Muscle Relaxants

What is muscle spasm?

Muscle spasm or spasticity is defined as involuntary muscle contraction due to increased muscle tone (hypertonicity) or muscle stiffness, so that the muscles undergo excessive contraction and are resistant to stretch, which is the relaxed state. It is usually associated with damage to the nerve pathways in the brain or spinal cord involved in control of muscle movement, abnormal nerve stimulation, or abnormal activity of the muscle itself. Another form of muscle spasm is clonus, which is painful reflex muscle spasm due to a series of spontaneous involuntary muscle contraction and relaxations.

Muscle spasms can be the result of certain disorders of the nervous system, including multiple sclerosis, motor neurone disease, cerebral palsy and meningitis; also tumours or inflammation of the spinal cord; or following stroke or injuries to the head or spine. Skeletal muscle spasm may be caused by a wide range of injuries, including, sprains, strains and fractures; also a prolapsed intervertebral disc or lumbago (lower back pain) can trigger muscle spasm. Other conditions associated with muscle spasm include fibrositis or fibromyalgia, which is chronic pain and stiffness in the muscles tendons and joints, non-articular rheumatism (affecting soft tissue such as tendonitis), acute torticollis, which is spasm and shortening of a muscle in the neck causing the head to become twisted. Spasticity can result in abnormal posture or gait, exaggerated deep tendon reflexes, increased pain and can affect overall quality of life.

Muscle relaxants

Muscle contraction and relaxation is part of the neuromuscular control system that results in coordinated movement. It is normally under control of the motor neurones that receive messages from the brain and spinal cord to instruct a specific skeletal muscle to contract or relax. Muscle relaxants used to help treat painful muscle spasm act directly at the level of neurotransmitter, which are chemicals that allow nerve cells to communicate and this reduces uncontrolled muscle contraction. Muscle spasm can be treated with muscle relaxant medications that act directly at the level of nerve impulse transmission but work by different mechanism of action.

Analgesic anticholinergic

Orphenadrine is a muscle relaxant that has several mechanisms of action, including analgesic and muscle relaxant properties. It is thought to have anticholinergic action, which means that it blocks the receptors for acetylcholine, a neurotransmitter that activates skeletal muscle contraction. Orphenadrine works at the level of the central and peripheral nervous system, to help control involuntary muscle spasm. The combination of analgesic and anticholinergic action helps relieve pain due to muscle spasm.

GABA analogues

Baclofen is an analog of gamma-aminobutyric acid (GABA), which is the major inhibitory neurotransmitter in the central nervous system and regulates how nerve cells in the spinal cord respond to stimulation. Baclofen stimulates GABA receptors which in turn inhibits the release of excitatory neurotransmitters like glutamate and aspartate that regulate sensory and motor neurones. This action suppresses nerve stimulation of reflexes at the spinal level that cause Involuntary muscle spasm and reduces pain associated with muscle spasm. Baclofen, however, does not have any effect on Neuromuscular transmission, which is the stimulation of the muscle to contract by release of acetylcholine by peripheral nerve cells.