Neurodevelopment (2)

Question 1

What happens after neurons migrate and form structures?

Answer 1

Axons and dendrites grow to connect with their targets. Growth cones at the tips guide them.

Question 2

What are growth cones and filopodia?

Answer 2

Growth cones are the tips of growing axons/dendrites. Filopodia are fingerlike extensions that sense signals to guide growth.

Question 3

What did Sperry discover with frog optic nerves?

Answer 3

Rotated frog eyes still sent axons back to the same target in the optic tectum, showing axons find precise targets.

Question 4

What is the chemoaffinity hypothesis?

Answer 4

Each target releases a chemical label, and axons are attracted to their specific label to find the correct connection.

Question 5

Why was the chemoaffinity hypothesis revised?

Answer 5

Axons follow specific routes guided by multiple signals along the way, not just a single chemical from the target.

Question 6

What is fasciculation?

Answer 6

The tendency
of developing axons to grow along the paths established by
preceding axons is called fasciculation

Question 7

What is topographic mapping?

Answer 7

Axons maintain spatial relationships from one neuron array to another (e.g., retina to optic tectum) even as structures grow.

Question 8

What did studies on retinal-tectum regeneration show?

Answer 8

After optic nerve injury, axons grow to fill available space in an orderly way, not necessarily returning to their original points.

Question 9

What is the topographic gradient hypothesis?

Answer 9

Axons grow from one topographic surface to another following intersecting signal gradients (e.g., anterior–posterior and medial–lateral) to maintain spatial maps.

Question 10

What other mechanisms help axons map topography?

Answer 10

Spontaneous neural activity and neuron-astrocyte interactions also guide accurate connections.

Question 11

What is synaptogenesis?

Answer 11

Formation of synapses between neurons after axons reach their targets.

Question 12

How fast do synapses form during development?

Answer 12

About 700,000 synapses per second.

Question 13

What is needed for synapse formation?

Answer 13

Coordinated activity between at least two neurons, chemical signals, spontaneous neurotransmitter release, and cell surface interactions.

Question 14

How do glial cells influence synaptogenesis?

Answer 14

Astrocytes and microglia help form and maintain synapses, process information, and provide support (e.g., cholesterol for neuron growth).

Question 15

What happens to synapses that don’t function properly?

Answer 15

They tend to be eliminated over time, ensuring only functional connections remain.

Question 16

Why does neuron death occur during development?

Answer 16

More neurons are produced than needed; about 50% die in waves to refine neural circuits.

Question 17

What are the two types of cell death in neurons?

Answer 17

Necrosis: passive, messy cell death causing inflammation. Apoptosis: active, programmed cell suicide, safe and orderly.

Question 18

Why is apoptosis safer than necrosis?

Answer 18

Apoptotic cells are packaged in membranes that attract microglia to engulf them, avoiding harmful inflammation.

Question 19

What can happen if apoptosis is blocked or overactivated?

Answer 19

Blocked apoptosis → cancer; Overactivated apoptosis → neurodegenerative disease.

Question 20

What triggers apoptosis in developing neurons?

Answer 20

1. Genetic programming for early death once neurons fulfill their function.
2. Failure to obtain life-preserving chemicals (neurotrophins) from target cells.

Question 21

How do life-preserving chemicals from target cells influence neuron survival?

Answer 21

Extra target structures reduce neuron death; destruction of some neurons increases survival of remaining neurons.

Question 22

What are neurotrophins and their roles?

Answer 22

NGF (Nerve growth factor) and BDNF( brain-derived neurotrophic factor). They promote neuron growth, survival, axon guidance, and synapse formation.