Ventricular zone
Hollow core of developing embryo, source of cells of nervous system
Marginal zone
Faces the overlying pia
First position
A cell in the ventricular zone extends a process that reaches upward towards the pia
Second position
The nucleus of the cell migrates upward from the ventricular surface toward the pial surface where the cell's DNA is copied
Third position
The nucleus, containing two complete copies of genetic instructions, settles back to the ventricular surface
Fourth position
The cell retracts its arm from the pial surface
Fifth position
The cell divides in two
Neural progenitors
Cells that can only become neurons or glia, but are still "plastic
Radial glial cells
Specialized glial cells that provide a scaffold for migrating neurons to climb to their destination
Symmetrical cell division
Both daughter cells become radial glial cells and expand population of neural progenitors
Asymmetrical cell division
One daughter cell receives more cytoplasm than the other during mitosis
Transcription factors
Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription
Subplate
A layer of cortical neurons lying below the cortical plate early in development; when the cortical plate has differentiated into the six layers of the neocortex, the subplate disappears
Neural precursor cells
Immature neurons
Cortical plate
Dense outer covering of spongy bone that makes up the central part of the alveolar process
Reelin
A protein that regulates the migration of young cortical neurons along the radial processes of radial cells
Cell differentiation
The process by which a cell becomes specialized for a specific structure or function
Semaphorin 3A
Protein that attracts dendrites and repels axons
The radial unit hypothesis
The concept that an entire radial column of cortical neurons originates from the same birthplace in the ventricular zone
Emx2 and Pax6
Two complementary gradients of transcription factors that have been discovered long the anterior-posterior axis of the ventricular zone of the developing neocortex
Pathway selection
The outgrowing axons must 'select' an appropriate
pathway from among many potential pathways
Target selection
The choice of which thalamic nucleus a neuron can innervate; the correct choice, of course, it he lateral geniculate nucleus
Address selection
Once the axon is on its path it needs to decide when to get off and terminate in a new brain region
Neurites
Axons and dendrites
Growth cone
A distinctive structure at the growing end of most axons and the site where new material is added
Lamellipodia
A flat, sheet like extensions from core of growth cones
Filopodia
A very fine, tubular outgrowths from the growth cone
Extracellular matrix
The substance in which animal tissue cells are embedded, consisting of protein and polysaccharides
Laminin
A key basement membrane glycoprotein
Integrins
A transmembrane protein that interconnects the extracellular matrix and the cytoskeleton
Fasciculation
A mechanism that causes axons growing together to stick together
Cell-adhesion molecules (CAMs)
The proteins that allow cells to recognize each other and contribute to proper cell differentiation and development
Pioneer axons
Axons that grow to their target very early in development and are then used as guides by later axons, which simply grow along the earlier axons to find the same general target area
Guidance cues
Markers in the environment that determine the direction and amount of growth experienced by the growth cones in terms of the molecules they express on their membranes
Chemoattractant
A diffusible molecule that acts over a distance to attract growing axons
Netrin
The first chemoattractant to be discovered in mammals, secreted by neurons in the bentral midline of the spinal cord, helps in axon elongation, and released from the floor plate
Slit
A protein secreted by midline cells that enable decussing axons to escape the influence of netrin
Chemorepellent
A diffusible molecule that acts over a distance to repel growing axons
Robo
A protein that is expressed on the surface of an axon as a slit receptor
Chemoaffinity hypothesis
Proposal that neurons or their axons and dendrites are drawn toward a signaling chemical that indicates the correct pathway
Ephrins
Protein that guide streams of migrating neural crest cells
Eph receptor
Ephrin receptor on a growing axon
Agrin
A protein deposited in the extracellular space at the site of contact with the neuromuscular junction
Basal lamina
Thin extracellular layer that lies underneath epithelial cells and separates them from other tissues
Muscle-specific kinase (MuSK)
Communicates with another molecule, called rapsyn, which appears to act like a shepherd to gather the postsynaptic acetylcholine receptors at the synapse
Rapsyn
A protein in muscle that binds to AChRs and clusters them at the NMJ
Neuregulin
Protein interacts with tyrosine-kinase receptors important for synapse formation
Programmed cell death
Apoptosis
Trophic factors
Small proteins in the brain that are necessary for the development, function, and survival of specific groups of neurons
Nerve growth factor (NGF)
A protein that promotes the survival and growth of axons in the sympathetic nervous system and certain axons in the brain
Neurotrophins
Chemicals that enhance the development and survival of neurons
NT-3, NT-4, and brain-derived neurotrophic factor (BDNF)
Important members of the neurotropin protein family
Trk receptors
Phosphorylate tyrosine residues which activate a second messenger cascade that turns off genes involved in apoptosis
Apoptosis
Programmed cell death
Necrosis
The abnormal condition of death
Synaptic capacity
The finite number of synapses a neuron can receive
The losses in the primary visual cortex during adolescence occurs at an average rate of?
5000 synapses per second.
Synaptic rearrangement
The rearrangement of synaptic connections during neurodevelopment
Unlike most of the earlier steps of pathway formation, synaptic rearrangement occurs as a consequence of?
Neural activity and synaptic transmission.
In a very real sense, we learn to see during?
A critical period of postnatal development.
Hebb synapses
A synapse that is strengthened by simultaneous activity in the pre- and postsynaptic neurons
Hebbian modifications
Rearrangements of Hebb synapses
Monocular deprivation
An experimental manipulation that deprives one eye of normal vision
Experience dependent
Certain brain functions that depend on particular, variable experiences and therefore may or may not develop in a particular person
Critical period
An optimal period shortly after birth when an organism's exposure to certain stimuli or experiences produces proper development
Unlike segregation of eye-specific domains, which evidently depends on asynchronous pattern of activity spontaneously generated in the two eyes, the establishment of binocular receptive fields depends on?
Correlated patterns of activity that arise from the two eyes as a consequence of vision.
Ocular dominance shift
A change in visual cortex interconnections that makes more neurons responsive to one eye or the other
Binocular competition
A process believed to occur during the development of the visual system whereby the inputs from the two eyes actively compete to innervate the same cells
Strabismus
Condition of being cross-eyed
Based on the analysis of experience-dependent plasticity in the visual cortex and elsewhere, we can formulate what two simple "rules" of correlation for synaptic modification?
Neurons that fire together wire together and neurons that four out of sync lose their link.
The magnitude of the Ca2+ flux passing through the NMDA receptor channel specifically signals?
The level of pre- and postsynaptic coactivation.
Long-term potentiation (LTP)
An increase in a synapse's firing potential after brief, rapid stimulation, believed to be a neural basis for learning and memory
Long-term depression (LTD)
A long-term decrease in the excitability of a neuron to a particular synaptic input caused by stimulation of the terminal button while the postsynaptic membrane is hyperpolarized or only slightly depolarized
What are the three current hypotheses for why critical periods of neuronal plasticity end?
Plasticity diminishes when axon growth creases, plasticity diminishes when synaptic transmission matures, or plasticity diminishes when cortical activation is constrained.