Know Your Brain: Blood-Brain Barrier

Where is the blood-brain barrier?

The blood-brain barrier surrounds most of the blood vessels in the brain. It is a structure that is formed primarily due to the establishment of tight junctions between endothelial cells (i.e. cells that line the walls of blood vessels). There are also several other cells and proteins contributing to the blood-brain barrier complex; for example, processes called astrocytic end-feet extend from astrocytes to surround blood vessels and provide support to the endothelial cells of the blood-brain barrier.

What is the blood-brain barrier and what does it do?

The blood-brain barrier acts as an additional boundary between the circulating blood and the extracellular space of the brain. The barrier is highly selective, meaning it only allows certain substances to cross from the bloodstream into the brain. This functions to protect the brain from toxins, pathogens, and even circulating neurotransmitters (e.g. glutamate) that can be potentially damaging to neurons if their levels get too high. Only water, certain gases (e.g. oxygen), and lipid-soluble substances can easily diffuse across the barrier (other necessary substances like glucose can be actively transported across the blood-brain barrier with some effort).

It is thought that the central component of the functional anatomy of the blood-brain barrier involves tight junctions formed between endothelial cells, the cells that make up the interior surface of the blood vessels in the brain. In other blood vessels throughout the body, there are spaces between these endothelial cells; small blood-borne substances can pass through such spaces and into surrounding tissues. The endothelial cells that make up the blood-brain barrier, however, are fused tightly together, which restricts passive diffusion across the blood vessel lining.

Watch this 2-Minute Neuroscience video to learn more about the blood-brain barrier.

Projections from astrocytes also extend to the walls of the blood vessels that are part of the blood-brain barrier and often completely surround those vessels. These projections, called astrocytic end-feet, appear to play critical roles in the formation of the blood-brain barrier. For example, they are thought to be involved with signaling that prompts endothelial cells to form the tight junctions necessary to create the blood-brain barrier. They also seem to have multiple functions involving the maintenance of the blood-brain barrier and possibly the transient opening of the barrier to allow important substances to cross in special circumstances.

While most blood vessels in the brain are ensconced in the blood-brain barrier, there are some regions that lack a blood-brain barrier, allowing substances to pass from the blood to the brain and vice versa more freely. For example, the circumventricular organs are a group of structures lacking a blood-brain barrier that are centered around the ventricles of the brain. It is thought blood vessels in the circumventricular organs are more permeable for a reason; for instance, the posterior pituitary gland needs to release hormones directly into the bloodstream and the subfornical organ is involved in cardiovascular regulation, which requires access to the circulatory system to monitor levels of hormones in the blood.

Although the blood-brain barrier is an important layer of protection between the peripheral blood circulation and the brain, in certain situations it can be problematic that access to the brain is so restrictive. For example, in the rare instance where there is an infection of the brain, the blood-brain barrier makes delivery of antimicrobial agents to the brain very difficult; it also impedes the passage of antibodies from the body to the brain. While in these cases the blood-brain barrier may be an obstacle to treatment, however, in general it provides an essential buffer between the circulating blood of the body and the brain.

Reference (in addition to linked text above):

Ballabh P, Braun A, & Nedergaard M (2004). The blood-brain barrier: an overview, structure, regulation, and clinical implications. Neurobiology of disease, 16 (1), 1-13.

YOUR BRAIN, EXPLAINED

Sleep. Memory. Pleasure. Fear. Language. We experience these things every day, but how do our brains create them? Your Brain, Explained is a personal tour around your gray matter. Building on neuroscientist Marc Dingman’s popular YouTube series, 2-Minute Neuroscience, this is a friendly, engaging introduction to the human brain and its quirks using real-life examples and Dingman’s own, hand-drawn illustrations.

Reading like a collection of detective stories, Your Brain, Explained combines classic cases in the history of neurology with findings stemming from the latest techniques used to probe the brain’s secrets. - Stanley Finger, PhD, Professor Emeritus of Psychological & Brain Sciences, Washington University (St. Louis), author, Origins of Neuroscience
Dingman weaves classic studies with modern research into easily digestible sections, to provide an excellent primer on the rapidly advancing field of neuroscience. - Moheb Costandi, author, Neuroplasticity and 50 Human Brain Ideas You Really Need to Know
An informative, accessible and engaging book for anyone who has even the slightest interest in how the brain works, but doesn’t know where to begin. - Dean Burnett, PhD, author, Happy Brain and Idiot Brain
...a highly readable and accessible introduction to the operation of the brain and current issues in neuroscience... a wonderful introduction to the field. - Frank Amthor, PhD, Professor of Psychology, The University of Alabama at Birmingham, author, Neuroscience for Dummies

Order Now

BIZARRE

This book shows a whole other side of how brains work by examining the most unusual behavior to emerge from the human brain. In it, you'll meet a woman who is afraid to take a shower because she fears her body will slip down the drain, a man who is convinced he is a cat, a woman who compulsively snacks on cigarette ashes, and many other unusual cases. As uncommon as they are, each of these cases has something important to teach us about everyday brain function.

Dingman brings the history of neuroscience back to life and weaves in contemporary ideas seamlessly. Readers will come along for the ride of a really interesting read and accidentally learn some neuroscience along the way. - Erin Kirschmann, PhD, Associate Professor of Psychology & Counseling, Immaculata University
Bizarre is a collection of stories of how the brain can create zombies, cult members, extra limbs, instant musicians, and overnight accents, to name a few of the mind-scratching cases. After reading this book, you will walk away with a greater appreciation for this bizarre organ. If you are a fan of Oliver Sacks' books, you're certain to be a fan of Dingman's Bizarre. - Allison M. Wilck, PhD, Researcher and Assistant Professor of Psychology, Eastern Mennonite University
A unique combination of storytelling and scientific explanation that appeals to the brain novice, the trained neuroscientist, and everyone in between. Dingman explores some of the most fascinating and mysterious expressions of human behavior in a style that is case study, dramatic novel, and introductory textbook all rolled into one. - Alison Kreisler, PhD, Neuroscience Instructor, California State University, San Marcos
Through case studies of both exceptional people as well as those with disorders, Bizarre takes us on a fascinating journey in which we learn more about what is going on in our skull. - William J. Ray, PhD, Emeritus Professor of Psychology, The Pennsylvania State University, author, Abnormal Psychology