How Do Nervous Impulses Begin?


Nervous impulses are the electrical signals that transmit information throughout the body. They play a crucial role in allowing us to perceive and respond to our environment. Understanding how these impulses begin is fundamental to our comprehension of the complex workings of the nervous system. In this article, we will explore the various subtopics involved in the initiation of nervous impulses, shedding light on the intricate processes that occur within our bodies.

The Structure of Neurons

Neurons, also known as nerve cells, are the building blocks of the nervous system. They are specialized cells responsible for transmitting electrical signals. To understand how nervous impulses begin, we must first examine the structure of neurons.

Neuron Components

A typical neuron consists of three main components:

  1. Cell Body: The cell body, also known as the soma, contains the nucleus and other cellular organelles necessary for the neuron’s survival and functionality.
  2. Dendrites: Dendrites are branching extensions that receive incoming signals from other neurons or sensory receptors.
  3. Axon: The axon is a long, slender projection that carries the electrical impulses away from the cell body to other neurons, muscles, or glands.

The axon is a crucial component in the initiation and propagation of nervous impulses, as we will explore in the following sections.

Resting Potential: The Starting Point

Before a nervous impulse can begin, the neuron must establish a resting potential. This refers to the electrical charge difference between the inside and outside of the neuron, with the inside being more negatively charged.

Sodium-Potassium Pump

The resting potential is maintained by the sodium-potassium pump, a protein complex embedded in the neuron’s cell membrane. This pump actively transports sodium ions (Na+) out of the neuron and potassium ions (K+) into the neuron, against their concentration gradients.

This exchange of ions creates an electrical potential difference across the cell membrane, with a higher concentration of positive ions outside the neuron and a higher concentration of negative ions inside. This difference in charges sets the stage for the initiation of a nervous impulse.

Depolarization: The Triggering Event

Depolarization is the key event that triggers a nervous impulse. It occurs when the electrical potential across the neuron’s membrane becomes less negative, moving towards zero or even becoming positive.

Threshold Potential

For depolarization to occur, the neuron must reach a threshold potential. This is the minimum level of depolarization required to generate an action potential, which is the electrical signal responsible for propagating the nervous impulse.

When the neuron’s membrane potential reaches the threshold, voltage-gated sodium channels located along the axon open, allowing an influx of sodium ions into the neuron. This sudden rush of positive ions further depolarizes the membrane, initiating the generation of an action potential.

Action Potential: The Electrical Signal

The action potential is a rapid, temporary change in the neuron’s membrane potential. It serves as the electrical signal that carries information along the neuron.

All-or-None Principle

The action potential follows the all-or-none principle, meaning that once initiated, it is an all-or-nothing event. It either occurs fully with a consistent amplitude or does not occur at all.

Propagation of the Action Potential

Once an action potential is generated in a specific segment of the neuron’s axon, it triggers adjacent segments to reach their threshold potentials. This process of depolarization and the subsequent generation of action potentials continues down the length of the axon, allowing the signal to propagate rapidly.

Synaptic Transmission: Passing the Signal

At the end of the axon, the nervous impulse needs to be transmitted to the next neuron or target cell. This occurs through synaptic transmission, a complex process involving chemical messengers called neurotransmitters.

Synaptic Cleft

The synaptic cleft is a small gap between the axon terminal of one neuron and the dendrites or cell body of the next neuron. The electrical signal cannot directly cross this gap; instead, it relies on neurotransmitters to transmit the signal.

Neurotransmitter Release

When the action potential reaches the axon terminal, it triggers the release of neurotransmitters into the synaptic cleft. These neurotransmitters bind to specific receptors on the postsynaptic neuron, initiating a new electrical signal in the receiving neuron and continuing the transmission of the nervous impulse.


The initiation of nervous impulses involves a series of intricate processes within neurons. From the establishment of resting potential and depolarization to the generation and propagation of action potentials, the coordination of these events allows for the rapid transmission of information throughout the body. Understanding the beginning of nervous impulses provides a foundation for comprehending the functioning of the nervous system as a whole.

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