Development of the nervous system

Question 1

What does the formation of the nervous system begin with?

Answer 1

The zygote (fertilised egg)

Question 2

What is a morula?

Answer 2

A solid ball of cells (16 cells). Formed on day 4 after the zygote has begun to divide

Question 3

Describe blastulation on day 5

Answer 3

Cells separate into two groups
1) inner cell mass (embryo)
2) Encompassing sac known as trophoblast (placenta) - these cells secrete fluid creating a cavity
Forms a blastocyst

Question 4

What are the two layers formed by the cells of the inner cell mass?

Answer 4

Epiblast - goes onto form most of the embryo
Hypoblast - becomes part of the gut

Question 5

What happens during day 13-19?

Answer 5

Gastrulation, formation of a groove known as the primitive streak

Question 6

What is the end result that forms a gastrula through gastrulation?

Answer 6

A three layer embryo, consisting of the layers ectoderm, mesoderm and endoderm.

Question 7

Which layer of the three layer embryo does the nervous system develop from?

Answer 7

Ectoderm

Question 8

What happens in front of the primitive streak after 3 layer embryo is formed (gastrula)?

Answer 8

The endotherm thickens to become the neuroectoderm, which forms the neural plate

Question 9

What happens after the neuroectoderm is made?

Answer 9

Uneven rates of cell-division - forms a groove known as the ‘neural groove’.

Question 10

What does the neural groove become?

Answer 10

The midline of the embryo

Question 11

What can be found on either side of the midline of the embryo?

Answer 11

Ridges of the ectoderm bulge

Question 12

What happens during day 22?

Answer 12

Tops eventually come together to form the neural tube. The interior becomes the fluid filled ventricles of the brain and central canal of the spinal cord.
Forms neurula - neurulation

Question 13

What happens on day 24?

Answer 13

Three major divisions of the brain are discernible.
Prosencephalon (telencephalon and diencephalon)
Mesencephalon
Rhombencephalon (metencephalon and myelencephalon)
+ neural tube

Question 14

How does a tube become a brain?

Answer 14

Channel between spinal cord and brain partially closes
Fluid is pumped in to swell the brain
Differential rates of cell growth determine regions of enlargement
Regions of swelling demarcate future brain regions

Question 15

What happens 3-4 weeks after the formation of neural tube?

Answer 15

The tube doesn’t remain in a straight line

Question 16

What is the name of the tube that grows over the rest of the brain?

Answer 16

The telencephalic tube which forms the cerebral cortex

Question 17

What happens as the telencephalic tube travels?

Answer 17

It forms the occipital and temporal lobes (and takes the fluid filled core with it)

Question 18

What happens by 6 months(fetus)?

Answer 18

Early stage sulci and gyri of the cerebral cortex

Question 19

Where do neurons come from?

Answer 19

During gastrulation, cells in the ectoderm around midline receive a chemical signal (e.g noggin)
From the notochord
Causes some of them to develop into neural precursor cells
Neural stem cells - divide (hall-mark of stem cells)
This stage is called Proliferation - symmetrical division

Question 20

What happens following neurulation?

Answer 20

Following neurulation, as the pre-cursors divide, they produce a primitive neuron (neuroblast) or glial cell (glioblast) and another precursor (asymmetrical division)

Question 21

What happens after the pre-cursors divide and produce either a neuroblast, glial cell, or precursor?

Answer 21

Migration - most neurons/glial cells are produced in the tube’s ventricular zone. Neuroblasts/glioblasts migrate to their final destination with the help of guidance mechanisms

Question 22

What happens when neuroblasts/glioblasts reach their target?

Answer 22

They need to decide what type of neuron or glial cell they want to be - determined by local chemical interactions with neighbouring cells.
Then interconnect to form neuronal circuits

Question 23

What do immature neurons produce?

Answer 23

A small number of extensions - neurites. Eventually commits to one of these being the axon and the others dendrite

Question 24

What do axons do specialised terminals for?

Answer 24

Known as growth cones - to find their targets

Question 25

What do growth cones consist of?

Answer 25

Lamellipodia (sheet like expansion) and filopodia (fine processes)

Question 26

What do receptors in filopodia do?

Answer 26

Sense attractant or repellent chemical cues in the evironment

Question 27

How do axonal growth cones navigate?

Answer 27

Using diffusible agents (chemoattractants or chemorepellents)
And non-diffusible agents
- contact attractants and contact repellents

Question 28

How does the volume of the brain quadruple between birth and adulthood?

Answer 28

Through synaptogenesis, myelination, and dendritic branching

Question 29

What is post-natal hydrocephalus?

Answer 29

Build-up of cerebrospinal fluid within the brain

Question 30

Why are postnatal changes possible?

Answer 30

The brain is still being wired up after birth, and postnatal wiring of the brain can be influenced by experience

Question 31

What is the main visual pathway in humans?

Answer 31

The geniculostriate system

Question 32

What does the left and right primary visual cortex receive and why?

Answer 32

Information from both of the eyes
- the temporal retina projects to the same side of the brain
- the nasal retina projects to the other side.
So both eyes are used

Question 33

What happens in carnivores and apes and their primary visual cortex?

Answer 33

Inputs carrying information from the two eyes form an alternating series of eye-specific domains in the primary visual cortex (ocular dominance columns)

Question 34

What is the critical period?

Answer 34

Needing stimulation in order to allow the system to get wired up.

Question 35

What is the critical period for vision in cats?

Answer 35

First three months

Question 36

What does monocular deprivation affect?

Answer 36

The width of ocular dominance in the visual cortex

Question 37

Describe the association between columns and deprived/nondeprived eyes?

Answer 37

Columns related to the non-deprived eye are wider than normal, those related to the deprived eye are shrunken

Question 38

What is the evidence of neuroplasticity occurring in adults?

Answer 38

London taxi drivers have bigger posterior hippocampi

The visual cortex responds to braille in late-blind individuals
N = 3 subjects
Complete blindness post-puberty due to glaucoma and/or cataract
PET using h2015 – radiolabelled water (injected into these people)
Reading braille leads to activity in the primary visual cortex

Question 39

What are the mechanisms that allow the brain to be so plastic?

Answer 39

Axonal sprouting and adult neurogenesis

Question 40

What is axonal sprouting

Answer 40

———-??

Question 41

What are the two areas that neurons and glial cells regenerate in during adult neurogenesis?

Answer 41

The olfactory bulb and the hippocampus

Question 42

Describe the olfactory bulb and it’s role in adult neurogenesis?

Answer 42

the area adjacent to the lateral ventricles provide the neuroblasts that later form neurons in the olfactory bulb

Question 43

Describe the hippocampus in adult neurogenesis

Answer 43

In the hippocampus, produced in area of the dentate gyrus called the sub-granular zone
Become integrated into synaptic circuits