Neural Development

Question 1

The brain has how many neurons?

Answer 1

10^11

*each of these makes connections with ~1000 other neurons

Question 2

Describe Phase 1 of the neural development

Answer 2

Different cell types (neurons, glia, muscle cells) develop independently at widely separate locations in embryo according to local program and are unconnected

Question 3

Describe Phase 2 of the neural development

Answer 3

Axons and dendrites grow out along specific routes setting up a provisional but orderly network of connections between various parts of the system

Question 4

Describe Phase 3 of the neural development

Answer 4

continues into adult life, connections are adjusted and refined through interactions with distant regions via electric signals

Question 5

Neurons are produced in association with what type of cells?

Answer 5

glial cells

Provide supporting framework and nutrition

Question 6

What do neurons and glial cells develop from?

Answer 6

ectoderm from a common precursor

Question 7

What is the CNS (brain, spinal cord, and retina) derived from?

Answer 7

neural tube

Question 8

What is the PNS (nerves, sensory neurons) derived from?

Answer 8

From neural crest

Question 9

What is the neural tube derived from?

Answer 9

a single layered epithelium and starts with a neural groove

Question 10

How is the neural tube formed?

Answer 10

Single layered epithelium
neural groove
gradually deepens as neural folds become elevated
folds meet and coalesce in the middle line and convert the groove into a closed tube = neural tube

Question 11

What is the center of the neural tube called?

Answer 11

neural canal

Question 12

What does the Delta notch signaling control?

Answer 12

differentiation into neurons (lateral inhibition)

Question 13

What acts as opposing morphogens, causing neurons at different dorso-ventral positions to express different gene regulatory proteins?

Answer 13

Signal proteins secreted from ventral and dorsal side of neural tube

Question 14

Where do neural crest cells originate at?

Answer 14

At the dorsal end of the neural tube

Question 15

When do neural crest cells migrate?

Answer 15

extensively during or shortly after closure of the neural tube or neurulation

Question 16

What do neural crest cells generate?

Answer 16

several differentiated cell types:

• neurons and glial cells of PNS
• epinephrine-producing cells of the adrenal gland
• many of the skeletal and connective tissue components of the head

Question 17

Describe the migration of neurons

Answer 17

Neurons migrate from their original birthplace and settle in a different location
After final division close to the inner face of the neural tube they crawl along radial glial cells
Radial glial cells extend from inner to outer end of the neural tube

Question 18

Describe dorsal neurons of spinal cord

Answer 18

Receive and relay sensory information from sensory neurons located in the periphery of the body

Question 19

Describe ventral clusters of the spinal cord neurons

Answer 19

Develop as motor neurons and send out long axons to connect with specific subset of muscles

Question 20

Describe intermediate neurons

Answer 20

Intermediate location has inter-neurons that connect specific set of nerve cells to each other

Question 21

True or False

Axon and dendrites are not distinguishable at first during development?

Answer 21

True

Tip of axon/dendrite has an irregular, spiky enlargement called growth cone

Question 22

What does the growth cone do?

Answer 22

crawls through surrounding tissue, trailing the axon or dendrite behind
Has an engine and steering apparatus that directs the process along the right path
Behavior dictated by its cytoskeletal machinery

Question 23

How are axon-specific proteins formed?

Answer 23

one of the growth cone starts migrating fast and develops the proteins and will form the axon

Question 24

What do growth cone cytoskeletal machinery throw out

Answer 24

filopodia and lamelopodia

Question 25

What controls the assembly/disassembly of actin filaments, which controls movement of the growth cone?

Answer 25

monomeric GTPases Rho and Rac

Question 26

Growth cones travel towards target along predictable routes. They exploit two major cues to find their way:

Answer 26

1. Extracellular matrix environment sensed by receptors present on membrane 2. chemotatic factors released by neighboring cells

Question 27

Growth cones often follow a path taken by other cells, this is called what?

Answer 27

contact guidance | Consequently, nerve fibers are usually found in bundles

Question 28

How is contact guidance mediated?

Answer 28

by homophilic cell adhesion

Question 29

What are two important classes of homophilic cell adhesion molecules?

Answer 29

Immunoglobulin superfamily cadherin family *provide a mechanism for selective guidance and recognition

Question 30

Matrix molecules such as laminin favor what?

Answer 30

axonal growth

Question 31

Chondroitin sulfate proteoglycans inhibit what?

Answer 31

growth

Question 32

What are secreted by cells and act as guidance factors at strategic points along path?

Answer 32

Chemotactic factors

Question 33

Chemotactic factors may be attractive or repulsive. what are some examples?

Answer 33

Netrin Slit Semaphorin

Question 34

Describe netrin effect on the mechanism of commissural neuron guidance

Answer 34

First stage depends on secretion of netrin by cells of the floor plate Netrin bints to TRPC channels Entry of extracellular Ca Activation of machinery for extension of filopodia and movement of growth cone

Question 35

What neurons in the neural tube do not have netrin receptors, so they do not migrate towards floor plate?

Answer 35

Non-commissural neurons

Question 36

Describe Slit effect on the mechanism of commissural neuron guidance

Answer 36

Midline cells secrete Slit Slit receptor = Roundabout (present on commissural neurons) Slit repels growth cones and blocks entry to the midline Growth cones become sensitive to semaphorin(repulsive) Trapped between 2 sets of repellants to travel narrow track

Question 37

When axonal growth cone reaches eventual target cells what happens?

Answer 37

They halt and communicate and make synapses with target cells Usually unidirectional signaling in nerve cells but in developing cells bidirectional Signal from target tissue regulate which grwoth cone synapse and where

Question 38

How many neurons die after they reach target cell?

Answer 38

50% because they are made in excess and target cell produces limited amount of specific neurotrophic factors needed for survival Those that do not get enough die by programmed cell death *can be reversed by increasing number of target cells and exacerbated by decreasing number of target cells

Question 39

What was the first prototypical neurotrophic factor to be identified?

Answer 39

Nerve growth factor NGF Belongs to the family of neurotrophins Tyrosine kinase NGF receptor Promotes survival of specific sensory neurons and sympathetic neurons

Question 40

What are the short term effects of NGF?

Answer 40

Effect on growth cone and neurite extension. Effect is local, direct rapid, and independent of communication with cell body

Question 41

What are the long term effects of NGF?

Answer 41

Effect on cell survival. mediated by its receptor, uptake into cells via endocytosis and stimulation of downstream signaling pathways

Question 42

Synaptic remodeling is dependent upon what 2 rules that create spatial order?

Answer 42

1. axons from cells in different regions of retina compete for tectal neurons (different times) 2. axons from neighboring sites which are excited at the same time cooperate/collaborate to retain and strengthen synapses with tectal neurons

Question 43

activity - dependent synaptic remodeling depends on what

Answer 43

electrical activity and synaptic signaling

Question 44

Describe the process on how denser distribution of synapses are formed

Answer 44

Each axon initially branches widely and makes multiple synapses with target cell Profusion of weak synapses Network subsequently trimmed by elimination of synapses and retraction of axon branches Accompanied by sprouting of axons to develop denser distribution of synapses that survive' Fuzzy initial map -> sharp final map

Question 45

How is adult memory formed?

Answer 45

Synapses are strengthened by external events that cause 2 or more neurons to be activated at the same time Entry of Ca through NMDA receptor triggers lasting change in synaptic strength Corresponding change in physical structure of synapse Individual dendritic spines remodeled, new spines appear with electrical stimulation