1. NEUROTRANSMITTERS AND SYNAPSES
Option E.4
IB Biology
Miss Werba

2. OPTION E - NEUROBIOLOGY
STIMULUS and RESPONSE
E.2
PERCEPTION of STIMULI
E.3
INNATE and LEARNED BEHAVIOUR
E.4
NTs and SYNAPSES
E.5
THE HUMAN BRAIN
E.6 FURTHER STUDIES IN BEHAVIOUR
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3. THINGS TO COVER Inhibitory vs Excitatory neurons
Interaction between inhibitory & excitatory neurons
Psychoactive drugs
Effects of THC & cocaine
Addiction
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5. TOPIC 6.5 REVIEW What are the three parts of the synapse?
What is the resting membrane potential?
What is the threshold level?
What is the maximum membrane potential before repolarisation occurs?
What are the four phases of the action potential?
How does a signal cross the synapse?
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6. TOPIC 6.5 REVIEW What are the three parts of the synapse?
Presynaptic neuron
Synaptic cleft
Postsynaptic neuron
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7. TOPIC 6.5 REVIEW What is the resting membrane potential? -70mV
What is the threshold level?
-50mV
What is the maximum membrane potential before repolarisation occurs?
+30-50mV
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8. TOPIC 6.5 REVIEW What are the four phases of the action potential?
Resting ( Threshold)
Depolarisation
Repolarisation
Hyperpolarisation ( Resting)
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9. TOPIC 6.5 REVIEW How does a signal cross the synapse?
Crosses the synapse as a chemical signal, via use of neurotransmitters
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10. POST-SYNAPTIC TRANSMISSION Command term = STATE
Some pre-synaptic neurons excite post-synaptic transmissions and others inhibit post-synaptic transmissions
Pre-synaptic neurons release neurotransmitters (NTs) into the synapse to transfer a stimulus to the post-synaptic neurons
Some pre-synaptic neurons generate excitatory post-synaptic potentials (EPSPs)  makes it easier for the post-synaptic neuron to reach threshold
Other pre-synaptic neurons generate inhibitory  post-synaptic potentials (IPSPs)  makes it harder for the post-synaptic neuron to reach threshold
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11. POST-SYNAPTIC TRANSMISSION Command term = STATE
Whether or not the post-synaptic neuron propagates (passes on) the action potential depends on:
Which NT diffuses across the synapse
Which receptors they bind to
Which ions flow in/out of the postsynaptic neuron
Whether or not depolarisation reaches threshold
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12. POST-SYNAPTIC TRANSMISSION Command term = STATE
Excitatory NTs cause depolarisation.
This is referred to as an Excitatory Post-Synaptic Potential (EPSP).
Inhibitory NTs cause hyperpolarisation.
This is referred to as an Inhibitory Post-Synaptic Potential (IPSP).
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13. Excitatory NTs cause depolarisation
POST-SYNAPTIC TRANSMISSION Command term = STATE
Excitatory NTs cause depolarisation
eg. acetylcholine (Ach), dopamine
NT opens Na+ channels  Na+ influx
membrane potential moves closer to threshold
action potential propagated
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14. Inhibitory NTs cause hyperpolarisation
POST-SYNAPTIC TRANSMISSION Command term = STATE
Inhibitory NTs cause hyperpolarisation
eg. γ–aminobutyric acid (GABA)
NT opens K+ channels  K+ efflux OR
NT opens Cl- channels  Cl- influx
membrane potential moves further from threshold
action potential not propagated
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16. SUMMATION Command term = EXPLAIN
The signals from the many pre-synaptic neurons accumulate
This is called summation
The overall charge needs to reach threshold for an action potential to be propagated:
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17. SUMMATION Command term = EXPLAIN
The CNS makes decisions about whether or not to propagate the action potential through the summation of the incoming impulses.
There are two main methods of summation:
TEMPORAL
Multiple APs arrive from one pre-synaptic neuron
SPATIAL
APs arrive from multiple pre-synaptic neurons
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18. SUMMATION Command term = EXPLAIN
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19. PSYCHOACTIVE DRUGS Command term = EXPLAIN
Psychoactive drugs can affect the brain and personality by influencing NT action.
Examples:
Increase the release of NTs
Decrease the release of NTs – eg. THC (cannabis)
Breakdown reuptake proteins so that the NTs are not able to be reused
Block reuptake proteins – eg. Cocaine
Mimic or block NTs by binding to post-synaptic receptors
Inhibit production of NTs
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20. PSYCHOACTIVE DRUGS Command term = LIST
Psychoactive drugs can therefore be inhibitory or excitatory
EXCITATORY PSYCHOACTIVE DRUGS
↑ post-synaptic transmission
INHIBITORY PSYCHOACTIVE DRUGS
↓ post-synaptic transmission
Cocaine
Alcohol
Nicotine
Opiates (heroin)
Caffeine
Benzodiazepines (valium)
Amphetamines (ecstasy)
Tetrahydrocannabinol or THC (cannabis)
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21. PSYCHOACTIVE DRUGS Command term = EXPLAIN
EXCITATORY PSYCHOACTIVE DRUGS
↑ post-synaptic transmission
Cocaine
Cocaine blocks dopamine reuptake
Dopamine remains in synapse
Results in increased post- synaptic transmission
Mood:
enhances feelings of pleasure
longer-lasting feelings
Behaviour:
Feelings of euphoria
Increased energy/alertness
Highly addictive
Associated with depression as body reduces production of own dopamine over time
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22. PSYCHOACTIVE DRUGS Command term = EXPLAIN
THC inhibits GABA release
GABA normally inhibits dopamine release
THC results in increased dopamine release
Mood:
enhances feelings of pleasure as dopamine is involved in the reward pathway
Behaviour:
intoxication
hunger
Memory impairment
Potential dependency
Associated with depression and other mood disorders
INHIBITORY PSYCHOACTIVE DRUGS
↓ post-synaptic transmission
Tetrahydrocannabinol or THC (cannabis)
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23. PSYCHOACTIVE DRUGS Command term = EXPLAIN
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25. E.4.6
ADDICTION
Addiction = a chronic, neurological disorder with genetic, psychosocial and environmental characteristics
It is characterised by changes in the brain resulting in a compulsive desire to use a drug.
Causes of addiction:
Genetic predisposition
Social factors
Dopamine secretion (reward pathway)
Lots of research being done here. Lots still to be done!!!
Click on picture of the ‘Mouse Party’ to explore the effects of psychoactive drugs and the science of addiction further
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26. E.4.6
ADDICTION
Reward centres in the brain play a key role in reinforcing behaviour that may lead to addiction.
Dopamine is the most prevalent NT in the reward pathways.
Drugs that stimulate dopamine secretion generate feelings of pleasure.
This makes the user likely to use the drug again and makes them very addictive.
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27. ADDICTION Some people are genetically predisposed to becoming addicts.
There is reference to an addiction gene and modified versions of other genes.
There is a tendency for children of addicts to become addicts themselves (but may be social/environmental).
They are doing research at the moment for gene therapy that could prevent addiction!
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28. ADDICTION Psychosocial factors also influence addiction. eg.
Peer pressure
Age
Availability
Legality
Religious attitudes
Community attitudes
Stress/abuse
Mental health
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29. Spiders on speed get weaving
SPIDERS ON DRUGS
Spiders on speed get weaving
29 April NewScientist.com news service
SPIDERS on marijuana are so laid back, they weave just so much of their webs and then ... well, it just doesn't seem to matter any more. On the soporific drug chloral hydrate, they drop off before they even get started.
A spider's skill at spinning its web is so obviously affected by the ups and downs of different drugs that scientists at NASA's Marshall Space Flight Center in Alabama think spiders could replace other animals in testing the toxicity of chemicals.
Different drugs have varying effects on the average arachnid addict. On benzedrine, a well-known upper, the house spider spins its web with great gusto, but apparently without much planning, leaving large holes. On caffeine it seems unable to do more than string a few threads together at random.
The more toxic the chemical, the more deformed the web. NASA researchers think that with help from a computer program they can quantify this effect to produce an accurate test for toxicity.
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30. NORMAL SPIDER WEB
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31. SPIDER EXPOSED TO MARIJUANA
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32. SPIDER EXPOSED TO CAFFEINE
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33. SPIDER EXPOSED TO SPEED
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34. SPIDER EXPOSED TO SLEEPING PILLS
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35. Sample questions Q1
State one example of an excitatory and one example of an inhibitory psychoactive drug. [2]
Explain the effects of cocaine on the brain. [3]
Discuss causes of addiction. [3]
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36. Sample questions Q2
OUTLINE Pavlov’s experiments into conditioning in dogs. [2] Q3
OUTLINE the role of inheritance and learning in the development of birdsong in young birds. [2]
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37. Sample questions Q2
Identify the percentage of homozygotes among drug users only. [1]
Calculate the actual number of homozygotes in group 2. [2]
Evaluate the evidence to support the hypothesis that the presence of the homozygous mutation is a risk factor in drug and alcohol use. [3]
Suggest a reason for the high incidence of homozygotes among drug and alcohol users. [1]
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38. Sample questions A1
excitatory: cocaine / nicotine / amphetamines; inhibitory: benzodiazepines / alcohol / THC; [2]
excitatory (psychoactive) drug; cocaine attaches to dopamine pumps/transporters (on presynaptic membrane); blocks uptake/recycling / causes dopamine to persist in the synaptic cleft; amplifies synaptic transmission / causes constant stimulation of postsynaptic neuron; causes euphoria/feelings of happiness/pleasurable effects; [3]
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39. Sample questions A1
addictive drugs trigger secretion of dopamine which causes feelings of pleasure/well-being/reward / users become dependent on feelings; genetic predisposition is most common with addiction to alcohol; social factors affect the incidence of addiction; it is not certain that a person who is genetically predisposed will develop addiction when exposed to the drug / OWTTE; although many drugs are (potentially) addictive, not every user becomes an addict; named social factors which must be explained: e.g. cultural traditions / peer pressure; social deprivation / traumatic life experiences / mental problems;
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40. Sample questions A2
7.8% (allow answers in the range of 7.7% to 7.9%) [1]
(15/100) * 80
= [2]
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41. Sample questions A2
group 1 and group 4 have small differences; supports that the homozygous condition is not a risk factor in alcohol use; group 1 and group 2 have large difference; group 2 have more chance of being homozygotes for the mutation; group 1 small difference with group 3; homozygous condition appears to be a risk factor in group 2and in group 3; numbers are very different in each population / small percentages; [3]
Homozygotes cannot inactivate cannaboids/THC, thus increased needs for drug or alcohol intake / chances of addiction [1]
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