Spasmolytics are drugs that relieve spasticity, a condition marked by involuntary muscle contractions, muscle stiffness, weakness and painful muscle spasms. Some spasmolytics are centrally acting and affect the spinal cord, while others are direct agents that work on the skeletal muscle cells. Chemically, centrally acting spasmolytics can be of three types. An ɑ2-agonist like tizanidine binds the ɑ2-adrenoceptor and inhibits the release of the excitatory neurotransmitter glutamate. It also promotes the release of glycine, which causes an influx of chloride into postsynaptic neurons, and reduces their excitability. Ɣ aminobutyric acid or GABA mimetics like baclofen activate the GABAB receptors, inducing hyperpolarization of neuronal membranes and reducing their excitability. They also inhibit the release of excitatory neurotransmitters and inactivate sensory, motor and interneurons. The last group of spasmolytics includes the benzodiazepines such as diazepam, which binds the allosteric site of GABAA receptors and causes an influx of chloride ions, hyperpolarizing the membrane to inhibit neurotransmission.