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Psychobiology: the phases of the action potential

• resting potential
the voltage-gated Na + channels and voltage-gated K + channels , concentrated in the axon mound and at the nodes of Ranvier, are closed. • Depolarization

membrane potential (Vm), did not exceed the threshold value . • The rising phase

exceeds the threshold some voltage-gated Na + channels begin to open further depolarizing the Vm. Other voltage-gated Na + channels with different sensitivity into action a chain until it reaches the potential to tip. • Potential
pointed
channels are sensitive to voltage and inactivate with a timer mechanism after about 1ms. Goes into much more than Na + and K + bait in this situation settles down in the Vm +50 mV. At this point, the threshold of action potentials, 1 ms later, the voltage-gated K + channels open. •
downturn
The cell repolarization is very fast because of concentration gradients of K + ions and electrical differences.
• Hyperpolarization
At this stage there are many channels open and K + hyperpolarized the cell and then is restored to-65mV. •
absolute refractory period
Vm returns to the rest but you can not new for less than 1 ms depolarization to a few ms.
This limits the discharge per second to about 500Hz. • Refractory Period on

At this stage some voltage-dependent Na + channels are inactive because they need a stronger than normal stimulus to trigger a new action potential. Determine a relationship between stimulation intensity and frequency of discharge. Some neurons have periods

refractory short, others have frequencies that change over time, others burst of refractory periods and longer.

conduction of action potentials in
axon mound rich in voltage-gated Na + channels, different electrical signals reach the cell and are integrated to give rise to the action potential. The signals can be excitatory or inhibitory . The first trigger the action potential.
Once unleashed begins to spread nell'assone unmyelinated, but not in elettrotonica because the cytoplasm is not a good conductor, opening voltage-dependent channels in step action potential actively. The speed is low.
Nell'assone myelinated, close to the myelin sheath, the signal can travel like a graded potential, which is a passive and almost instantaneous leakage current. The node of Ranvier, rich in voltage-gated Na + channels, riamplifica signal.