Smooth Muscle

A smooth Muscle is a non-striated muscle that is extremely important to function and control throughout the body. The portion of control of smooth muscle is done by the “autonomic nervous system” which allows for involuntarily control.

Involuntary control is one defining aspect of the muscle and is the primary portion that differs from some of the other types of muscle.

This means that you may not consciously control these types of muscles. Hormones may be released that can affect smooth muscles in some cases. This type of muscle can contract and relax.

Smooth muscle is one of the 3 main muscle structures of the human body.

The other two types of muscle are:

–  Cardiac Muscle
–  Skeletal Muscle

Smooth muscle is found in several areas such as:

–   Large arteries
–   Small arteries
–   Veins
–   Bladder
–   Respiratory tract
–   Gastrointestinal tract
–   Eyes (some aspects)
–   Uterus
–   Kidney
–   and others.

There is a large difference between all three different types of muscle.

There are 2 types of arrangements of muscle cells

1.)  Multi-unit

–  Multi Unit are specific fibers that are activated by a nerve fiber, usually its own.

–  They can be found to line the large airways and large blood vessels.

2.)  Single-unit

–  Single Unit is much more common and refers to the visceral aspect, because it is often found on the “viscera” (eternal organs) of the body including intestines.


A large portion, of the structure of smooth muscle is Myosin and Actin.

The action of these two allow the capability for contraction, this occurs through the tensile structures allow the entire muscle to contract.

1.)  Myoscin
  –  Two heavy chains – constitute the head and tail domains
  –  Each chain contain N-terminal
  –  Also a C-terminal takes on a coil appearance
–  This causes the structure of myosin to appear to be a two-headed snake wrapped around itself.

2.)  Actin

–  Is a thin filament that forms the contractile portion.
–  There is an α-actin (alpha-actin) type is the most common isoform and γ-
–  There are also lots of actin (mainly β-actin) that does not take part in the contraction


Smooth muscles have a single nucleus and several mitochondria

Within the cytoskeleton of proteins is myosin and actin are protein filament and this is the action process of the muscle.

However, smooth muscle does not contain troponin like skeletal and cardiac but rather calmodulin.

ATP continues to be very important for contraction of smooth muscles.

The function of smooth muscle is to maintain the dimensions and structure of organs and other areas.

When the organ may need to contract or function – smooth muscles allow for this function.