Neurotransmission
Overview
Neurotransmission, also known as synaptic transmission, is the process by which signaling molecules called neurotransmitters are released by a neuron (the presynaptic neuron), and bind to and activate the receptors of another neuron (the postsynaptic neuron). This is a fundamental process that underlies all brain activity, including cognition, sensation, and motor control.
Neurotransmitters
Neurotransmitters are endogenous chemicals that enable neurotransmission. They transmit signals across a chemical synapse, such as a neuromuscular junction, from one neuron (nerve cell) to another "target" neuron, muscle cell, or gland cell. Neurotransmitters are released from synaptic vesicles in synapses into the synaptic cleft, where they are received by receptors on the target cells. Many neurotransmitters are synthesized from simple and plentiful precursors such as amino acids, which are readily available from the diet and only require a small number of biosynthetic steps for conversion.
Types of Neurotransmitters
There are several different ways neurotransmitters can be classified, including by function and by chemical class. For example, they can be divided into small molecule neurotransmitters, which are synthesized in the presynaptic terminal and packaged into synaptic vesicles, and neuropeptides, which are synthesized in the cell body and transported down the axon to the presynaptic terminal.
Mechanism of Neurotransmission
Neurotransmission begins when an action potential reaches the presynaptic terminal, causing voltage-gated calcium channels to open and allow calcium ions to enter the terminal. The influx of calcium ions causes synaptic vesicles to fuse with the membrane and release their neurotransmitter contents into the synaptic cleft. The neurotransmitter molecules then diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron. This binding can either directly open ion channels, allowing ions to flow into or out of the cell, or it can activate second messenger systems that modulate the cell's response to other signals.
Role in Disease
Abnormalities in neurotransmission have been implicated in a variety of diseases, including neurological disorders like Alzheimer's disease and Parkinson's disease, psychiatric disorders like depression and schizophrenia, and other conditions like addiction and chronic pain.
Pharmacology
Many drugs act by modifying neurotransmission. For example, drugs can alter the synthesis of neurotransmitters, affect their release and removal, or change the response of the receptors that they bind to. Understanding the mechanisms of neurotransmission can therefore help in the development of new treatments for a wide range of diseases.