The muscles that move the skeleton are ones that we can move at will. They are called voluntary muscles. Among them are the ones that move the eyes, tongue, soft plate and the upper part of the gullet.
They are muscles in the body that we cannot move at will. These are called involuntary muscles. This type of muscle is found in the walls of veins and arteries, stomach, intestines, gall bladder the lower parts of the throat and in several other internal organs. Thousands of tiny involuntary muscles in the skin move the hair. When you are chilled or frightened and have goose flesh, or goose pimples, the little lumps on your skin are due to the tiny muscles in the skin pulling your hairs erect.
The eye provides a good distinction between voluntary and involuntary muscles. Voluntary muscles enable you to control the movements of your eye, in order to look in the direction you wish. However, you cannot control that widens and narrows the pupil of your eye. This muscle is involuntary. But the distinction between voluntary and involuntary muscles does not always hold true. For instance, when you shiver with cold or fright, the muscles that shake your body are voluntary muscles. Ordinarily, you can control these muscles, but, when shievering,you have no control over either starting or stopping the action of these muscles. They act if they were involuntary. Certain circus performers can swallow various objects and then at will bring them up without difficulty. These performers have learned to control their involuntary stomach and throat muscles, as though they were voluntary muscles.
