Development of the CNS

Question 1

Which embryonic feature has an inductive relationship with the overlying ectoderm?

Answer 1

Notochord

Question 2

What are some of the main derivatives of ectoderm?

Answer 2

– the central nervous system
– the peripheral nervous system
– the sensory epithelium of the ear, nose and eye
– the epidermis, hair and nails
– the subcutaneous, mammary and pituitary gland
– the enamel of teeth

Question 3

What is the initial step in the process of neurulation?

Answer 3

The appearance of the notochord and the mesoderm induce the overlying ectoderm to thicken and form the neural plate.

Question 4

What is the neural plate made of?

Answer 4

Neuroectoderm.

Question 5

What signalling needs to take place for neurulation to occur?

Answer 5

upregulation of FGF, inhibition of BMP-4
noggin and chordin expression
Neural plate switching from E-cadherin expression to N-cadherin expression.

Question 6

Disruption of neural crest migration can result in what malformations?

Answer 6

Treacher Collins syndrome

Di George syndrome

Question 7

What is Treacher Collins sydrome and what causes it?

Answer 7

Under development of zymgomatic bones and ears. Mutation in the TCOF-1 gene or retinoic acid exposure.

Question 8

What is Di George syndrome?

Answer 8

22q11.2 deletion syndrome. Causes cleft palate, cardiac abnormalites, abnormal facies, thymic aplasia.

Question 9

When does the neural tube close?

Answer 9

Week 4, anterior neuropore by day 25 and posterior by day 27.

Question 10

What cells make up the inner mantle layer of the neural tube?

Answer 10

Neuroblast cells

Question 11

What layer of the neural tubes goes on to become the grey matter of the spinal cord?

Answer 11

Mantle layer

Question 12

What layer of the neural tube becomes the white matter of the spinal cord?

Answer 12

Marginal layer

Question 13

What does the marginal layer of the neural tube consist of?

Answer 13

nerve fibres emerging from neuroblasts.

Question 14

What kind of innervation do dorsal root fibres carry?

Answer 14

sensory

Question 15

What kind of innervation do ventral root fibres carry?

Answer 15

motor

Question 16

What kind of fibres do spinal nerves contain?

Answer 16

Both

Question 17

What are the name of the 3 primary brain vesicles present in week 3?

Answer 17

Forebrain - prosencephalon
Midbrain - mesencephalon
Hindbrain - rhombencephalon

Question 18

What are the names of the 5 primary brain vesicles present in week 5? What do these go on to become?

Answer 18

Telencephalon - cerebrum
Diencephalon - thalamus, hypothalamus and epithalamus
Mesencephalon - midbrain
Metencephalon - pons and cerebellum
Myelencephalon - medulla oblongata

Question 19

What neural tube defect causes anencephaly?

Answer 19

Failure of the closure of the anterior neuropore.

Question 20

What neural tube defect causes spina bifida?

Answer 20

Failure of closure of the posterior neuropore.

Question 21

How can neural tube defects be prevented?

Answer 21

Folic acid taken prior to conception and in early

stages of pregnancy.

Question 22

How is hydrocephalus treated?

Answer 22

Relief of intracranial CSF pressure by shunting fluid

Question 23

What cell types form the meninges? When does this occur?

Answer 23

Mesenchymal cells and neural crest cells
Day 20-35, these cells migrate around the
neural tube

Question 24

When does the developing eye appear?

Answer 24

22 days

Question 25

From what part of the developing brain to optic vesicles form?

Answer 25

Piencephalon of the forebrain

Question 26

How does the optic stalk form?

Answer 26

Placode cells become collumnar and start to invaginate.

Question 27

What is the blood supply of the developing retina and lens?

Answer 27

Hyaloid artery - branch of the ophthalmic artery.

Question 28

What germ layer are lens cells derived from? What is unusual about adult lens fibres?

Answer 28

Ectoderm. They have no organelles or nuclei.

Question 29

The optic cup has a bilaminar structure. What do the two different layers go on to form?

Answer 29

Outer layer forms the pigmented layer of retina.

Inner layer forms the neural layer of retina (forms rods and cones.)

Question 30

What parts of the eye develop from the layers of the retina at the rim of the optic cup?

Answer 30

Iris and ciliary body

Question 31

What substance does the ciliary body produce?

Answer 31

Aqueous humour.

Question 32

When does the inner and outer layer of the optic stalk fuse and the cavity of the stalk disappear?

Answer 32

Week 7

Question 33

What important stage of optic nerve development occurs in week 9?

Answer 33

The hyaloid artery and vein become the central artery and vein of the retina. The optic stalk is now the optic nerve.

Question 34

The anterior chamber of the eye is formed when a space develops between what two parts of the eye?

Answer 34

Cornea and the lens.

Question 35

The posterior chamber of the eye is formed when a space between what two parts of the eye?

Answer 35

lens and retina.

Question 36

Which signalling molecule is responsible for eye field separation? How does it work?

Answer 36

SHH. Upregulates PAX-2 in optic stalks and restricts PAX-6 to the optic cups and lens.

Question 37

Describe microphtalmia. What causes this condition?

Answer 37

Eye is too small - results from genetic abnormalities, intrauterine infections, foetal alcohol syndrome.

Question 38

Describe anophtalmia. What causes this condition to develop?

Answer 38

Absence of the eye. genetic/infection. failure of optic vesicle to develop.

Question 39

Descibe cyclopia. What causes this condition to develop?

Answer 39

Single eye. failure of the prosencephalon to divide the orbits of the eye.

Question 40

Describe Colomboma Iridis.

Answer 40

cleft in the iris. failure of choroid fissure to close.

Question 41

What causes congenital cataracts?

Answer 41

genetic causes, rubella infection between week 4 and 7 gestation.