6 - Development of the Nervous System

Question 1

*Neuralation

Answer 1

Question 2

Neural tube formation 1 2 3

Answer 2

1) Neural tube is initially one cell thick 2) Neural tube is hollow 3) There is a rostral to caudal gradient in the formation of the nervous system (rostral is older)

Question 3

* Neural tube formation

Answer 3

Question 4

*Closure of neural tube

Answer 4

Question 5

*Defects in neural tube closure

Answer 5

Anacephaly, spina bifida

Each of the five sections of closure are independent. Any of these can be defective, leading to pathology.

Question 6

Way to reduce probability of spina bifida

Answer 6

Increase dietary folate during pregnancy

Question 7

Segmentation of the neural tube 1 2

Answer 7

1) Rostral end of the neural tube starts to swell 2) Forms three distinct vesicles: prosencephalon, mesencephalon, rhombencephalon

Question 8

Parts of brain formed by neural tube vesicles

Answer 8

Prosencephalon forms forebrain Mesencephalon forms midbrain Rhombencephalon forms hindbrain

Question 9

Further segmentation of neural tube vesicles 1 2 3

Answer 9

• Prosencephalon splits into telencephalon and diencephalon • Rombencelphalon splits into 7 segments • Rest is spinal cord

Question 10

Segmentation of rhombencephalon

Answer 10

Splits into metencephalon and myeloencephalon (pons and medulla).

Question 11

Formation of retinae

Answer 11

Optic vesicles split from diencephalon

Question 12

Derivatives of the neural crest 1 2 3 4`

Answer 12

1) PNS (dorsal root ganglia, sympathetic, parasympathetic ganglia), enteric ganglia, Schwann cells) 2) Melanocytes 3) Muscle, cartilage, bone of the face 4) Dentine

Question 13

*Neural crest migration

Answer 13

• From neural crest under skin
• To site of dorsal root ganglia
• From neural crest through somite to sympathetic ganglia

Question 14

Name for surface lining primitive nervous system

Answer 14

Neuroepithelium (brain is largely empty space)

Question 15

Ventricular surface

Answer 15

Surface of neuroepithelium that lies against empty space where brain will form

Question 16

Where do cells in neuroepithelium divide?

Answer 16

Retract back to ventricular surface, divide, then re-establish contact with other surface

Question 17

Ventricular zone 1 2 3

Answer 17

1) Where the neuroepithelium adds layers to generate cortex. 2) All neurons are formed at ventricular surface (ventricular zone) which contains stem cells 3) Inside-out formation of neurons

Question 18

Cells that aid neuron migration from ventricular zone to cortex

Answer 18

Radial glia (neuroepithelium derivative)

Question 19

How do radial glia behave?

Answer 19

Wrap around migrating neuron, leading process guides neuron migration. Also act as stem cells

Question 20

*Example of kind of cell growth from ventricular zone

Answer 20

Question 21

What can happen when there is a defect in ventricular zone cortex formation?

Answer 21

Cortex can be malformed as a result of mutations in genes that affect migration. Can produce profound mental retardation

Question 22

Examples of mutations in genes leading to cortex melformation

Answer 22

1) Reelin formation (involved in forming layers in cortex) 2) Doublecortin mutation (leads to lissencephaly)

Question 23

Effect of fragile X syndrome on brain

Answer 23

Most common form of male autism. Mutation of fragile X retardation gene (FMR1) affects synaptic and dendritic development.

Question 24

Example of a mental illness that might have developmental origins

Answer 24

Schizophrenia

Question 25

Signalling molecules involved in spinal cord formation

Answer 25

Sonic hedgehog, retinoic acid, noggin, chordin (expressed in floorplate and notochord)

Question 26

Signalling centres of spinal cord development

Answer 26

Roof plate (furthest from notochord), floor plate (closest to notochord)

Question 27

Effect of sonic hedgehog

Answer 27

Inductive agent. Makes neurons in high concentrations of sonic hedgehog turn into motor neurons. Expressed at highest levels in floorplate (therefore get motor neurons in ventral horn of spinal cord)

Question 28

Induction of interneurons

Answer 28

Sonic hedgehog induces lsl-1 (which induces motor neurons), which induces en-1 (which induces interneurons)

Question 29

Axon development 1 2 3

Answer 29

1) Initial scaffold of axon tracts laid down by pioneer axons 2) Axon is towed into position by a growth cone 3) Growth cone steers axon towards diffusible and membrane-bound signals

Question 30

Are axons present when neurons first form?

Answer 30

No

Question 31

Growth cone

Answer 31

A dynamic structure of the neuron cytoskeleton (actin and microtubules). Follows concentration gradient of diffusible factors (EG: NGF)

Question 32

When does the refinement period of neural development occur?

Answer 32

The few months after birth

Question 33

Effect of refinement of the nervous system 1 2 3

Answer 33

1) Embryonic processes create crude nervous system. 2) Refinement leads to permanent changes that establish mature functional nervous system. 3) Occurs postnatally

Question 34

Evidence for nervous system refinement in visual system 1 2 3 4

Answer 34

1) If cover eye shortly after birth in a kitten for six months, eye becomes blind. 2) Cortical blindness. Retina is normally developed 3) At birth, within visual cortex, terminals from one eye form interdigitated patches with those from the other eye. 4) Deprived eye has greatly reduced representation in the cortex, open eye has greatly enhanced representation.

Question 35

Effect of timing of eye closure on cortical mapping of eye

Answer 35

Progressively weaker effect with time (variable between species - ten years in a human). Defines critical period of left and right eye mapping.