Development of the Nervous System

Question 1

What is the name given to the proliferation of the ectoderm in the dorsal midline?

Answer 1

Neural plate

Question 2

What happens to the neural plate as it thickens?

Answer 2

It folds up the sides and eventually the two neural folds fuse to form a tube The space in the middle is the neural canal

Question 3

What is the name given to the bunch of cells at the tip of the neural fold that are excluded in the fusion?

Answer 3

Neural crest

Question 4

Which cells do the neural tube and neural crest cells give rise to?

Answer 4

Neural tube – all cells of the CNS Neural crest – all cells of the PNS

Question 5

What is the name given to the wall of the neural tube?

Answer 5

Neuroepithelium

Question 6

What three types of cells do neuroepithelium give rise to?

Answer 6

Neuroblasts – all cells with cell bodies in the CNS, this includes motor neurone and interneurons as their cell bodies are in the CNS, whereas sensory neurons do not come from neuroblasts but from the neural crest cells

Glioblasts – these become neuroglia (astrocytes + oligodendrocytes ONLY, not microglia which has a different source. Ependymal cells are a type of glial cell but they have a separate lineage outlined below)

Ependymal cells – line the ventricles and the central canal

Question 7

Are motor neurons produced from neuroepithelium?

Answer 7

Yes – although most of their axons are outside the CNS, their cell bodies are within the spinal cord

Question 8

State four cell types that neural crest cells can differentiate into.

Answer 8

Sensory neurons of dorsal root ganglia and cranial ganglia

Autonomic post-ganglionic neurons

Schwann cells

Non-neuronal cells e.g. melanocytes

Question 9

Describe the arrangement of the neuroepithelium.

Answer 9

Neuroepithelium has an inner layer and an outer layer Most cells are connected to both the inner and outer layer but the nuclei are at different positions

Question 10

Describe the differentiation of the neuroepithelium.

Answer 10

Firstly, you get cells withdrawing away from the outer membrane towards the inner membrane where it undergoes mitosis One of the daughter cells will remain attached to the inner membrane and the other daughter cell will move away from the inner membrane and become a neuroblast. The neuroblast will develop processes and one will become the axon. These axons are directed away from the inner membrane. Eventually, three layers are formed with the neuroblast cell body in the grey matter layer and its axon in the white matter layer

Question 11

What are the three layers formed by the differentiation of the neuroepithelium?

Answer 11

Ependymal, grey matter and white matter AKA germinal layer, mantle layer, marginal layer

Question 12

Glioblasts show a similar pattern of differentiation to neuroblasts. State one difference.

Answer 12

Glioblasts can migrate into the white matter NOTE: glioblasts do not develop axons (but they do develop processes)

Question 13

What guides the process of differentiation and migration?

Answer 13

Signalling molecules

Question 14

Which factors are important with regards to signalling molecules?

Answer 14

Concentration and timing

there is no point producing signalling molecules if the developing neurones don’t have the right receptors. Also, Some of the signalling molecules have different effects at different stages of development

Question 15

What can the grey matter of the neural tube be divided into?

Answer 15

Alar plates and basal plates

Question 16

Which types of neurons do the alar plate and basal plate give rise to?

Answer 16

Alar plate – interneurons Basal plate – interneurons and motor neurons

Question 17

Which structures around the neural tube release signalling molecules and what effect do they have on the cells in the neural tube?

Answer 17

Notochord and ectoderm Notochord releases signalling molecules that induce the cells nearest to it to differentiate into motor neurons Ectoderm produces signalling molecules that inhibit the cells nearest to it from differentiating into motor neurons

Question 18

Around 4 weeks, you get differentiation of the wall of the anterior neural tube to form three primary vesicles. Name these primary vesicles.

Answer 18

Prosencephalon – future forebrain (prosen= leaning forwards)

Mesencephalon – future midbrain (mesen=middle)

Rhombencephalon – future hindbrain (rhombus shaped)

Question 19

Describe the changes that occur to these three vesicles in the week or so following their formation.

Answer 19

The first and third vesicles divide into two

1. Prosencephalon - telencephalon (future cerebral cortex) + diencephalon (thalamus and hypothalamus)
2. mesencephalon stays the same (becomes midbrain)
3. Rhombencephalon - pons + medulla

Question 20

What important structure begins to appear quite late in development (around 8 weeks) and where does it appear from?

Answer 20

Cerebellum – appears as an out pouching from the back of the pons

Question 21

Name the three flexures in the developing brain.

Answer 21

Cephalic Pontine(related to pons) Cervical

Question 22

Describe the formation of the 4th ventricle.

Answer 22

In the neural tube in the region that will become the brainstem (rhombencephalon), the roof plate rapidly proliferates and causes the alar plates to split apart so that they are lateral to the roof plate The space left from the proliferation of the roof plate will become the 4th ventricle

Picture plate shows what I am saying

Question 23

Describe the arrangement of motor, sensory and autonomic cranial nuclei within the brainstem.

Answer 23

Motor = medial Sensory = lateral Autonomic = in between

Question 24

What structure divides the motor nuclei from the sensory nuclei in the brainstem?

Answer 24

Sulcus limitans

Question 25

How do neuroblasts migrate from the inner membrane to the outer membrane in the brain?

Answer 25

They attach themselves to radial glial cells and climb up them towards the outer membrane Radial glial cells have their cell bodies anchored to the inner membrane and have a single long process to the outer membrane

Question 26

What happens to neuroblasts that stay in the middle of the cortex?

Answer 26

They become the basal ganglia

Question 27

How many layers of cells are there within the cerebral cortex?

Answer 27

SIX

Question 28

What can a deficiency of folic acid in pregnancy lead to?

Answer 28

Spina bifida

Question 29

What is anencephaly

Answer 29

Neural tube needs to close at both ends. Anencephaly is when the rostral end does not close and you essentially get no brain/little brain that is open and lacks a skull to protect it

anencephaly= without

Question 30

What is encephalocele

Answer 30

rostral end of neural tube doesn’t close completely causing Herniation because part of the skull in the occipital area didn’t fuse properly so contents herniate out

encephalo= brain

cele= hernia/tumour/swelling

Question 31

what is iniencephaly

Answer 31

extreme retroflexion of head ( bend back) caused by incomplete closure of the rostral end of the neural tube

from anatomy- inion is at the back of the skull on the occipital bone

Question 32

What are the three types of spina bifida

Answer 32

Spina bifida: incomplete closure on the caudal part of neural tube. the bony surrounding around the spinal cord is not completely closed. It has three types:

1. spina bifida occulta,
2. meningiocele and (herniation of the meninges)
3. myelomeningocele. (herniation of the meninges and spinal cord(myelo))
   - Spina bifida occulta: occulta means hidden. This means that there is no herniation through the opening in the vertebral spine despite the incomplete closure.
   - Meningiocele: meninges have herniated through (see pic above). The spinal cord doesn’t herniate
   - Myelomeningiocele: meninges + spinal cord both herniate through the opening (myelo=spinal cord or bone marrow)

Question 33

what is craniorachischisis

Answer 33

Craniorachischisis: most severe form of neural tube defect. This is when both ends of the neural tube do not close, causing an open and exposed brain and spinal cord (see pics online)

Cranio=brain

Rachi=spine

Schisis= split