Mechanisms of Neural Development and Plasticity

Question 1

Characteristics of Nervous System

Answer 1

• extensive
• massively complex
• billions of nerve cells
• trillions of connections

Question 2

Neurogenesis

Answer 2

creating the right number of nerve cells

Question 3

migration and differentiation

Answer 3

getting the right cells to the right place

Question 4

axon guidance

Answer 4

growing an axon to the right target area

Question 5

synaptogenesis

Answer 5

making connections with potentially useful partners

Question 6

activity-dependent refinement

Answer 6

testing and perfecting the neural circuit

Question 7

the origin of neural tissue

Answer 7

trilaminar germ disc (ectoderm, mesoderm, endoderm)

Question 8

which germ layer gives rise to nervous system

Answer 8

ectoderm. infolds and then breaks away to form neural tube

Question 9

how does the neural tube start?

Answer 9

as a single layer of replicating neuroepithelial cells

Question 10

outer surface of neural tube?

Answer 10

pial cells

Question 11

inner luminal surface?

Answer 11

ventricular surface

Question 12

What if each neuroepithelial cell made one too many / few divisions?

Answer 12

can occur by mutation of microcephalin genes (involved in centrosome function, dysfunction –> too few divisions. small brain with normal organisation but reduced function

Question 13

what are neuroepithelial cells progenitors of?

Answer 13

neurons and glia

Question 14

how do neuroblasts know where to go?

Answer 14

they migrate away from place of birth through the use of right chemical signals

Question 15

what tells the new born nerve cells what type of cell to become?

Answer 15

morphogens

Question 16

what tells the new born nerve cells where to go?

Answer 16

guidance chemicals (reelin)

Question 17

combo of morphogens switch on genes that insert receptors into outer membrane

Answer 17

these detect guidance chemicals they’ve been programmed for.

Question 18

What do basal ganglia cells become?

Answer 18

inhibitory neurones

Question 19

what do cells born in cerebral hemiphere do?

Answer 19

go towards reelin and become excitatory neurones

Question 20

where do neuroblasts go?

Answer 20

towards the pia matter

Question 21

how are cortical layers created?

Answer 21

from inside to outside. different types of cells are generated at different times in response to changing chemical signals

Question 22

what do superificial layer of cortex send signals to?

Answer 22

other coritcal areas

Question 23

middle layers of cortical layers

Answer 23

recieve subcortical and cortical inputs

Question 24

deep layers

Answer 24

subcortical structures

Question 25

inhibitiroy intermeurones

Answer 25

migrate to deep layers

Question 26

astrocytes

Answer 26

born in cortex

Question 27

when are neurones are born?

Answer 27

3 months into pregnancy

Question 28

What will happen if reelin chemical is absent?

Answer 28

loss of reelin leads to lissencephaly- severe learning difficulties and seizures

Question 29

What will happen if they have impneuroblastsaired motility?

Answer 29

Due to mutation of one copy of the X-linked DCX gene, which encodes a microtubule-associated protein. Without a functional protein, migration is severely disrupted.

Question 30

What will happen if they have impneuroblastsaired motility?

Answer 30

loss of doublecortin protein in female leads to heterotopia. range from nomoral intellect to severse learning difficulty + epilespy

Due to mutation of one copy of the X-linked double cortical X gene, which encodes a microtubule-associated protein. Without a functional protein, migration is severely disrupted.

Question 31

what are growing tips of neurites called?

Answer 31

growth cones

Question 32

what are filopodia?

Answer 32

supported by actin bundles, they seek out chemical guidance signals. attractive guidance signals causes actin bundles to grow

Question 33

what do repulsive guidance signals on filopedia do?

Answer 33

causes actin bundles to shrink

Question 34

what do attractive guidance signals on filopedia do?

Answer 34

causes actin bundles to grow

Question 35

how do dendrites grow?

Answer 35

follow guidance signals

Question 36

what do growth cones follow?

Answer 36

a series of way points. eg. nociceptor relay cells in developing spinal cord.

Question 37

what do floor plate signalling proteins do in spinal cord?

Answer 37

axons are attracted to the floor plate

Question 38

Contact with floor plate alters gene expression

Answer 38

less attractive receptors, more repulsive receptors so axons repel from floor plate

Question 39

where can growth cones grow?

Answer 39

through tissues they can stick to. filopodia needs to bind to the extracellular matrix for traction. there are matching binding molecules (.e.g integrin) that bind to the matrix proteins (e.g. laminin)

Question 40

what do axons do when exploring target region?

Answer 40

make trail contacts with potentially useful cells

Question 41

synaptogenesis

Answer 41

1) filopodia extend from dendrites, seeking contact from passing axons
2) complementary surface proteins bind
3) triggering formation of synaptic structures
e. g. muscle spindle la afferent + own muscle motor neurone

Question 42

failed synaptogenesis

Answer 42

If surface molecules can’t bind to one another, the filopodium retracts

eg. muscle spindle Ia afferent + antagonist motor neurone

Question 43

when is the glia birthed?

Answer 43

6 months of pregnancy

Question 44

when does myelination occur?

Answer 44

from birth

Question 45

when does synaptogenesis occur?

Answer 45

from 3 months

Question 46

activity dependent refinement, how are trail contacts strengthened or weakened?

Answer 46

according to their usefulness

Question 47

how do you identify usefulness of an excitatory synapse?

Answer 47

trial and error. when synapse activates, does the dendrite depolarise? if yes, its useful and works

Question 48

long term potentiation of fast excitatory synpase

Answer 48

1) activation of a single synapse will produce little effect
2) NMDA receptors remain closed
3) if this happens a lot, then the synapse is probably not doing anything useful

Question 49

what happens if synapse is part of an effective circuit?

Answer 49

1) . . then many synapses will activate simultaneously, depolarising the dendrite
2) NMDA receptors open and allow Ca++ entry- only at active the synapses
3) increased [Ca++]in triggers processes that strengthen these effective synapses

Question 50

what happens to synapses that are often active when the post-synaptic cell depolarises

Answer 50

GROW

MAKE MORE TRANSMITTER

MAKE MORE AMPA RECEPTORS

Question 51

when does synaptic plasticity decrease?

Answer 51

during development. effective in the foetus and still high in babies so they adapt to abnormal conditions. PLasticity fades with age and wiring in the major pathways become permanent. Critical period is where big changes can occur

Question 52

why can young babies grow effective ciruits in abnormal situations?

Answer 52

high synaptic plasticity. eg this child lost half of his cerebral cortex, but the other half now controls both sides of his body.

Question 53

what happens if young brain has a compromised eye?

Answer 53

Normally, inputs from the two eyes have an equal share of visual cortex.
But if one eye is compromised in early life, then its synapses will not be part of an effective circuit
and will make very few connections

Question 54

why can plasticity be maladaptive?

Answer 54

if an eye is permanently compromised, it doesnt matter if there are few connections

Question 55

when is best time to fix something like a cataract?

Answer 55

Within first year of life as otherwise plasticity decreases and wont be as adaptable.

Question 56

when is best time to fix something like a cataract?

Answer 56

Within first year of life as otherwise plasticity decreases and wont be as adaptable. even if you fix cataract later on, they still wont be able to see properly