Sometimes you may have atrial flutter that develops into atrial fibrillation and vice versa. The risk factors for and the symptoms and causes of atrial flutter are similar to those of atrial fibrillation. For example, strokes are also a concern in someone with atrial flutter. As with atrial fibrillation, atrial flutter is usually not life-threatening when it's properly treated.
Nerves and Nerve Types. There three types of nerves in the central nervous system: motor neurons, sensory neurons and autonomic neurons. Motor nerves send impulses or signals from the brain and spinal cord to all of the muscles in the body.
Our bodies have three types of muscles: skeletal muscles, cardiac muscles and smooth muscles. Skeletal muscles are the muscles that increase and strengthen with exercise, cardiac muscles keep the heart beating and smooth muscles line the hollow or tube-like organs of the body.he cells in multi-unit muscles can function independently of each other, while the muscle cells of single-unit muscles work together as a unit. An example of multi-unit muscle cells are the cells that constrict or dilate the iris of the eye.