Myogenic
Encyclopedia
Myogenic contraction refers to a contraction
initiated by the myocyte
cell itself instead of an outside occurrence or stimulus such as nerve innervation.
have resting membrane potentials that are unstable. This instability is usually due to ion channels in the cell membrane
that spontaneously open and close (e.g. If channels
in cardiac pacemaker
cells). When the membrane potential
reaches depolarization threshold an action potential
(AP) is fired, excitation-contraction coupling
initiates and the myocyte
contracts.
are unstable resting membrane potentials that continuously cycle through depolarization
- and repolarization
phases. However, not every cycle reaches depolarization threshold and thus an action potential
(AP) will not always fire. Owing to temporal summation (depolarization
potentials spaced closely together in time so that they summate), however, cell membrane depolarization will periodically reach depolarization threshold and an action potential
will fire, triggering contraction of the myocyte
.
s are unstable cell membrane potentials that reach depolarization threshold with every depolarization
/repolarization
cycle. This results in AP's
being fired according to a set rhythm. Cardiac pacemaker
cells, a type of cardiac myocyte in the SA node of heart, are an example of cells with a pacemaker potential
.
s are stretched. The resulting influx of Ca2+ ions lead to the initiation of excitation-contraction coupling
and thus contraction
of the myocyte.
Action potential
Excitation-contraction coupling
Myogenic mechanism
(Myogenic reflex)
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
initiated by the myocyte
Myocyte
A myocyte is the type of cell found in muscles. They arise from myoblasts.Each myocyte contains myofibrils, which are long, long chains of sarcomeres, the contractile units of the cell....
cell itself instead of an outside occurrence or stimulus such as nerve innervation.
Unstable Membrane Potentials
Many cellsCell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
have resting membrane potentials that are unstable. This instability is usually due to ion channels in the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
that spontaneously open and close (e.g. If channels
Funny current
Funny current refers to a specific current in the heart....
in cardiac pacemaker
Cardiac pacemaker
right|thumb|350px|Image showing the cardiac pacemaker which is the SA nodeThe contraction of heart muscle in all animals with hearts is initiated by chemical impulses. The rate at which these impulses fire controls the heart rate...
cells). When the membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
reaches depolarization threshold an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
(AP) is fired, excitation-contraction coupling
Excitation-contraction coupling
Excitation-contraction coupling is a term coined in 1952 to describe the physiological process of converting an electrical stimulus to a mechanical response . This process is fundamental to muscle physiology, whereby the electrical stimulus is usually an action potential and the mechanical...
initiates and the myocyte
Myocyte
A myocyte is the type of cell found in muscles. They arise from myoblasts.Each myocyte contains myofibrils, which are long, long chains of sarcomeres, the contractile units of the cell....
contracts.
Slow wave potentials
Slow wave potentialSlow wave potential
In physiology, a slow-wave potential is a membrane potential that cycles between depolarizations and repolarizations. Slow wave potentials are generated by myocytes. Due to temporal summation, a slow-wave potential will periodically reach threshold and generate an action potential. This in turn...
are unstable resting membrane potentials that continuously cycle through depolarization
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
- and repolarization
Repolarization
In neuroscience, repolarization refers to the change in membrane potential that returns the membrane potential to a negative value after the depolarization phase of an action potential has just previously changed the membrane potential to a positive value. Repolarization results from the movement...
phases. However, not every cycle reaches depolarization threshold and thus an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
(AP) will not always fire. Owing to temporal summation (depolarization
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
potentials spaced closely together in time so that they summate), however, cell membrane depolarization will periodically reach depolarization threshold and an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
will fire, triggering contraction of the myocyte
Myocyte
A myocyte is the type of cell found in muscles. They arise from myoblasts.Each myocyte contains myofibrils, which are long, long chains of sarcomeres, the contractile units of the cell....
.
Pacemaker potentials
Pacemaker potentialPacemaker potential
In the pacemaking cells of the heart , the pacemaker potential is the slow, positive increase in voltage across the cell's membrane that occurs between the end of one action potential and the beginning of the next action potential...
s are unstable cell membrane potentials that reach depolarization threshold with every depolarization
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
/repolarization
Repolarization
In neuroscience, repolarization refers to the change in membrane potential that returns the membrane potential to a negative value after the depolarization phase of an action potential has just previously changed the membrane potential to a positive value. Repolarization results from the movement...
cycle. This results in AP's
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
being fired according to a set rhythm. Cardiac pacemaker
Cardiac pacemaker
right|thumb|350px|Image showing the cardiac pacemaker which is the SA nodeThe contraction of heart muscle in all animals with hearts is initiated by chemical impulses. The rate at which these impulses fire controls the heart rate...
cells, a type of cardiac myocyte in the SA node of heart, are an example of cells with a pacemaker potential
Pacemaker potential
In the pacemaking cells of the heart , the pacemaker potential is the slow, positive increase in voltage across the cell's membrane that occurs between the end of one action potential and the beginning of the next action potential...
.
Stretch
This mechanism involves the opening of mechanically-gated Ca2+ channels when some myocyteMyocyte
A myocyte is the type of cell found in muscles. They arise from myoblasts.Each myocyte contains myofibrils, which are long, long chains of sarcomeres, the contractile units of the cell....
s are stretched. The resulting influx of Ca2+ ions lead to the initiation of excitation-contraction coupling
Excitation-contraction coupling
Excitation-contraction coupling is a term coined in 1952 to describe the physiological process of converting an electrical stimulus to a mechanical response . This process is fundamental to muscle physiology, whereby the electrical stimulus is usually an action potential and the mechanical...
and thus contraction
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
of the myocyte.
See also
Membrane potentialMembrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
Action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
Excitation-contraction coupling
Excitation-contraction coupling
Excitation-contraction coupling is a term coined in 1952 to describe the physiological process of converting an electrical stimulus to a mechanical response . This process is fundamental to muscle physiology, whereby the electrical stimulus is usually an action potential and the mechanical...
Myogenic mechanism
Myogenic mechanism
The myogenic mechanism is how arteries and arterioles react to an increase or decrease of blood pressure to keep the blood flow within the blood vessel constant....
(Myogenic reflex)