Transcript Nervous System

SL-HL
E1:Stimulus and response
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Stimuli: A stimulus is a change in the environment (internal or
external) that is detected by a receptor, and elicits a response.
Response : A response is the activity of a cell or organism in terms of
movement, hormone secretion or enzyme production, as a result of a
stimulus.
A response can be normal response or reflex. Examples? Difference?
Reflex Arc
 Reflex – rapid, predictable, and involuntary responses to
stimuli. A reflex is a rapid, unconscious response.
 Reflex arc – direct route from a sensory neuron, to an
interneuron, to a motor neuron.
Week 6
PN 1050
Slide 7.23
Neurons and
the Reflex Arc
Explain how animal responses can be affected by
natural selection, using two examples
• 1 Genetic variation,
• 2 Expression of genetic variation in the
phenotype. Some phenotypes are better able to
survive and reproduce in a particular environment;
• natural selection operates, determining the survivors
and the genes that are perpetuated.
As structure of an organism, natural selection is just as
applicable to an inherited behavioural trait.
• When the European
hedgehog detects
danger, the first response
is to pull the spines down
around the back legs and
part of the face-leaving
only a small gap to peer
out from.
SL-HL
E2 Perception of stimulus
What are the receptors?
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For light
For chemicals
For pressure
temperature
Human eye
Rod cells
Cone cells
Visual stimuli’, Edge enhancement and Contralateral processing.
Edge enhancement
Contalateral processing
Human ear
SL-HL
E3 Innate and learned behavior
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Distinguish between innate and learned behavior.
Design experiments to investigate innate behavior in invertebrates’ including either
taxis or a kinesis.
Analyse data from invertebrate behaviour experiments in terms of the effect on
chances of survival and reproduction.
Discuss how the process of learning can improve the chance of survival.
Outline the role of inheritance and learning in the development of birdsong in young
birds.
INNATE (instinctive)
BEHAVIOR and LEARNED
BEHAVIOR
• Innate behavior develops independently of the
environmental context, whereas learned behavior
develops as a result of experience.
INNATE BEHAVIOR IN INVERTEBRATES
Most of their actions are reflex. There are
two types of invertebrate behavior.
1- Taxis: direction of the stimulus
determines the direction of the response.
e.g: Planaria moving towards the food
(chemotaxis)
Euglona moving towards the light
(phototaxis)
2- Kinesis: rate of movement is related to
the intensity of the stimulus not the
direction.
Examples:
Woodlice, move randomly and quickly in dry conditions, but slow down
and stop in a humid area.
Hydra that may bring the tentacles in contact with a food source, and
which speeds up when a food source is nearby.
Analysis of data from behaviour experiments with
nonvertebrate animals
How can we analyze this graph?
Bumble bees behavior
Learned behaviour and conditioning
When an animal changes its behavior in
response to some development in its
environment, the change may be due to
learning.
• habituation, Imprinting
• Conditioning is a form of learning
associated with a reward (or punishment).
Pavlov’s experiment
Birds songs
• A young bird leaves the nest but does not become
sexually mature until the following spring.
• A male that has been hatched and reared in isolation
can sing but not the species specific song.
• If a young bird hears the adult song but its hearing is
blocked before spring it is unable to repeat the song.
• This means it has to hear its own singing and match
what it hears with what was programmed into its memory
as a young bird.
• If a young bird hears the adult song but its hearing is
blocked after it has started to sing in the spring it is able
to continue to repeat the song correctly even though it
can no longer hear itself.
• There are two learning phases in this bird
1.when it is young
2. start with sexual maturity.
How learning can improve the
chance of survival?
• Learning reduces non-adaptive behavior.
Discuss
Example?
• A horse will avoid touching an electric
fence if it is experienced the shock from
one.
• Vervet monkeys have three different
warning calls – leopard, snake and eagle.
SL-HL
E4 Noeurotransmitters and synapses
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State that some presynaptic neurons excite postsynaptic transmission and others
inhibit postsynaptic transmission.
Explain how decision-making in the CNS can result from the interaction between the
activities of excitatory and inhibitory presynaptic neurons at synapses.
Explain how psychoactive drugs affect the brain and personality by either increasing
or decreasing postsynaptic transmission.
List three examples of excitatory and three examples of inhibitory psychoactive
drugs.
Explain the effects of THC and cocaine in terms of their action at synapses in the
brain.
Discuss the causes of addiction, including genetic predisposition, social factors and
dopamine secretion.
Excitory and Inhibitory synapses
• An action potential will
only be generated in the
post-synaptic neurone if
the combined effects of
the excitatory action
potentials and inhibitory
action potentials exceed
the threshold level.
• This is known as
summation, which helps
decision making.
The CNS consists of vast numbers of interconnected neurones; in fact,
our brain typically contains at least 1011 neurones (that is 100 000 000
000) linked by 1014 synapses.
Psychoactive drugs modify
synapses
1. Block removal of neurotransmitters (Cocaine)
2. Mimic neurotransmitter (Nicotine)
3. Block receptor for neurotransmitter
4. Block release of neurotransmitters. (THC)
5. Enhance effect of neurotransmitter (Alcohol)
6. Enhance release of neurotransmitter
The actual effect is determined by whether
the synapse is excitory or inhibitory
Drug action
Neurotransmitter
Result
Blocks
Excitatory
Depression
Enhances
Excitatory
Stimulation
Blocks
Inhibitory
Stimulation
Enhances
Inhibitory
Depression
Effect of drugs
EXCITATORY DRUGS
INHIBITORY DRUGS
Nicotine
Benzodazepines
Cocaine
Alcohol
Amphetamines
Tetrahydrocannabinol THC
Cocaine:
Blocks removal of neurotransmitters.
Dopamine remains in the synaptic gap:
increased energy and alertness, more
talkative, increases pleasure feeling, blood
pressure increases.
Gradually body makes less dopamine and
becomes dependent on presence of
cocaine.