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

THE PHYSICAL BRAIN

Fueling the Brain

Fueling

the Brain

The brain is an energy-hungry organ. Unlike

other organs in the body, it is fueled solely

on glucose, a simple sugar that is quick and

easy to metabolize.

Blood supply

The heart supplies blood to the whole body, but around a sixth

of its total effort is devoted to sending blood up to the brain.

Blood reaches the brain by two main arterial routes. The two

carotid arteries, one running up each side of the neck, deliver

blood to the front of the brain (and the eyes, face, and scalp). The

back of the brain is fed by the vertebral arteries, which weave

upward through the spinal column. Deoxygenated blood then

accumulates in the cerebral sinuses, which are spaces created

by enlarged veins running through the brain. The blood there

drains out of the brain and down through the neck via the

internal jugular veins.

The vascular system delivers 26 fl oz (750 ml) of blood to the

brain every minute, which is equivalent to 1.7 fl oz (50 ml) for

every 3.5 oz (100 g) of brain tissue. If that volume drops below

about 0.7 fl oz (20 ml), the brain tissue stops working.

Crossing the blood-brain barrier

The blood-brain barrier is a physical and metabolic

barrier between the brain and its blood supply. It offers

extra protection against infections, which are hard to

combat in the brain using the normal immune system,

and could make the brain malfunction in dangerous

ways. There are six ways that materials can cross the

barrier. Other than that, nothing gets in or out.

DOES FOCUSED

CONCENTRATION USE

MORE ENERGY?

The brain never stops

working, and the overall

energy consumption stays

more or less the same

24 hours a day.

Cellular wall

The physical blood-brain barrier is created by the

cells that make up the walls of capillaries in the brain.

Elsewhere in the body, these are loosely connected,

leaving gaps, or loose junctions. In the brain, the

cells connect at tight junctions.

BLOOD VESSEL

BRAIN

BLOOD-BRAIN

BARRIER

Paracellular transport

Water and water-soluble

materials, such as salts and ions

(charged atoms or molecules),

can cross through small gaps

between capillary-wall cells.

Diffusion

Cells are surrounded

by a fatty membrane, so

fat-soluble substances,

including oxygen and alcohol,

diffuse through the cell.

Fat-soluble

substance

CI

R

CL

E

O

F

(^) W
IL
L
IS
Vertebral
artery
Water-soluble
substance
Molecule
moves
through cell
Tight junction
Carotid artery

FROM THE

HEART

Astrocytes collect material from

blood and pass it to neurons

ASTROCYTE

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