Development Of CNS

Question 1

What is gastrulation?

Answer 1

The process by which all three germ layers are created.

Question 2

How do we produce the neural tube?

Answer 2

Gastrulation produces the notochord

Notochord induces neurolation

Induction of neural plate

Elevation of lateral edges of neural plate

The depressed mid-region is the neural groove

Neural folds gradually approach each other in the midline and fuse, producing the neural tube.

Question 3

What is the notochord and what does it do?

Answer 3

Solid rod of cells running in the midline with important signalling role.

Notochord directs conversion of overlying ectoderm to neuroectoderm.

Question 4

How long does it take / when does the neural tube close?

Answer 4

By day 28-32, the neural tube is completely closed.

Whole process takes 10 days.

Question 5

How do neural tube defects occur?

Answer 5

Results from failure of neural tube to fuse or failure of the neuropores (anterior and posterior) to close.

Can occur caudally or cranially.

Cranially - anencephaly (missing part of brain)

Caudally - spina bifida

Question 6

What is spina bifida?

Answer 6

When you have two spines as the neural tube doesn’t fuse properly caudally.

Can occur anywhere along the length, most common in lumbosacral region.

Neurological deficits occur but, it is not associated with cognitive delay.

Hydrocephalus nearly always occurs.

Question 7

What other neural tube defects can occur?

Answer 7

Anencephaly - failure of NT to close cranially
Absence of cranial structures, including brain.

Rachischisis - Failure of neural fold elevation

Both incompatible with life

Question 8

How do you diagnose and prevent NTDs?

Answer 8

Raised maternal a-fetoprotein (not specific but sign something is wrong)

USS

Folic acid pre-conceptually and for first trimester reduces NTDs by 70%

Question 9

What embryonic structure does the spinal cord come from?

Answer 9

Most of the length of the neural tube gives rise to the spinal cord.

Question 10

How does the corda equina develop?

Answer 10

At the 3rd month, the spinal cord is the same length as the vertebral column.

Thereafter, the column grows faster.

Spinal roots must elongate because they still exit at the intervertebral foramen.

This forms the cauda equine.

Question 11

What is the forebrain made from?

Answer 11

Prosencephalon

Question 12

What is the midbrain made from?

Answer 12

Mesencephalon

Question 13

What is the hindbrain made from?

Answer 13

Rhombencephalon

Question 14

At 5 weeks of development, five secondary brain vesicles are formed. What are they?

Answer 14

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

Question 15

Why does the neuraxis not remain straight?

Answer 15

Growth and development at the cranial NT exceeds available space linearly, so it must fold up.

Cervical flexure: spinal cord - hindbrain junction.

Cephalic flexure: midbrain region

Question 16

What does the ventricular system develop from and what is its role?

Answer 16

Develop from tubular structures of the developing CNS (lumen of the tubes is the ventricles).

In an adult, these ventricles are interconnected and filled by CSF produced by the choroid plexus cells.

The ventricular system cushions the brain and spinal cord within their bony cases.

Question 17

What is hydrocephalus?

Answer 17

A ventricular system abnormality.

Most common in newborns suffering from spina bifida.

It is readily treatable using a shunt.

Can occur anywhere there is a blockage of the ventricular system.

Question 18

What are the layers of the early neural tube, from the inside out?

Answer 18

Neuroepithelial layer
Intermediate (mantle) layer -neuroblasts
Marginal layer -processes

The roof and floor plates regulate dorsal and ventral patterning.

Made from the alar (sensory) plate and the basal (motor) plate.

Question 19

What are neural crest cells?

Answer 19

Cells of the lateral border of the neuroectoderm tube.

Become displaced so enter the mesoderm and undergo epithelial to mesenchymal transition.

Question 20

What cells of the nervous system are derived from neural crest cells?

Answer 20

Cranial nerve ganglia

Spinal (dorsal) root ganglia

Sympathetic ganglia (chain and pre-aortic)

Parasympathetic ganglia

Schwann cells

Glial cells

Leptomeninges (arachnoid and pia)

Question 21

What head, neck and midline structures are derived from neural crest cells?

Answer 21

CT and bones of face and skull

Odontoblasts

Dermis (face and neck)

C cells of the thyroid gland

Question 22

What other are derived from neural crest cells?

Answer 22

Conotruncal septum (heart)

Melanocytes

Adrenal medulla

Question 23

What conditions can you get from abnormal neural crest migration?

Answer 23

Hirschsprung disease (aganglionic megacolon) -only affect one structure.

DiGeorge syndrome (thyroid deficiency, immunodeficiency secondary to thymus defect, cardiac defects, abnormal faecies) -affects multiple structures.

Question 24

What are the secondary brain vesicles of the prosencephalon (forebrain) and what are their mature derivatives?

Answer 24

Telencephalon - cerebral hemispheres

Diencephalon - thalamus

Question 25

What is the secondary brain vesicle of the mesencephalon (midbrain) and what is the mature derivative?

Answer 25

Mesencephalon - midbrain

Question 26

What are the secondary brain vesicles of the rhombencephalon (hindbrain) and what are their mature derivatives?

Answer 26

Metencephalon - pons, cerebellum

Myelencephalon - medulla oblongata