Magnesium is a Muscle Relaxant
Muscles 101
The function of muscles is to produce force and
cause motion. Either as locomotion of the organism
itself or movement of internal organs.
There are three classifications:
- Skeletal muscle.
Anchored by tendons to bone to effect skeletal movement, such
as locomotion or posture
- Cardiac muscle.
Found only in the heart; responsible for pumping blood; similar to
skeletal muscle
- Smooth muscle.
Found within walls of organs/structures such as esophagus, stomach,
intestines, bronchi, uterus, urethra, bladder, blood vessels; responsible for sustained
contractions.
When referring to the muscular system, "contraction"
means that muscle fibers generate tension with the help of motor neurons.
We use our muscles by selectively contracting them via:
- Voluntary
(conscious)
contraction of skeletal muscle (controlled by
action potential signals from the central nervous system ) .
E.g. movement of quadriceps muscle to kick a ball, or eye
movement occurs as a result of conscious effort originating
in the brain . The brain sends action potential signals
through the nervous system to the motor neuron that innervates several muscle fibers.
In the case of some reflexes, the signal to contract can originate in the spinal
cord through a feedback loop with the brain's grey matter.
- Involuntary
(without conscious thought) contraction of cardiac or smooth
muscle (non-conscious brain activity or stimuli from the body to the muscle ).
Necessary for survival.
E.g. contraction of the heart muscle for heartbeat,
peristalsis (pushes food through GI tract)
Calcium pumps move calcium powered by
ATP produced by magnesium-dependent
Na/K pumps
Plasma membrane Ca2+ -ATPase (PMCA)
pump moves calcium into and out of all eukaryote
(nucleus-containing) cells. Ca2+ is an important
second messenger (relays messages from membrane receptors to intracellular
targets), so intracellular levels must be maintained at low concentrations to prevent
noise, in order to have messages delivered properly (called cell signaling).
- PMCA
and the sodium calcium exchanger (NCX)
are the main regulators of intracellular Ca2+ concentrations.
Since PMCA transports Ca2+ into the extracellular space, it is also
an important regulator of the calcium concentration in the extracellular space.
- The PMCA pumps
are powered by the hydrolysis of Mg-dependent
ATP (One Ca 2+ ion removed for each molecule
of ATP hydrolysed).
PMCA binds tightly to (has high
affinity for) Ca2+ ions but does not remove Ca2+ at a
very fast rate, and is well-suited for maintaining Ca2+ at its normally very low
levels. In contrast, NCX has a low affinity, but a high capacity and is thus better
suited for removing large amounts of Ca2+ quickly, as is needed
in neurons after an action potential
Sarcoplasmic reticulum Ca2+ -ATPase
(SERCA) pump. in muscle cells
-The
SERCA
pumps
are powered by the hydrolysis of Mg-dependent
ATP
Magnesium roles in contraction/relaxation of muscle
The Mg-dependent Na/K pumps maintain appropriate
intracellular/extracellular potassium/sodium ion concentrations
The electrical action potential signal in a muscle
cell to initiate a contraction involves complex movement of sodium
and calcium ions into and potassium ions out of the muscle cell to propogate an
action potential and depolarize the cel l.
There must then be a rapid restoral of the ions
against their electrochemical gradients for the cell to repolarize and be ready
for the next action potential.
Magnesium - Cell "Battery"/ATP
Production
Muscle contraction(The Calcium
Cycle)
Mg++ levels inside and outside the cell have an important role
in the intracellular calcium cycle in muscle cells
Occurs in response to a nerve's electrical action potential stimulus. Contraction
of cardiac and smooth muscle requires rapid shifting of intracellular calcium
ions intracellular calcium is released from the sarcoplasmic reticulumor calcium
enters the cell from the outside .
Muscle relaxation
Mg-dependent Na/K-ATPase pumps
are vital for production of mitochondrial
ATP energy needed to enable
pumps to quickly shunt Ca++ back into the
sarcoplasmic reticulum and PMCA pumps
to pump Ca++ out of the cell
Procedure t o relax
a muscle. Intracellular calcium is quickly pumped back into the sarcoplasmic reticulum
via SERCA pumps and is pumped out of the cell
via PMCA pumps after the calcium cycle is completed.
Magnesium
is a "Calcium Channel Blocker"
(for some cell
membrane-bound calcium channels) Mg limits the influx of extracellular calcium into the cell
cytoplasm
Magnesium++
serves
as an important gating mechanism limiting the influx of extracellular calcium into
the cytosol via PMCA pumps. Magnesium is thus similar
to calcium channel blocker drugs, which lower blood pressure by blocking calcium
entry into heart and smooth muscle cells of blood vessels.
Magnesium effects on cardiac system
Magnesium in skeletal muscle contractions
