Final Exam: Chapter 23 Wiring the Brain Flashcards
Radial glial cells
- neural progenitors
- dividing cells that give rise to all neurons and astrocytes
- cerebral cortex
- multipotent stem cells
mature cortical cells
-neuron or glia Determined by factors such as: -age of precursor cell -position within ventricular zone -environment at the time of division
Specialization of mature cells
- Dorsal Ventricular Zone: cortical pyramidal neurons and astrocytes
- Ventral Telencephalon: inhibitory interneurons and oligodendroglia
1. subplate layer is first to migrate away
2. layer VI
3. layer V
4. layer IV
5. Layer III
6. Layer II
neural precursor cells
- immature neurons
- many migrate by slithering alone thin fibers emitted by radial glial cells, span distance of ventricular zone and pia toward surface of brain; after, radial glia withdraw their radial processes
- if this were only process, cortical “protomap:” basically reflects areas in ventricular zone of fetal telencephalon
- but it is not: neurons also have distinct molecular identities, different transcription factors (Pax6 and Emx2)
Cortical plate
- precursor cells destined to become adult cortex
- first cells to arrive become layer VI, then next become V then IV etc
- new waves of neural precursor cells migrate out past existing cortical plate: cortex assembled inside out
Cell differentiation
-cell takes on appearance and characteristics of a neuron
-result of specific spatiotemporal pattern of gene expression
1. neurons differentiate, then astrocytes, then oligondendrocytes
2. preprogrammed before migration is completed
3. migration and differentiation proceed
caudal –> rostral along neuronal tube
Radial unit hypothesis
- entire radial column of cortical neurons originates from the same birthplace in ventricular zone
- explains dramatic expansion of human neocortex over evolution
Determining anterior-posterior locations
-neurons destined for anterior region of neocortex, higher levels of Pax6
-neurons destined for posterior cortex: higher levels of Emx2
Differences in transcription factors -> different gene epression and protein production –> used to attract neural precursor cells to appropriate destinations
dev of long range connections: pathway formation in CNS
- Pathway selection (where)
- Target selection (LGN–network)
- address selection (which layer)
EXAMPLE of retinal ganglion - path such as nasal retina vs temporal retina to dorsal thalamus
- which to innervate, innervate lateral geniculate nucleus
- correct layer, sort in respect to one another
-Depends on communication - direct cell to cell
- contact between cells and extracellular secretions of other cells
- communication via action potential and synaptic transmission
growth cone
- growing tip of neurite (axonal and dendritic processes still similar, collectively called neurites)
- specialized to identify appropriate path for neurite elongation
- axon needs to advance along substrate: EXTRACELLULAR MATRIX, must have appropriate proteins
- -laminin: glycoprotein, permissive substrate
- -integrins: surface molecules: bind laminin
- ——>this promotes axonal elongation
- also FASCICULATION: mechanism that causes growing neurons to stick together using CAMs in membranes to bind tightly, axons grow in unison
Guidance cues
- determine direction and amount of growth
- can be attractive or repulsive
Chemoattractant
- diffusible molecule, acts over distance
- axons attracted to entrain
- example: netrin, secreted by midline cells
Chemorepellent
- chases axons away so they can escape the “siren song” of netrin
- slit, protein secreted by midline cells
- robo protein is slit receptor
- not present until after axon passes midline, signal causes robo to be upregulated, THEN slit works
synapse
growth cone comes in contact with target
formation of synapse at neuromuscular junction
- agrin: protein secreted by growth cone
- agrin in basal lamina (extracellular space at site of contact) binds to MuSK in muscle cell membrane
- ACh receptors cluster in post synaptic membrane via rapsyn
