Myoneural junction

The PNS has two neurohormones (neurotransmitters) acetylcholine (ACh) and acetylcholinesterase (ACliE). ACh is a neurotransmitter responsible for die transmission of nerve impulses to effector cells of die parasympathetic nervous system. ACh plays an important role in die transmission of nerve impulses at synapses and myoneural junctions. ACh is quickly... 

Nerve Agent Substances that interfere with the central nervous system. Organic esters of phosphoric acid used as a chemical warfare agent because of their extreme toxicity (tabun-GA, sarin-GB, soman-GD, GF, and VX). All are potent inhibitors of the enzyme, acetylcholinesterase, which is responsible for the degradation of the neurotransmitter, acetylcholine in neuronal synapses or myoneural junctions. Nerve agents are readily absorbed by inhalation and/or through intact skin. 

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. 

They are singularly effective against cholinesterase which hydrolyzes the acetylcholine generated in myoneural junctions during the transmission of motor commands. In the absence of effective cholinesterase, acetylcholine accumulates and interferes with the coordination of muscle response. Such interference in the muscles of the vital organs produces serious symptoms and eventually death. 

Blocks myoneural junction causes chloride-dependent hyperpolarization, flaccid paralysis... 

Mechanism of Action A cholinergic drug that prevents destruction of acetylcholine by inhibiting the enzyme acetylcholinesterase, thus enhancing impulse transmission across the myoneural junction. Therapeutic Effect Improves intestinal and skeletal muscle tone stimulates salivary and sweat gland secretions. 

Acetylcholine cause stimulation of skeletal muscles and in larger concentration at the myoneural junction can produce paralysis of skeletal muscles. 

Piperazine causes paralysis of ascaris by blocking acetylcholine at the myoneural junction unable to maintain their position in the host, live worms are expelled by normal peristalsis. 

Carbamates effect the reversible carbamylation of acetylcholinesterase, permitting accumulation of acetylcholine at cholinergic neuroeffector junctions (muscarinic effects), at the myoneural junctions of skeletal muscle, and in the autonomic ganglia (nicotinic effects). CNS function is also impaired. However the relatively large dissociation constant of the carbamyl-enzyme complex indicates that it dissociates more readily than does the organophosphate-enzyme complex, mitigating the toxicity of the carbamate pesticides. The reversibility of the carbamyl-enzyme complex affects (limits) the utility of blood enzyme measurements as a diagnostic tool. 

The junction between two neurons is called a synapse. Synapses are terminals at which the action potential may be arrested, redirected or relayed synapses at muscle fibres are called neuromuscular junctions (or myoneural junctions). There is a very narrow gap, the synaptic... 

Drugs acting at the myoneural junction produce complete paralysis of all volvmtary muscle so that movement is impossible and mechanical ventilation is needed. It is plainly important that a paralysed patient should be in a state of full analgesia and unconscious during surgery. Using modem anaes-... 

Goudsouzian NG, Standaert FG. The infant and the myoneural junction. Anesth Analg 1986 65(11) 1208-17. 

Myasthenia gravis is a disease in which nerve impulses do not reach the nerves in muscle endings (myoneural junction) it is caused by inadequate secretion or loss of acetylcholine resulting from action of acetylcholinesterase, an enzyme that destroys acetylcholine at the myoneural junction. 

Postsynaptic nicotinic receptors in the peripheral nervous system are designated as (in autonomic ganglia) and N2 (at myoneural junctions). Nicotinic receptors are of the ion channel type. They are pentameric proteins that are composed of one, two, or more distinct subunits, each of which contains multiple membrane-spanning regions, and the individual subunits surround an internal channel (28). Nicotinic receptors are highly heterogeneous, and subcategorization has been difficult those in neuronal tissue are believed to... 

B. Csillik, Functional Structure of the Post-Synaptic Membrane in the Myoneural Junction, Publishing House ofthe Hungarian Academy of Sciences, Budapest, 1965,/ / . 95-112. 

---