Relaxants, of muscle

Titin Reaches from the Z line to the M line Largest protein in body. Role in relaxation of muscle. 

Sodium and potassium are used for the electrochemical transfer of signals in the nervous system. The contraction and relaxation of muscles are regulated by an interplay of calcium and... 

By destroying the protein, the toxin prevents the release of the neurotransmitter acetylcholine from small packets at the ends of nerves by exocytosis. These nerves, attached to voluntary muscles, need acetylcholine to allow the flow of signals (impulses) between the nerve and the muscle. By preventing the release of acetylcholine, botulinum toxin blocks muscle contraction, causing paralysis and relaxation. The therapeutic action relies on relaxation of muscles, generally in the face. It is therefore used to treat blepharospasm (uncontrolled contractions) and stroke-induced permanent facial muscle contractions. 

The role of calcium in this function is not fully understood. Some researchers have proposed that calcium is the link bciwccn the electrical and mechanical events in contraction. It has been shown b vitro that when calcium ions are applied locally, muscle fibers can be triggered to contract. It has further been postulated that relaxation of muscle libels is brought about by an intracellular mechanism for reducing the coneentraliun of calcium ions availahle lo ihe muscle h lamenls. Others postulate thai contraction occurs because calcium inactivates a relaxing substance, which is released front the sarcoplasmic reticulum in the presence of ATP (adenosine iriphosphate). 

The carrier-mediated active transport system of calcium is responsible for the relaxation of muscle. However, the rate of efflux from sarcoplasmic reticulum membranes during reversal of the transport process is 102 to 104 orders too low to account for the massive calcium release from sarcoplasmic reticulum in stimulated muscle. Instead, passive diffusion of calcium across the sarcoplasmic reticulum membrane will proceed during excitation of muscle178,179,186. The rate of calcium release observed during excitation is 1.000-3.000 p moles/mg protein/min which is an increase of about 104 to 10s over the resting state. 

The syndrome is characterized by myotonia, i.e., failure of immediate relaxation of muscle after voluntary contraction, usually made worse by cold and relieved by repeated movement. 

Muscle rigidity (decreased ability for relaxation of muscle)... 

Absence seizures are brief periods of loss of consciousness (15 seconds or so) with little motor activity, maybe just eyelid blinking or muscle jerking. Sometimes there is complete relaxation of muscles. This type of epilepsy is common in children. 

The essential contractile components of muscle are the microfibrils which consist principally of two filamentous proteins called actin and myosin, together with another protein, troponin. The detailed processes involved in the contraction and relaxation of muscle are very complicated and will not be dealt with here. They involve the sliding back and forth over each other of the actin and myosin filaments, the binding and releasing of Ca + and the utilisation of ATP as the source of energy. 

In muscle there is an extensive endoplasmic reticulum called the sarcoplasmic reticulum. It seems to be primarily concerned with regulating Ca " ion fluxes during the contraction-relaxation cycle. The components of the sarcoplasmic reticulum are in contact with invaginations of the cell membrane which conduct the wave of depolarization into the interior of the muscle cell and to the myofibrils. Relaxation of muscle is brought about by accumulation of calcium within the sarcoplasmic reticulum, whereas contraction occurs as a consequence of an increase in calcium released from the sarcoplasmic reticulum secondary to an... 

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