Leg cramps, which often occur at night, occur when the muscles in the legs contract involuntarily. Muscles contract in response to a sequence of events. First a motor neuron in the spinal cord becomes activated, which triggers the release of acetylcholine---a neurotransmitter that binds to muscle cells. Acetylcholine initiates an action potential in the muscle fiber that triggers the release of calcium needed for myosin---a motor protein---to move along the muscle fiber. As the body breaks down acetylcholine, the action potential is terminated, and decreasing calcium causes the muscles to relax again. Conditions and disorders that trigger or interfere with any of these steps can cause leg cramps resulting in pain.
Dehydration
Dehydration occurs when the body does not have enough fluid and water. The human body consists mostly of water which functions to dissolve minerals and nutrients, carry substances such as oxygen to cells, regulate body temperature, lubricate the joints and flush out waste products. Without enough water all the cells in the body suffer, including those in the muscles. Dehydration decreases the amount of blood, therefore decreasing the amount of oxygen available for cells, which can interfere with the muscles' ability to relax, resulting in leg cramps and pain.
Addison's Disease
Addison's disease, also called adrenal insufficiency, describes a medical condition in which the adrenal glands fail to produce enough hormones. The adrenal glands, two small glands located above each kidney, produce steroid hormones such as cortisol and aldosterone and catcholemines such as epinephrine and norepinephrine. Addison's disease causes symptoms including chronic fatigue, muscle weakness, loss of appetite and weight loss, says the National Endocrine and Metabolic Diseases Information Service. If left untreated, Addison's disease can worsen into an adrenal crisis that causes dehydration; severe pain in the lower back, abdomen and legs due to muscle cramping; low blood pressure; and a loss of consciousness.
Hypothyroidism
The thyroid, a butterfly-shaped gland in the neck, produces hormones that control the body's metabolism---the rate at which reactions in the body occur. When the thyroid fails to produce enough of these hormones, a condition known as hypothyroidism, it affects many functions including the speed of chemical reactions, the rate of tissue growth, and the speed of electrical impulses between nerves and muscles. Common symptoms include sensitivity to cold, muscle pain, weakness, fatigue and weight gain.
Restless Leg Syndrome
Restless leg syndrome describes a neurological disorder characterized by the uncontrollable urge to move the legs. Those with restless leg syndrome experience unpleasant sensations that many patients describe as a burning, creeping or tugging sensation, notes the National Institute of Neurologic Disorders and Stroke. For some the symptoms remain mild and occur infrequently. For others, the symptoms become severe, causing leg irritation and pain that interrupts sleep and daily activities.
