Transcript Reflexes - Awesatomic!

Brain and
Mind
Reflexes
• A reflex is an automatic response to a stimulus.
• Reflexes are very fast
• Simple reflexes help an animal to survive. Examples
include hiding from predators, finding food / shelter /
mates
• The big disadvantage with relying on simple reflexes is
that the animal can’t adapt its behaviour if the
environment changes.
• Complex animals like humans can make conscious
decisions to aid survival (like putting a coat on if
we’re cold).
• Sometimes our reflexes can also be modified due to
experience.
Reflexes
Simple reflexes:- A newborn baby shows
reflexes such as sucking, gasping, the startle
reflex and swimming. These help the baby to
survive.
Conditioned reflexes:- These are reflexes that we learn
in response to a stimulus. For example, Pavlov rang a
bell whenever he gave his dog food. After a while, the
dog would produce saliva when he heard a bell even
though there was no food present – he had learned to
associate the sound of the bell with food.
Modifying reflexes:- we can modify certain reflexes
as we get older. For example we can overcome the
reflex telling us to empty our bladder as soon as its
full. We can also overcome the reflex telling us to drop
a hot plate. Impulses travel from our brain to the
effectors involved, preventing the simple reflex from
taking place.
Reflex arc
Receptors detect a
stimulus
Electrical impulse sent
along sensory neuron
Impulses move through
spinal cord
Impulses sent along
motor neuron to effector
Nervous system
stimulus
processing
centre
effector
Imagine you put your hand on
a pin. This is detected by
special cells in the skin which
send an electrical impulse
receptors
along sensory neurones to your
spinal cord. Impulses are then
sent via your motor neurons to
the muscles in your arm. The
muscles contract and you pull
your hand away.
response
Nervous system
Central nervous
system (CNS) – brain
and spinal cord
Peripheral
nervous system
– includes
sensory and
motor neurons
that carry
impulses all
around the body
Motor neuron
Motor neurons carry
electrical impulses from
the CNS to effectors
(muscles or glands)
The axon of a motor
neuron is covered with
a fatty layer called a
myelin sheath.
This speeds up the rate
at which an impulse
can travel along the
neuron.
(makes connections
with other neurons)
A synapse is a small gap
between 2 neurons.
Synapses
When an impulse arrives
at the synapse, a
Mitochondrion
chemical called a
(provides energy)
neurotransmitter is
released.
Neurotransmitter
This chemical diffuses
across the synapse and
binds to receptors on the Neurotransmitter
diffuses across
other side.
Neurotransmitter
released into
synapse
This triggers an
electrical impulse in the
second neuron.
The neurotransmitter
then binds to uptake
receptors on the first
neuron, and is
reabsorbed.
Neurotransmitter
binds to receptors
on motor neuron
Direction of
electrical
impulse
Drugs and synapses
• Some synapses release a neurotransmitter called serotonin.
• Some drugs like ecstasy or prozac bind to the uptake
channels at these synapses.
• This means that when serotonin is released, it stimulates the
neurons but can’t be reabsorbed.
• Therefore, serotonin becomes concentrated in the synapse
and keeps binding to receptors, overstimulating the neurons.
• This results in enhancing someone’s mood, or making them
feel happy.
(other drugs may work by preventing neurotransmitters being
released, or preventing them from binding to the receptors on
motor neurones. These drugs prevent electrical impulses
being generated in certain neurons - eg pain killers.)
The brain
The folded part of the brain is
called the cerebral cortex. This is
responsible for our language,
learning and memory. It contains
billions of neurons.
In this diagram, the size of the
body part represents the surface
area of the sensory region of the
cerebral cortex associated with it.
Eg, fingertips are very sensitive,
so have a large sensory region of
the brain linked to them.
Learning
• When we have a new experience, new
neuron pathways are created.
• When we repeat the experience, these
new pathways are strengthened.
• This means that electrical impulses are
more likely to pass along these new
pathways.
• So repetition helps you learn because it
strengthens neural pathways.
Age and learning
Children can form new neuron pathways very
easily.
Therefore children learn from experience very
quickly.
As we get older, it becomes harder to form
new neuron pathways.
Feral children have been isolated from other
humans, and survived in the wild.
They have had no experience with human
language.
If a feral child is brought back into society
after the age of about 8, it is very difficult to
teach them language.
This is because the time when it is easy to
lean language had already passed.
Memory
• As you read a sentence you are using your short term memory.
• This lasts only a short while, and can only remember about 7
items.
• To remember something like the words of a song, you need to
move information into your long term memory.
• Rehearsal can help you remember by moving info into your
long term memory.
• Associating information with some kind of pattern, or with a
smell, colour or sound also helps you remember.
• This is because if you process information, you move it into
your long term memory.
• We don’t fully understand how memory works, but there are
different ‘models of memory’ which suggest different theories –
like the multi-store model and working memory model.