

A

“Mushroom-shaped gyri”; occurs following perinatal stroke in the full-term infant, usually due to vascular insufficiency of the carotids; less-infarcted tissue in the crest of the gyri continues to grow and develop while more infarcted tissue within the sulci does not

43
Q

When do most neural tube defects occur?

A

Weeks 2-3 of gestation

44
Q

Folic acid guidelines

A

50% of NTDs are related to folate deficiency

Recommended: 0.4mg/day for at least 4 weeks before coming pregnant, or 4.0mg/day for women with prior history of pregnancy with NTD

45
Q

How much does the normal brain weigh?

A

1,200-1,400g

46
Q

Clinical Presentation of Chiari Type I Malformation

A

Usually presents as headache - especially during Valsalva, in which venous return to chest is diminished causing increased dural venous pressure; CSF cannot be displaced into spinal cord to accomodate and so intracranial pressure increases, causing HA

Likely a mesodermal disorder of underdevelopment of occipital somites and posterior fossa; NOT NTD

47
Q

Features of Chiari Type II Malformation

A

Elongation of the cerebellar vermis, which becomes pushed down through the foramen magnum blocking CSF flow; abnormalities of the brainstem including “beaking” and “kinking” of the midbrain and medulla

48
Q

Which morphogens promote caudal structure development? Where do they come from?

A

Wnts, FGFs, and Retinoic Acid secreted by the primitive node promote caudal structure development

49
Q

What are HOX genes?

A

Hox genes code for transcription factors that active the expression of downstream genes, which in turn active different programs of differentiation

Hox gene expression varies along the AP axis (i.e. in the rhombomeres)

50
Q

What is the main “head organizer” morphogen?

A

Cerebrus

51
Q

What morphogens does the primitive streak secrete? What do they do?

A

The primitive streak secretes chordin, noggin, and follastatin; these morphogens inhibit BMPs and create a BMP gradient that is higher laterally (dorsally) than medially (ventrally)

52
Q

Sonic hedgehog

A

Secreted by the notocord; signals the thickening of embryonic ectoderm to form the neural plate

53
Q

Sulcus limitans

A

A crease in the neural tube that separates the ventral and dorsal cell populations

54
Q

Basal plate

A

Ventral population of cells in the neural tube

55
Q

Alar plate

A

Dorsal population of cells in the neural tube

56
Q

What are secondary zones of neurogenesis?

A

Specific regions of the brain that are hot spots of postnatal neurogenesis; i.e. the external granule layer of the cerebellum

Cells that give rise to the external granule layer of the cerebellum are initially located near the rim of the 4th ventricle; before they are post-mitotic, they migrate to the external granule layer where they proliferate, exit the cell cycle, and migrate into the cerebellum

57
Q

Subventricular zone

A

Secondary zone of neurogenesis for olfactory neurons; neurons are initially located near the anterior wall of the lateral ventricles, then migrate to the subventricular zone where they proliferate, exit the cell cycle, and give rise to the olfactory bulb neurons

58
Q

Polyneuronal

A

The situation during embryonic and early postnatal life in which each muscle fiber is innervated by several motor neurons (prior to selective synapse elimination)

59
Q

Roles of neurotrophins

A

Axon growth and synapse formation
Selective synapse elimination
Activity-dependent modulation of synaptic transmission (LTP)
Mediation of long-term consequences of abnormal brain function

60
Q

Brain abnormality seen in ASD

A

Abnormally large increases in size, especially in white matter areas, during the first few postnatal years

Neuronal cell bodies are often smaller and dendrites branch less

61
Q

What mechanism underlies the greater seizure susceptibility of the neonatal brain?

A

During embryonic development, the presence of a Na/K/Cl co-transporter allows intracellular accumulation of Cl-, resulting in a more depolarized value for ECl; consequently, activation of GABA receptors leads to depolarization

In the adult, a Cl- extruder protein is expressed; this shifts ECl to be near or negative to the resting membrane potential such that activation of GABA receptors leads to hyperpolarization

62
Q

What is meant by a cell’s birthdate?

A

The time at which a cell underwent its last round of DNA synthesis; after this, the cell divides and exits the cell cycle

63
Q

Where do the 6 layers of the cerebral cortex arise?

A

From the marginal zone + cortical zone

64
Q

Where do radial glial cells live?

A

Intermediate zone of the pre-plate

65
Q

Nogo

A

A molecule expressed by CNS myelin that prevents axonal regeneration in the adult CNS

66
Q

How do pre- and post-synaptic terminals align during axon growth?

A

Neurexins interact with pre-synaptic Ca2+ channels and neuroligands interact with post-synaptic, intracellular synaptic organizing proteins (PSD95) to “bridge the gap” of the synapse

67
Q

What developmental change does the ACh undergo between embryonic and adult stages?

A

nAChR is formed by 5 subunits - 2 alpha (ACh binding), beta, delta, and either gamma (embryonic) or epsilon (adult); epsilon subunit increases AChR open time, allowing greater depolarization to occur

Nervous System I (10 decks)

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