Question

The most likely explanation for this patient's symptoms is a presynaptic deficiency. What is the likely cause of this deficiency?

1) Impairment of the voltage-sensitive Na⁺ channels responsible for the increase in cytosolic Na⁺ that triggers the release of ACh into the synapse
2) Impairment of the voltage-sensitive K⁺ channels responsible for the increase in cytosolic K⁺ that triggers the release of ACh into the synapse
3) Impairment of the voltage-sensitive Ca++ channels responsible for the increase in cytosolic Ca++ that triggers the release of ACh into the synapse
4) Impairment of the voltage-sensitive Cl⁻ channels responsible for the increase in cytosolic Cl⁻ that triggers the release of ACh into the synapse

Answer 1

A presynaptic deficiency causing a patient's symptoms is most likely due to the impairment of voltage-sensitive Ca++ channels that facilitate the release of ACh into the synapse.

Step-by-step explanation:

The most likely explanation for this patient's symptoms is a presynaptic deficiency caused by impairment of the voltage-sensitive Ca++ channels responsible for the increase in cytosolic Ca++ that triggers the release of Acetylcholine (ACh) into the synapse. This process is crucial for neurotransmitter release, which occurs when an action potential reaches the axon terminal, leading to the depolarization of the presynaptic membrane and consequent opening of these specific Ca++ channels. The influx of Ca++ ions into the neuron initiates a cascade that drives the fusion of synaptic vesicles with the presynaptic membrane, allowing for the release of neurotransmitters into the synaptic cleft.

Therefore, among the provided options, the correct cause of the deficiency is: 3) Impairment of the voltage-sensitive Ca++ channels responsible for the release of ACh into the synapse.