- Mass of 1-2 kg in adult. so about 2% of body weight. Consumes 20%
of oxygen, 25% glucose, and 15% blood flow.
- Mass at birth = .2*Mass of adult brain.
Cortex (thinking part) has
Explosion in cortex size due to limited increase in genome length:
Cortex evolution is recent, about the last 3 million years.
cortex function:
- 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
=
. Surface area is axon dominated=
. - 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.
- new view: dendrites do some operations on input. Effective multiplication
of rapidly stimulated dendrite. Also an effective division.
- 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).
Power requirements
- Assume v pulses/second. Then
. Unmylenated axons have
. Membranes
have a dielectric constant of about 6.
source psfile jl@crush.caltech.edu index
brain_information