 Dear students, in this module we shall discuss some general properties of action potentials. The action potentials are also known as spikes or nerve impulses. They are generated by the plasma membranes of excitable cells which are neurons, muscle cells, receptor cells and some secretory cells. The action potentials differ in different types of cells due to different channel properties. The shapes, magnitudes and time course of all action potentials generated by a single type of cell is always are essentially identical. The action potentials propagate along the nerve fiber without reduction i.e. without decrement in amplitude. The speed of propagation of action potential also remains constant. Iske lawa ek action potential ko generate karne ke liye minimum strength of stimulus bhi required hoti hai and that minimum strength is known as threshold. These threshold or threshold potential ranges from minus 50 millivolt to minus 30 millivolt for various types of neurons. The if a threshold is weak then it fails to produce an action potential. Iske neti je me jo depolarization hoti hai that causes failed, abortive and non-propagated excitation which is called local response. Dear students, one more important property of action potentials is that action potentials are all are none events. An excitable membrane responds to a stimulus either with a full-fledged propagating action potential or it does not respond at all. This is known as all are none law. There is no in-between action potential. This principle just works like the gunfire. Dis tarise ek gun ka trigger dabane se ek fire hota hai aur goli ek khas raftar ke saath chalti hui ek khas faas le tak jati hai. Trigger dabane ke liye je force required hoti hai that is called threshold. Agar hum boh zor se trigger dabane, yani supra threshold provide karein to iske matlab yeh nahi hoga ke fire zyada tez hoga aur goli zyada door tak jayegi. Iske tarise agar half-way trigger ko press kya jayeg to ye nahi ke goli haaf chalegi, palke wo chalegi hi nahi. Similar is the principle of working of action potentials. Dear students, another important property of action potentials is that they are regenerative. Action potentials jab ek threshold potential initiate kawadeta hai ek action potential ko, to uske baad action potential apni self-perpetuation krta hai. It becomes regenerative. Action potential actually thode se time ke liye ek thode si place me produce hota hai. Action potential agar wahi pe khatam hojaye toh phir signal ko central nervous system tak nahi ponchaye jaasekega. Iske liye, zoroori hai ke action potential me yeh bali property paye jayeg iske tahit wo apne aapko, jis tariheka wo start me produce hoa hai, wo continuously usse perpetuate krta rahe. This property is called regeneration. So the, this also requires no further stimulus, yeh bhaigar kisi further stimulus ke bhi continue rahegi regenerative property. The time duration of an action potential varies in neurons, but in mammalian neurons of peripheral nervous system, this typically lasts for only a millisecond or so, one or two milliseconds me ek action potential mukammal hojate. As compared to this, the invertebrates neurons produce action potentials which have a timing of about 10 to 100 milliseconds. In vertebrates, the hearts or heart muscles produce action potentials of longer durations which may take about 500 milliseconds. This is required for the regulation of cardiac cycle. Dear students, the movement of ions that occurs during an action potential actually involves a small number of ions. The number of ions which are used in maintaining a resting membrane potential are quite large. Jis waqt, action potential ke liye ionic changes runama hoti hain, to us waqt is number me ju tabdili aati hai, jis ki bhaja se bohot bhai action potential me tabdili ya runama hoti hain, actual number of ions is not very large at that moment. We can take an example of squid joint axon jis me ek action potential ke liye jab depolarization karne ke liye sodium ions enter hoti hain. To ye ju sodium ions enter hoti hain, inki ratio agar counting me dekhiai to that is only 0.0003% of the total sodium ions that are present inside the cell.