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Home , Cerebellum, Cerebral cortex, Cortex (anatomy), Grey matter, Neocortex

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White matter (the wiring: the mainly talks to itself)

Neocortex:

Cerebellum: unconscious control of posture & movement

1. Golgi-stained section of cerebral 2. One of Ramon y Cajal’s faithful drawings showing nerve cell diversity in the brain

cajal : perhaps 1 km2 of plasma membrane - a molecular reaction substrate for 1024 voltage- and ligand-gated ion channels.

light to : 3 further cell types

1. : trophic interface with blood, maintain blood brain barrier, buffer excitotoxic , support

astros : insulation

oligos

Production persists into adulthood: radiation myelopathy 3. : resident macrophages of the CNS. Similarities and differences with Langerhans cells, the professional antigen-presenting cells of the skin. 3% of all cells, normally renewed very slowly by division and immigration.

Normal microglia Most adult are already produced by birth

Peak synaptic density by 3 months

EMBRYONIC POSTNATAL

week: 0 6 12 18 24 30 36 Month: 0 6 12 18 24 30 36 Year: 4 8 12 16 20 24

Cell birth Migration 2*

Neurite outgrowth

Myelination 1* elimination

Modified from various sources inc: Andersen SL Neurosci & Biobehav Rev 2003 Rakic P Nat Rev Neurosci 2002

Bourgeois Acta Pediatr Suppl 422 1997 timeline 1 Synaptogenesis 100% * RTH

D BI

E

A

Density of synapses in T PUBERTY primary H at different post- 0% conception. 100%

(logarithmic scale) RTH Cat BI

D

E

A

T PUBERTY

H The density values equivalent 0% to 100% vary between 100% but in Man the peak value is Macaque 6 3 RTH

350 x10 synapses per mm BI

D

E PUBERTY

A

T

The peak rate of synapse H formation is at birth in the 0% macaque: extrapolating to 100% the entire cortex, this Man RTH BI amounts to around 800,000 D

E

synapses formed per sec. A PUBERTY

T

H 0% (Modified from Bourgeois, JP, 10 days 100 days 2.5 years 25 years Acta Pediatr Suppl. 422: 1997) synapse density Plasticity in the adult : phantom limbs.

Referred phantom hands

These phenomena could be explained if cortical afferents (blue) sprout new connections (red to occupy the vacated sensory field, but the timescale is too short. There may be more widespread (but latent) cortical connectivity than we are accustomed to believe.

Ramachandran Myelination continues through the 2nd decade in some regions There is evidence that cannot myelinate until they form synapses, so the schedule may reflect gradual acquisition of hard-wired status.

myelin schedule * 2. The : site of transfer of declarative from short term into long term storage in the .

Dentate : 1 of 2 significant sites of neuro genesis in the adult brain

Hippocampus

Dentate gyrus

hippocampus in the adult rat

2 million granule neurons in the adult rat

About 10,000 new granule neurons produced per day, ie, 0.5% of total.

New granule cells differentiate as proper neurons but only survive for about 1m. May compete for survival or have a specific transient role.

Rate of division enhanced by environment enrichment, activity & learning.

Reduced by stress & steroids and no doubt affected by hormones during puberty.

Sources include: Cameron & McKay, J Comp Neur 2001 Gould E, et al, 2001 Shors, TJ et al, Nature 2001 Monje M & Palmer T, Curr Op Neurol 2003 Modified from Cameron & McKay J Comp Neur 2001 rat dentate The mitotic dance in the early neuroepithelium: exponential growth

Cell numbers in Man: cerebral cortex 15 billion 70 billion other 5 billion

In the macaque, all cortical neurons are produced in 2 months between E40 & E100, during which the average rate of production is 3000.sec-1

Cell cycle ... 7hrs Early

neurogenesis 1 Later development: linear growth by unequal divisions producing 1 post-mitotic (dark blue) and 1 renewed (light blue)

2

ventricular 1 germinal zone

ventricle neurogenesis 2 Vascular niches in the hilus of the dentate gyrus support

Therapeutic cranial X-irradiation halts the production of neurons, but this is an inflammatory effect. Il-6 made by microglia switches the fate of the dividing stem cells from neurons to glia.

NORMAL STRESSED

new new granule microglia glioblasts stem cell

Sources include: Alvarez & Lim Neuron 2004 Kemperman & Neumann Science 2003 niches Childhood development of the CNS

At 9 months, the computer rolls off the production line apparently complete. We have a fair understanding of the mechanics of assembly, but very little idea of what happens while the software is installed during the ensuing 24 years. Stages in cognitive development have been defined,but we have almost no mechanistic understanding of what they entail.

Science can respond to social priorities. Much of what we know about the production line arose from shock at the consequences for the developing brain of foetal irradiation.

We now live in an age worried by problems with software installation in the young. Is there a single cause for their sometimes unwelcome behaviour? Something in the water? Big Macs? EMF?

I seriously doubt the latter, but we know so little about what goes on during installation that anything is possible.

homily

More than 90% of cortical neurons connect to other parts of the cortex: less than 10% connect with othe parts of the brain and the spinal cord

I remote excitatory connections II local excitatory collaterals

III Pyramidal local inhibitory connections cells IV 75%

V VI 25%

90% intracortical connections WM

10% connections to other parts of the CNS

cell types The adult complement of neurons is in place by birth

Peak synaptic density by 3 months

EMBRYONIC POSTNATAL

week: 0 6 12 18 24 30 36 Month: 0 6 12 18 24 30 36 Year: 4 8 12 16 20 24

Cell birth Migration * Neurite outgrowth Synaptogenesis Myelination * Synapse elimination

Modified from various sources inc: Andersen SL Neurosci & Biobehav Rev 2003 Rakic P Nat Rev Neurosci 2002

Bourgeois Acta Pediatr Suppl 422 1997 timeline 1. Pre-GD3 PDGFR development DM20 CNP

2. OPC/O2-A - local embryonic origin PDGFR DM20 CNP - migration and peak + GD-3 proliferation perinatally 3. Premyelinating oligodendrocyte DM20 - susceptible to CNP MBP perinatal stress and GalC irradiation in childhood and in adult 4.Myelinating oligodendrocyte DM20 + PLP CNP MBP

oligo 1