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Conduction of Nerve Impulse

A nerve impulse is defined as an electric signal that goes through the dendrites to create an action potential or a nerve impulse. An action potential results from the movement of ions in and out of a cell and it particularly includes sodium and potassium ions. They are transferred in and out of the cell via sodium and potassium channels and sodium-potassium pumps.

Conduction of nerve impulses happens because of the presence of active and electronic potentials with conductors. Internally, the transmission of signals amidst the cells is done via a synapse. The electrical synapse got its application in escape reflexes, the heart, and the retina of vertebrates. Nerve conductors consist of relatively higher membrane resistance and low axial resistance. They are significantly utilized when there is a need for fast response and timing being important. The ionic currents pass across the two cell membranes when the action potential nears the stage of such synapse.

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Mechanism of transmission of nerve impulse

The axon, also called nerve fibers, is present in the form of a cylindrical tube where the inside of the axon is filled with axoplasm and the outside is full of axolemma. Nerve fibers are immersed in extracellular fluid. The solution is in ionic form available in axoplasm and extracellular fluid.

The negatively charged chloride ions get neutralized outside the axon because of the presence of positively charged sodium ions. Negatively charged protein molecules also get neutralized in the presence of potassium ions inside the axoplasm. The membrane of a neuron is negative inside whereas positive outside. Resting potential is described as the difference between the two charges. The difference in charge can differ from seventy to ninety mV as a result of the membrane that would be polarized. The sodium- potassium pump functions to keep the resting potential in its equilibrium.

The pump is positioned on the axon membrane. The potassium ions get pumped from extracellular fluid to axoplasm, and sodium ions are pumped out of the axoplasm to the extracellular fluid.

The sodium-potassium pump ceases to function when a stimulus is provided to a membrane of a nerve fiber. The stimulus could be electrical, mechanical, or chemical. Potassium ions move out of the membrane while the sodium ions move inside the membrane as a consequence of negative charges that are present outside along with positive charges that are present inside.

Conduction of Nerve Impulse

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The nerve fibers either get depolarized or are considered to be in their potential action. The action potential that gets transported along the membrane is known as the nerve impulse. It is about + 30 mV. The sodium-potassium pump starts to function only when the action potential is fulfilled. As an outcome, the axon membrane gets a resting potential via repolarization.

Now the process occurs in reverse. This is the opposite of the process that took place during an action potential. Here, potassium ions will move inside and sodium ions will move outside. Impulse would not be transmitted across the nerve fiber in the course of the refractory period.

In the case of white fibers, saltatory propagation generally occurs. That is, impulse jumps from one node to another node and it keeps increasing with the increasing speed of nerve impulse. It is about twenty times faster than that of the non-medullated nerve fibers. The transfer of nerve impulses would depend upon the fibre’s diameter. For example, the nerve impulse of a mammal is about one hundred and twenty meters per second while the nerve impulse of a Frog is thirty meters per second.

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Special faster connections

Electrical synapses that are fast are used in reflexes, the retinas of different vertebrates, and also the heart. This is because they are much faster as they do not require the slow diffusion process of neurotransmitters through the synaptic gap. Hence, electrical synapses are utilized when the fast response and coordination of timing are important.

These synapses directly join the presynaptic and postsynaptic cells directly. When an action potential reaches this kind of synapse, the ionic currents cross the two cell membranes and move inside the postsynaptic cell using the pores termed as connexions. Hence, presynaptic action potential stimulates the postsynaptic cell directly.

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