7120 Lecture Notes - Lecture 5: Neural Tube, Chemokine, Neuroglia
21 Jun 2018
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CHAPTER 5 – development of the brain
Maturation of the vertebrate brain
- CNS begins to form at 2weeks in fetus
- Forward end forms hindbrain, midbrain and forebran
- Rest becomes spinal cord
- Fluid filled cavity in the neural tube becomes the central canal of the spinal cord and the four
ventricles of the brain with CSF
- Birth; av brain weighs approx. 350grams, 1000g at 1, 1200/1400 adult
Growth and development of neurons
- Proliferation: production of new cells
oEither remain as stem cells or become neurons and glia and migrate to other places
- Migration: move once differentiated
oSlow ones mightn’t reach destination until adulthood
oImmunoglobins and chemokines guide migration
Deficit = impaired migration, retardation, decreased axon growth
- Differentiation
oForms axons and dendrites
oAxon grows first; maybe towards target through jungle of other cells
oDendrite form when location is reached
- Myelination
oGlia produce insulating fatty sheaths to speed up transmission
Forms first in spinal cord and then in hindbran, midbrain and forebrain
oContinues for decades
- Synaptogenesis
oFormations of synapses
Begins before birth, continues through life
Discard old ones
New neurons later in life
- Olfactory receptors; half life of 90 days
find more resources at oneclass.com
find more resources at oneclass.com
- Stem cells in nose: immaure through life; divide with one remaining immature and the other
differentiates to replace dying olfactory cell
- Stem cells in inferioir brain do similar thing with daughter cells
- Hippocampus – new neurons in some animal; helps with memory and learning
- All skin cells less than a year old
- Skeletal muscle cells; 15 years old on average
- Heart cells; as old as the person
o1% replaced per year
- Cerebral cortex; same as you – forms no or few new neurons after birth
oExcept say after injury ie stroke where remodeling may occur
Pathfinding by axons
- Chemical pathfinding
oWeiss; put leg on a salamander for axons to attch
Worked – moved in synchrony with the leg next to it
Suggested nerves attached at random
oSpecificity of axon connections
Roger sperry; shows how sensoty axons find their way to correct targets
Cut optic nerves of newts (grows back in them)
Grew back and connected with tectum (main amphibious visual area)
Cut agin, and rotated eye 180degrees
oWhen axons grew back; went to same place
Saw world upside and right way
oFollowed chemical pathway
oChemical gradients
Growing axon follows path of cell-surface molecules attracted by chemicals and
repelled by some too to steer in right direction
Connect with areas of same concentration
- Competition among axons as a general principle
oAxons form synapses in approx. the right area of their location
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Cns begins to form at 2weeks in fetus. Fluid filled cavity in the neural tube becomes the central canal of the spinal cord and the four ventricles of the brain with csf. Proliferation: production of new cells: either remain as stem cells or become neurons and glia and migrate to other places. Migration: move once differentiated: slow ones mightn"t reach destination until adulthood, immunoglobins and chemokines guide migration. Deficit = impaired migration, retardation, decreased axon growth. Differentiation: forms axons and dendrites, axon grows first; maybe towards target through jungle of other cells, dendrite form when location is reached. Myelination: glia produce insulating fatty sheaths to speed up transmission. Forms first in spinal cord and then in hindbran, midbrain and forebrain: continues for decades. Stem cells in nose: immaure through life; divide with one remaining immature and the other differentiates to replace dying olfactory cell. Stem cells in inferioir brain do similar thing with daughter cells.
