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?

• 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

• 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