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