Muscle relaxants drugs
Muscle relaxants are drugs that are administered to relax muscles. They are given to relieve the discomfort of muscle spasm or involuntary muscle contracture and also in cases of surgery to relax muscles and provide easier access for the surgeon. Some nonprescription drugs are available to combat painful contraction of the uterus during a woman’s menstrual period.
Muscles can be divided into two classes, the voluntary or skeletal muscles and the involuntary or smooth muscles. The heart muscle, the myocardium, is a unique type of muscle that does not fit into either category. Skeletal muscles are those that are under voluntary control. The muscles that move the arms, that move the legs when you walk or run, or those that are involved in chewing are all skeletal muscles. They come into play only when you will them. Smooth muscles are those that are not under conscious control. The muscles in the digestive organs are smooth muscles.
Usually it is the skeletal or striated muscles that will require therapy for painful spasm or will need to be relaxed to allow the surgeon to gain access to the abdomen easily. Muscle spasm may be associated with a trauma or may be brought on by multiple sclerosis, cerebral palsy, stroke, or an injury to the spinal cord. Severe cold, an interruption of blood supply to a muscle, or overexertion of the muscle also can lead to spasms. A muscle spasm actually is an increase in muscle tone brought on by an abnormality in motor control by the spinal nerves.
Skeletal muscles are controlled by large nerves in the spinal cord. The nerve cell or neuron is part of the spinal cord, but its projections, the axon and the many dendrites course outward to connect to muscle cells. The nerve axon is a sensory device that senses the muscle cells’ current condition. The dendrites are motor fibers that deliver the instructions to change its state to the muscle fiber. The area at which the muscle and nerve connect is called the neuromuscular junction. It is here that the end releases a chemical called a neurotransmitter that crosses the microscopic space between the nerve and muscle and causes the desired response. Five such neurotransmitters have been described: acetylcholine, serotonin, norepinephrine, glycine, and gamma-amminobutyric acid or GABA. Of these, the functions of three are known. Acetylcholine excites muscle activity and glycine and GABA inhibit it.
Muscle relaxants may act either peripherally, that is directly on the muscle, or centrally, in the spinal cord. Most such drugs act centrally, though how they perform their task is not understood. These drugs do not act directly on the muscle to relax it, they do not interfere with conduction along the nerve fiber, they do not stop the neurotransmitter from being released or crossing the nerve-muscle junction, and they do not alter the ability of the muscle to respond to the neurotransmitter. Somehow they act centrally to depress the central nervous system and may have a sedative effect.
The dosage of any muscle relaxing agent must be carefully tailored to achieve the desired result without overdosing the patient. Because these drugs have a sedative action the patient should be warned not to drive, operate machinery or perform any other task that requires wakefulness. An overdose of the drugs can put the patient to sleep and may well depress muscle function to the extent that the bladder will not contract normally and urine retention will occur. Also, some drugs will produce a change in the color of the urine of which the patient should be made aware.
Few Muscle Relaxant drugs:-
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carisoprodol (Soma)
chlorphensin carbamate (Maolate)
chlorzoxazone (Paraflax)
cyclobenzaprine HCl (Flexeril)
Metaxolone (Skelaxin)
methocarbamol (Robaxin)
orphenadrine (Banflex, Flexain, Marflex, Norflex, etc.)