Embryology

Question 1

Briefly describe neurulation.

Answer 1

The formation of the neural tube.

This is induced by the notochord (mesoderm) stimulating folding of the overlying ectoderm.

Question 2

Describe the 5 sealing segments of the neural tube.

Answer 2

1st part of neural tube closure represents the middle of the back – zippers shut
2nd region starts at the top of the head and zippers forwards and backwards from there
3rd region zippers from the face up towards the forehead
4th region is from the nape of the neck upward
5th region heads upwards from your bum to seal off the tube completely

Question 3

Name and briefly describe 2 conditions resulting from neural tube defects (which are from failure of the neural tube to close).

Answer 3

Spina bifida - most common of the neural tube closure defects resulting from the 5th region not sealing properly (from the bum to the lower part of the back)

Anacephaly - most drastic defect. When the 2nd region of the spinal tube fails to close - the whole top of the head from around the top of the nose up doesn’t form (stillbirth)

Question 4

Name the segmentation of the rostral end of the neural tube and what they develop into.

Answer 4

Forms 3 distinct vesicles:
o	Prosencephalon (forebrain)
o	Mesencephalon (midbrain)
o	Rhombencephalon (hindbrain)

Question 5

What does the prosencephelon divide into?

Answer 5

Prosencephalon splits into the telencephalon (cortex) and diencephalon (thalamus and hypothalamus)

Question 6

How many segments does the rhombencephalon divide into?

Answer 6

7.

Question 7

List neural crest derivatives.

Answer 7

• Peripheral nervous system
o	Dorsal root ganglia
o	Sympathetic and parasympathetic
o	Enteric ganglia
o	Schwann cells
• Melanocytes
• Muscle cartilage and bone of skull, jaws, face and pharynx
• Dentine

Question 8

What’s odd about the way the brain fleshes itself out during development?

Answer 8

It builds from the inside-out. Stem cells line the ventricular zone and their duaghter progeny cells grow out through the inner layers to form the outermost layer using special radial glia as scaffolds.

Question 9

Name a couple of cortical development disorders.

Answer 9

• Reelin expresses itself during the migratory phase – tells the cells that they have arrived where they should be
o Reelin mutation results in too few cells
o A profound mental retardation ensures
• DCX (doublecortin gene) mutation results in lissencephaly which means that there are virtually no cells in the cortex and inflated ventricles
- both result in levels of profound mental retardation

Question 10

Describe Fragile X syndrome

Answer 10

Most common cause of male autism
Mutation of fragile X mental retardation gene (FMR1)
Affects synaptic and dendritic development

Question 11

Where do motor neurons synapse in spinal cord segments?

Answer 11

Ventral horn

Question 12

Where is sensation processed in the spinal cord segment?

Answer 12

Dorsal horn

Question 13

How is the topography of the nervous system defined? (Dorsal from ventral importantly)

Answer 13

Chemical signals/signalling molecules

Question 14

Briefly describe the role of SHH (sonic hedgehog).

Answer 14

Notochord releases SHH (sonic hedgehog) and sets up the floor plate which starts to produce its own SHH and sets up a chemical gradient – polarity for ventral and dorsal

Question 15

Interneurons drive motor neurons. Where are they found?

Answer 15

Just dorsal to motor neurons in the ventral horn of the spinal cord segment

Question 16

Describe the role of pioneer axons.

Answer 16

These establish the major axes of the brain and spinal cord

They set up the coordinates of growing axons especially in the kinks at the rostral end

Question 17

Describe how a growth cone works.

Answer 17

These cause axons to grow out in that given direction.

They follow a chemical gradient of neurotrophic growth factors. There are also repellent signals that can be released.

Question 18

What is the critical period in which neural connectivity is being establish and modulated over contralateral bilateral organs?

Answer 18

The first 10 years of human life.