Lecture 31: Neural Development Flashcards
There are 3 phases of neural development. What is characteristic of phase 1?
Different cell types develop independently at widely separate locations in the embryo and are unconnected
There are 3 phases of neural development. What is characteristic of phase 2?
Axons and dendrites grow out along specific routes, setting up provisional orderly network of connections between various parts of the system
There are 3 phases of neural development. What is characteristic of phase 3?
Connections are adjusted and refined through interactions with distant regions via electric signals
This phase continues throughout adult life
Neurons are produced in association with what other cell type?
Glial cells
What is the function of glial cells in relation to neurons?
Glial cell provide supporting framework and nutrition to neurons
Both neurons and glial cells develop from __________ from a common precursor
Ectoderm
What are the 3 components of the CNS?
What is the CNS derived from?
Brain, spinal cord, retina
Derived from neural tube
What are the 2 components to the PNS?
What is the PNS derived from?
Nerves, sensory neurons
Derived from neural crest
The neural tube is derived from a single layered epithelium. It starts with a _______________ on the dorsal side of the embryo, and gradually deepens as _____________ become elevated, ultimately closing as a neural tube
Neural groove
Neural folds
What is the center of the neural tube called?
Neural canal
What type of signaling pathway controls differentiation into neurons? How does it do this?
Delta Notch
Lateral inhibition and positive feedback
Signal proteins secreted from ventral and dorsal sides of neural tube act as opposing ___________, causing neurons at different dorsoventral positions to express different gene regulatory proteins
Morphogens
What morphogen is secreted by the roof plate of the neural tube?
BMP (TGF-beta family)
These have to do with pattern formation and secretion of extracellular matrix
What morphogen is secreted from the floor plate of the neural tube?
Shh
Neural crest cells originate from which end of the neural tube?
Dorsal end
___________ is the process by which the neural tube actually closes
Neurulation
Neurulation results in what 3 cell types?
Neurons and glial cells of the PNS
Epinephrine producing cells of the adrenal gland
Many of the skeletal and connective tissue components of the head
What does the fate of neural crest cells depend on?
Depends on where they migrate to and settle
The migration of neurons in the neural tube is facilitated by the ability to crawl along the length of the neural tube on what type of cell process?
Radial glial cell processes
T/F: The first round of cortical neurons to divide tend to migrate the furthest distance
False - cells that divide first travel the least distance, cells that divide later must travel beyond each layer of cortical neurons that has already formed
The tip of an axon or dendrite has an irregular, spiky enlargement called a _____________
Growth cone
How do growth cones work?
They crawl through surrounding tissue, trailing the axon or dendrite behind
They have an “engine” and “steering apparatus” that direct the process
What dictates growth cone behavior?
Cytoskeletal machinery
What two things are “thrown out” by growth cones?
Filopodia
Lamelopodia
What 2 monomeric GTPases control assembly/disassembly of actin filaments, thus controlling the movement of the growth cone?
Rho and Rac
Growth cones travel towards target cells along predictable routes. What two major cues do growth cones exploit to find their way?
Extracellular matrix environment (sensed by receptors present on the membrane)
Chemotactic factors released by neighboring cells (may be attractive or repulsive)
_____________ ___________ is the process by which growth cones follow a path taken by other cells
Contact guidance
Contact guidance is mediated by what type of molecules?
Homophobic cell adhesion molecules
What are the 2 important classes of homophilic cell adhesion molecules?
Immunoglobulin superfamily
Cadherin family
What type of matrix molecules favor axonal outgrowth?
Laminin
What type of matrix molecules inhibit axonal outgrowth?
Chondroitin sulfate proteoglycans
What are the 6 mechanisms of growth cone guidance?
ECM adhesion Guidance by pioneer neuron Contact inhibition Cell surface adhesion Chemoattraction Chemorepulsion
__________ neurons of the spinal cord receive and relay sensory info from sensory neurons located in the periphery of the body
Dorsal
___________ clusters of spinal cord neurons develop as motor neurons and send out long axons to connect with specific subsets of muscles
Ventral
Intermediate locations have _____________ that connect specific sets of nerve cells to each other
Interneurons
Where are growth cones located during spinal cord development in terms of sensory, motor, and interneurons?
Growth cone of sensory neuron is ENTERING spinal cord
Growth cone of motor neuron is LEAVING spinal cord
Growth cones of interneurons remain inside spinal cord
What path do commissural neurons take?
They come from roof plate, grow vertically downward then take sudden 90 degree turn, abruptly leaving
The path of commissural neurons is due to the force of chemotactic factors. Name the chemoattractant discussed in class
Netrin
The path of commissural neurons is due to the force of chemotactic factors. Name the repulsive chemotactic factors discussed in class.
Slit and Semaphorin
The binding of the chemoattractant Netrin by cells of the floor plate leads to what?
Netrin binds to its receptor, causes opening of TRPC channels and allows entry of extracellular calcium
This leads to activation of machinery for extension of filopodia and movement of the growth cone
T/F: Non-commisural neurons in the neural tube do not have netrin receptors, so they do not migrate toward the floor plate
True
During commissural neuron guidance, midline cells secrete ________
Slit
What is the receptor for Slit?
Roundabout
What is the action of slit?
Repels growth cones and blocks entry to the midline
What do target cells secrete to signal the axonal growth to stop and synapse?
Growth factor (neurotropic factors)
What happens to cells that receive adequate growth factor? What about the ones that don’t?
Cells that receive adequate growth factor will form synapses
Cells that do not get adequate growth factor will die off
What was the first prototypical neurotrophic factor to be identified?
Nerve growth factor (NGF)
What family does nerve growth factor (NGF) belong to?
What type of receptor does it bind?
Belongs to family of neurotrophins
NGF receptor is a tyrosine kinase (TrkA)
What is the action of nerve growth factor (NGF)
Promotes survival of specific sensory neurons and sympathetic neurons
What are the short term effects of nerve growth factor (NGF)?
Local, direct, and rapid effect on growth cone and neurite extension independent of communication with cell body
What are the long term effects of nerve growth factor (NGF)?
Effect on cell survival
Mediated by its receptor (TrkA), uptake into cells via endocytosis and stimulation of downstream signaling pathways
Retinal neurons show selectivity for tectal position.
The posterior retina moves favorably along which part of the tectum?
Anterior
What chemotactic factor is responsible for the selectivity of retinal neurons for tectal position? Is it stimulatory or inhibitory?
Ephrin; inhibitory
Neurons that fire together wire together - meaning that synapses are strengthened by external events that cause 2 or more neurons to be activated at the same time. How does this apply to memory?
The more you stimulate a certain nerve pathway (like studying), the increasing strength of that synapse via calcium entry through NMDA receptor. This eventually leads to individual dendritic spine remodeling, and new ones forming
