Lecture 17: Nervous Development II

Question 1

The tophographical arrangement of the myelencephalon is almost identical to the spinal cord. What is the major topographical change?

Answer 1

Pronounced expansion of the roof plate to form the thin roof over the fourth ventricle

Question 2

Expression of which set of genes seems to be responsible for the differentiation of specific nuclei in the myelencephalon?

Answer 2

Hox genes

Question 3

What do the mutations weaver and reeler have to do with the building of the cerebral cortex?

Answer 3

Weaver: related to abnormal function of the cerebellum, bc of abnormal migration of radial glial cells in the cerebellum that would normally form the granular layer

Reeler: characterized by abnormal behavior and the absence of normal cortical layering

Question 4

What is the relation of reelin to reeler?

Answer 4

Reelin is the extracellular protein that was mutant in the mutant mouse Reeler. Reelin may serve as a stop signal for radial neuronal migration or as an insertational signal for migrating neurons.

Question 5

Relate columnar radial units to the organization of the cerebral cortex

Answer 5

The cerebral cortex is a matrix of discrete columnar radial units that consist of radial glial cells and the neuroblasts that migrate along them. The radial units begin as pro- liferative units, with most cortical neurons generated between days 40 and 125.

Question 6

What are the major derivatives of the metencephalon?

Answer 6

Pons (basal plate) & Cerebellum (alar plate)

Question 7

The cerebellum forms in the region of the rhombic lips (rhombomeres 1-8). The rhombic lips are the product of what inductive interaction?

Answer 7

Roof plate and neural tube via BMP signaling

Question 8

What are the superior cerebellar peduncles?

Answer 8

During cerebellar development, many fibers emanating from the vast number of neurons generated in the cerebellar cortex leave the cerebellum through a pair of massive superior cerebellar peduncles, which grow into the mesencephalon.

*Massive fiber bundles b/w the cerebellum and mesencephalon

Question 9

What are the major derivatives of the alar plates of the mesencephalon?

Answer 9

Tectum (corpora quadrigemina)

*Which is composed of both superior colliculi (visual system) and inferior colliculi (auditory system)

Question 10

Where is Otx-2 located and how is it related to Shh?

Answer 10

Otx-2 confines Shh to the basal part of the midbrain

Question 11

Where do the cerebral peduncles form and what is their function?

Answer 11

• Ventrolateral region of the mesencephalon
• They carry fibers between the cerebral hemispheres and spinal cord

Question 12

What are the major derivatives of the Diencephalon?

Answer 12

Epithalamus, thalamus, hypothalamus

Question 13

What are the three patterning centers in the forebrain?

Answer 13

• Rostral patterning center (FGF-8)
• Dorsal patterning center (BMPs and Wnts)
• Ventral patterning center (Shh)

Question 14

Describe the formation of the corpus striatum and corpus callosum

Answer 14

corpus striatum: formed from telecephalic vesicles

Question 15

What is the Rhinencephalon (also the archicortex and paleocortex)?

Answer 15

Functional component of the telecephalon that is involved in olfaction.

Question 16

What is the neocortex?

Answer 16

Morphologically dominant cerebral hemispheres

• In early development, much of the telencephalon is occupied by rhinencephalic areas, but with the expansion of the cerebral hemispheres the neocortex takes over as the component occupying most of the mass of the brain.

Question 17

What is the Arnold-Chiari malformation and what is its relation to hydrocephalus?

Answer 17

Arnold-Chiari leads to hydrocephalus. Parts of the cerebellum herniate into the foramen magnum and mechanically prevent the escape of cerebrospinal fluid from the skull. This condition can be associated with some form of closure defect of the spinal cord or vertebral column.

Question 18

Relate the cranial nerves to the pharyngeal pouches and to their modalities

Answer 18

• Cranial nerves develop similarly to spinal nerves but they are either motor (ventral root based) or sensory (dorsal root based), spinal nerves are typically mixed
• each nerve supplies a different pharyngeal arch

CN I and II (olfactory and optic): regarded as extensions of brain tracts rather than true nerves

CN III, IV, VI, and XII: motor nerves

CN V, VII, IX, and X: mixed nerves with motor & sensory

Question 19

Decribe the origin of the cranial nerve ganglia

Answer 19

Neurons in some parts of the ganglia are of neural crest origin, and neurons of other parts of ganglia arise from plac- odal ectoderm.

Question 20

Why is CN II not a true nerve?

Answer 20

because it is often regarded as an extension of the brain tract rather than an actual nerve

Question 21

What is rachischisis?

Answer 21

a closure defect of the spinal cord

Question 22

Describe what substance, when present in amniotic fluid in elevated amounts, can be diagnostic of closure defects

Answer 22

elevated levels of α-fetoprotein

Question 23

Describe types of closure defects from least serious to most serious

Answer 23

least serious = spina bifida occulta, spinal cord and meninges are in place but the neural arch of one or more vertebrae are incomplete

intermediate severe = meningocele, dura mater is missing from the area of defect but spinal cord is in place

most severe = myelomeningocele, spinal cord buldges out or is entirely displaced into the protruding subarachnoid space