Development Of The Nervous System

Question 1

What is gastrulation?

Answer 1

When the bilaminar disc becomes the trilaminar disc Go from hypoblast and epiblast to endoderm, mesoderm and ectoderm

Question 2

How is the neural tube formed?

Answer 2

Induction of the neural plate

Elevation of its lateral edges

The depressed mid region is the neural groove

Neural folds crash ally approach each other in the midline and fuse, producing the neural tube

Question 3

What does the notochord serve as the basis of?

Answer 3

The midline, axial skeleton and neural tube

Question 4

Where does fusion of the neural folds begin?

Answer 4

In the cervical region, then proceeds in both a cranial and caudal direction

Question 5

What is neurulation?

Answer 5

The notochord-driven induction of ectoderm leading to formation of the neural plate and neural tube

Question 6

When does neurulation begin?

Answer 6

Third week

Question 7

When do the anterior and posterior neuropores close?

Answer 7

Anterior - day 25

Posterior - day 28

Question 8

What are the different neural tube defects and how do they occur?

Answer 8

Spina bifida - failure of the neural tube to close caudally

Anencephaly - failure of the neural tube to close cranially

Question 9

Where does spina bifida most commonly occur?

Answer 9

The lumbosacral region (but can occur anywhere along the length of the spinal cord)

Question 10

What normally happens as a result of spina bifida?

Answer 10

Neurological deficits

Hydrocephalus nearly always

Not associated with mental retardation

Question 11

What can happen if hydrocephalus is not treated in spina bifida?

Answer 11

Can cause cognitive delay

Question 12

What are the different types of spina bifida?

Answer 12

Spina bifida aculta - no visible cyst, stays within the body column. Can be asymptomatic

Meningocoele - The arachnoid and meninges herniate out of the spinal cord

Myelomeningocoele - Both the neural tissue and meninges herniate out

Question 13

What happens in anencephaly?

Answer 13

Failure of neural tube closure cranially

Absence of cranial structures including the brain

Not compatible with life

Question 14

What is rachischisis?

Answer 14

Failure of neural fold elevation leading to a splayed neural tube

Question 15

How are neural tube defects diagnosed?

Answer 15

Raised maternal serum alpha-fetoprotein

Ultrasound scan

Question 16

How to prevent neural tube defects?

Answer 16

Take folic acid for 3 months pre-conception and then for the first trimester

Question 17

What is the cauda equina?

Answer 17

When the vertebral column grows faster than the spinal cord, the spinal roots need to elongate to exit at their intervertebral foramen, and so form the cauda equina beneath the spinal cord

Question 18

Names for the forebrain, midbrain and hindbrain?

Answer 18

Forebrain = prosencephalon

Midbrain = mesencephalon

Hindbrain = rhombencephalon

Question 19

How do the forebrain, midbrain and hindbrain develop?

Answer 19

During neural fold formation, three primary brain regions develop.

After neural tube closure in the fourth week, the dilations become the three primary brain vesicles

Question 20

When do the secondary brain vesicles develop?

Answer 20

At 5 weeks of development

Question 21

What are the folds in the cranial neural tube?

Answer 21

Cervical flexure: spinal cord-hindbrain junction

Cephalic flexure: midbrain region

Question 22

Why do flexures develop in the neural tube?

Answer 22

Because there is not enough available space if the tube just grows linearly.

Question 23

Role of the ventricular system?

Answer 23

Cushion the brain and spinal cord within their bony cases

Question 24

How is congenital hydrocephalus treated?

Answer 24

Use a shunt

Question 25

What can cause hydrocephalus in a newborn?

Answer 25

Any blockage in the ventricular system E.g. tumour, infection

Question 26

What do the roof and floor plates of the neural tube do later on?

Answer 26

Regulate dorsal and ventral patterning Alar plate - sensory Basal plate - motor

Question 27

Where are neural crest cells found intitially and what do they do?

Answer 27

In the lateral border of the neuroectoderm tube Become displaced and enter the mesoderm. Undergo epithelial mesenchymal transition

Question 28

In the nervous system, name some things that are derived from neural crest cells

Answer 28

Cranial nerve ganglia Dorsal root ganglia Sympathetic/parasymapthetic ganglia Schwann cells Glial cells Leptomeninges (arachnoid and pia)

Question 29

What is derived from neural crest cells outside of the nervous system?

Answer 29

Connective tissue and bones of face and skull Dermis of face and neck C-cells of thyroid gland Conotruncal septum of the heart Melanocytes Adrenal medulla

Question 30

What can cause defects in neural crest cell migration?

Answer 30

Environmental insult, especially alcohol Genetics

Question 31

What is the syndrome seen when there is a defect in neural crest cell migration affecting multiple structures?

Answer 31

DiGeorge syndrome * Cardiac defects * Abnormal faces * Thymus aplasia * Cleft palate * Hypocalcaemia * 22 chromosome

Question 32

What is the name of the syndrome when there is a defect in neural crest cell migration affecting one structure?

Answer 32

Hirschsprung's disease (aganglionic megacolon)

Question 33

What are the layers of the neural tube?

Answer 33

The neuroepithelial layer made of neuroepithelial cells The intermediate layer (mantle layer) made of neuroblasts The marginal layer which has processes