Smooth Muscle

Human anatomy > Autonomic Nervous System > Smooth Muscle

The smooth muscle cells are characterized by a single nucleus and a spindle-shaped figure. They are also non-striated and have no organized myofilaments. They are designed to contract simultaneously because of their organized muscle layers that are closely interconnected to each other.

Functions of the Smooth Muscles

The smooth muscles have several important functions. The most important is the ability to compress, contract or extend ducts, organs, tubes and sacs. As such, smooth muscles are found primarily in the heart, digestive tract and the stomach. The stomach contains the circular smooth layer inside and the longitudinal smooth layer outside. These two layers help in the proper digestion and metabolism of ingested foodstuffs taken in by the body. 

Smooth Muscle Cell

Smooth muscles are one of the major factors why proper heart function occurs. Without the smooth muscles, the heart will not be able to contract, relax and pump blood to the rest of the body.

Due to the elasticity of the smooth muscles, it is an important component of the kidneys, lungs, vagina, and blood vessels. These body parts need to be elastic to perform their functions. You can imagine what can happen if these were not elastic. The kidneys will not be able to control micturation when the limited space for urine is filled up. The lungs could not expand after inhalation, so you will not be able to exhale. The vagina will not be able to adjust to the size of the penis, and the blood vessels would burst during increased pressure because it could not expand its lumen to accommodate the increased input. These are some of the many functions of smooth muscles.

Difference from Skeletal Muscles

While skeletal muscles are predominant, the smooth muscles are found in certain areas of the body. They are slower to react to stimuli than the skeletal muscles. The smooth muscles are controlled involuntarily, while the skeletal muscles are controlled voluntarily. The skeletal muscles have no autorhythmicity, while the smooth muscles have this characteristic. While the skeletal muscles are attached to the bones, the smooth muscles are found in the walls of hollow organs, glands and arteries or veins.

Autorhythmicity of the Smooth Muscle

This involves its periodic spontaneous contraction resulting from the fluctuation of the depolarization and repolarization of the smooth muscles’ action potential. Depolarization is the process wherein a reduction occurs between the difference of the charges inside and outside of the cell. Repolarization is the opposite process. A gap junction between cells facilitates the authorhythmicity of the action of smooth muscles.

Cardiac Muscles

One specific example for smooth muscles are the cardiac muscles. Although the cardiac muscles contain characteristics of both the skeletal and smooth muscles, it still demonstrates how smooth muscles perform. Just like smooth muscles, cardiac muscles have a single nucleus for each cell. The myofilaments are not uniformly arranged, thereby giving a striated appearance.  

Smooth muscles, together with the skeletal and cardiac muscles, are important components of the body. Without them, your organ systems would fail. This would lead to organ failure, coma and eventual death.

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