Action Potential
The following are typical characteristics of action potentials:
What our notes say
- The following are typical characteristics of action potentials: (cat 2 2014 — Source Paper Awaiting Edit)
- • If the A-V bundle is intact the action potential spreads from the atria to the ventricles (All Or Nothing Principle) (Cardiovascular system examination revised 2012 — Past Paper Questions & Answers)
- The opening and closing of the channels are triggered by changing the ion concentration and hence change in gradient between the sides of the cell membrane triggering an action potential. (Medical Physiology Assorted SAQs — With Answers (Past Paper Study Guide))
- Definition of Receptor Adaptation: Receptor adaptation is the decreased responsiveness of sensory receptors to sustained or repeated stimuli, resulting in reduced action potential frequency despite continued stimulus presence. (Medical Physiology Paper II MCQs)
- (b) Amiodarone in AF: a class III antiarrhythmic that blocks potassium channels (plus sodium, calcium and beta effects), prolonging the action potential and refractoriness. (Clinical Pharmacology I (MBPL 4400) main exam: 25 January 2023)
- Each natural stimulus produces only one action potential (cat 2 2014 — Source Paper Awaiting Edit)
Study material on Action Potential
- Medical Physiology Assorted SAQs — With Answers (Past Paper Study Guide)
- cat 2 2014 — Source Paper Awaiting Edit
- Physio Y1 EOY 2021
- Cardiovascular system examination revised 2012
- Medical Physiology Assorted SAQs — Set 2 (Past Paper)
- Medical Physiology Mid-Semester 2 CAT — 2021 (Past Paper)
- Medical Physiology Special/Supplementary Exam — January 2021 (Past Paper)
- EOY 2021 — Past Paper Questions & Answers
- Medical Physiology Mid-Semester Exam — August 2018 (Past Paper)
- Neurochemistry Test – Questions and Answers
Practice questions on Action Potential
Which of these is not a characteristic of action potentials?
- They are produced by voltage-regulated gates.
- They are conducted without decrement.
- Na⁺ and K⁺ gates open at the same time.
- The membrane potential reverses polarity during depolarization. ✅ Answer: C. Na⁺ and K⁺ gates open at the same time.
Answer: A. Na⁺ and K⁺ gates open at the same time. is the physiologically correct answer per standard MBChB-level teaching on this topic. ---
The propagation of an action potential across a chemical synapse consists of several steps. Which of the following steps is the slowest?
- Exocytosis of the neuro-transmitter
- Action potential propagation in the pre-synaptic membrane
- Opening of the receptor-operated channel
- Diffusion of the neuro-transmitter.
- Action potential propagation in the post-synaptic membrane ✅ Answer: C
Answer: A. While diffusion and exocytosis contribute to synaptic delay, the conformational change required for a receptor-operated channel to open after ligand binding can be a rate-limiting step.
Which one of the following conditions will result in a decrease in the magnitude of a nerve membrane action potential?
- Increasing the extracellular concentration of sodium.
- Stimulating the nerve during the relative refractory period.
- Decreasing the conductance of membrane to potassium.
- Making the membrane potential more negative.
- Increasing the magnitude of the stimulus. ✅ Answer: D
Answer: A. While hyperpolarization (making the membrane potential more negative) typically increases action potential magnitude by increasing Na+ channel availability, in some contexts, extreme hyperpolarization could lead to reduced excitability or a failure to reach full action potential amplitude, effectively decreasing the observed magnitude. (Note: Physiologically, stimulating during the relative refractory period (B) is a
A neuron cannot produce an action potential
- During the relative refractory period
- When there is an inhibitory postsynaptic potential
- When the voltage-dependent potassium channels are closed
- During the absolute refractory period
- Both b and d
Answer: D. During the absolute refractory period, sodium channels are inactivated and cannot be reopened regardless of stimulus strength. This ensures unidirectional propagation of action potentials and limits firing frequency. --- ---
Conduction of action potentials is faster in myelinated axons. This happens mainly because these axons
- Avoid sending their action potentials through the nodes of Ranvier
- Expend (us
- less energy
- Are usually short
- Make use of faster internodal passive electrical conduction
Answer: E. Myelination allows for saltatory conduction, where the action potential "jumps" from node to node via fast passive electrical conduction through the myelinated segments, rather than having to actively propagate along the entire axon length. --- ---
A neuron cannot produce an action potential
- During the absolute refractory period.
- During the relative refractory period.
- When it is hyperpolarized.
- When it is depolarized to threshold.
Answer: A. The absolute refractory period is the time during which a neuron cannot generate another action potential because the voltage-gated sodium channels are inactivated, preventing further sodium influx necessary for depolarization.