Developing The Nervous System
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What is genome?
It is a set of instructions for making an organ of the body, not a blueprint
What does genome refer to?
The 40000 genes that orchestrate the process
What are many of our genes shared with?
Fruit fly, Drosophila
Why do neuroscientist use zebra fish to study brain development?
It’s embryo is transparent - allowing each cell to be watched under the microscope as it develops
What is mouse used to study brain development?
It breeds rapidly and it’s genome has been mapped and almost completely sequenced
What are chicks and Frogs used to study brain development?
The large embryos allow microsurgical manipulations such as what happens when cells are moved to abnormal positions
What is the first step in brain development?
Cell division
What is another key step in brain development?
Cell differentiation
What is cell differentiation?
Individual cells stop dividing and take on specific characteristics such as neurons or glial cells
How does cell differentiation work?
It orders things spatially and different kinds of neurons migrate to various locations in a process called pattern transformation
When does the first major event of pattern transformation take place?
Third week of human gestation
What is the embryo like in the third week of gestation?
It is just two connected sheets of diving cells
What happens at pattern formation?
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
Where does signals directing the cells come from?
Layer beneath neural p,ate that goes on to form the midline skeleton and muscles of the embryo
What happens in the fourth week of gestation?
Neural plate rolls up, closes into a tube and sinks into the embryo, where it becomes enveloped by future epidermis
What happens in the next few weeks after the fourth week?
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
What happens when the neural tube fail to close?
Spina bifida
What happens when the head end fail to close?
Anencephaly
What is spina bifida?
Birth defect where the spine or spinal cord don’t form properly
What is anencephaly?
Birth defect where baby is formed without parts of the brain and skull
What is the underlying principle of patterning?
Cells get to know their position relative to the principal axes of the nervous system
How do cells know their relative positions?
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
What is an example do the position-sensing mechanism?
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
What happens when the Sonic hedgehog is close?
It induces the expression of a gene that makes a particular type of interneuron