Neural embryology

Question 1

when is neural development (when the notochord and neural plate develop)

Answer 1

Day 18 to Day 21

Question 2

what do the walls and cavity of the prosencephalon become (what are the intermediate secondary vesicles)

Answer 2

prosencephalon becomes telencephalon and diencephalon; telencephalon becomes the cerebrum (walls) and lateral ventricles (cavity); diencephalon becomes the thalamus (walls) and 3rd ventricle (cavity)

Question 3

what does the mesencephalon become (adult derivatives of walls and cavity)

Answer 3

midbrain (walls) and cerebral acqueduct (cavity)

Question 4

what does the hindbrain (rhombencepalon) become (secondary intermediates and adult derivatives of walls and cavities)

Answer 4

metencephalon and myelencephalon;
metencephalon becomes pons and cerebellum (walls) and upper half of 4th ventricle
myelencephalon becomes the medulla and lower half of 4th ventricle

Question 5

what germ cell layer do microglia originate from

Answer 5

mesoderm

Question 6

what cells of the nervous system originate from the neural crest cells

Answer 6

PNS neurons and Schwann cells

Question 7

what cells of the nervous system originate from the neuroectoderm

Answer 7

CNS neurons, oligodendrocytes, astrocytes, ependymal cells

Question 8

what lab abnormalities indicate a neural tube defect; how is diagnosis confirmed

Answer 8

increased AFP in amnionic fluid and maternal serum, increased AChE in amnionic fluid (confirms diagnosis)

Question 9

what increases risk of neural tube defects

Answer 9

folate deficiency around conception and pregnancy

Question 10

describe the anatomic defect of spina bifida occulta

Answer 10

bony spinal canal doesn’t close all the way; no spinal cord herniation; dura intact; tuft of hair or skin dimple can be seen at the level of the defect

Question 11

what’s the difference between meningocele and meningomyelocele

Answer 11

in meningocele the spinal canal is open and only the meninges herniate whereas in meningomyelocele the spinal cord also herniates out

Question 12

what early developmental abnormality leads to anencephaly

Answer 12

failure of the forebrain to develop leads to no cerebrum, an open calvarium and polyhydramnios because swallowing centers are missing

Question 13

what are two risk factors for anencephaly

Answer 13

diabetes mellitus type I and folate deficiency

Question 14

what developmental abnormality leads to eventual holoprosencephaly and what is the clinical presentation

Answer 14

failure of the cerebrum to separate into two lateral hemispheres (during week 5-6); newborns can have cleft lip/palate and, in severe cases, cyclopia

Question 15

what genetic abnormality leads to holoprosencephaly

Answer 15

sonic hedgehog mutations can lead to holoprosencephaly

Question 16

what is a Chiari II (Arnold Chiari malformation) and what is the likely cause

Answer 16

herniation of the cerebellar tonsils and vermis through the foramen magnum; likely due to aqueductal stenosis and hydrocephalus

Question 17

what other CNS condition does Chiari II present with (besides aqueductal stenosis and hydrocephalus)

Answer 17

Chiari II is often seen with lumbosacral meningomyelocele (paralysis below this point)

Question 18

describe Dandy-Walker malformation

Answer 18

an enlarged fourth ventricle leads to agenesis of the vermis

Question 19

what two conditions are associated with Dandy-Walker malformations

Answer 19

hydrocephalus and spina bifida

Question 20

what is syringomelia and what nerve fibers does it usually impact first

Answer 20

syringomelia is a condition in which there is a cystic cavity in the spinal cord; nerve fibers passing through the anterior commissure are usually impacted first leading to cape-like distribution of pain and temperature deficits in the upper extremity

Question 21

what is the most common site for syringomelia

Answer 21

C8 - T1

Question 22

what developmental abnormality is syringomelia associated with

Answer 22

Chiari I malformation (ectopia, aka displacement, of the cerebellar tonsils)

Question 23

what symptoms are usually seen in Chiari I malformation

Answer 23

usually asymptomatic in childhood and manifests with headaches and cerebellar deficits

Question 24

what progenitor structure forms the innervation of the anterior 2/3 of the tongue

Answer 24

1st and 2nd brachial arches form anterior 2/3 of the tongue

Question 25

what progenitor structure forms the innervation of the posterior 1/3 of the tongue

Answer 25

3rd and 4th brachial arches form the posterior 1/3 of the tongue

Question 26

what progenitor structure forms the muscles of the tongue

Answer 26

occipital myotome