Define smooth muscle.

Smooth muscle is a type of muscle tissue that is involuntary and non-striated, meaning it does not have the striped appearance of skeletal muscle. Smooth muscle is found in the walls of hollow organs such as the intestines, blood vessels, and bladder, and is responsible for involuntary movements such as peristalsis and vasoconstriction.

Smooth muscle, also known as involuntary muscle, is a type of non-striated muscle tissue found in the walls of hollow organs such as the stomach, intestines, blood vessels, and uterus.

Characteristics of Smooth Muscle:

- Non-striated: Smooth muscle cells do not have the visible banding pattern (striations) characteristic of skeletal and cardiac muscle.
- Involuntary: Smooth muscle contractions are involuntary, meaning they are not consciously controlled.
- Spindle-shaped cells: Smooth muscle cells are elongated and spindle-shaped, with a central nucleus.
- Single nucleus: Smooth muscle cells contain a single nucleus, unlike skeletal and cardiac muscle cells which have multiple nuclei.
- Gap junctions: Smooth muscle cells are connected by gap junctions, which allow for the rapid spread of electrical impulses and synchronized contractions.
- Slow contractions: Smooth muscle contractions are relatively slow and sustained compared to those of skeletal and cardiac muscle.
- Plasticity: Smooth muscle can adapt to changes in its environment and alter its contraction patterns over time.
- Autonomic innervation: Smooth muscle is primarily innervated by the autonomic nervous system, which controls involuntary functions such as digestion and blood flow.

Smooth muscle plays a crucial role in maintaining homeostasis and performing involuntary actions necessary for various bodily functions, including:

- Regulating the flow of fluids and gases through hollow organs
- Controlling blood pressure and heart rate
- Moving substances through the digestive tract and urinary system
- Creating muscle tone in blood vessels, airways, and other organs