How does our brain develop throughout our lifetime? Flashcards
Nervous System is organized at all stages
-During all stages of development, nervous system is highly organized
-Organization is result of:
–Genes
–Environment & Experience
–Interaction of the two
Prenatal Nervous System Development
-nervous system develops from the ectoderm (18 days of gestation)
-Embryo = 3 layer disk
–Ectoderm (nervous system & skin)
—-Neural Plate is formed by thickening of ectoderm, whole process called “Neurulation”
–Mesoderm (skeleton & muscles)
–Endoderm (internal organs)
Neural Groove (20 days)
-Uneven rates of cell division in the neural plate cause formation of Neural Groove —- future CNS (brain and spinal cord)
-Neural Crest cells are progenitors for entire PNS
Neural Tube
-Neural groove joins together to form Neural Tube with a fluid-filled Central Canal
-Central canal will form ventricles and spinal cord canal – cerebral spinal fluid
-Cells lining neural tube will be progenitors for entire CNS
-Cranial end forks out to form brain plate
Brain Structures that form at 24 days
-Cerebral cortex, Limbic system, Basal Ganglia
-Thalamus & Hypothalamus
-Substantia nigra & Ventral tegmental area
-Cerebellum, Pons, Medulla
-Cranial end of neural tube swells as a result of new cells being born (neurogenesis)
-Neural crest cells - Neurons of somatic and autonomic nervous system
22 days of gestation
-Neural groove joins together to form Neural Tube with a fluid-filled central canal
–Brain plate also forms (part of ectoderm that continues to get thicker
–Central canal will form the ventricles and spinal cord canal - cerebral spinal fluid
–Cells lining neural tube will be progenitors for entire CNS
-Cranial end forks out to form brain plate
25 days of gestation
Neural tube
40 days of gestation
Forebrain, midbrain, hindbrain, spinal cord
50 days of gestation (1st trimester)
-when it actually starts to look like a brain
-Diencephalon
-Telencephalon
100 days of gestation (1st trimester)
-(double gestation) you get an actual cerebral hemisphere and start to form hindbrain structures
-cerebellum
-pons
-medulla
2nd trimester
41 weeks is when brain looks like a normal one
6 Stages of Neural Development
- Neurogenesis - production of neuronal cells from non-neuronal precursors
- Cell migration - movement of cells to form distinct brain regions
- Differentiation - transformation of precursor cells into neurons & glia
- Synaptogenesis - establish synaptic connections
- Neuronal cell death - not all make it and some are marked for death
- Synapse rearrangement - loss or development of synapses, almost like pruning
Neurogenesis
-Most neurons generated before birth, some during childhood, and some during adulthood
-Cells lining central canal = ventricular zone
-Precursor cells divide symmetrically to expand ventricular zone (mitosis)
–Cells lining the central canal = ventricular zone
-Asymmetric division: Cell division switched to “asymmetric division”
–One daughter cell migrates out and one stays and continues to divide
–All cells develop here and then move away
Cell migration
-Cells move away from the ventricular zone
-What brain region a cells ends up in is dictated by where it was born in the ventricular zone
-Radial glial cells act as guides → These cells connect the ventricular zone with a particular spot in the marginal zone
-This migration is directed by cell adhesion molecules (CAMS)
-As the marginal zone fills, produces cortical plate
-As neurons migrate, they push past previous neurons to populate the outermost part of the cortical plate
-This is how we get six layers of the cortex – waves of cells form the laminar
structure in an inside-out manner
Differentiation
-When cells arrive at destination, they begin to express genes to make the specific proteins they need
-They differentiate – take on a specific final morphology (glia, neurons, and particular subtypes of each)
-What controls what a cell will differentiate into?
–Intrinsic factors – internal genetic/molecular signals
–Extrinsic factors – molecular/chemical influences around cell
Extrinsic Factor - Sonic Hedgehog
-Notochord (green) releases sonic hedgehog into ventral developing spinal cord, producing motor neurons (gold)
-Transplant notochord to the dorsal side
Extrinsic Factor - Sonic Hedgehog
-Notochord (green) releases sonic hedgehog into ventral developing spinal cord, producing motor neurons (gold)
-Transplant notochord to the dorsal side
Extrinsic Factor - Sonic Hedgehog
-Notochord (green) releases sonic hedgehog into ventral developing spinal cord, producing motor neurons (gold)
-Transplant notochord to the dorsal side
Extrinsic Factor - Sonic Hedgehog
-Notochord (green) releases sonic hedgehog into ventral developing spinal cord, producing motor neurons (gold)
-Transplant notochord to the dorsal side
Synaptogenesis
-Almost all neurons are generated by birth; but most synapses form postnatal
-Neurons must grow axons and dendrites
-Neurons must make correct synapses/
connections
-growth cones
-Cells/tissue secrete chemicals that attract/repel specific axons/dendrites
–Chemoattractive or chemorepulsive molecules
–Two structures that should be connected share a common chemical
substrate that lays down the pathway between them
Neuronal Cell Death
-Initial neurogenesis overproduces cells
-Selective elimination of those not necessary
-Depends on if it receives neurotropic factors from target cells that it synapses with
Apoptosis
-Unneeded cells are instructed to die via
a phenomenon of programmed cell death, or apoptosis
–Ca2+ influx causes Diablo protein to
be released
–Diablo blocks inhibitors of apoptosis
proteins (IAPs)
–Causes widespread biochemical
changes, leading to cell death
Synapse rearrangement/modeling
-Initial synaptogenesis overproduces synapses
-Selective elimination – pruning
-Selective formation of new synapses (continues for life)
-Regulated by neuronal activity (action potentials)
-“Neurons that fire together, wire together”
Development continues into adulthood
-Goes on forever - maturation continues into adulthood
-Gray matter decreases and white matter increases until age 18
-You have enough neurons, they just become stronger pathways
-Striatum - reward center
-Missing connectivity between striatum and PFC
When something goes wrong
Some children suffering from fetal alcohol syndrome do not have a corpus collosum
Brain growth & development is protracted
-Brain weight lowers when we are in our older ages– due to a reduce in myelination
–Active/passive propagation not occurring as quickly
-Older people have dementia due to a decrease in white matter
