-Ions will achieve its own equilibrium potential and summed together they will
amount to the resting potential (cells background state)
-If the interior of a neuron is made to have a greater positive charge than the resting
potential the membrane will depolarize
-Similarly the application of an increased negative charge within the cell will result in
membrane hyper polarization.
- Depolarizations tend to be excitatory in nature, stimulating activity in the neuron,
whereas hyperpolarizations tend to be inhibitory
-If the charge change related to a depolarization is sufficiently large, a very particular
electrical phenomenon called a spike (an action potential)will be triggered
-Action potential: when a small pulse of positive current is injected into a neuron, small
depolarizations are produced. Once threshold is achieved, an action potential is generated.
The different phases of the action potential are the resting potential, rising phase,
overshoot, falling phase, undershoot
-sometimes a single postsynaptic potential (PSP) is enough to induce a spike, but often the
combined effect of a number them is required.
-Some nerve cells exhibit a phenomenon termed summation whereby a series of small
PSPs coming from one or a number of sources have an additive effect. Their individual
charges are summed to achieve the threshold required for spike production.
-Other cells require a series of PSPs that rather than being added together each elicit a
slightly larger PSP than themselves until the action potential threshold is reached. This
phenomenon is termed Synaptic facilitation.
-The spike lasts for just one or two milliseconds, but can move along an axon at speeds in
excess of 100 m/s
-Once the depolarization of the cell membrane reaches the action potential threshold gates
in the membrane open, allowing Na+ to enter the cell, increasing the measured voltage very
rapidly. The increasing Na+ conductance is followed by an increase in K+ conductance out of
the cell as an attempt is made to return to equilibrium. The Na+ gates now begin to close
(termed Na+ inactivation) and the measured voltage begins to fall. It falls below the resting