Development of the Nervous System

Question 1

Over what time frame does the nervous system undergo development?

Answer 1

It is the first system to begin development, and the last to complete development

Question 2

What does the early development of the nervous system reflect?

Answer 2

The fact that its formation is a priority for the embryo

Question 3

What is meant by the nervous system being a very plastic system?

Answer 3

It is changing all the time, even after birth

Question 4

What is the clinical relevance of the length of time it takes the nervous system to develop?

Answer 4

It is most susceptible to insult during pre-natal development

Question 5

What effect does alcohol have on the developing nervous system?

Answer 5

It disrupts communication between developing neurones

Question 6

What is the notocord?

Answer 6

A solid cord of cells

Question 7

What is the notocord formed by?

Answer 7

Prenotocordal cells migrating through the primitive pit

Question 8

What does the definitive notocord serve as?

Answer 8

The baseline for the midline, axial skeleton, and neural tube

Question 9

What does the notocord release?

Answer 9

Lots of diffusion limited signalling molecules

Question 10

What can the signalling molecules released by the notocord act on?

Answer 10

Only cells that are close, and have the right receptor

Question 11

What is the result of interaction between the notocord and ectoderm?

Answer 11

Formation of neuroectoderm

Question 12

What does the formation of neuroectoderm cause?

Answer 12

The induction of the neural plate

Question 13

What happens to the neural plate in development?

Answer 13

The lateral edges of the neural plate elevate, and the depressed midregion becomes the neural groove

Question 14

What happens to the neural folds during development?

Answer 14

They gradually approach each other in the midline and fuse

Question 15

Where does fusion of the neural folds begin?

Answer 15

In the future cervical region (in the middle), and then proceeds in both cranial and caudal directions

Question 16

What is produced by fusion of the neural folds?

Answer 16

The neural tube

Question 17

By what stage in development is the neural tube completely closed?

Answer 17

Day 28-32

Question 18

What do neural tube defects result from?

Answer 18

The failure of the neural tube to close

Question 19

What happens if failure of the neural tube to close occurs caudally?

Answer 19

Gives spina bifida

Question 20

Where in the spinal cord does spina bifida occur?

Answer 20

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

Question 21

What occurs with spina bifida?

Answer 21

• Neurological defects
• Hydrocephalus nearly always

Question 22

Are the neurological defects in spina bifida associated with cognitive delay?

Answer 22

No

Question 23

What is hydrocephalus?

Answer 23

Accumulation of the CSF within the ventricular system

Question 24

What can hydrocephalus lead to?

Answer 24

• Brain impairments
• Congitive delay

Question 25

What happens if failure of the neural tube to close occurs cranially?

Answer 25

Anencephaly

Question 26

What is anencephaly?

Answer 26

Failure of formation of the head structures, including brain

Question 27

What is the prognosis of anencephaly?

Answer 27

It is incompatible with life

Question 28

What is the most severe form of anencephaly?

Answer 28

Rachischisis

Question 29

What is rachischisis?

Answer 29

Failure of neural fold elevation

Question 30

How can neural tube defects be deteted?

Answer 30

* Raised maternal serum alpha-fetoprotein * USS

Question 31

What causes neural tube defects?

Answer 31

Multi-factoral aetiology

Question 32

What can reduce the incidence of neural tube defects?

Answer 32

Folic acid pre-conceptually (3 months) and in the first trimester

Question 33

By how much does folic acid reduce the incidence of neural tube defects?

Answer 33

70%

Question 34

When is dose of folic acid to prevent neural tube defects increased?

Answer 34

When there is a known increased risk, *e.g. past pregnancies or family history*

Question 35

What does the lumen of the neuroectoderm tube become?

Answer 35

The ventricular system

Question 36

What is the ventricular system comprised of in the adult?

Answer 36

Interconnected 'reservoirs' filled by CSF, produced by cells of the ventricular lining

Question 37

What is the role of the CSF in the ventricular system?

Answer 37

Cushion the brain and spinal cird within their body cases

Question 38

When can hydrocephalus occur?

Answer 38

When there is any blockage of the ventricular system, *e.g. tumour or infection*

Question 39

When is hydrocephalus most common?

Answer 39

In newborns suffering from spina bifida

Question 40

How is hydrocephalus treated?

Answer 40

By the use of a shunt, which shunts fluid into the jugulovenous system or the peritoneum

Question 41

What forms cranially after neural tube closure in the 4th week?

Answer 41

3 dilations

Question 42

What do the dilations that form after neural tube closure become?

Answer 42

The primary brain vesicles; forebrain, midbrain, and hindbrain

Question 43

What happens after the formation of the primary brain vesicles?

Answer 43

*At 5 weeks of development,* 5 secondary brain vesicles are formed

Question 44

What secondary brain vesicles are formed from the forebrain?

Answer 44

* Telencephalon * Diencephalon

Question 45

What does the telencephalon form?

Answer 45

Cerebral hemispheres

Question 46

What does the diencephalon form?

Answer 46

Thalamus

Question 47

What secondary brain vesicles form from the midbrain?

Answer 47

Mesencephalon

Question 48

What does the mesencephalon form?

Answer 48

The midbrain

Question 49

What secondary brain vesicles form from the hindbrain?

Answer 49

* Metencephalon * Myelecephalon

Question 50

What does the metencephalon form?

Answer 50

The pons and cerebellum

Question 51

What does the myelecephlon form?

Answer 51

Medulla oblongata

Question 52

What does most of the length of the neural tube give rise to?

Answer 52

The spinal cord

Question 53

How does the length of the spinal cord compare to that of the vertebral column during embryological development?

Answer 53

At the 3rd month, the spinal cord is the same length as the vertebral column, but thereafter, the vertebral column grows faster, as the trunk of the fetus grows more rapidly

Question 54

What is the result of the vertebral column growing faster than the spinal cord after the 3rd month of embryological development?

Answer 54

Spinal roots must elonagate, *because they still exit at their intervertebral foramen*

Question 55

What does the elongation of the spinal roots during embryological development form?

Answer 55

The cauda equina

Question 56

What do the anatomical divisons of the brain and spinal cord undergo?

Answer 56

Patterning and organisation

Question 57

What layers are present in the early organisation of the neural tube?

Answer 57

* Neuroepithelial layer on inside * Intermediate (mantle) layer * Marginal layer on outside

Question 58

What does the neuroepithelial layer of the neural tube produce?

Answer 58

CSF

Question 59

What does the intermediate layer of the neural tube produce?

Answer 59

Neuroblasts

Question 60

What do the roof and floor plates of the neural tube regulate?

Answer 60

Dorsal and ventral patterning

Question 61

What does the alar plate of the neural tube form?

Answer 61

Sensory structures

Question 62

What does the basal plate of the neural tube form?

Answer 62

Motor structures

Question 63

What happens as the neuroectodermal tube grows?

Answer 63

It runs out of space, causing it to bend

Question 64

What is produced from the bending of the neuroectoderm tube?

Answer 64

It produces flexures

Question 65

What flexures are produced from the bending of the neuroectoderm tube?

Answer 65

* Cervical flexure * Cephalic flexure

Question 66

Where does the cervical flexure form?

Answer 66

Spinal cord-hindbrain junction

Question 67

Where does the cephalic flexure form?

Answer 67

In the midbrain region

Question 68

What is the result of the flexures on the neuroaxis?

Answer 68

Means it does not remain straight

Question 69

What happens to cells of the lateral border of the neuroectoderm?

Answer 69

They become displaced, and enter the mesoderm, undergoing epithelial to mesenchymal transition to become neural crest cells

Question 70

What does the neural crest give rise to?

Answer 70

* Dorsal root ganglion * Sympathetic ganglion Suprarenal gland and chromatic cells * Preaortic ganglia * Enteric ganglia

Question 71

What are the adult nervous system derivatives of the neural crest cells?

Answer 71

* Cranial nerve ganglia * Spinal root ganglia * Sympathetic ganglia * Parasympathetic ganglia * Schwann cells * Glial cells * Leptomeninges

Question 72

What are the adult head, neck, and midline derivatives of the neural crest cells?

Answer 72

* Connective tissue and bones of the face and skull * Odontoblasts * Dermis of the face and neck * C cells of the thyroid gland

Question 73

What are the adult derivatives of the neural crest cells?

Answer 73

* Nervous system components * Head, neck, and midline components * Conotruncal septum of heart * Melanocytes * Adrenal medulla

Question 74

What is the clinical relevance of the complex migratory pattern of neural crest cells?

Answer 74

They are extremely vulnerable to environmental insult

Question 75

Do defects in neural crest migration affect a single component, or multiple components?

Answer 75

Can be either

Question 76

Give an example of where neural crest cell migration defects affect a single component

Answer 76

Hirschsprungs disease

Question 77

What happens in Hirschsprungs disease?

Answer 77

Ganglia of enteric nervous system doesn't form

Question 78

Give three examples of where defects in neural crest migration affect multiple components

Answer 78

* DiGeorge syndrome * Cardiac defects * Abnormal facies