Explain (a), (b)
a. When the drug nicotine is added to the end-plate region of a skeletal muscle, it has a stimulating effect on the muscle.
b. The effect of nicotine is blocked when curare is added to the muscle.
a.
When action potential develops in motor nerve, it travels along nerve to its ending on muscle fibers. At motor end plate, nerve secretes acetylcholine (neurotransmitter). Acetylcholine bind with nicotinic type receptors on muscle membrane and open acetylecholine gated channels. Opening of the acetylcholine-gated channels allows large quantities of sodium ions to diffuse to the interior of the muscle fiber membrane. This initiates an action potential at the membrane. The action potential depolarizes the muscle membrane and spread inward along T tubules. It leads to release of Ca+ 2 ion form sarcoplasmic reticulum. Ca +2 ion binds to trophonin C and uncover myosin binding site on actin .Therefore cross link forms between actin and myosin and then slide thick filament on thin filament producing contraction of muscle .
Nicotine acts on the nicotinic acetylcholine receptors and increases the activity of these receptors. Therefore when the drug nicotine is added to the end-plate region of a skeletal muscle, it has a stimulating effect on the muscle.
b.
Curare competitively block (competitive antagonist) the nicotinic type acetylecholine receptors on muscle membrane. Therefore it block the effect of nicotine on muscle .
Labels: Excitable tissue, Excitable tissue MCQs, Excitable tissue SEQs, Physiology SEQ