The developing brain

Question 1

3 Fundamental layers in the embryonic development

Answer 1

ectoderm (outer most layers)
mesoderm (middle layer)
endoderm (inner most layer)
–> all body tissues are developed from those 3 layers (signals in the surrounding tissues turn off and on different genes so the tissue type in the body is diverse)

Question 2

Neural induction

Answer 2

Signals from mesoderm trigger some ectoderm cells to become nerve tissue.
Subsequent singling interactions refine the nerve tissue into the basics categories of neutrons or glia and then into subclasses of each cell type.

Question 3

Proliferation

Answer 3

division of brain cells.
neutrons arise from a small pool of neural stem and progenitor cells->can divide and develop into a variety of mature cell types.
first there is a series of divisions in order to increase the number of cells –> early divisions are symmetric and result in 2 identical daughter cells–> daughter cells divide further–> cells begin to divide asymmetrically .

Question 4

Microphaly

Answer 4

genetic disorder the is characterised by severe reduction in brain size, associated with serious neurological disabilities and is sometimes fatal.

Question 5

Megalencephaly

Answer 5

disorder caused by excessive proliferation. brain is abnormally big and heavy

Question 6

brain development stages

Answer 6

Induction–> proliferation–> migration

Question 7

Migration

Answer 7

after induction and division the new neutrons migrate from the inner surface of the embryonic brain (where they formed) to their long term locations in the brain.
The process begins 3-4 weeks after the baby is conceived.
Ectoderm starts to thicken and build up along the midline of the embryo.

Question 8

Formation of the brain

Answer 8

Cells continue to divide, a flat neural plate grows–> formation of parallel ridges rise along either side of the midline of embryo–> ridges extend from headend (location of “future brain”) along the length of embryo (location of spinal cord)–> ridges fold towards each other and fuse into a hollow tube–> head end of the tube thickens into 3 bulges–> formation of hind brain midbrain and forebrain–>after 7 weeks (in humans) eyes start to develop and brain hemispheres appear–> new neurones are produced and move from inner surface of the neural tube to the marginal zone (outer surface)–> neurones stop dividing and form intermediate zone where they accumulate as the brain develops

Question 9

Most common guidance mechanism that cue neutrons to migrate to their final destination

Answer 9

Radial glia (accounting for ca. 90% of migration). Radial glia project radially from intermediate zone to cortex--> Neurones use these glia as scaffolding.
The process occurs in an "inside-out" manner- cells the arrive the earliest form the deepest layer of the cortex and late arriving ones (young) form the outermost layer.

Question 10

Making connections (between neurones)

Answer 10

After reaching the final locations neurones begin making connections that will determine different functions (vision, hearing etc..). this process depends increasingly on external experience, and continues after birth.
Neurones become interconnected through the short dendrites and long axons whereas axons transmit signals to other neurones and dendrites receive messages from axons of other neurones.

Question 11

Synapse formation

Answer 11

once axons reach their targets (with growth cones and their signalling cues) the synapse begins to form. at the synapse, a tiny gap (cleft) separates the signalling axon from receiving dendrite.
Synapse formation is highly specific (by the signalling molecules that guide the axon to their target location and the dendrite that initiate contact with axons –> both sides produce proteins that span the space between them and form the synapse.–> once initial contact was established synapse keeps differentiating

Question 12

The synapse

Answer 12

Presynaptic side is a tiny axon terminal, contacting the dendrite is specialised for releasing certain neurotransmitters. It consists of little NT packets and proteins that regulate their release.
Postsynaptic side is the dendritic side has receptors that respond to specific NT
NT is released from presynaptic side–> NT floats around in the synaptic cleft–> bind to receptors in postsynaptic side –> at the end of the process NT are recycled back in the releasing axon (reuptake) or is metabolised and destroyed.