Answer:
The nerve impulse is not transmitted with the same speed in all neurons. It depends on whether or not the axon is surrounded by cells, the Schwann cells, which produces a white substance, the myelin sheath, which prevents the passage of the nerve impulse and causes you to "jump" between the spaces without the sheath of Myelin (Ranvier nodules), so the speed will be higher.
This type of nerve impulse spread is called "saltatory conduction or spread."
Explanation:
Neurons are cells that have the ability to transmit the nerve impulse in the form of an electric current. The nerve impulse only spreads in one direction. When a neuron is stimulated, electrical changes originate that begin in the dendrites, pass through the neuronal body, and end in the axon.
Neurons can also be classified according to whether or not they have myelin:
- Myelinic neurons Its axons are thicker and the nerve impulse spreads more quickly thanks to the saltatory conduction.
- Unmyelinated neurons They grow myelin, so they drive the nerve impulse more slowly.
The nerve impulse is transmitted along a neuron through a depolarization process:
- Initially, the membrane is polarized. On the outside of the membrane, ions with positive charge abound and on the inside, those with negative charge. This is maintained by the action of the sodium-potassium pump and is called the resting potential.
- When a stimulus arrives, the permeability increases for the sodium ions, which enter the cell, so that the polarity is reversed at that point, leaving more positive charge inside in that area. This alteration is called action potential.
- This depolarization leads to the redistribution of the ions, the nearby sodium channels open, and the adjacent area is also depolarized, and this, in turn, to that of the area that follows, as if they were the dominoes . In this way the nerve impulse travels like a wave along the axon.
- Once the nerve impulse has traveled the entire axon, in thousandths of a second, repolarization or restoration of the ion concentrations characteristic of the resting state occurs.
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