Developing The Nervous System

Question 1

What is genome?

Answer 1

It is a set of instructions for making an organ of the body, not a blueprint

Question 2

What does genome refer to?

Answer 2

The 40000 genes that orchestrate the process

Question 3

What are many of our genes shared with?

Answer 3

Fruit fly, Drosophila

Question 4

Why do neuroscientist use zebra fish to study brain development?

Answer 4

It’s embryo is transparent - allowing each cell to be watched under the microscope as it develops

Question 5

What is mouse used to study brain development?

Answer 5

It breeds rapidly and it’s genome has been mapped and almost completely sequenced

Question 6

What are chicks and Frogs used to study brain development?

Answer 6

The large embryos allow microsurgical manipulations such as what happens when cells are moved to abnormal positions

Question 7

What is the first step in brain development?

Answer 7

Cell division

Question 8

What is another key step in brain development?

Answer 8

Cell differentiation

Question 9

What is cell differentiation?

Answer 9

Individual cells stop dividing and take on specific characteristics such as neurons or glial cells

Question 10

How does cell differentiation work?

Answer 10

It orders things spatially and different kinds of neurons migrate to various locations in a process called pattern transformation

Question 11

When does the first major event of pattern transformation take place?

Answer 11

Third week of human gestation

Question 12

What is the embryo like in the third week of gestation?

Answer 12

It is just two connected sheets of diving cells

Question 13

What happens at pattern formation?

Answer 13

A small patch of cells on the upper surface of the belayer is instructed to make the entire brain and spinal cord, theses cells form a structure called neural plate, the front destined to form the brain, the rear to be spinal cord

Question 14

Where does signals directing the cells come from?

Answer 14

Layer beneath neural p,ate that goes on to form the midline skeleton and muscles of the embryo

Question 15

What happens in the fourth week of gestation?

Answer 15

Neural plate rolls up, closes into a tube and sinks into the embryo, where it becomes enveloped by future epidermis

Question 16

What happens in the next few weeks after the fourth week?

Answer 16

Profound changes in cell shape, division & migration and cell-cell adhesion. Patterning progresses to finer and finer levels of resolution, ultimately conferring individual identity on to young neurons

Question 17

What happens when the neural tube fail to close?

Answer 17

Spina bifida

Question 18

What happens when the head end fail to close?

Answer 18

Anencephaly

Question 19

What is spina bifida?

Answer 19

Birth defect where the spine or spinal cord don’t form properly

Question 20

What is anencephaly?

Answer 20

Birth defect where baby is formed without parts of the brain and skull

Question 21

What is the underlying principle of patterning?

Answer 21

Cells get to know their position relative to the principal axes of the nervous system

Question 22

How do cells know their relative positions?

Answer 22

Embryo sets up a number of localised polarising regions in the neural tube that produces signal molecules, the molecule diffuses away from its source to form a gradient of concentration with distance

Question 23

What is an example do the position-sensing mechanism?

Answer 23

Top to bottom (dorsoventral) axis of the spinal cord. The bottom part of the neural tube expressed a secreted protein called Sonic hedgehog which diffuses away from the floor plate and affects cells on the dorsoventral axis according to their distance from the floor plate

Question 24

What happens when the Sonic hedgehog is close?

Answer 24

It induces the expression of a gene that makes a particular type of interneuron

Question 25

What happens when the Sonic hedgehog is far?

Answer 25

The lower concentration induces expression of another gene making motor neurons

Question 26

What happens when a neuron acquires its individual identity and stops dividing?

Answer 26

It extends its axon with an enlarged tip known as growth cone

Question 27

What is a growth cone used for?

Answer 27

It is specialised for moving through tissue, once it’s target has been reached, the growth cone loses its power of movement and forms a synapse

Question 28

What is axonal guidance?

Answer 28

Accurate and selects target cell with high precision

Question 29

How do growth cones get to target cell?

Answer 29

Growth cones may have to cross over other growth cones heading for different places and guidance cues that attract or repel the cones help them find their way

Question 30

What parts of the nervous system is subjected to activity-dependent refinement?

Answer 30

The pruning of axons and the death of neurons

Question 31

What do sharp vision require?

Answer 31

Point to point mapping between neurons in the eye and the brain

Question 32

How is sharp vision achieved?

Answer 32

Through the influence patterned electrical activity in the retina, an initial exuberant set of connections is sculpted during a critical period after which a basic pattern of visual system is complete

Question 33

How long does the visual system take to complete?

Answer 33

A year in humans