Relaxation of the skeletal muscl

The various skeletal muscle relaxants that may be used during general anesthesia are listed in Table 35-3. These drugp are administered to produce relaxation of the skeletal muscles during certain types of surgeries, such as those involving the chest or abdomen. They may also be used to facilitate the insertion of an endotracheal... 

Cryptopine was isolated by Smiles (579) from opium in 1867. Its effect (580) is in many respects similar to that of papaverine and berberine. In dogs it produces hypotension, inhibition of cardiac activity, stimulation of respiration, inhibition of faradization of the vagus, and decrease in the oculocardiac reflex in rabbits, it produces relaxation of the skeletal muscle (581). For guinea pigs the LD100 s.c. was found to be 160 mg/kg (582). Mercier el al. (583, 584) reported the effect of cryptopine on the intestine, the nervous system, blood pressure, cardiac activity, and respiration to range between that of papaverine and berberine. 

Aceclidine is mostly used in ophthalmology for constriction of the pupil and reduction of intraocular pressure in glaucoma. Oxylidine is being used as a tranquilliser in patients with neurotic states and early states of hypertension. It is also recommended for the treatment of cerebral atherosclerosis. Its oral dose is 0.02—0.5 g. Qualidile is a curare-like drug used in general anaesthesia. The preparation is injected intravenously at a dose of 1 mg kg S muscle relaxation lasts for 10 minutes, slight inhibition of respiration being observed. A dose of 2 mg kg produces complete relaxation of the skeletal muscles, accompanied by apnoea. In spite of the fact that the review is well documented, it is difficult to form an idea about the clinical merits of these compounds. Some clinical information has been published recently a comparison of Qualidile with NiV -diallyl-bisnortoxiferine or tubocurarine chlorides loc. cit.) would be of special interest. 

In short, the centrally acting muscle relaxants find their abundant application in a plethora of conditions, namely strains and sprains, which may ultimately be responsible for causing acute muscle spasm. Besides, they also particularly possess intemeuronal-blocking characteristics at the level of the spinal cord, which may give rise to the much desired relaxation of the skeletal muscle. Interestingly, most of them exhibit a distinct general CNS-depressant activities. 

Interestingly, anticholinesterases, ACH and ion antagonize competitively pancuronium bromide effectively however, its activity is virtually enhanced by general anaesthetics, for instance halothane, ether, enflurane etc. (see Chapter 4). Therefore, the latter substantial potentiation in pharmacological activity is particularly useful to the anaesthetist due to the faet that it is administered invariably as an adjunct to the anaesthetic procedure in order to cause simultaneous relaxation of the skeletal muscle. 

Although skeletal muscle comprises the bulk of muscle tissue in the body, smooth muscle is far more important in terms of homeostasis. Most smooth muscle is found in the walls of tubes and hollow organs. Contraction and relaxation of the smooth muscle in these tissues regulates the movement of substances within them. For example, contraction of the smooth muscle in the wall of a blood vessel narrows the diameter of the vessel and leads to a decrease in the flow of blood through it. Contraction of the smooth muscle in the wall of the stomach exerts pressure on its contents and pushes these substances forward into the small intestine. Smooth muscle functions at a subconscious level and is involuntary. It is innervated by the autonomic nervous system, which regulates its activity. 

Pharmacology In isolated nerve-muscle preparation, dantrolene produced relaxation by affecting contractile response of the skeletal muscle at a site beyond the myoneural junction and directly on the muscle itself. In skeletal muscle, the drug dissociates the excitation-contraction coupling, probably by interfering with the release of calcium from the sarcoplasmic reticulum. 

This type of response may be caused by several mechanisms. For instance, the muscle relaxation induced by succinylcholine, discussed in more detail in chapter 7, is due to blockade of neuromuscular transmission. Alternatively, acetylcholine antagonists such as tubocurarine may compete for the receptor site at the skeletal muscle end plate, leading to paralysis of the skeletal muscle. Botulinum toxin binds to nerve terminals and prevents the release of acetylcholine the muscle behaves as if denervated, and there is paralysis. This will be discussed in more detail in chapter 7. 

ADRENAL MEDULLA HORMONES. Adrenaline (epinephrine) and its immediate biological precursor noradrenaline (norepinephrine, levartei-nol) are the principal hormones of the adult adrenal medulla. See Fig.l. Some of the physiological effects produced by adrenaline arc contraction of the dilator muscle of the pupil of the eye (mydriasis), relaxation of the smooth muscle of the bronchi constriction of most small blood vessels dilation of some blood vessels, notably those in skeletal muscle increase in heart rate and force of ventricular conlraction relaxation of the smooth muscle of the intestinal tract and either contraction or relaxation, or both, of uterine smooth muscle. Electrical stimulation of appropriate sympathetic (adrenergic) nerves can produce all the aforementioned effects with exception of vasodilation in skeletal muscle. 

Magnesium sulfate Skeletal muscle spasms myositis Muscle relaxant effect may be caused by decreased excitability of the skeletal muscle membrane and decreased transmission at the neuromuscular junction 2°/o aqueous solution or ointment from positive pole 2°/o ointment... 

Include pseudocholinesterases responsible for metabolism of the skeletal muscle relaxant, suc-cinylcholine. Genetically determined defects in plasma esterases may result in prolonged actions of succinylcholine in some persons. 

Cross RA, Jackson AP, Citi S, Kendrick-Jones J, Bagshaw CR (1988) Active site trapping of nucleotide by smooth and non-muscle myosins. J Mol Biol 203 173-181 Dabrowska R (1994) In Raeburn D, Giembycz MA (eds) Airways smooth muscle biochemical control of contraction and relaxation. Birkhauser, Basle, pp 32-59 Dabrowska R, Goch A, Galazkiewicz B, Osinska H (1985) The influence of caldesmon on ATPase activity of the skeletal muscle actomyosin and bundling of actin filaments. Biochim Biophys Acta 842 70-75... 

The Role of Calcium in the Regulation of the Skeletal Muscle Contraction-Relaxation Cycle Henry G. Zot and James D. Potter... 

Pharmacological studies of curare were initiated in the middle of the nineteenth century by the French physiologist Claude Bernard (1813— 1878). The dominant pharmacological effect of curare is the paralysis of the whole skeletal muscle in both warm- and cold-blooded animals. The sequence of the paralytic effects of the skeletal muscle is well defined. At first, the eyes, ears, and toes are affected, and next the muscles of the arms and legs. Paralysis of the muscles of the neck then occurs, and finally the respiratory muscles are affected, resulting in suffocation in warm-blooded animals. The muscle relaxant activity of curare is strengthened by diethylether. Because curare can release stored histamine in the tissues, it may cause hypotension and excessive secretion in the trachea. 

The mode of action of many skeletal muscle relaxants, for example carisoprodol (Soma), baclofen (Lioresal), and chlorzoxazone (Paraflex), is not clearly understood. Many of tiiese dragp do not directly relax skeletal muscles, but dieir ability to relieve acute painful musculoskeletal conditions may be due to their sedative action. Cyclobenzaprine (Flexeril) appears to have an effect on muscle tone, tiius reducing muscle spasm. 

The skeletal muscle relaxants are contraindicated in patients with known hypersensitivity. Baclofen is contraindicated in skeletal muscle spasms caused by rheumatic disorders. Carisoprodol is contraindicated in patients with a known hypersensitivity to meprobamate. Cyclobenzaprine is contraindicated in patients with a recent myocardial infarction, cardiac conduction disorders, and hyperthyroidism, hi addition, cyclobenzaprine is contraindicated within 14 days of the administration of a monoamine oxidase inhibitor. Oral dantrolene is contraindicated in patients with active hepatic disease and muscle spasm caused by rheumatic disorders and during lactation. See Chapter 30 for information on diazepam. 

An anesthetic gas, cyclopropane has a rapid onset of action and may be used for induction and maintenance of anesthesia Skeletal muscle relaxation is produced with full anesthetic doses. Cyclopropane is supplied in orange cylinders. Disadvantages of cyclopropane are difficulty in detecting the planes of anesthesia, occasional laryngospasm, cardiac arrhythmias, and postanesthesia nausea, vomiting, and headache Cyclopropane and oxygen mixtures are explosive, which limits the use of this gas anesthetic. 

Enflurane (Ethrane) is a volatile liquid anesthetic that is delivered by inhalation. Induction and recovery from anesthesia are rapid. Muscle relaxation for abdominal surgery is adequate, but greater relaxation may be necessary and may require the use of a skeletal muscle relaxant. Enflurane may produce mild stimulation of respiratory and bronchial secretions when used alone Hypotension may occur when anesthesia deepens. 

The skeletal muscle relaxant that acts directly on the contractile mechanism of the muscle fibers is... 

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