Chapter6 Flashcards
How do neurons develop?
Through processes in embryo growth
What initiates the formation of immature nerve cells?
Signaling molecules
What is the stage after the formation of immature nerve cells?
Cell division (proliferation)
What happens during cell division?
Increase brain cells by billions
What occurs during migration?
Neurons travel to destinations
What do surrounding tissues produce to influence cell type development?
Signals
What process occurs when mesoderm signals induce ectoderm cells?
Neural induction
What are the basic categories of nerve tissue?
Neurons or glia
What determines the fate of a developing cell?
Proximity to signaling molecules
What is sonic hedgehog?
A signaling molecule
What cells are formed with high sonic hedgehog exposure?
Specialized glia
What cells are formed with medium sonic hedgehog exposure?
Motor neurons
What cells are formed with low sonic hedgehog exposure?
Interneurons
Do interneurons relay messages to muscles?
No
Is the mechanism of molecular signaling similar in different species?
Yes
What type of cells give rise to neurons?
Neural stem and progenitor cells
What do early divisions of neural stem cells result in?
Two identical daughter cells
What process allows rapid brain growth?
Neurogenesis
What happens to neural stem cells after early development?
Few remain
Where is adult neurogenesis limited?
Memory regions
What may cause microcephaly?
Protein defects
What is characterized by severe reduction in brain size?
Disorder causing neurological disabilities
What disorder is associated with excessive proliferation of brain cells?
Megalencephaly
What happens to new neurons after neural induction and proliferation?
They migrate
When does the human brain begin to form?
3 weeks gestation
What is the first stage of brain development?
Neural tube
When can individual sections of the brain be recognized?
4 weeks
When can ridges of the brain be observed?
6 months
What do the ridges in the embryo develop into?
Neural tube
What three bulges form from the thickening of the neural tube?
Hindbrain, midbrain, forebrain
At what week do the first signs of eyes and brain’s hemispheres appear?
Week 7
Where do new neurons move from in the neural tube?
Ventricular zone
What is the outer surface of the neural tube called?
Marginal zone
What do neurons form after they stop dividing?
Intermediate zone
What is the most common guidance mechanism for neuron migration?
Radial glia
What percentage of migration in humans is accounted for by radial glia?
90 percent
What is the role of glia in neuron migration?
Scaffolding for neurons
How does radial migration occur?
Inside-out manner
Which neurons form the deepest layer of the cortex?
Earliest arriving neurons
What type of migration do some neurons perform sideways?
Tangential migration
What can influence the migration process?
Alcohol, cocaine, radiation
What is a consequence of improper migration?
Intellectual disability, epilepsy
What can mutations in migration-regulating genes cause?
Genetic forms of intellectual disability
What occurs after neurons reach their final locations?
Making connections for functions
What happens internally during fetal development?
Induction, proliferation, and migration
What is the primary neural signalling molecule?
Axons
What is the longest human axon?
Spinal cord to toes
How many times longer than its diameter is the longest human axon?
Nearly a million times
What is an enlargement at the tip of an axon called?
Growth cone
What is one of the functions of a growth cone?
Seeking out its precise destination
What guides a growth cone to its destination?
Molecular cues
What do receptors on the growth cone respond to?
Environmental cues
What do attractive cues do for growth cones?
Lay a path
What is the effect of repellent molecules on growth cones?
Funnel through corridors
What happens when environmental molecules bind to the growth cone?
Directional response
What are some examples of signaling molecules?
Netrin, semaphorin, ephrin
Why are simpler animals useful for human studies?
Similar protein functions
What is the trend in protein family size across species?
Smaller in flies/worms
What was netrin first discovered in?
a worm
Where does netrin guide axons in mammals?
spinal cord
What begins to form when axons reach their targets?
synapse
What separates the axon from the dendrite at a synapse?
tiny space
What triggers the release of neurotransmitters?
Electrical signals
What do neurotransmitters diffuse across?
Synaptic space
What do neurotransmitters affect in the receiving neuron?
New electrical signal
What determines the response of a receiving neuron?
Combined effects of cues
What gives rise to the brain’s capacity for information processing?
Trillions of synapses
What must be highly specific for proper information processing?
Formation of synaptic connections
What guides each axon to its proper target?
Mechanisms
What mediates target recognition for axons?
Additional molecules
Who initiates contact with axons?
Dendrites
What do both sides of the synapse produce?
Proteins
What differentiates the presynaptic side?
Releases neurotransmitters
What becomes specialized in the axon terminal?
Releasing neurotransmitter packets
What forms on the postsynaptic side?
Receptors for neurotransmitters
What is the dentate gyrus involved in?
Pattern separation
What capacity does the human brain’s trillions of synapses provide?
Information processing
Defects in molecules contribute to which disorders?
Autism
What underlies synapse degradation during aging?
Loss of certain molecules
What signals determine neurotransmitter type in neurons?
Array of signals
Which neurotransmitter do motor neurons use?
Acetylcholine
What do certain immature neurons produce in culture?
Norepinephrine
What neurotransmitter do neurons produce when cultured with cardiac tissue?
Acetylcholine
What influences the production of specific neurotransmitters in neurons?
Genetic and environmental signals
What determines the chemical messenger a neuron produces?
Location of the synapse
What is myelination?
Fatty wrapping of axons
What does myelination do?
Increases signal speed
How much can myelination increase signal speed?
By as much as 100 times
What are nodes of Ranvier?
Gaps in the sheath
What is saltatory conduction?
Jumping between nodes
What does myelin formation occur throughout?
Lifespan
What happens to the neural network after initial growth?
It’s pared back for efficiency.
What percentage of neurons survive to function in an adult?
About half.
What is apoptosis?
Programmed cell death.
What activates apoptosis in neurons?
Insufficient trophic factors.
How are connections between neurons in a young primate’s cerebral cortex compared to an adult?
More numerous and twice as concentrated
What determines the survival of neuron connections during pruning?
Relative activity of connections
What role do astrocytes and other glia play in neuron connection pruning?
Important role
How are advances in brain development studies relevant?
Medical treatments
What diseases are now considered from a developmental perspective?
Adult disorders
What is a potential cause of schizophrenia?
Incorrect brain pathways
What role do genes play in autism spectrum disorders?
Susceptibility
What is considered a realistic possibility following brain injury?
Regeneration
Why is understanding brain construction important?
Reorganization ability
