Nerve Impulse Study Guide


A nerve impulse is a wave of electrical chemical changes in a nerve fiber’s membrane that occurs after stimulation. The nerve cells have a nucleus and other organelles. However, the nerve cells’ thread lines and long extensions are unique, where the nerve impulse is transmitted. So, let’s learn about the mechanism of nerve impulse.

Understanding Neurons and Nerve Impulses

  • The nervous system is composed of nerves. The nerve is a bundle of nerve cells that transmits electrical impulses.
  • The nerve impulse is the message that the neuron wants to convey. The nerve impulse travels at lightning speed because these are electrical impulses.
  • The process is similar to a light switch in a room.
  • You flip the switch, and the electricity flows quickly through the wires in the wall and reaches the light.
  • The speed is so fast that the light is switched on as soon as you flip the switch. The nerve impulse travels just as fast through the nerve network in the body.


What is a Nerve Impulse?

It is interesting to know how the nervous system moves from one to the next cell. The impulse jumps as a chemical transmitter. The two cells are not connected but have a small gap. The small space between a neuron and the next cell is the synapse.

Nerve impulseThe nerve impulse is electric. It results from an electrical charge difference across the neurons’ plasma membrane. This causes the difference in electrical charge to come about.

Common phrases in Nerve Impulse study

Resting Potential

  • When the neuron does not actively transmit a nerve impulse, it is resting. This is when it is sitting, ready to transmit the nerve impulse. The sodium-potassium pump has a charge difference across the cell membrane in the resting phase.
  • The energy in ATP is used to pump the positive sodium ion out from the cell and the potassium ion into the cell.
  • This causes the inside of the neuron to become negatively charged compared to the extracellular fluid that surrounds the neuron.
  • It happens because several positively charged ions are present outside the cell compared to what is present.
  • It is this difference in the electric charge, which is called resting potential.

Action Potential

  • The nerve impulses cause a sudden reversal in the electrical charge across the resting neuron’s membrane.
  • The charge reversal is called the action potential. This starts when the neuron gets a chemical signal from another cell.
  • When the signal is received, then the gate in the sodium ion channel opens up and allows the positive sodium ion to flow back into the cell. This causes the cells inside to get positively charged compared to the cells outside.
  • The charge reversal ripples down to the axon rapidly in the form of an electric current.
  • The myelin sheath is a protective layer and is wrapped around the neuron axons.
  • It causes the action potential to jump across the axon membrane from one to the other instead of spreading smoothly along the membrane.
  • This causes the speed of the impulse to increase.
  • The area where the axon terminal meets another cell is the synapse.
  • The cell and the axon terminal are separated by a synaptic cleft.
  • When the action potential reaches the axon terminal, this causes a release in the chemical molecules.
  • These molecules travel through the synaptic cleft and bind the other cell’s membrane receptors.
  • If the other cell is also a neuron, this starts an action potential in the other cells.

Continuous Conduction

  • Continuous conduction is a way of nerve impulse transmission.
  • It happens in the “Unmyelinated axons”.
  • Action potential is generated alongside the complete length of the axon.
  • Therefore, it takes a bit of time to produce and transmit action potential.

Saltatory Conduction

  • Saltatory conduction is the quickest way of nerve impulse transmission. It happens in the “Myelinated axons”.
  • Myelinated axons own myelinated sheaths.
  • In the myelinated sheaths, there are unventilated spaces referred to as nodes of “Ranvier”.
  • Hence, nerve impulses bounce from 1 node of Ranvier to next instead of touring alongside the entire length of the axon.
  • Hence, nerve impulses travel rapidly alongside myelinated axons.


Polarization is when the membrane becomes positively charged and inside negatively charged. An action potential is produced whilst an electrical stimulus is given to a nerve fibre. The membrane, in preference to potassium ions, turns into permeable to sodium ions.


In depolarization, the gated Na ion channels on the membrane of the neurons abruptly open and permit Na ions present outside the membrane to hurry into the cell. As the Na ions quickly enter the cell, the inner charge of the nerve modifies from -70 mV to -55 mV.


Repolarization is triggered through the closing of Na ion channels and the opening of K ion channels.

Refractory Period

The refractory period of a neuron is the time wherein a nerve cell is not able to fire an action potential. Two subsets exist in phrases of neurons: relative refractory period and absolute refractory period.

Resting Membrane Potential

A neuron at rest is -ve charged: the interior of a cell is about 70 millivolts more -ve than the outside (−70 mV). This voltage is known as the resting membrane potential.


Synapse is an intersection between 2 neurons. It connects nerve cells and other cells.

Nerve Impulse: Types of Potential

Types of potential

Mechanism of Transmission of Nerve Impulse

  • The nerve fibres are cylindrical in shape in which the interior of it is packed with axoplasm and the exterior is protected with axolemma.
  • The nerve fibres are buried in ECF. The answer is in the ionic form that is found in extracellular fluid and axoplasm.
  • Outside the nerve fibre, the -ve charged Cl ions are neutralised in the presence of +ve charged Na ions. -ve charged protein molecules are neutralised withinside the presence of Na ions within the axoplasm.
  • The neuron membrane is negative inside and positive outside. Resting potential will be the distinction in charge.
  • The distinction in charge may range from 70 to 90 millivolts, as an end result, the membrane might be polarised.
  • Sodium potassium pump set off to hold resting potential in equilibrium.
  • The pump is located on the axon membrane. Now the Na ions are pumped from ECF to axoplasm and Na ions are pumped from axoplasm to extracellular fluid.
  • The sodium-potassium pump stops running while a stimulus is implemented to a membrane of an axon. The stimulus can be both chemical, electrical, or mechanical.
  • The K ions rush outside the membrane and Na ions rush withinside the membrane as an end result -ve charges are present outside and +ve charges are inside.
  • The nerve fibres are both depolarized or they’re stated to be withinside the action potential. The action potential travelling alongside the membrane is referred to as the nerve impulse.
  • It is around + 30 mV. The sodium-potassium pump begins to function as soon as the action potential is completed. As an end result, the axon membrane will gain a resting potential through repolarization.
  • Now the method takes place in the opposite order. It is a reverse of the technique that has taken place all through an action potential. Here, K ions will be rushed inside and Na ions will be rushed outside. Impulse could not be transmitted via the nerve fibre during the refractory period.


  • The brain impulse starts when a neuron gets a chemical stimulus. This is the mechanism of nerve impulse.
  • The impulse travels from the axon membrane with an electrical action potential and reaches the axon terminal.
  • The axon terminal then releases the neurotransmitters, which carry the nerve impulse to the next cell.


1. What happens in a nerve impulse?

Impulse is something that happens very fast. The nerve impulse causes an electrical charge across the neuron membrane. The nerve impulse is electrical because they happen when there is a difference in electric charge. A nervous impulse is called an action potential.

2. What is a nerve impulse example?

Imagine what happens when your finger touches a hot stove? You react quickly and remove your finger. This is an example of a nerve impulse.

3. Where do nerve impulses go?

The nerve impulse ends at the synapse.

4. How can nerve impulses be prevented?

If the potassium channel is opened, this does not let the action potential generate and causes the nerve impulse to stop.

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