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

THE PHYSICAL BRAIN

Human and Animal

Human and

Animal Brains

The human brain is one of the defining features of our

species. Comparing the human brain with the brains of

other animals reveals connections between brain size and

intelligence and between an animal’s brain anatomy and

the way it lives.

Brain shapes

All brains are located in the head,

in close proximity to the primary

sense organs. However, it would be

a mistake to visualize animal brains

as rudimentary variations, in size

and structure, of the human brain.

All vertebrate brains follow the

same development plan, but

anatomies vary widely to match

different sensory and behavioral

needs. More variety can be seen in

the brains of invertebrates, which

account for 95 percent of all animals.

Brain sizes

The size of a brain indicates

its total processing power. For

example, a honeybee’s tiny brain

contains 1 million neurons, a Nile

crocodile’s has 80 million, while

a human brain has around 80–

billion neurons. The link with

intelligence is clear. However,

with larger animals, it is important

to compare brain and body size to

give a more nuanced indication

of cognitive power.

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Octopus
An octopus’s brain contains 500 million
neurons. Only a third are located in the head;
the rest are in the arms and skin, where they
are devoted to sensory and motor controls.
Doughnut-
shaped
brain
Leech
The 10,000 cells in a leech’s nervous system
are arranged in chains of cell clusters called
ganglia. The brain is a big ganglia, with 350
neurons, located at the front of the body.
Esophagus
runs through
middle of
brain
Nerves branch
out into head
and body from
each ganglion
Sizing up
There are two ways to compare brain sizes,
by total weight and as a percentage of body
weight. The largest brain, at 17 lb (7.8 kg),
belongs to the sperm whale, but that is a
minute fraction of its 44-ton (45-tonne) body.

KEY

Cerebellum

Optic lobe

Cerebrum

Pituitary

gland

Medulla

Olfactory

bulb

0 0.004 oz (0.1g) 1 g 0 0.04 oz (0.2g) 1 g

0 0.16% 2 0 0.04% 2

Brain mass

Brain mass as a

percentage of body mass

0.04 oz 0.04 oz

US_014-015_Human_and_Animal_brains.indd 14 07/10/2019 11: