**Question:** Resting membrane potential of muscle fibre is

A. -80 mV
B. -60 mV
C. -90 mV
D. +50 mV

**Correct Answer:** -80 mV

**Core Concept:**

The resting membrane potential (RMP) is the potential difference across the cell membrane of a cell at rest, without any external stimulus. In the context of muscle fibres, it refers to the potential difference across the plasma membrane of a muscle fibre when it is not actively contracting. The RMP is crucial for muscle cell excitability and proper muscle function. In the case of muscle fibres, the RMP contributes to the overall electrical excitability of the muscle tissue.

**Why the Correct Answer is Right:**

The correct answer, -80 mV, represents the typical resting membrane potential of a muscle fibre. This value is typically found in both skeletal and cardiac muscle cells. A more negative membrane potential (lower millivolts) indicates a more hyperpolarized membrane, which generally enhances excitability. Conversely, a less negative membrane potential (higher millivolts) results in reduced excitability. In the case of muscle fibres, a more negative RMP allows for better muscle contraction initiation and propagation.

**Why Each Wrong Option is Incorrect:**

A resting membrane potential of -60 mV (Option B) is too depolarized compared to the correct value of -80 mV. This would result in reduced excitability and make muscle contraction less likely to occur.

A resting membrane potential of -90 mV (Option C) is even more depolarized than the correct value. This would make the muscle fibre membrane even less likely to initiate and propagate muscle contraction, potentially leading to muscle weakness and a reduced ability to contract.

An RMP of +50 mV (Option D) is highly depolarized, making the muscle fibre membrane less likely to initiate and propagate muscle contractions, leading to impaired muscle function and reduced contractility.

**Clinical Pearls:**

Understanding the resting membrane potential of muscle fibres is crucial for understanding muscle function, neuromuscular transmission, and muscle contraction. Adequate muscle contraction requires a proper resting membrane potential, which is achieved by proper membrane ionic balance and the presence of specific proteins, such as sodium and potassium channels, in the muscle fibre membrane. Impaired membrane potential can lead to muscular weakness, reduced contractility, and other muscle-related disorders.