Which of the follow statements about action potentials are true?
I) A neuron’s resting potential is -55 mV.
II) An all-or-nothing response means once the threshold is reached, the action potential will fire.
III) The refractory period means there is a time where the neuron can’t fire.

• A. I & II only.
• B. I & III only.
• C. II & III only.
• D. I, II, & III.

Answer: (C)

Verified step by step guidance

1. Understand the concept of a neuron's resting potential: A typical neuron's resting potential is around -70 mV, not -55 mV. This is the electrical charge difference across the neuron's membrane when it is not actively sending a signal.
2. Examine the all-or-nothing response: This principle states that once the threshold potential is reached (usually around -55 mV), the neuron will fire an action potential. This is a true statement.
3. Consider the refractory period: This is the time after an action potential during which a neuron is unable to fire another action potential. This is also a true statement.
4. Evaluate statement I: Since the resting potential is not -55 mV, statement I is false.
5. Determine the correct combination: Based on the analysis, statements II and III are true, making the correct answer 'II & III only.'