people and especially athletes with little experience are familiar with
the sudden pain of a muscle cramp. The muscular cramps are spontaneous,
often painful muscle contractions.
contraction, or spasm, happens unexpectedly, with either no stimulation
or some trivially small one. The muscle contraction and pain
several minutes, and then slowly ease. Cramps may affect any muscle,
but are most common in the calves, feet, and hands.
they are harmless, and in most cases, not related to any underlying
disorder. Nonetheless, cramps and spasms can be manifestations of many
neurological or muscular diseases.
The terms cramp
somewhat vague, and they are sometimes used to include types of
abnormal muscle activity other than sudden painful contraction. These
include slow muscle relaxation, and spontaneous contractions of a
muscle at rest (fasciculation). Fasciculation is a type of painless
muscle spasm, marked by rapid, uncoordinated contraction of many small
muscle fibers. Causes
contraction begins when electrical signals are sent from the brain
through the spinal cord along nerve cells called motor neurons. These
include both the upper motor neurons within the brain and the lower
motor neurons within the spinal cord and leading out to the muscle. At
the muscle, chemicals released by the motor neuron stimulate the
internal release of calcium ions from stores within the muscle cell.
These calcium ions then interact with muscle proteins within the cell,
causing the proteins (actin and myosin) to slide past one another. This
motion pulls their fixed ends closer, thereby shortening the muscle
itself. Recapture of calcium and unlinking of actin and myosin allows
the muscle fiber to relax.
Abnormal contraction may be caused
abnormal activity at any stage in this process. Certain mechanisms
within the brain and the rest of the central nervous system help
regulate contraction. Interruption of these mechanisms can cause spasm.
The muscle membrane itself may be over sensitive, causing contraction
without stimulation. Calcium ions may not be recaptured quickly enough,
causing prolonged contraction.
Interruption of brain
overly sensitive motor neurons may result from damage to the nerve
pathways. Possible causes include neurodegenerative diseases, trauma,
spinal cord injury, and nervous system poisons such as strychnine and
certain insecticides. Nerve damage may lead to a prolonged or permanent
muscle shortening called contracture.
Changes in muscle
responsiveness may be due to or associated with:
exercise. Curiously, relaxation of a muscle actually requires energy to
be expended. The energy is used to recapture calcium and to unlink
actin and myosin. Normally, sensations of pain and fatigue signal that
it is time to rest. Ignoring or overriding those warning signals can
lead to such severe energy depletion that the muscle cannot be relaxed,
causing a cramp. This is the reason why the effort is not indicated
after a heavy meal, when blood flow is directed away from the muscles.
and salt depletion. This may be brought on by protracted vomiting or
diarrhea, or by copious sweating during prolonged exercise, especially
in high temperatures. Loss of fluids and salts--especially sodium,
potassium, magnesium, and calcium--can disrupt ion balances in both
muscle and nerves. This can prevent them from responding and recovering
disorders that affect the energy supply
muscle. These are inherited diseases in which particular muscle enzymes
This causes stiffness due to
relaxation of the muscle, but does not cause the spontaneous
contraction usually associated with cramps. However, many patients with
myotonia do experience cramping from exercise. Symptoms of myotonia are
often worse in the cold.
may be due to fatigue,
medications, metabolic disorders, nerve damage, or neurodegenerative
disease, including amyotrophic lateral sclerosis. Most people
experience brief, mild fasciculation from time to time, usually in the
next page ... →
cramps - symptoms, diagnosis, treatmentDecember