Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

The Animal Self: Neurobehavioral Correlates 131

“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

Fig. 7.3. Diagram of an action potential with abscissa representing time course. (A)
Voltage change (measured inside the axon) from -70 (resting) to +30 (peak) millivolts,
then down to -80 before going back to the resting value. (B) Change in membrane
charge from inside negative (resting) to inside positive (result of sodium influx), which
returns to the resting stage following potassium efflux. The change from negative to
positive is called depolarization; the opposite, hyper-polarization. (C) Changes in sodium
and potassium permeability across axonal membrane corresponding to changes in poten-
tial. Note that while post-synaptic membrane potential changes take place in the den-
drites and cell body, action potential starts only at the axon hillock when local membrane
potential depolarizes to a threshold of about -50 millivolts. Once initiated, an action
potential propagates non-stop down to the axonal terminal.

of neurotransmitters from the nerve ending into the synaptic cleft,
and by the receipt of these messages by the specific receptors on the
post-synaptic membrane. Upon receiving the message, the post- synaptic
membrane produces a graded resting potential (not action potential)