How the Brain Works The Facts Visually Explained by DK (z-lib.org)

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The blood-brain barrier

Infections from the rest of the

body do not ordinarily reach the

brain due to a system called the

blood-brain barrier. As a general

rule, blood capillaries in the rest of

the body leak fluid easily (and any

viruses and germs it contains) into

surrounding tissues through gaps

between the cells that form the

blood vessel’s wall. In the brain,

these same cells have a much

tighter fit, and the flow of materials

between the brain is instead

controlled by astrocytes that

surround the blood vessels.

Selectively permeable

Normal blood vessels allow fluid to pass

through easily. However, while oxygen,

fat-based hormones, and non-water-soluble

materials pass through the blood-brain

barrier unhindered, water-soluble items are

blocked so they don’t reach the CSF.

Site of fluid production

CSF is made from plasma, the liquid

part of blood. Most of it is produced by the

choroid plexus, a network of blood vessels

that runs throughout the ventricular system.

Circulation

around

spinal cord

As well as the brain, CSF

surrounds the spinal

cord, flowing down

along the back of the

spinal cord, into the

central canal, then up

along the front.

1

3

SKULL

CEREBELLUM

THIRD VENTRICLE

CHOROID PLEXUS

FOURTH

VENTRICLE

SPINAL CORD

CENTRAL CANAL

NORMAL

BLOOD VESSEL

BRAIN

BLOOD VESSEL

Pia mater

Dura mater

Arachnoid mater

CSF travels

downward

at back of

spinal cord

CSF flows into

ventricles

Water-soluble

substances

enter via pore

between cells

Fat-soluble

substances pass

though cell

membranes

Fat-soluble

substances

move freely

Substances pass

out of vessel

through pore

Tight junction

between cells

Astrocyte

cells surround

blood vessels

Some water-soluble

substances enter brain

AL

TE

R

AL

VE

NTRICLE

KEY

Blood flow

Flow of

cerebrospinal fluid

Reabsorption

The CSF is reabsorbed

into the circulatory system,

where it remixes with the

blood. CSF is renewed at a rate

of three to four times a day.

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