Neuro Embryology

Question 1

What is the MOST important event in embryogenesis?

The structure that induces this event is derived from which structure?

Answer 1

GASTRULATION

INDUCED by the NOTOCHORD! (which develops from Hensen’s node)

Question 2

Describe the formation of the Neural Tube.

Answer 2

1. Notochord develops from Hensen’s Node
2. Notochord induces the neuroectoderm to form the neural plate
3. Neural groove folds and forms the Neural Tube
4. Anterior and Posterior Neuropores will close at Day 26

Question 3

Talk about induction of the Dorsal and Ventral Aspects of the Neural Plate.

Answer 3

Ventral Induction –> Primarily induction by the Notochord (forms Motor neurons)

Dorsal Induction –> Epidermal Ectoderm influences neural tube to form ROOF and ALAR plates and affect neural crest before they migrate

Question 4

Differentiate between the Alar and Basal Plates.

Answer 4

Alar Plate –> Sensory Nuclei and derived from here!

Basal Plate –> Motor neurons are derived from here!

Question 5

What is the most common tumor associated with Neuroblasts?

Answer 5

Medulloblastomas in the Posterior Cranial Fossa (Central Nerve Tumor)

Question 6

Do neural cells or glial cells develop first?

What are the last of the cells to differentiate?

Answer 6

NEURAL cells are FIRST and then Glioblasts

Ependymal cells are LAST to differentiate

Question 7

Where is the end of the spinal cord in:

3 Month Fetus

5 Month Fetus

Neonate

Adult

Answer 7

3 Month Fetus - Extends throughout the ENTIRE length of the vertebral column

5 Month Fetus - Vertebral Column is LONGER than the spinal cord; Conus Medullaris is @ S1

Neonate - Conus Medullaris is @ L3

Adult - Conus Medullaris is @ L1-2 Interspace

Question 8

What is Rachischisis?

What is Cranioschisis?

Answer 8

Rachischisis - Vertebral column defect with exposure of primitive spinal cord and/or or nerves.

Cranioschisis - Cranial defect with exposure of the primitive brain (Failure of closing the Rostral Neuropore)

Question 9

Differentiate between:

1. Spina Bifida Occulta
2. Meningocele
3. Meningomyelocele

Answer 9

1. Spina Bifida Occulta - vertebral column defect with herniation of meninges or neural tissue. Usually presents as cystic, midline, hairy mass in lumbar region of vertebral column. This anomaly may be due to the failure of the roof plate of the neural tube to induce the development of overlying spinous processes. Spina bifida occulta may be asymptomatic for years.

2. Meningocele - vertebral column defect with herniation of meninges.

3. Meningomyelocele - vertebral column defect with herniation of meninges, spinal cord and/or or nerves.

Question 10

Describe Hyrdocephalus.

Which diseases is it most commonly associated with?

Answer 10

May be due to congenital stenosis of a portion of the ventricular system or certain fetal infections (CMV, toxoplasmosis), and some autosomal recessive syndromes such as Hurler’s.

*** Hydrocephaly is commonly associated with meningomyelocele, and Arnold-Chiari and Dandy-Walker malformations.

Question 11

Describe Arnold-Chiari malformation.

Which other congenital defect does it present with?

Answer 11

Common cerebellar anomaly

*** Almost always present with meningomyelocele

*** A-C malformations involve an elongation of the cerebellar vermis, which herniates through the foramen magnum and overlies a dorsally flexed medullospinal segment.

Question 12

Describe Dandy-Walker Malformation.

Answer 12

Characterized by internal hydrocephalus secondary to partial or complete obstruction of the medial and lateral apertures, partial or complete absence of the cerebellar vermis, and a posterior cranial fossa cyst that is continuous with the fourth ventricle.

**** NO VERMIS of the cerebellum!!!

Question 13

Differentiate between:

1. Cranial Meningocele
2. Meningohydroencephalocele
3. Anencephaly
4. Cranial Rachischisis
5. Meningoencephalocele

Answer 13

1. Cranial Meningocele - Cranial defect with herniation of meninges

2. Meningohydroencephalocele - Cranial defect with herniation of meninges, BRAIN and VENTRICLES

**** Failure of Closing the Neuropore!

3. Anencephaly - Failure of closing the rostral neuropore

4. Cranial Rachischisis - Congenital absence of the forebrain usually with cranial defect of frontal and parietal bones. This fatal anomaly is due to the failure of the neural tube to close.

5. Meningoencephalocele - Cranial defect with herniation of meninges and brain tissue