Transcript B6 Brain and Mind

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B6 Brain and Mind
OCR 21st Century Additional Science
M Barker
Shirebrook Academy
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B6.1 How do animals respond to
changes in their environment?
The Nervous System
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The CENTRAL NERVOUS SYSTEM (CNS) enables us to react
to changes in our surroundings (“stimuli”). It consists mainly
of the brain, the spinal chord, nerve cells (“neurones”) and
receptors.
Types of receptor:
1) Light receptors in the eyes
2) Sound receptors in the ears
3) Taste receptors on the tongue
4) Smell receptors in the nose
5) Touch, pressure and temperature receptors in the skin
6) Changes of position receptors in the ears (balance)
Nervous Reactions
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When we react to a stimulus our bodies use the following
pattern and these signals are sent using electrical impulses:
Stimulus
Receptor
For example, consider a
man and a camel:
Coordinator
Effector
Response
Oh
No!
What are the stimulus, receptor, coordinator, effector and
response in this situation?
Examples of reactions
Stimulus
Bright light
Sour taste
Losing balance
Sit on a drawing
pin
Receptor
(i.e. the thing
that detects the
stimulus)
Effector
(i.e. the thing
that will do the
reaction)
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Response
(i.e. action
taken)
Simple reflexes in humans
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Babies can demonstrate simple reflexes:
1) Stepping reflex
2) Startle (or moro) reflex
3) Grasping reflex
4) Rooting reflex
5) Sucking reflex
The Iris Reflex
When the light is bright
the radial muscles relax,
the circular muscles
contract and the pupil
increases in size.
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When the light is bright
the radial muscles _____,
the circular muscles
_______ and the pupil
________ in size.
Reflex Actions in Animals
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Simple animals rely on reflex actions
for most of their behaviour:
Stimulus in a simple animal
Feeling hungry
Feeling cold
Feeling threatened
What is their response?
Slower responses - hormones
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Nervous impulses are electrical signals and are transmitted
quickly through the body. The body can also produce a slower
response using chemical messengers called hormones.
Examples of bodily processes that use hormones:
Controlling of water
content by the
kidneys and the brain:
The menstrual cycle,
using hormones from
the brain and ovaries:
The development of nervous and hormonal communication
systems depended on the evolution of multicellular organisms.
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B6.2 How is information passed
through the nervous system?
Conscious actions
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A conscious action is one where the brain makes a considered response.
Here’s what happens:
4) The brain
3) Here another sensory neurone
decides to move
carries the signal to the brain
away the hand
5) This impulse is
sent by MOTOR
NEURONES to the
hand muscles (the
effectors) via the
spinal chord…
2) The impulse is carried
by SENSORY NEURONES
to the spinal chord
1) Receptors in
your skin detect
a stimulus
Stimulus
6) Which then
moves the hand
away
Receptor
Motor Neurone
Sensory Neurone
Effector
Coordinator
Response
Reflex actions
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Sometimes conscious action is too slow to prevent harm, e.g…
In situations like this
the body bypasses the
brain to produce a
quicker response.
Here’s how it works…
Reflex actions
2. Sensory
neurone
1. Receptor
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3. Relay
neurone in the
spinal chord
4. Motor
neurone
5. Effector
Types of nerve cell (“neuron”)
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Nerve cells (neurons) are elongated with branched endings to
connect to many muscles fibres and aid the transmission of
electrical impulses:
Nucleus
Axon – a long extension
of cytoplasm surrounded
by a membrane
Muscle strands
(effector)
Fatty sheath to increase the speed of
transmission and to insulate the
neuron from surrounding cells
The CNS and the PNS
The Central Nervous System (CNS)
is the spinal cord and brain:
The Peripheral Nervous System
(PNS) is the collection of neurones
connected to the CNS:
There are two types of neurone we need to
consider:
1) Sensory neurone
Impulse
These carry impulses
from the receptors to
the CNS
2) Motor neurone
Impulse
These carry impulses
from the CNS to
effectors
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Synapses
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Neurones never ____ each other – there is a small gap
between them called a _____. A signal is sent from one
_______ to the next by a _______ transmitter across the
synapse (called a “neurotransmitter”). These transmitters are
then ________ back into the sensory neurone to be used
again. This process only reacts with specific chemicals that
bind to the receptor molecules.
Words – chemical, synapse, neurone, touch, reabsorbed
Drugs and the Nervous System
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Drugs are classed as “a substance that affects the central
nervous system, causing changes in psychological behaviour and
possibly addiction”. They do this by affecting the
transmission of impulses. Consider Ecstasy for example:
Ecstasy (MDMA) blocks the
sites in the brain’s synapses
where the transmitter
substance serotonin is removed.
Beta blockers and Prozac can also affect
the transmission of impulses.
The Cerebral Cortex
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The cerebral cortex is the part of our brain most concerned
with intelligence, memory and consciousness. By studying the
effects (e.g. memory/sight loss) when different parts of the
brain are damaged scientists have been able to identify which
parts of the brain control which functions.
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Other techniques of studying the brain
1) An electroencephalogram (EEG) is a
visual record of the electrical activity
generated by neurons in the brain. It
works by amplifying and detecting the
electrical signals from the brain.
2) Magnetic resonance imaging
(MRI) scanning is a new
technique that produces images
of different cross sections of
the brain and uses colours to
represent activity.
Conditioned reflexes - Pavlov’s Dog
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I won the Nobel Prize in 1904 and am
most famous for investigating
“conditioned responses”:
Ivan Pavlov,
1849-1936
1) Steak + dog = saliva
2) Steak + bell + dog = saliva
3) Bell + dog = saliva
Notice that the final response (saliva) has no direct relation to
the stimulus (the bell). Conditioned reflexes can increase an
animal’s chance of survival!
Reflex actions
Sometimes the brain can modify a
reflex response via a neuron to
the motor neuron of the reflex
arc, meaning that you could keep
hold of a hot object:
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B6.4 How do humans develop more
complex behaviour?
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Human Brains
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Ug. My chances of survival were made a
lot better when my brain got bigger.
Notice I can now use simple tools!
Mammals have complex brains with
billions of neurons. The interaction
between our ancestors and their
environment caused neuron
pathways to form in the brain.
Learning Complex Behaviour
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PET scan showing
areas “activated” by
doing algebra.
When the brain is asked to do certain tasks different areas
are “activated”. New experiences cause new neuron pathways
to develop, while pathways that are not used are eventually
destroyed. This is why we become better at certain tasks
when we practice them more often.
Feral children
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Task: to find out what “feral children” are, what has caused
their condition and what the consequences are.
Memory
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Our memory is divided into two types: short term and long
term.
Short term memory is capable of storing a limited amount of
information for a limited amount of time. Long term memory
is when more information is stored over a much longer time.
Ways of improving
short term memory,
e.g. a phone number
Ways of improving
long term memory
e.g. exam revision
Using Models to Explain Memory
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We can understand memory better by using models to explain
it, for example:
What could cause a model to be limited in explaining how
memory works?