**Question:** RMP of smooth muscle is

A. -30 mV
B. -70 mV
C. -40 mV
D. -50 mV

**Core Concept:**

The resting membrane potential (RMP) of smooth muscle cells plays a crucial role in determining the excitability and contraction of the muscle. In physiological conditions, the RMP is typically between -40 mV and -60 mV, depending on the type of smooth muscle, with a more negative value indicating higher excitability.

**Why the Correct Answer is Right:**

The correct answer, -70 mV, represents the RMP of a specific type of smooth muscle, specifically the gastrointestinal tract smooth muscle. The gastrointestinal tract smooth muscle tends to have a more negative RMP due to the presence of hyperpolarizing potassium channels (K+ channels) and the absence of depolarizing sodium channels (Na+ channels). This results in a more stable resting membrane potential and increased excitability, allowing for rapid and robust contractions during digestion.

**Why Each Wrong Option is Incorrect:**

A. -30 mV is too depolarized and would result in low excitability and poor contraction in smooth muscle.
C. -40 mV is slightly depolarized compared to the correct answer (-70 mV) and may lead to reduced excitability and contraction.
D. -50 mV is also depolarized, similar to option A, and would not be suitable for smooth muscle contraction.

**Why the Correct Answer is Right:**

The resting membrane potential of smooth muscle is crucial for maintaining the muscle's excitability and readiness to contract. A more negative membrane potential, as seen in option D (-70 mV), ensures that the membrane is well-protected against depolarization, allowing for efficient and timely contraction when required.

**Why Each Wrong Option is Incorrect:**

A. A more positive membrane potential (-30 mV) would cause the membrane to be less resistant to depolarization, leading to reduced smooth muscle contraction efficiency.
C. A membrane potential closer to the correct answer (-40 mV) would be less effective in protecting the membrane against depolarization, potentially compromising muscle contraction.
D. A more negative membrane potential (-50 mV) is similar to option C and would also result in reduced efficiency of smooth muscle contraction.

**Clinical Relevance:**

Understanding the resting membrane potential and its influence on smooth muscle excitability is essential in medical practice, particularly for diagnosing and treating disorders of smooth muscle contraction, such as those seen in gastrointestinal disorders, respiratory muscle weakness, and cardiovascular diseases.

**Why Each Wrong Option is Incorrect:**

A. A membrane potential closer to the correct answer (-40 mV) would be less effective in protecting the membrane against depolarization, potentially compromising muscle contraction.
C. A membrane potential closer to the correct answer (-40 mV) would be less effective in protecting the membrane against depolarization, potentially compromising muscle contraction.
D. A more negative membrane potential (-50 mV) is similar to option C and would