SHANNON KEHR PHYSIOLOGY APRIL 1, 2014 Muscle Relaxers

What is a Muscle Relaxer? A muscle relaxer, also known as a muscle relaxant, is a drug which affects skeletal muscle function and decreases the muscle tone. It may be used to alleviate symptoms such as muscle spasms, pain.

History of Muscle Relaxers The earliest known use of muscle relaxant drugs dates back to the 16th century, when European explorers encountered natives of the Amazon were using poison-tipped arrows that produced death by skeletal muscle paralysis. By 1943, neuromuscular blocking drugs became established as muscle relaxants in the practice of anesthesia and surgery.

Muscle Relaxers and the Nervous System Muscle relaxers refer to two major therapeutic groups: neuromuscular blockers and spasmolytics

Neuromuscular Blockers Spasmolytics Neuromuscular blockers act by interfering with transmission at the neuromuscular end plate and have no central nervous system activity. They are often used during surgical procedures and in intensive care and emergency medicine to cause temporary paralysis. Spasmolytics, also known as "centrally acting" muscle relaxants, are used to alleviate musculoskeletal pain and spasms and to reduce spasticity in a variety of neurological conditions. Two Therapeutic Muscle Relaxers

Neuromuscular Blockers Most neuromuscular blockers function by blocking transmission at the end plate of the neuromuscular junction. Normal end plate function can be blocked by two mechanisms. Non depolarizing agents, such as tubocurarine, block the agonist, acetylcholine, from binding to nicotinic receptors and activating them, thereby preventing depolarization. Alternatively, depolarizing agents, such as succinylcholine, are nicotinic receptor agonists which mimic Ach, block muscle contraction by depolarizing to such an extent that it desensitizes the receptor and it can no longer initiate an action potential and cause muscle contraction. Both of these classes of neuromuscular blocking drugs are structurally similar to acetylcholine, the endogenous ligand, in many cases containing two acetylcholine molecules linked end-to- end by a rigid carbon ring system, as in pancuronium (a nondepolarizing agent).

Spasmolytics Spasmolytic agents generally work by either enhancing the level of inhibition, or reducing the level of excitation. Inhibition is enhanced by mimicking or enhancing the actions of endogenous inhibitory substances, such as gamma-Aminobutyric acid (GABA). GABA is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system. In humans, GABA is also directly responsible for the regulation of muscle tone. Spasmolytics are referred to as “centrally acting muscle relaxants” because they can be used to target specific regions of the body such as low back and neck.

Spasmolytics

Types of Muscle Relaxers Carisoprodol “Soma” Cyclobenzaprine “Flexeril” Diazepam “Valium” Metaxalone “Skelaxin” Methocarbamol “Robaxin”

Side Effects Heart Failure Paralysis Sedation Dizziness Headache Drowsiness Nausea and Vomiting Irritability