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The Smooth Muscle

Table of Contents
The Lungs
The Trachea
The Testes
The Submaxillary Gland
The Liver
The Stomach and Duodenum
The Blood
The Arteries and Veins
The Adipose Tissue
The Skin
The Pituitary Gland
The Pancreas
The Thyroid
The Kidney
The Spinal Cord
The Cerebellum
The Elastic Cartilage
The Bone
The Smooth Muscle
The Striated Muscle


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Smooth muscle is the second type of muscle, and works to provide movement to the internal organs and the glands.


Unlike the skeletal muscles, they are controlled by involuntary nerve impulses, and can not be controlled by the conscious mind. They are also not built to perform quick, successive movements like the cardiac muscle, or support intense strain like the skeletal muscles, but instead provide continuous, controlled movement.


Unlike the cells of striated muscle, smooth muscle cells contain only one nucleus, and are tapered with a bulge in the center, as opposed to the long, cylindrical cells of the skeletal muscle.


These cells are organized into multi-layered sheets, and line the inside of the digestive organs, the organs of the excretory system, inside the iris of the eye, within the respiratory system, and within the glands of the body.


Many organs contain two layers of smooth muscle, one longitudal, running the length of the organ, and a second layer that runs circularly around the girth of the organ. This allows for the continual motion present in the action of smooth muscle.


Movement of the smooth muscle is controlled by nerve impulses and hormones, which cause the muscle to contract in much the same way skeletal muscle does.


However, individual nerves can not reach all the areas the smooth muscle in an organ, so one nerve impulse is often carried from one muscle cell to another, creating a wave of slow contraction along the organ.


The continual contraction and relaxation of the longitudal and circular layers of the smooth muscle in organs such as the small intestine and esophagus allow food to be pushed along the digestive tract, so nutrients can be absorbed in different areas, and wastes can be expelled outside of the body.

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