To determine which statement about graded potentials is not true, let’s examine each option:
- a) They are short lived: This statement is true. Graded potentials are transient changes in membrane potential that diminish over time and distance.
- b) They can live on receptor endings: This statement is also true. Graded potentials occur at receptor endings and can initiate an action potential if the threshold is reached.
- c) They can be called postsynaptic potentials: This statement is true. Graded potentials that occur in postsynaptic neurons in response to neurotransmitter release are indeed called postsynaptic potentials.
- d) They increase amplitude as they move away from the stimulus point: This statement is not true. Graded potentials decrease in amplitude as they propagate away from the stimulus point due to the passive nature of their spread.
Therefore, the answer is d) they increase amplitude as they move away from the stimulus point. Graded potentials diminish over distance, contrasting the statement that they increase.