Start of Part 2 Eric W. Harris, PhD.

Here lies the brain (midine view) National Geographic Magazine, February 2014

Gray Matter, White Matter, Gyri, Lobes “White matter” (fiber tracts) “Gray matter” (cell bodies) Gyrus (infolding of cortex) Lobe (major infolding)

The Basic Subdivision of Cerebral Cortex

Some Functional Subdivisions of the Cerebral Cortex

Brodman Areas – the ultimate subdivision?

Under the hood – some pieces and parts… (connects the hemispheres ) (protect the brain)

The functional building block of the brain – the Neuron (“brain cell”) Santiago Ramon y Cajal (1852 – 1934) 4 – 100 microns ( x in., or – in.)

Validation for Cajal left: Cajal Legacy Instituto Cajal (CSIC), Madrid | right: Courtesy Thomas Deerink and Mark Ellisman (NCMIR, UCSD) 1906 Nobel Prize in Medicine and Physiology

Basic Structure of a Neuron Dendrites Axon ell body ~85 Billion neurons in the human brain

Important properties of neurons  Neurons have a negative “membrane potential” (i.e., inside negative vs. outside)  Most neurons have many (thousand) inputs that constantly change this “membrane potential”  Neurons will send a signal if they become sufficiently less negative (more positive, “depolarized”)  This signal starts is a wave of “positivity” that regeneratively propagates down the axon  Neurons can send signals quickly (~100 m/sec) to other neurons, muscles, glands etc.  Compared to other cells, neurons have high energy demands, and low energy reserves.  Neurons do not divide and replace themselves – if damaged enough to die, they are not replaced (with few exceptions).

Neuronal “Resting Membrane Potential” Voltage Display

Source of the Resting Membrane Potential  Specialized molecules pump ions into and out of the neuron (Na + out, K + in), yielding different concentrations of these ions inside vs. outside of the cell. In effect, the pump creates Na + and K + “batteries”. ( A big part of the energy demand)  Specialized channels allow more or less of these ions to flow in (or out) of the cell, in effect “dialing in” more or less of each “battery”  Other ions also contribute, so it’s not as simple as just Na+ and K+…

End of Part 2 See Part 3 for more