action potentials

neurons

nerve cells that are capable of initiating and conducting electrical activity throughout the body

• communication and control of body functions

neuroglia

cells that support neurons

dendrites

receive incoming signals

• passive, graded synaptic potentials

cell body

“integrates” multiple incoming signals via summation

axon

carries the output signal

• all-or-none action potential

action potentials

• active, self regenerating. 

• no decrement with distance (maintain same amplitude). 

• “all-or-none” brief (1 ma) fixed duration.

• depolarizing supra-threshold

graded potentials

• passive (electrotonic) like a cable. 

• degrade with distance and time. 

• variable amplitude and variable duration. 

• hyper or de polarizing sign

• sub-threshold

action potential (firing)

“all-or-none” wave of elevated potential that will result in some action on the part of the cell

• vesicle release, muscle contraction, signal propagation. 

Na+ channels have two gates:

• activation (open / close). 

• inactivation (block / unblock). 

Na+ channels open: 

• sodium flows IN

• cells depolarize

with positive voltage (Na+):

• Na channels activate fast

• Na channels inactivate slow

with negative voltage (Na+)

• Na channels de-activate fast

• Na channels un-inactivate slow

K+ channels have one gate:

activation (open / close)

K+ channels open:

• potassium flows out. 

• cell re-polarizes. 

with positive voltage (K+):

• K channels activate slow. 

• K channels DON’T inactivate

with negative voltage (K+):

K channels de-activate slow

trigger zone for action potential initiation

high density of voltage-gated sodium channels that trigger action potentials

• ultimate “output” of dendritic integration.