nervous system development

Question 1

Primary neurulation: What are the main events of the two phases?

Answer 1

Phase 1: Neural Plate formation

Phase 2: neural tube formation

Question 2

Where are the mesenchyme cells located that is the location of the start of secondary neurulation? Explain the three phases

Answer 2

Mesenchyme located in the tailbud, or caudal eminence.
Phase 1- Mesenchyme in tail bud forms neural chord
Phase 2- Lumen forms within neural cord (eventually becomes continuous w/central canal of spinal cord
Phase 3- Tailbud regresses early in fetal period

Question 3

What results from errors in primary neurulation? Characteristics? Examples/explanations?

Answer 3

Neural tube defects (Dysraphic errors).
Faulty neural tube closure. Closure defects usually occur at the ends, where the neuropores were located.
Meroanencephaly- Calvaria missing, as well as forebrain/midbrain. Diagnosed by ultrasound and elevated apha fetoprotein levels.
Encephalomeningocoele- skull defect, brain and meninges herniate
Cranial meningocoele- only meninges herniate, sac filled w/CSF
Cranium bifidum- opening b/w skull bones

Question 4

Explain the 4 types of spina bifida

Answer 4

1. Myeloschisis- neural plate open dorsally. No swelling. . Most severe type. Legs paralyzed.
2. Meningomyelocoele- Herniation of spinal cord and meninges. Cystic swelling, may be covered by skin or membrane.
3. Meningocoele- Herniated meningial sac.
4. spina bifida occulta- Vertebral defect, doesn’t close. Usually asymptomatic.

Question 5

Spina bifida cystica includes which two types?

Answer 5

Meningomyelocoele and meningocoele

Question 6

What is diastematomyelia?

Answer 6

bone spur in spinal canal. May be associated w/hair tuft or dimple

Question 7

(Mero)anencephaly and spina bifida relative alpha fetoprotein levels?

Answer 7

anencephaly very high, then spina bifida.

Question 8

What supplement during pregnancy can reduce NT defects incidence by 50%?

Answer 8

folic acid supplements

Question 9

What 3 cell types are derived from the neuroepithelium of the neural tube? What order are they formed in?

Answer 9

1. neuroblasts- pre-neurons.
2. glial cells- will form astorcytes and oligodendrocytes (collectively called macroglia).
3. ependymal cells- become epithelial cells in the ventricles

Question 10

What are radial glia?

Answer 10

Special population of glial cells, guide the migration of neuroblasts and glioblasts. They are only temporary glial cells.

Question 11

What 3 layers form in the wall of the neural tube?

Answer 11

Ventricular- Closest to lumen of NT. Becomes ependymal cells.
Intermediate- Area to which neuroblasts migrate. Will become gray matter.
Marginal- Most superficial layer. Becomes white matter.

Question 12

The intermediate layer of the neural tube differentiates into what parts? What forms in each, and what causes the formation?

Answer 12

1. Dorsal half becomes alar plate. Dorsalizing signals cause formation of sensory neurons here.
2. Ventral half becomes basal plate. Ventralizing signals cause the formation of motor neurons here.

Question 13

What is the sulcus limitans?

Answer 13

A groove that runs the length of the spinal cord, forming a boundary between sensory and motor parts.

Question 14

What is the ventral signal from the notocord? Dorsal signal?

Answer 14

Ventral signal is shh, and dorsal signal is BMP.

Question 15

Which of the 3 flexures in the neural tube cause ventral bending?

Answer 15

1. Cervical flexure- at junction of brain and spinal cord.

2. Mesencephalic flexure- Forms in area that will become brain.

Question 16

Which of the 3 flexures in the neural tube cause dorsal bending?

Answer 16

Rhombencephalic flexure- eventually causes brain to fold back on itself

Question 17

What are the three brain regions are visible at the open neural fold stage, and where are they compared to the mesencephalic flexure? What do they further divide in to?

Answer 17

1. prosencephalon- before flexure. Divides into diencephalon and telencephalon.
2. mesencephalon- at flexure.
3. rhombencephalon- after flexure. Divides into metencephalon and myelencephalon

Question 18

What mediates the subdivision of the hindbrain into temporary segments called ________?

Answer 18

Expression of hox genes. called rhombomeres.

Question 19

What is holoprosencephaly? Possible cause?

Answer 19

Failure of regionalization of prosencephalon. CNS and facial malformations. Alcohol use may be a factor.

Question 20

Forebain vs. brainstem?

Answer 20

Forebrain includes divisions of prosencephalon, which are the diencephalon and telencephalon. Brainstem is the mesencephalon, and the divisions of the rhombencephalon which are the metencephalon and myelencephalon

Question 21

What forms in the roof of most ventricles, and what does it do

Answer 21

choroid plexus, which secretes CSF.

Question 22

Communicating v. non-communicating hydrocephalus?

Answer 22

Communicating (non obstructive)- CSF can get into sub arachnoid space, but cannot be resorbed.
Non-communicating (obstructive)- CSF cannot get into subarachnoid space.

Question 23

What is the primary precursor of the peripheral nervous system?

Answer 23

Neural crest.

Question 24

What are ectodermal placodes?

Answer 24

Thickening of ectodermal surface. Contribute to primary sensory neurons in the peripheral nervous system.

Question 25

The ganglia of CN 5, 7, 9, and 10 have what in common?

Answer 25

Primary sensory neurons derived from neural crest AND ectodermal placodes.

Question 26

Telencephalon gives rise to

Answer 26

1. Cerebrum

2. Lateral ventricle

Question 27

Diencephalon gives rise to

Answer 27

1. Thalamus

2. Hypothalamus

Question 28

Mesensephalon gives rise to?

Answer 28

Midbrain

Question 29

metencephalon gives rise to?

Answer 29

1. Pons
2. upper half of 4th ventricle
3. Cerebellum

Question 30

Myelencephalon gives rise to?

Answer 30

1. Medulla

2. Lower half of 4th ventricle