Lecture 36 Flashcards

1
Q

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

A

10 to the 11

1000 connections

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2
Q

State and describe the phases of neural development

A

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)

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3
Q

state the range of length that axons can occur in

A

1 mm to 1 m in length

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4
Q

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

A

glial

provide supporting framework and nutrition to neurons

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5
Q

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

A

both develop from the ectoderm

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6
Q

Compare where the CNS and PNS are derived from.

A

The CNS is derived from the neural tube

The PNS is derived from the neural crest

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7
Q

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)

A

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

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8
Q

what signaling induction method controls differentiation into neurons?

A

delta notch

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9
Q

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

A

the dorsal end of the neural tube

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

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10
Q

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

A

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

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11
Q

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.

A

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

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12
Q

what structure do neurons migrate along?

A

radial glial cell processes

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13
Q

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

A

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

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14
Q

What are Rho and Rac? what is their function?

A

Rho and Rac are monomeric GTPases

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

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15
Q

what structures do growth cones use to move?

A

they throw out filopodia and lamelopodia in order to move

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16
Q

how is the behavior of growth cones dictated?

A

by it’s cytoskeletal machinery

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17
Q

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

A

False

Growth cones travel towards their target cells along predictable routes

18
Q

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

A

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

chemotactic factors: attractive or repulsive chemicals released by neighboring cells

19
Q

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

A

when growth cones follow a path take by other cells

this results in nerve fibers forming in bundles

20
Q

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

A

Immunoglobulin superfamily

Cadherin family

both provide a mechanism for selective guidance and recognition

21
Q

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

A

laminin stimulates axonal outgrowth

chondrotin sulfate proteoglycans inhibits growth

22
Q

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

A

True

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

23
Q

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

A

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

24
Q

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

A

1st

floor plate

25
Q

Compare the short term and long term effects of NGF

A

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

26
Q

Compare the short term and long term effects of NGF

A

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

27
Q

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

A

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)

28
Q

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

A

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

29
Q

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

A

True

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

30
Q

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

A

True

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

31
Q

What do dorsal neurons do?

A

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

32
Q

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

A

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

33
Q

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

A

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

34
Q

Describe phase 1 of commissural neuron guidance

A

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

35
Q

Describe phase 2 of commissural neuron guidance

A

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.

36
Q

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

A

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)

37
Q

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

A

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

38
Q

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?

A

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

39
Q

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?

A

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

40
Q

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 ____ ______ _______.

A

opposing morphogens

gene regulatory proteins