Pharmacology Study Set 3
Quiz 9 :
Skeletal Muscle Relaxants
Skeletal muscle contraction is the contraction of the skeletal muscle fibers when impulses reach the muscles. It takes place by sliding filament theory mechanism. The physiological events that takes place before skeletal muscle contraction or that leads to skeletal muscle contraction are: 1) Nerve impulse is initiated in the central nervous system i.e. the spinal cord. Motor neurons from here reaches the neuromuscular junction. 2) At the neuromuscular junction, the nerve endings of the neuron contain acetylcholine neurotransmitters which are secreted into the synapse between neuron and the muscle. 3) This acetylcholine neurotransmitter then reaches the nicotine-muscular receptors (Nm receptors) on the muscle fibers. 4) When the neurotransmitter activates the muscle fibers by binding to it, sodium-potassium channel is stimulated resulting in moving of sodium into the muscle cell and moving out of potassium from the muscle cells. 5) This causes depolarization of the muscle cell. 6) As this depolarization spreads on the muscle fiber surface, calcium ions are released from it leading to contraction of the muscle. Stimulation of muscle fiber is initiated in the spinal cord from which nerve impulse reach the neuromuscular junction through motor neurons. Neurotransmitter release here activates muscle fiber to cause its contraction.
a. The drug Cyclobenzaprine is included under the category of centrally acting skeletal muscle relaxants. The patient gives the information about his drinking habits that might lead to drug interaction. The fact is that drugs that depress central nervous system (CNS) like alcohol potentiate the action and adverse effects of all skeletal muscle relaxants. b. The drug Metaxalone is included under the category of centrally acting skeletal muscle relaxants. It is also given that the patient had been prescribed streptomycin for the throat infection. The streptomycin is known to directly inhibit the neuromuscular function causing skeletal muscle relaxation. c. The drug Methocarbamol is included under the category of centrally acting skeletal muscle relaxants. He is also being given lidocaine for the treatment of heart arrhythmia. The two drugs being administered have CNS depressant effect that might affect the ability of a patient to perform tasks.
The skeletal muscle relaxants are not clinically used to prolong the procedure of surgery rather to ease the procedure. It is not necessary that the centrally acting muscle relaxants must inhibit the nicotinic receptors for exhibiting physiological effects. The use of drugs is not limited by the amount of histamine released from the mast cells. The class includes both botulinum toxin A and B. The mechanism of action depends on the type of drugs for example centrally acting muscle relaxants relieves muscle spasms through a central action. Hence, the incorrect options are b, c, d and e. The intubation for airway management might be accomplished quickly by the skeletal muscle relaxants. The drug succinylcholine is associated with rapid muscle breakdown resulting in life-threatening rhythms of heart, cardiac arrest and death in children. Hence, the correct option is .