Post-tetanic potentiation is due to –
**Core Concept**
Post-tetanic potentiation (PTP) is a phenomenon where the amplitude of the post-tetanic response is greater than the sum of the individual twitches. This occurs due to an increase in the number of available release sites at the neuromuscular junction, leading to an increased release of acetylcholine (ACh) during subsequent stimuli.
**Why the Correct Answer is Right**
The underlying mechanism of PTP involves the depletion of readily releasable synaptic vesicles, which leads to an increase in the number of available release sites. This is due to the fusion of synaptic vesicles with the presynaptic membrane, making the vesicles unavailable for release. However, the remaining synaptic vesicles are still available for release, leading to an increased amplitude of the post-tetanic response. This process is mediated by the calcium channels at the presynaptic terminal, which facilitate the release of ACh.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the mechanism of post-tetanic potentiation.
* **Option B:** This option is incorrect because it does not specifically address the increase in available release sites at the neuromuscular junction.
* **Option C:** This option is incorrect because it does not accurately describe the role of calcium channels in the process of post-tetanic potentiation.
**Clinical Pearl / High-Yield Fact**
Post-tetanic potentiation is an important clinical phenomenon that can be observed in patients with neuromuscular junction disorders, such as myasthenia gravis. In these patients, the post-tetanic response may be exaggerated, leading to muscle weakness and fatigue.
**Correct Answer: D. Increased release of acetylcholine due to increased number of available release sites.**