Question

Which is not the correct difference between white and red muscle fibres? \(\begin{array}{ll}\text { White muscle fibre } & \text { Red muscle fibre }\end{array}\) 1\. Less myoglobin \(-\) 1. More myglobin 2\. Number of mitochondria is less \- 2. Number of mitochondria is more 3\. Amount of sarcoplasmic reticulum is low \(-3\). Amount of sarcoplasmic reticulum is high 4\. Aerobic muscle \(-4\). Anaerobic muscle (a) 1 (b) 2 (c) 3 (d) 4

Short answer

The incorrect pair is 'White muscle fibres are aerobic muscle - Red muscle fibres are anaerobic muscle', making the answer (d) 4.

Step-by-step solution

Identify the Statements

First, examine all four statements. Each one presents a pair of opposites between white and red muscle fibers.

Verify the Statements

Now, check each pair of statements with what you know about white and red muscle fibers. Remember that white muscle fibers are fast-twitch, have fewer mitochondria, and less myoglobin than red muscle fibers, which are slow-twitch. Also, the amount of sarcoplasmic reticulum may be different in both types of muscle fibers. Lastly, consider the difference between aerobic and anaerobic muscles.

Identify the Incorrect Statement

After examining each pair of statements, identify the incorrect one. The incorrect pair is 'White muscle fibres are aerobic muscle - Red muscle fibres are anaerobic muscle'. This is because it's the other way around - red muscle fibers are associated with aerobic processes while white muscle fibers are related to anaerobic processes due to their differences in content of mitochondria and myoglobin.

Key concepts

Myoglobin Content in Muscle Fibers

Understanding myoglobin content in muscles is crucial for comprehending how muscles store and utilize oxygen. Myoglobin is a protein in muscle cells that binds oxygen, somewhat similar to hemoglobin in the blood.

Red muscle fibers are rich in myoglobin, giving them their characteristic hue and allowing them to sustain aerobic activity for extended periods by using oxygen efficiently. This is why red muscles are often associated with endurance. On the other hand, white muscle fibers contain less myoglobin, which is why they fatigue more quickly but are able to produce quick, powerful bursts of speed. The myoglobin acts as an oxygen reservoir that ensures a steady supply for aerobic respiration, even when blood oxygen levels might be low.

Think of red fibers as marathon runners with consistent pace and endurance, while white fibers are like sprinters relying on explosive energy for short durations. Misunderstanding this concept might lead you to the wrong assumption in comparing the oxygenation characteristics between the fiber types.

Mitochondria in Muscle Cells

Moving on to the role of mitochondria in muscle cells, these organelles are often referred to as the 'powerhouses' of the cell. They generate the majority of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.

Red muscle fibers are equipped with a higher number of mitochondria. This abundance is what contributes to their aerobic capacity, allowing for the production of energy through oxidation of nutrients in the presence of oxygen. Intense endurance training can even increase the number of mitochondria in these muscle cells, further boosting their efficiency at aerobic respiration.

Conversely, white muscle fibers have fewer mitochondria, leading to a preference for anaerobic respiration. They generate ATP quickly through glycolysis, which does not require oxygen but leads to the faster accumulation of lactic acid and subsequent muscle fatigue. This difference in mitochondria content is a key distinguishing factor in muscle fiber functionality and performance.

Sarcoplasmic Reticulum in Muscle Fibers

The sarcoplasmic reticulum (SR) plays a paramount role in muscle contraction. It is a specialized form of the endoplasmic reticulum found in muscle cells, and it stores calcium ions (Ca²⁺). During muscle contraction, the SR releases Ca²⁺, which is necessary for the contractile proteins to interact and produce tension.

Red muscle fibers tend to have a less extensive SR compared to white fibers. Since red fibers contract more slowly and rely on aerobic respiration, the demand for rapid calcium release is lower. In contrast, white fibers require a quick and powerful contraction, thus having a more developed sarcoplasmic reticulum to rapidly mobilize Ca²⁺ for faster contraction cycles.

It's a common misconception to understate the importance of the sarcoplasmic reticulum in distinguishing the properties of different muscle fibers, which can lead to errors in understanding muscle physiology.

Aerobic vs Anaerobic Muscles

Lastly, the comparison of aerobic vs anaerobic muscles brings us back to the fundamental difference between red and white muscle fibers. Aerobic muscles, like red fibers, rely on the presence of oxygen to generate ATP. They are designed for sustained, long-duration activities such as distance running or cycling.

Aerobic muscles maximize energy production through oxidative phosphorylation, a process heavily dependent on myoglobin and mitochondria. Anaerobic muscles, which include white fibers, are structured to excel in short bursts of high-intensity activity where oxygen is scarce. They quickly generate energy through processes like glycolysis.

Confusing these two types, as seen in the initial exercise, is a critical error. Red muscle fibers are intrinsically aerobic, while white muscle fibers are anaerobic. Recognizing this association aids in understanding muscular responses to different physical demands and exercise types.