Lecture 36

Question 1

How many neurons does the brain have and how many connections with other neurons does each of these neurons have?

Answer 1

10 to the 11

1000 connections

Question 2

State and describe the phases of neural development

Answer 2

Phase 1: Different cell types develop independently at widely separate locations in an embryo according to their local programming (they are unconnected at this point)

Phase 2: axons and dendrites grow out along specific routes setting up a “provisional” but orderly network of connections (synapse formations) between various parts of the nervous system

Phase 3: connections are adjusted and refined through interactions with distant regions via electric signals (Continues to occur into adult life)

Question 3

state the range of length that axons can occur in

Answer 3

1 mm to 1 m in length

Question 4

neurons are produced in association with ____ cells. define this term.

Answer 4

glial

provide supporting framework and nutrition to neurons

Question 5

Neurons develop from which layer of the gastrula? what about glial cells?

Answer 5

both develop from the ectoderm

Question 6

Compare where the CNS and PNS are derived from.

Answer 6

The CNS is derived from the neural tube

The PNS is derived from the neural crest

Question 7

Describe the formation of the neural tube, beginning with the single layered epithelium. (include the term that describes the inner portion of the neural tube)

Answer 7

a neural groove appears on the dorsal side of the embryo, and it’s deepening forms the neural folds

neural folds elevate and then “coalesce” in the middle line to form the neural tube

the neural canal is found within the neural tube

Question 8

what signaling induction method controls differentiation into neurons?

Answer 8

delta notch

Question 9

where does the cells of the neural crest originate? how to they reach their final position?

Answer 9

the dorsal end of the neural tube

they migrate during or shortly after the closure of the neural tube (neurulation)

Question 10

The fate of the neural crest cells depends on what? state the 3 types of cells that are generated from neural crest cells.

Answer 10

where they migrate

neurons and glial cells of the PNS

epinephrine-producing cells of the adrenal gland

many of the skeletal and CT components of the head

Question 11

Describe the distribution of the neurons in terms of the time they were “born” and their final distance migrated along the radial glial cell processes.

Answer 11

first born neurons settle closest to their site of formation (means they have a shorter migration distance compared to later born neurons)

Question 12

what structure do neurons migrate along?

Answer 12

radial glial cell processes

Question 13

What is a growth cone? what is it’s function? (include axon formation)

Answer 13

growth cone: spikey enlargement at the tip of an axon/dendrite

it crawls through surrounding tissue, allowing the axon/dendrite to trail behind it

a single growth cone starts migrating faster than all of the others and develops “axon-specific proteins” to form the axon

Question 14

What are Rho and Rac? what is their function?

Answer 14

Rho and Rac are monomeric GTPases

they control the assembly/disassembly of actin filaments, which control the movement of growth cones

Question 15

what structures do growth cones use to move?

Answer 15

they throw out filopodia and lamelopodia in order to move

Question 16

how is the behavior of growth cones dictated?

Answer 16

by it’s cytoskeletal machinery

Question 17

True or False: it is difficult to predict the route that growth cones will take in order to reach their target cells. explain

Answer 17

False

Growth cones travel towards their target cells along predictable routes

Question 18

What are the 2 major cues that growth factors use to find their way to their target cells? explain them

Answer 18

extracellular matrix environment: they use receptors present on their membrane to sense the environment

chemotactic factors: attractive or repulsive chemicals released by neighboring cells

Question 19

What is contact guidance? what does this usually result in?

Answer 19

when growth cones follow a path take by other cells

this results in nerve fibers forming in bundles

Question 20

What are the 2 important classes that mediate homophilic cell adhesion? what makes these so useful?

Answer 20

Immunoglobulin superfamily

Cadherin family

both provide a mechanism for selective guidance and recognition

Question 21

What do matrix molecules such as laminin favor? what a bout chondrotin sulfate proteoglycans?

Answer 21

laminin stimulates axonal outgrowth

chondrotin sulfate proteoglycans inhibits growth

Question 22

True or false: extracellular matrix adhesion is a method of growth cone guidance. explain.

Answer 22

True

the developing neuron’s growth cone will adhere to the extracellular matrix to pave the way for the neuron’s axon/dendrites.

Question 23

What was the first prototypical neurotrophic factor to be identified? state it’s family it belongs to and the receptor it works with. state the function of it

Answer 23

nerve growth factor (NGF)

belongs to the “neurotrophin” family and works with tyrosine kinase (TRkA) receptors

promotes survival of specific sensory neurons and sympathetic neurons

Question 24

The ____ stage of commissural neuron guidance depends on netrin by cells of the ___ ____.

Answer 24

1st

floor plate

Question 25

Compare the short term and long term effects of NGF

Answer 25

short term: effect on growth cone and neurite extension. the effect is local, direct, rapid, and independent of communication with the cell body Long term: effect on cell survival. mediated by it's receptor, uptake into cells via endocytosis and stimulation of downstream pathways

Question 26

Compare the short term and long term effects of NGF

Answer 26

short term: effect on growth cone and neurite extension. the effect is local, direct, rapid, and independent of communication with the cell body Long term: effect on cell survival. mediated by it's receptor, uptake into cells via endocytosis and stimulation of downstream pathways

Question 27

Describe the differences in preferences between posterior retinal neurons and anterior retinal neurons AND why this occurs.

Answer 27

posterior retinal neurons prefer anterior tectal neurons anterior retinal neurons have no preference Ephrin serves as a repellent to posterior retinal neurons (its present in the posterior tectal membrane)

Question 28

Explain what the phrase "neurons that fire together, wire together" means. explain why (Phase 3 stuff)

Answer 28

synapses are strengthened by external events that cause 2 or more neurons to be activated at the same time. the entry of Ca2+ through the glutamate receptor (NMDA receptor) triggers a lasting change in synaptic strength

Question 29

True or False: during synapse remodeling, there are actually observable physical differences that occur to neurons. explain.

Answer 29

True individual dendritic spines are remolded and new spines can even be formed

Question 30

True or False: during synapse remodeling, there are actually observable physical differences that occur to neurons. explain.

Answer 30

True individual dendritic spines are remolded and new spines can even be formed

Question 31

What do dorsal neurons do?

Answer 31

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

Question 32

What do ventral clusters of the spinal cord develop as? why?

Answer 32

motor neurons so that they can send out long axons to connect to a specific subset of muscle.

Question 33

Where are inter-neurons found and what is their purpose?

Answer 33

they are found in the "intermediate location" and serve to connect specific sets of nerve cells to one another

Question 34

Describe phase 1 of commissural neuron guidance

Answer 34

netrin (an attractive chemotactic factor) is secreted by the cells of the floor plate

Question 35

Describe phase 2 of commissural neuron guidance

Answer 35

Nectrin binds to receptors on the developing neuron and opens TRPC (transient receptor potential C) channels extracellular Ca2+ then flows through the TRPC channels and activates the machinery that moves the growth cone (via extension of filopodia) Midline cells then secrete "slit" chemotactic factor, which binds to "roundabout" receptors on the neuron and block the growth cone from entering the midline growth cones them become sensitive to "semaphorin" chemotactic factor. Semaphorin and slit then trap the growth cone between them into a narrow track. the growth cone will then reach it's target cell, stop moving, and create a synapse as long as it receives a neurotrophic factor.

Question 36

Describe Phase 3 of commissural neuron guidance (include what stage of life this occurs in)

Answer 36

each axon initially branches widely, making mulitple synapses with the target tissue however phase 3 "trims" (profusion) the weak synapses away the synaptic remodeling that occurs in this phase, continues to happen during adulthood and is dependent upon electrical activity and synaptic signaling (stimulation)

Question 37

explain the amount of neurons that are created, what they need to survive, and where this substance comes from.

Answer 37

most neurons are created in excess, meaning up to 50% may die after reaching their target cell Neurons need a neurotrophic factor in order to survive (programmed cell death occurs if they do not receive a neurotrophic factor) Neurotrophic factors are produced (in limited amount) by the target cell

Question 38

What would happen to the dying neurons that did not receive a neurotrophic factor if you increased the number of target cells? what about if you decreased the number of target cells?

Answer 38

increasing the number of target cells: would reverse the death process of the dying neuron bc it would provide the neuron with neurotrophic factor decreasing the number of target cells: would exacerbate the death of the neuron because there would be less neurotrophic factor to go around

Question 39

What would happen to the dying neurons that did not receive a neurotrophic factor if you increased the number of target cells? what about if you decreased the number of target cells?

Answer 39

increasing the number of target cells: would reverse the death process of the dying neuron bc it would provide the neuron with neurotrophic factor decreasing the number of target cells: would exacerbate the death of the neuron because there would be less neurotrophic factor to go around

Question 40

Signal proteins secreted from the ventral and dorsal sides of the neural tube act as ____ _____, causing neurons at different dorso-ventral positions to express different ____ ______ _______.

Answer 40

opposing morphogens gene regulatory proteins