For each of the electrical potentials A–E, select the best option for a possible description from the following list

A. Option 4 All or none-propagated potentials in excitable tissues. Action potentials travel as a wave of reversed polarity caused by an initial increase in membrane perme-ability to sodium followed by a slower increase in membrane permeability to potassium.

B. Option 2 The voltage gradient between the inside and the outside of a cell. This poten-tial is maintained actively by metabolic processes and disappears if these processes are poisoned. Resting membrane potentials range from about 60 to about 90 millivolts, negative inside with respect to outside.

C. Option 5 The graded, non-propagated potential changes seen in sensory end organs. When a stimulus is applied to a sensory end organ it causes a non-propagated depolariza-tion whose size is related to the strength of the stimulus. When the generator potential reaches the threshold for firing, it gives rise to an action potential that travels along the axon away from the end organ.

D. Option 3 The unstable membrane potentials seen in smooth and cardiac muscle. The membranes of pacemaker cells show an unstable membrane potential that falls spontane-ously until it reaches the threshold for firing when it gives rise to one or more propagated action potentials.

E. Option 1 The graded, non-propagated potential changes across cell membranes induced by neurotransmitter substances. When an impulse reaches the terminal processes of a pre-synaptic nerve, it causes neurotransmitter to be released that induces post-synaptic potentials in the post-synaptic neurone. When the potential reaches the thresh-old for firing in the post-synaptic nerve an action potential is induced that travels over the entire membrane of the post-synaptic cell.