THE MUSCULOSKELETAL
SYSTEM
,• Muscle is one of the four primary tissue types of the body, and the body
contains three types of muscle tissue: skeletal, cardiac, and smooth
muscle.
• All three muscle tissues have some properties in common; they all
exhibit a quality called excitability as their plasma membranes can
change their electrical states (from polarized to depolarized) and send an
action potential along the entire length of the membrane.
• While the nervous system can influence the excitability of cardiac and
smooth muscle to some degree, skeletal muscle completely depends on
signalling from the nervous system to work properly.
• On the other hand, both cardiac muscle and smooth muscle can respond
to other stimuli, such as hormones and local stimuli.
• The process of contracting occurs when actin filaments are pulled by
myosin filaments.
,• This occurs in striated muscle (skeletal and cardiac) after specific binding sites
on the actin have been exposed in response to the interaction between calcium
ions (Ca2+) and proteins (troponin and tropomyosin) that “shield” the actin
binding sites.
• Ca2+ also is required for the contraction of smooth muscle, although its role is
different: here Ca2+ activates enzymes, which in turn activate myosin heads.
• All muscles require adenosine triphosphate (ATP) to continue the process of
contracting, and they all relax when the Ca2+ is removed and the actin-binding
sites are re-shielded.
• Muscle elasticity refers to its ability to return to its original state when relaxed,
a feature possible due to elastic fibers.
• Extensibility means it can stretch, while contractility refers to the ability to pull
on attachment points and shorten with force.
• The actin and myosin proteins are arranged very regularly in the cytoplasm of
individual muscle cells in both skeletal muscle and cardiac muscle, which
creates a pattern, or stripes, called striations.
, • Skeletal muscle fibers are multinucleated structures that compose the
skeletal muscle.
• Cardiac muscle fibers each have one to two nuclei and are physically and
electrically connected to each other so that the entire heart contracts as
one unit (called a syncytium).
• Because the actin and myosin are not arranged in such regular fashion in
smooth muscle, the mononuclear cytoplasm of a smooth muscle fiber
has a uniform, nonstriated appearance, resulting in the name smooth
muscle.
• Smooth muscle in the walls of arteries is a critical component that
regulates blood pressure, and smooth muscle in the skin, visceral organs,
and internal passageways is essential for moving all materials through
the body.
SYSTEM
,• Muscle is one of the four primary tissue types of the body, and the body
contains three types of muscle tissue: skeletal, cardiac, and smooth
muscle.
• All three muscle tissues have some properties in common; they all
exhibit a quality called excitability as their plasma membranes can
change their electrical states (from polarized to depolarized) and send an
action potential along the entire length of the membrane.
• While the nervous system can influence the excitability of cardiac and
smooth muscle to some degree, skeletal muscle completely depends on
signalling from the nervous system to work properly.
• On the other hand, both cardiac muscle and smooth muscle can respond
to other stimuli, such as hormones and local stimuli.
• The process of contracting occurs when actin filaments are pulled by
myosin filaments.
,• This occurs in striated muscle (skeletal and cardiac) after specific binding sites
on the actin have been exposed in response to the interaction between calcium
ions (Ca2+) and proteins (troponin and tropomyosin) that “shield” the actin
binding sites.
• Ca2+ also is required for the contraction of smooth muscle, although its role is
different: here Ca2+ activates enzymes, which in turn activate myosin heads.
• All muscles require adenosine triphosphate (ATP) to continue the process of
contracting, and they all relax when the Ca2+ is removed and the actin-binding
sites are re-shielded.
• Muscle elasticity refers to its ability to return to its original state when relaxed,
a feature possible due to elastic fibers.
• Extensibility means it can stretch, while contractility refers to the ability to pull
on attachment points and shorten with force.
• The actin and myosin proteins are arranged very regularly in the cytoplasm of
individual muscle cells in both skeletal muscle and cardiac muscle, which
creates a pattern, or stripes, called striations.
, • Skeletal muscle fibers are multinucleated structures that compose the
skeletal muscle.
• Cardiac muscle fibers each have one to two nuclei and are physically and
electrically connected to each other so that the entire heart contracts as
one unit (called a syncytium).
• Because the actin and myosin are not arranged in such regular fashion in
smooth muscle, the mononuclear cytoplasm of a smooth muscle fiber
has a uniform, nonstriated appearance, resulting in the name smooth
muscle.
• Smooth muscle in the walls of arteries is a critical component that
regulates blood pressure, and smooth muscle in the skin, visceral organs,
and internal passageways is essential for moving all materials through
the body.
