The document discusses how animals respond to changes in their environment through the nervous system. It describes the central nervous system, including the brain and spinal cord, as well as different types of receptors. It then explains how stimuli trigger responses through a pattern of stimulus, receptor, coordinator, and effector. Several examples of stimuli and the resulting responses are provided.

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B6 Brain and MindB6 Brain and Mind
W Richards
The Weald School
OCR 21st
Century Additional Science

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B6.1 How do animals respond toB6.1 How do animals respond to
changes in their environment?changes in their environment?

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The Nervous SystemThe Nervous System
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)

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Nervous ReactionsNervous Reactions
When we react to a stimulus our bodies use the following
pattern and these signals are sent using electrical impulses:
Stimulus Receptor Coordinator Effector Response
For example, consider a
man and a camel: Oh
No!
What are the stimulus, receptor, coordinator, effector and
response in this situation?

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Examples of reactionsExamples of reactions
Stimulus Receptor
(i.e. the thing
that detects the
stimulus)
Effector
(i.e. the thing
that will do the
reaction)
Response
(i.e. action
taken)
Bright light
Sour taste
Losing balance
Sit on a drawing
pin

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Simple reflexes in humansSimple reflexes in humans
Babies can demonstrate simple reflexes:
1) Stepping reflex
2) Startle (or moro) reflex
3) Grasping reflex
4) Rooting reflex
5) Sucking reflex

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The Iris ReflexThe Iris Reflex
When the light is bright
the radial muscles relax,
the circular muscles
contract and the pupil
increases in size.
When the light is bright
the radial muscles _____,
the circular muscles
_______ and the pupil
________ in size.

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Reflex Actions in AnimalsReflex Actions in Animals
Simple animals rely on reflex actions
for most of their behaviour:
Stimulus in a simple animal What is their response?
Feeling hungry
Feeling cold
Feeling threatened

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Slower responses - hormonesSlower responses - hormones
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 passedB6.2 How is information passed
through the nervous system?through the nervous system?

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Conscious actionsConscious actions
A conscious action is one where the brain makes a considered response.
Here’s what happens:
Stimulus Receptor Sensory Neurone Coordinator
Motor Neurone Effector Response
1) Receptors in
your skin detect
a stimulus
3) Here another sensory neurone
carries the signal to the brain
4) The brain
decides to move
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
6) Which then
moves the hand
away

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Reflex actionsReflex actions
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…

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Reflex actionsReflex actions
1. Receptor
2. Sensory
neurone
3. Relay
neurone in the
spinal chord
4. Motor
neurone
5. Effector

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Types of nerve cell (“neuron”)Types of nerve cell (“neuron”)
Nucleus
Muscle strands
(effector)
Axon – a long extension
of cytoplasm surrounded
by a membrane
Nerve cells (neurons) are elongated with branched endings to
connect to many muscles fibres and aid the transmission of
electrical impulses:
Fatty sheath to increase the speed of
transmission and to insulate the
neuron from surrounding cells

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The CNS and the PNSThe CNS and the PNS
There are two types of neurone we need to
consider:
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:
2) Motor neurone
Impulse
These carry impulses
from the CNS to
effectors
1) Sensory neurone
Impulse
These carry impulses
from the receptors to
the CNS

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SynapsesSynapses
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

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Drugs and the Nervous SystemDrugs and the Nervous System
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.

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The Cerebral CortexThe Cerebral Cortex
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 brainOther 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.

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Conditioned reflexes - Pavlov’s DogConditioned reflexes - Pavlov’s Dog
Ivan Pavlov,
1849-1936
I won the Nobel Prize in 1904 and am
most famous for investigating
“conditioned responses”:
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!

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Reflex actionsReflex 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 moreB6.4 How do humans develop more
complex behaviour?complex behaviour?

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Human BrainsHuman Brains
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.

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Learning Complex BehaviourLearning Complex Behaviour
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.
PET scan showing
areas “activated” by
doing algebra.

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Feral childrenFeral children
Task: to find out what “feral children” are, what has caused
their condition and what the consequences are.

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MemoryMemory
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

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Using Models to Explain MemoryUsing Models to Explain Memory
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?