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\begin{document}

\begin{itemize}

\item Mass of 1-2 kg in adult. so about 2\% of body weight. Consumes 20\%
of oxygen, 25\% glucose, and 15\% blood flow.

\item Mass at birth = .2*Mass of adult brain. 

\end{itemize}

Cortex (thinking part) has 

\begin{itemize}

\item \( 5cm^{2} \) for rat

\item \( 5*10^{2}cm^{2} \) for chimps

\item \( 2*10^{3}cm^{2} \) for humans. about 1mm depth. \( \sim 3*10^{10}neurons \) in cortex. About \( 10^{14}synapses \) in human cortex.

\item Human genome is about 1 meter of DNA with 1 base pair/3.8 Angstroms.
so \( 2.5*10^{9}basepairs \) about 2 bits/base pair so \( 5*10^{9}bits \). Maximum. (actually there is alot
of redundancy). So memory can't be stored in DNA.

\item Cortex develops in response to stimulus.

\end{itemize}

Explosion in cortex size due to limited increase in genome length:

\begin{itemize}

\item fruit fly: 4 cm, \( 10^{5} \)neurons

\item chicken: 40cm 

\item mouse: 1m, \( 5*10^{6} \)neurons

\item human \( 10^{11} \)neurons

\end{itemize}

Cortex evolution is recent, about the last 3 million years.

cortex function:

\begin{itemize}

\item neuron components: cell body\~{}20 micron diameter, axon 1 micron radius,
2 cm long, dendrites 1 micron radius 2 mm long. So total axon length
= \( 10^{11}cm \). Surface area is axon dominated=\( 6*10^{7}cm^{2} \).

\item old view: axons = output devices (electrically active), dendrites
= input devices (electrically passive). Pulse length of 1 msec in
axon. Frequency varies alot. Pulse strength of about .1 volts.

\item new view: dendrites do some operations on input. Effective multiplication
of rapidly stimulated dendrite. Also an effective division.

\item synapses connect axons to dendrites. Distance of 50 angstroms across
junction. = about .1 msec to cross. Connections can be excitatory
(glutamate=MSG) or inhibitory (gaba).

\end{itemize}

Power requirements

\begin{itemize}

\item Assume v pulses/second. Then \( P\simeq \frac{C}{A}\frac{(\triangle V)^{2}}{2}Av\sim .5\nu watts \). Unmylenated axons have \( \frac{C}{A}\simeq \frac{\mu farad}{cm^{2}} \). Membranes
have a dielectric constant of about 6. 

\end{itemize}

\end{document}
