Lecture 2 - Prenatal Development

Question 1

What does Axon Growth and Synapse Formation begin with?

Answer 1

The axon growth cone

Question 2

What happens at the tip of a growing axon?

Answer 2

It extends and retracts filopodia (finger like processes)

Question 3

What are the two ways growth cones find their way to the target?

Answer 3

1. Chemoaffinity Hypothesis
2. Topographic Gradient Hypothesis

Question 4

What is Chemoaffinity Hypothesis?

Answer 4

Target-specific chemical labels –> axons grow into the chemical gradient

Question 5

What is this hypothesis supported by?

Answer 5

• In vitro studies (no spatial cues, only chemical)
• Discovery of Several chemicals labels that attract or repel neurons

Question 6

What studies are the Chemoaffinity Hypothesis not supported by?

Answer 6

1. Targets transplanted in new positions can become incorrectly innervated.
2. The route to the target is often circuitous, rather than linear

Question 7

What is the Revised Chemoaffinity Hypothesis?

Answer 7

1. Pioneer Growth Cones follow CAMs and other guidance molecules (chemical trails)
2. Subsequent growth cones follow the pioneer growth cones via fasciculation

Question 8

What is Fasciculation?

Answer 8

The tendency of growing axons to follow previous axons

Question 9

What is CAMs?

Answer 9

Cell Adhesion Molecules

Question 10

What is a Topographic Gradient Hypothesis?

Answer 10

Two intersecting gradients (up-down and left-right) of chemicals on the originating tissue guide axonal growth from one topographic array (such as a retina) to another (the optic tectum)

Question 11

What is the Topographic Gradient Hypothesis supported by?

Answer 11

Maintenance of topographic integrity

Question 12

What is a Synapse formation called?

Answer 12

Synaptogenesis

Question 13

What does synaptogenesis require?

Answer 13

Requires neuron-neuron “talk”

Question 14

What do Glial Cells (Astrocytes) key for?

Answer 14

Synaptogensis

Question 15

How is synapse formation studied In vitro?

Answer 15

Neurons cultured with astrocytes form 7 times as many synapses as those without astrocytes.

Question 16

How is synapse formation studied In vivo?

Answer 16

Stydies with KO mice similarly demonstrate the importance for synapse-promoting and inhibiting signals secreted by astrocytes

Question 17

What happen to neurons during proliferation?

Answer 17

There is an overproduction of neurons - about 50% more than actually needed

Question 18

What neurons die?

Answer 18

The Neurons that make incorrect connections - as not all neurons are essential

Question 19

What do New Neurons make?

Answer 19

More focused synapses

Question 20

What does cell death increase?

Answer 20

The overall accuracy of synaptic connections

Question 21

What is Apoptosis?

Answer 21

Genetically programmed (good) cell death that is clean and organized

Question 22

What is Necrosis?

Answer 22

Bad, passive cell death that is mixed up

Question 23

What causes neurons to die?

Answer 23

1. Genetically programmed (some neurons)

2.) Competition for target supplied neurotrophins

Question 24

What is the first neurotrophic to be isolated?

Answer 24

Nerve Growth Factor

Question 25

What are a few Neurotrophins?

Answer 25

- Nerve Growth Factor - Brain Derived Neurotrophic Factor - Glial Cell-Line Derived Neurotrophic Factor

Question 26

What are Five Functions of Neurotrophins?

Answer 26

1.) They promote neuronal growth 2.) They promote neuronal survival 3.) They can function as axon guidance molecules 4.) They can stimulate synaptogensis 5.) Their absence can trigger apoptosis

Question 27

What are methods for Studying CNS development?

Answer 27

1.) Non Human Animals (zebrafish, frog, chicks) 2.) Humans - Prenatal - Postnatal

Question 28

What happens to the brain after birth?

Answer 28

It doubles in volume

Question 29

When is the CNS fully mature?

Answer 29

Late Adolescence

Question 30

What is the last region of the CNS to develop?

Answer 30

Prefrontal Cortex

Question 31

What happens during Dendritic Branching?

Answer 31

- Parallels pattern of Migration - Deeper layers migrate first and are first to sprout dendrites

Question 32

What happens during Synaptogensis?

Answer 32

- Peaks after birth in most brain areas - Primary Vision Cortex: around 4-8 months - Primary Frontal Cortex: second year

Question 33

What happens during Myelination?

Answer 33

- Rough parallels functional development - Sensory Areas: first few months - Motor Areas: soon after sensory areas - PFC: continues into adolescence

Question 34

What happens during regressive changes (pruning)?

Answer 34

- Periods of synaptic loss/refinement

Question 35

What happens during postnatal development of the Prefrontal Cortex?

Answer 35

Relatively Slow, more gradual development, continuing into late adolescence. Linked to parallel development of "higher" cognitive executive functions

Question 36

What are four executive functions of the PFC?

Answer 36

1. Working memory (temporary memory used while a task is being performed) 2. Planning and carrying out sequences of actions 3. Following rules for social behaviours 4. Context dependent inhibition of inappropriate responses "time and place"