The Biology of the Brain
(Including some fun facts)
Reason for the Brain
• Why do animals have brains?
– Most animals need a brain to navigate around the
world, to make decisions and predictions about
what will happen next and to react to external
information and forces. Brains are for figuring out
and predicting the external world we inhabit and
for representing external information and telling
our bodies how to respond.
Brain Facts
• Are there any animals that don’t have brains?
How do you think brains developed in
the first place?
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Deliberate movement
Evolution of the senses
Usefulness
Processing sensory information
Brain Facts
• Octopi are very clever but they don’t have a
single brain
The Nervous System
Why are people sometimes unable to
walk following spine damage?
• Damage to the spine can either sever or
disable the communication between the brain
and the legs. This is because the part of the
nervous system responsible for taking
messages from the brain to the legs is no
longer working properly because the pathway
has been broken.
Nervous System Facts
Neurons
Neurons
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Dendrites
Cell body or Soma (nucleus)
Axon
Motor Neurons
Sensory Neurons
Remember
• Q: What are the building blocks of the nervous
system?
• A: The nervous system is made up of billions
of cells called neurons that perform a variety
of different functions including taking
instructions from the brain to the body and
taking sensory information from the body to
the brain.
The Myelin Sheath
• The myelin sheath protects the long axon and
speeds up electrical nerve signals.
• Some researchers think you can increase the
thickness of your myelin sheath (and therefore
how fast your brain works) by eating certain
shellfish.
How are neurons similar to and
different from other cells in the body?
Similar
• a) are surrounded by a cell membrane
• b) have a nucleus that contains genes
• c) contain cytoplasm, mitochondria and other organelles and
• d) carry out basic cellular processes such as protein synthesis and
energy production.
Different
• a) have specialized extensions called dendrites and axons that bring
information to and take it away from the cell body (respectively).
• b) communicate with each other through electrochemical processes
and
• c) contain some specialized structures (e.g. synapses) and chemicals
(e.g. neurotransmitters).
Neurons Communicate
• Synapses are very small gaps between the
tentacles of two neurons
• The electrical signal can’t pass across the gap
between synapses
• Synapse releases special chemicals, called
‘neurotransmitters’ which travel across the
gap and trigger an electrical impulse in the
next neuron.
Neurotransmitters
• Chemical messengers released by terminal
buttons through the synapse.
• We should know at least 4 types and what
they do
Acetylcholine
• Enables muscle action, learning & maybe
memory
• Lack of ACh has been linked to Alzheimer's
• Too much means muscle spasms & death
• Too little can mean paralysis
Dopamine
• Influences learning, meaning & attention
• Too much is linked to schizophrenia
• Too little is linked to Parkinson’s
Serotonin
• Affects mood, hunger, sleep & arousal
• Too little is linked to depression
• Too much Serotonin Syndrome
Endorphins
• Natural pain killer
• “Runner’s High”
• Linked to pain control & pleasure
Action Potential
• When the neuron is resting, it pumps
positively charged sodium atoms (from
ordinary salt) to the outside of the cell where
they build up like water behind a dam. When
an electrical signal arrives, the floodgates
open and the charged atoms rush back inside
the cell, causing an electrical charge to shoot
along the axon.
Action Potential
How Neurons Communicate
Interesting Facts
• If you laid all the neurons in your brain end to end they
would be long enough to go around the equator of the
earth 4 times!
• If you counted all the neurons in your brain at the rate of
one a second and never lost count, it would take 645 years
to count them all!
• The number of potential connections that can be made
between neurons is greater than the number of known
atoms in the universe!
• You could fit 30,000 brain neurons on the head of a pin!
• However other neurons can be several feet long. For
instance, the length of a giraffe’s longest neuron (from it’s
toe to its neck) is 15 feet!
How long does it take?
• Although electricity in the world seems to
travel instantaneously, electrical signals in the
body can take more time and increase with
the distance traveled. In fact, electricity in the
body can travel up to 3 million times slower
than electricity in the world. This is partly
because electrical impulses have to be
converted to neurotransmitters between each
of the synapses along the way rather than
travelling directly.
Why does it feel so quick?
• Electrical signals over short distances, like those within
your brain, can travel as fast as 400km/hour. As the
distances get longer the messages take more time but
even over longer distances the perception is of
something happening immediately. For instance,
imagine eating grapes. Your hand picks a grape and
sends the signal to your brain that it is squishy. Your
brain decides on that basis that the grape is rotten and
instructs the hand to throw it away rather than eating
it. This process can seem almost instantaneous yet it
does take a significant amount of time.
How do neurons connect together to
form pathways for thought?
• Neurons connect to create networks that allow us to think,
remember and predict.
• Number of connections between neurons
• Complexity of the patterns
• This is what gives the brain its immense processing power.
• Each of the brain’s 80 billion neurons can have up to 10,000
connections
• This means that the human brain has more than 500,000
times as many connections as even the most advanced
computer chip
• The human brain can also be running lots of these networks
all at the same time, a problem that computer scientists
have not yet been able to master
Stronger Pathways
• Different experiences cause the neurons to
fire messages to each-other
• The more they are used, the stronger they get.
• Cells that fire together, wire together
Grapes or olives?
• Now, if I were to see an olive for the first time
I would notice that it was round and green like
a grape so my network for grapes might start
firing already. This would mean that my brain
is expecting the olive to be sweet. If this is the
case it will come as a great shock when the
olive is actually salty!
Facts
Do you grow more neurons as you get
older?
• When you are born you have almost all the
neurons you will ever have in your cortex.
• The number doesn’t change from one age to
• The number of connections do
• When a child is born the brain starts sending
out connections to all the other neurons
• At first these connections are very sparse and
thin
The neurons remain the same
• The human brain is made up of 80 billion neurons that
remain the same throughout the person’s life
• Our brain becomes massively connected as we
experience everything for the first time
• ‘Use it or lose it!”
• The process of dying away is called ‘pruning’
• Most pruning happens during childhood which is why
children are often better at learning new skills than
adults are
• The networks that remain after this first surge of
connection, pruning and strengthening form the basis
for all thought, feeling and memory later in life
The 10% Myth
No-one is really sure where the 10% myth arose.
It’s possibly a mis-quotation from the 1930s that
the average human uses 10% of their brain at any
one time. Even this much milder claim has been
refuted. In fact we use nearly every part of our
brain and most of the brain is active all of the
time. The myth has been perpetuated in pop
culture and is frequently used in advertisements.
Part of its appeal may be the idea that we have a
huge amount of potential that, if we only knew
how, we could tap into to do incredible things
beyond out current capabilities.
As we age . . .
It is now well known that intellectual challenges
help to slow down the decline of the brain in old
age. People such as musicians and scientists who
keep working well past retirement age often
show very few signs of mental aging. In fact, even
doing regular crosswords and brainteasers may
help to slow down mental decline in old age,
although problem solving may seem like hard
work, it probably is the exercise that keeps your
brain in tip-top condition and ensures you don’t
lose the parts of the brain that you need later on