Chapter 32, Problem 37A

Summary Introduction

To predict:

The possible consequences of cardiac and smooth muscles had the same structure as skeletal muscle.

Introduction:

A muscle is a group of fibers that are bound together. There are three types of muscle: skeletal muscle, smooth muscle and cardiac muscle. Smooth muscle is called involuntary muscle because it cannot be controlled consciously. The lining of the esophagus, stomach and small and large intestines are made of smooth muscles. The involuntary muscle of the heart is called cardiac muscle. Most of the muscles of the body are skeletal muscles. These are voluntary muscles as their movements are controlled consciously.

Answer to Problem 37A

If cardiac and smooth muscles had the same structure as skeletal muscle, they would get tired soon and stop functioning. The heart and the digestive organs are made of involuntary muscles and if they have structures similar to skeletal muscles they would function as voluntary muscles. This would not allow them to contract continuously and rhythmically. After some time they would get fatigued and the heart would stop beating.

Explanation of Solution

Skeletal muscles are made of fibers that are arranged in antagonistic pairs. The contraction of the sarcomere (functional unit of muscle) causes contraction of the muscle. These are voluntary muscles that control the movement of bones. Smooth and cardiac muscles are involuntary muscles. Smooth muscle is non- striated and its involuntary contractions allow food to move through the digestive tract. Cardiac muscle cells are arranged in a network or web that allows the heart muscle to contract rhythmically.

If cardiac and smooth muscles had the same structure as skeletal muscle, they would contract only when a nerve impulse reaches the muscle. A heart muscle must contract continuously for it to function properly. If a cardiac muscle is similar to skeletal muscle, it would function as a voluntary muscle and would soon get tired. If we feel tired, we do not move our hands or legs but if we stop moving our heart muscles, it would be fatal. The same thing happens with the muscles of the digestive tract. The smooth muscles contract and relax involuntarily in order to facilitate the movement of food through food pipe but if they were made of skeletal muscles, this would be under our control which would make digestion difficult.

Moreover, muscle cells can metabolize aerobically and anaerobically. So if muscles of the heart and digestive tract are made of skeletal muscles, they would get fatigued due to lack of oxygen after strenuous activity. This would result in lactic acid build up in the muscles. This can be dangerous for the person.