Open Questions: Neurobiology

[Home] [Up] [Glossary] [Topic Index] [Site Map]

Introduction

Neurons

Synapses

Neural circuits

Functional modules

Brain imaging studies

Mirror neurons

Spindle neurons

Neurogenesis

Recommended references: Web sites

Recommended references: Magazine/journal articles

Recommended references: Books

Introduction

Neurons

The basic units of the human central nervous system, as with the rest of the body, are cells. There are about 200 different types of cells in the body as a whole, but only two main types in the nervous system: neurons and glia. Estimates of the numbers of neurons in the brain are around 50 to 100 billion (5×10¹⁰ to 10¹¹). There are about 10 times as many glia.

Although the neurons are at a numerical disadvantage, they are far more complex than glia and do most of the active work of the nervous system. Until fairly recently, the importance of glia wasn't well understood, but now it is recognized that glia are essential because they provide nutrition and structural support for neurons, and because they facilitate the all-important transmission of electrical signal through neurons.

Of course, neurons have been much better known than glia, because of the much more active role that they play in the operation of the nervous system. The basic function of any neuron is to transmit electrical signals throughout the nervous system. Because of the way that neurons are networked together in complex ways, they are able to perform any type of computation, much like electronic digital computers. The latter are also complex networks of units (transistors) which also work by transmitting electrical signals. Although the organization and logical operation differ significantly between a brain and a digital computer, they do have in common the characteristic of performing computations by the swiitching of electrical signals within a huge network.

A typical neuron consists of three basic parts:

A cell body, or soma, much like the body of any other type of cell, that contains the cell nucleus and various other essential organelles.
Many dendrites, which are slender, branched projections from the surface of the cell body.
A single axon, which is typically a relatively long filamentary projection from the cell body.

The dendrites are the part of a neuron which receive electrical signals from other neurons, through a junction to be discussed later, called a synapse. A single neuron may have up to ten thousand or so dendrites.

The axon is the part of the neuron which carries an electrical signal away from the cell body, on to the dendrites of many other neurons. An axon is always in only one of two states: resting or excited. It is this binary property which makes neurons similar to the basic functional units of an electronic computer, which are also either "on" or "off". In humans, axons can be as long as a meter or so, long enough to reach from the base of the spine to the toes. Within the brain, axons are normally much shorter, but may extend several centimeters. This is still quite long in comparison to an axon's width, which is about one micron (one ten-thousandth of a centimeter).

Recommended references: Web sites

Site indexes

Open Directory Project: Neurobiology: Categorized and annotated links. A version of this list is at Google, with entries sorted in "page rank" order. May also be found at Netscape.
Open Directory Project: Neuropsychology: Categorized and annotated links. A version of this list is at Google, with entries sorted in "page rank" order. May also be found at Netscape.
WWW Virtual Library: Neuroscience: Extensive categorized and annotated list of links.
Internet Neuroscience Resources: Good list maintained by Eric H. Chudler.
Neuroguide.com: Neurosciences on the Internet: "A searchable and browsable index of neuroscience resources available on the Internet: Neurobiology, neurology, neurosurgery, psychiatry, psychology, cognitive science sites and information on human neurological diseases." Maintained by Neil Busis.
Yahoo News Full Coverage: Brain Research: Links to recent news stories from various sources. Also includes links to sites dealing with brain research.
Galaxy: Neuroscience: Categorized site directory. Entries usually include descriptive annotations.
Galaxy: Neuropsychology: Categorized site directory. Entries usually include descriptive annotations.
Galaxy: Psychobiology: Categorized site directory. Entries usually include descriptive annotations. More here.

Sites with general resources

New Scientist Special Report on the Human Brain: Primarily offers links to many news articles from the past several years of New Scientist magazine. But there are also other features, including facts and figures, external links, frequently-asked questions, and a short bibliography.
NeuroWiki: Group-maintained encyclopedia of neuroscience, based on Wiki software. Still in early stages of development.
Eric H. Chudler: Home page of an associate professor at the University of Washington, who provides many external links and maintains the educational site called Neuroscience for Kids.
Neuroscience for Kids: Although apparently targeted towards students in elementary and secondary schools, there is a large amount of information here for a general audience. Useful external links are scattered throughout many of the topics. Some of the best areas are Explore the Nervous System, Internet Neuroscience Resources, Brain Facts and Figures, The Neuroscientist Network (questions and answers), and Neuroscience in the News.
Neuroscience@nature.com: A portal to relevant Nature Publishing Group resouces in the field of neuroscience.
Brain Mechanisms of Pain: Overview: Several pages dealing with pain, by Robert C. Coghill. Includes images and movies created by functional imaging techniques to illustrate brain activity during the experience of pain.
The Blue Brain Project: Home page of a research project, based at the Brain Mind Institute, to build a unified computer model of the brain. A key component of the project is to simulate the neocortical column. The simulation will be performed in collaboration with IBM Research.

Surveys, overviews, tutorials

Category: Neuroscience: Topic category from Wikipedia.
The Brain from Top to Bottom: A superb, interactive tutorial on brain structure and function. Covers most important topics, like memory, emotions, and the senses. It offers separate discussions on three different levels: beginner, intermediate, and advanced. Discussions are also classified in terms of level of physical organization (social, psychological, neurological, cellular, and molecular). Each discussion has many internal cross references to others, as well as external links on each page.
A Brief Introduction to the Brain: An introduction to neurobiology that covers topics from neurons to brain structure to the architecture of the overall nervous system. Most topics are treated only in brief overview form.
Neuroscience: Complete online textbook, by Dale Purves, George J. Augustine, David Fitzpatrick, Lawrence C. Katz, Anthony-Samuel LaMantia, James O. McNamara, and S. Mark Williams. Index. Part of the NCBI Bookshelf.
Comparative Mammalian Brain Collections: "Provides browsers with images and information from one of the world's largest collection of well-preserved, sectioned and stained brains of mammals. Viewers can see and download photographs of brains of over 100 different species of mammals (including humans)." Discussses a variety of issues in brain science, such as brain evolution, development, circuitry, and functions. Has some good external references.
The Anatomical Basis of Mind: A monograph in ten chapters, by Ben Best. It covers many topics, such as basic neuron physiology, nervous system development, anatomy of the brain, and neurotransmitters. The intention was to explain "the functioning of mind", but it provides useful information whether or not it achieves the ultimate objective. There's a good references and bibliography section.
Cognitive Neuroscience: A ScienceWeek "symposium" consisting of excerpts and summaries of articles from various sources.
Are Immune System Molecules Brain-Builders - And Destroyers?: March 2008 Scientific American article, subtitled "Researchers stumble across immune proteins that play an unexpected - and very different - role in the brain."
The Forgotten Brain Emerges: December 2004 Scientific American Mind article, subtitled "After disregarding them for decades, neuroscientists now say glial cells may be nearly as important to thinking as neurons are."
The Addicted Brain: Insights from Imaging: Brief sidebar from a March 2004 Scientific American article: The Addicted Brain.
Ultimate Self-Improvement: Brief September 2003 Scientific American article about the discover over the past decade that the brain is more changeable than had been supposed.
All in the Mind: October 2001 Scientific American News Scan article, subtitled "Fact or Artifact? The Placebo Effect May Be A Little Of Both."
Young Cells in Old Brains: Brief September 2001 Scientific American profile of Elizabeth Gould, who has discovered a great deal about neurogenesis in adult brains.
Study Finds Placebo Effect Is Fake: May 2001 Scientific American news article about a review of clinical trials testing for a placebo effect, and concluding the effect is largely nonexistent.
Getting Wired: June 1999 Scientific American Science and the Citizen article, subtitled "New observations may show how neurons form connections."

Recommended references: Magazine/journal articles

Deconstructing the Mosaic Brain
Tom Curran
The Scientist, August 2011: Sequencing the DNA of individual neurons is a way to dissect the genes underlying major neurological and psychological disorders.
Cortical Crosstalk
Jef Akst
The Scientist, November 2009: Scientists are eavesdropping on the brain's conversations in search of clues underlying complex behaviors.
Scientists Use Genetics to Map and Control Brain Functions
Gero Miesenböck
Scientific American, September 2008
New Brain Cells Go to Work
R. Douglas Fields
Scientific American, August 2007
Seeking the Neural Code
Miguel A. L. Nicolelis; Sidarta Ribeiro
Scientific American, December 2006: Learning how rats escape from cats also reveals how a storm of electrical pulses sweeping across the brain is translated into information.
Mirrors in the Mind
Giacomo Rizzolatti; Leonardo Fogassi; Vittorio Gallese
Scientific American, November 2006
Brain, Repair Yourself
Fred H. Gage
Scientific American, September 2003
The Mutable Brain
Marguerite Holloway
Scientific American, September 2003
Rethinking the "Lesser Brain"
James M. Bower; Lawrence M. Parsons
Scientific American, August 2003
Gray Matters
Jessa Netting
Science News, April 7, 2001, pp. 222-223: The nervous systems conists of cells known as glia, as well as neurons. Astrocytes are the most common type of glia, and seem to be necessary for neurons to grow and transmit signals.
[References]
Climbing Through the Brain
Robert Kunzig
Discover, August 1998, pp. 60-69: During gestation, fetal neurons migrate from the central position in which they develop out towards their final location in cortex.
The Attentive Brain
Stephen Grossberg
American Scientist, September-October 1995, pp. 438-449: The author has been developing a computational approach, called Adaptive Resonance Theory, to model how the brain matches sensory inputs with learned expectations. This theory may help explain perception, learning, and the recognition of information.

Recommended references: Books

Home