Action Potentials, Axons, and Dendrites

Action Potential Introduction

In the past decades, Physiologists have always been puzzled by how nerves work to their target tissues. Based on the rapid development of electrophysiology, people have discovered the electrical activity of neurons. Scientists have observed that signal transmission can be mediated by action potential from neurons to the responding tissues. Action potential refers to rapid, sudden, and short-lived changes in the membrane. It is produced in different cell types, such as endocrine cells, muscle cells, neurons, and even plant cells.

Between two neighboring neurons, the action potential may lead to the release of chemical neurotransmitters between them. Chemical neurotransmitters can stimulate or inhibit neurons from firing their action potentials. Scientists also found that the action potentials are generated based on the balance of excitatory and inhibitory inputs to neurons in humans. Generally speaking, based on the function of both excitability and inhibitory properties, an action potential will occur when the membrane potential of a neuron reaches about -50 mV.

Fig.1 Structure of a typical neuron.

Introduction of Axons, and Dendrites

The axon is where the action potential is generated, and it is the spike initiation zone for action potentials. With the long and thin structure, it serves as the transmission part of the neuron. After initiation, action potentials travel down axons, which leads to the release of neurotransmitters. This area is characterized by a high concentration of voltage-activated sodium channels.

The dendrite is the receiving part of the neuron to collect synaptic inputs from axons. The protrusions, also known as dendritic spines, are designed to capture the neurotransmitters released by the presynaptic neuron. In general, there are ligand-gated ion channels with high concentrations. The total amount of dendritic inputs determines whether the neuron will fire an action potential.

Functions of Action Potentials

As the basic units of communication between neurons, action potentials play a role in a series of cell types. In neurons, action potentials play an important role in the cell communication. The action potential is the start in the chain of events, which lead to a contraction in muscle cells. In beta cells of the pancreas, the release of insulin is caused by the action potential.

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