Hierarchical Brain

An explanation of the human brain

First published 1st February 2024. This is version 1.5 published 2nd March 2024.
Three pages are not yet published: sleep, memory and an index.
Copyright © 2024 Email info@hierarchicalbrain.com

Warning - the conclusions of this website may be disturbing for some people without a stable mental disposition or with a religious conviction.


A chemical synapse passes a signal from the presynaptic neuron to the postsynaptic neuron by releasing neurotransmitter chemicals into the gap between the two that are then detected by the postsynaptic neuron. This page gives details of this process, and includes copious Wikipedia links and some references that can provide even more detail.

An understanding of the content of this page is not required for an understanding of the hierarchy of levels of description of the workings of the human brain that are described on these web pages.

Many of the same neurotransmitter chemicals are also used in the process of neuromodulation that affects neurons and synapses over a wider area.

Contents of this page
Overview - The definition and function of a neurotransmitter.
Creation/Synthesis - How a neurotransmitter is created.
Storage - How it is stored in the presynaptic neuron between creation and release.
Release - The details of the release of a neurotransmitter into the synaptic cleft.
Reception - How the chemicals are received by the postsynaptic neuron.
Recycling - How the neurotransmitter chemicals and their storage bubbles are recycled for reuse.
References - references and footnotes.







References For information on references, see structure of this website - references

  1. ^ Foundations of Neuroscience - Open Edition - Henley (2021) downloadable here, Chapter 9 entitled “Neurotransmitter synthesis and storage”
    Under the heading “Synthesis and Storage of Small Molecule Transmitters” (page 93 in downloaded version): “Most small molecule neurotransmitters are synthesized by enzymes that are located in the cytoplasm (the exception is norepinephrine...). This means that small molecule neurotransmitters can be synthesized and packaged for storage in the presynaptic terminal using enzymes present in the terminal.”
  2. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 9
    End of chapter introduction (page 92 in downloaded version): “Additionally, a neuron typically will synthesize and release only one type of small molecule neurotransmitter but can synthesize and release more than one neuropeptide.”
  3. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 9
    Under the heading “Synthesis and Storage of Neuropeptides” (pages 102-103 in downloaded version): “Unlike small molecule neurotransmitters, neuropeptides are synthesized in the cell body and transported to the axon terminal.
    Under the heading “Axonal Transport”: “The packaged peptides need to be transported to the presynaptic terminals to be released into the synaptic cleft. ... The packaged neuropeptides are transported to the synaptic terminals via fast anterograde axonal transport mechanisms.”
  4. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 10 entitled “Neurotransmitter release”
    Under the heading “Active zones” (pages 107 in downloaded version): “The voltage-gated calcium channels are concentrated in the presynaptic terminal at active zones, the regions of the membrane where small molecule neurotransmitters are released. At active zones, some synaptic vesicles are docked and are ready for immediate release upon arrival of the action potential. Other neurotransmitter-filled vesicles remain in a reserve pool outside of the active zone.”
  5. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 10
    Under the heading “Vesicle Docking” (page 108 in downloaded version): “Docking of synaptic vesicles packaged with small molecule neurotransmitters occurs through the interaction of three membrane-bound proteins called SNARE proteins. Synaptobrevin is called a v-SNARE because it is located on the Vesicular membrane. Syntaxin and SNAP-25 are called t-SNARES because they are located on the terminal membrane, which is the Target membrane. The interaction of these three proteins leads to vesicle docking at the active zone.”
  6. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 10
    Under the heading “Exocytosis” (page 109 in downloaded version): “The influx of calcium through the voltage-gated calcium channels initiates the exocytosis process that leads to neurotransmitter release. Calcium enters the cell and interacts with another vesicle-bound protein called synaptotagmin. This protein is a calcium sensor, and when calcium is present at the active zone, synaptotagmin interacts with the SNARE proteins. This is the first step toward exocytosis of the synaptic vesicle.”
  7. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 10
    Under the heading “Neurotransmitter Action” (page 110 in downloaded version): “After exocytosis of the transmitter molecules, they enter the synaptic cleft and bind to receptors on the postsynaptic membrane. Receptors fall into two main categories: ligand-gated channels and G-protein coupled receptors.”
  8. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 11 entitled “Neurotransmitter action: ionotropic receptors”
    Start of introduction (page 113 in downloaded version): “Ionotropic receptors, also called neurotransmitter-gated or ligand-gated channels, are ion channels that open in response to the binding of a neurotransmitter.”
  9. ^ ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 11
    Paragraph after animation 11.1 (page 115 in downloaded version): “The receptors can only be opened by a specific ligand. Neurotransmitters and receptors fit together like a lock and key; only certain neurotransmitters are able to bind to and open certain receptors.”
  10. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 11
    At the end, under the heading “Key takeaways” (page 129 in downloaded version): “Glutamate is an excitatory neurotransmitter that opens non-selective cation channels that allow the influx of sodium, causing an EPSP. GABA and glycine are inhibitory neurotransmitters that open chloride channels, causing an IPSP.”
  11. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 12 entitled “Neurotransmitter action: G-protein-coupled receptors”
    End of introduction (page 123 in downloaded version): “GPCRs [G-protein-coupled receptors] have slower effects than ionotropic receptors, but they can have long-lasting effects, unlike the brief action of a postsynaptic potential.”
  12. ^ Ibid. Foundations of Neuroscience - Open Edition - Henley, Chapter 13 entitled “Neurotransmitter clearance”
    Summary at start of chapter (page 136 in downloaded version): “After neurotransmitters have been released into the synaptic cleft, they act upon postsynaptic receptors.... That action must be terminated in order for proper neuronal communication to continue. This is accomplished mainly through two processes: neurotransmitter transport and/or degradation. Transport physically removes the neurotransmitter molecule from the synaptic cleft. Degradation breaks down the neurotransmitter molecule by enzyme activity.”
  13. ^ Principles of Neural Science - Fifth edition - Kandel et al. McGraw-Hill US 2012 - or see GoogleScholar.
    Page 185, top of right-hand column, under the heading “Neurotransmitters Bind to Postsynaptic Receptors”: “Indeed, chemical synaptic transmission can be seen as a modified form of hormone secretion.”
  14. ^ Ibid. Principles of Neural Science
    Page 211, end of right-hand column, under the heading “Excitatory and Inhibitory Synapses Have Distinctive Ultrastructures”: “ ...the effect of a synaptic potential - whether it is excitatory or inhibitory - is determined not by the type of transmitter released from the presynaptic neuron but by the type of ion channels in the postsynaptic cell activated by the transmitter. Although some transmitters can produce both excitatory and inhibitory postsynaptic potentials, by acting on distinct classes of ionotropic receptors at different synapses, most transmitters produce a single predominant type of synaptic response; that is, a [particular] transmitter is usually inhibitory or excitatory.”
  15. ^ Ibid. Principles of Neural Science
    Page 228, first paragraph under the heading “Dendrites Are Electrically Excitable Structures That Can Fire Action Potentials”: “Propagation of signals in dendrites was originally thought to be purely passive. However, intracellular recordings from the cell body of neurons in the 1950s and from dendrites beginning in the 1970s demonstrated that dendrites could produce action potentials. Indeed, we now know that the dendrites of most neurons contain voltage-gated Na+, K+, and Ca2+ channels in addition to ligand-gated channels and leakage channels.”
  16. ^ Ibid. Principles of Neural Science
    Page 255, right-hand column, end of first paragraph under the heading “Second Messengers Can Endow Synaptic Transmission with Long-Lasting Consequences”: “Second messengers can also effect long-term changes lasting days to weeks as a result of alterations in a cell’s expression of specific genes. Such changes in gene expression result from the ability of second-messenger cascades to control the activity of transcription factors, regulatory proteins that control mRNA synthesis.”
  17. ^ Synaptic vesicle recycling: steps and principles - Rizzoli 2014
    doi: 10.1002/embj.201386357 downloadable here or see GoogleScholar.
    Beginning of abstract: “Synaptic vesicle recycling is one of the best-studied cellular pathways. Many of the proteins involved are known, and their interactions are becoming increasingly clear. However, as for many other pathways, it is still difficult to understand synaptic vesicle recycling as a whole. While it is generally possible to point out how synaptic reactions take place, it is not always easy to understand what triggers or controls them.”

Page last uploaded Sat Mar 2 02:55:42 2024 MST