Transcript Neurotransmitters & Synapses - IB

Neurotransmitters & Synapses
E.4.1 State that some presynaptic
neurones excite postsynaptic
transmission and others inhibit
postsynaptic transmission
Communication via Synapses
• Synapses are a fundamental part of neural
pathways
• Regulate decision-making in terms of
• Exciting or
• Inhibiting the post-synaptic neuron
Neurotransmitters are:
• Excitatory
• they excite the post-synaptic neuron (+ ions move
in)
• Contributing to depolarization & propagation of the
AP
• Inhibitory
• Hyperpolarize the post-synaptic neuron (+ ions
move out)
• Prevent the AP
Will the post-synaptic neuron respond?
• Which NT diffused?
• Which receptors do they bind to?
• Which ions flow in/out of the post-synaptic
neurone?
• Whether or not depolarization reaches
threshold
Excitatory Neurotransmitters
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e.g. Ach, dopamine
NT binds
Na+ channels open
Na+ rushes in
Membrane potential
depolarizes
• AP propagated
Inhibitory Neurotransmitters
• e.g. - GABA, serotonin
• NT binds to receptor
• K+ channels open, K+
rushes out
• OR Cl- channels open,
Cl- rushes in
• Membrane potential
becomes more negative
• Ac AP is prevented from
p propagating
E.4.2 Explain how decision
making in the CNS can result
from the interaction between
the activities of excitatory and
inhibitory presynaptic neurones
at synapses.
Decision making in the CNS
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Action potential
Calcium ions rush to the end of the axon
Neurotransmitter fuse with membrane
Neurotransmitters released into synaptic cleft
Binds to specific receptors on the postsynaptic neurone
Decision making in the CNS
• Temporal Summation
1.
2.
3.
AP arrive in rapid succession
Depolarization in the axon
hillock is summative
If it reaches threshold before
repolarization, the AP is
propagated
• Spatial Summation
1.
2.
3.
4.
5.
AP arrive simultaneously
from multiple sources
Some NT are excitatory
Other NT are inhibitory
Summation is the axon hillock
is summative
If it reaches threshold the AP
is propagated
E.4.3 Explain how psychoactive
drugs affect the brain &
personality by either increasing
or decreasing postsynaptic
transmission.
How do psychoactive drugs affect the
brain?
2 Main Neurotransmitters
Acetylcholine
Noradrenaline/Norepinephrine
Acetylcholine (Ach)
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Released by all motor neurones
Activate skeletal muscles
Works with parasympathetic nervous system
Causes relaxation
Ach synapses = cholinergic synapses
Nicotine stimulates these synapses
– Causes calming effect
Noradrenaline/Norepinephrine
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Depolarizes the the postsynaptic neurone
Works with the sympathetic system
Causes “fight or flight”
Noradrenalin synapses = adrenergic synapses
Cocaine & amphetamines stimulate
adrenergic synapses
– Increased alertness, energy, and euphoria
Comparison of synapses
Cholinergic
Adrenergic
Neurotransmitter
Acetylcholine
Noradrenaline
System
Parasympathetic
Sympathetic
Effect on Mood
Calming
Increased energy,
alertness, euphoria
Drugs increasing
transmission at
synapse
Nicotine
Cocaine and
amphetamines
Psychoactive drugs
• Increase or decrease the release of NTs
• Breakdown re-uptake proteins which are
responsible for returned used components of
NTs to the pre-synaptic neurone
• Block re-uptake proteins (e.g. cocaine)
• Mimic or block NTs, binding to the receptors
on post-synaptic membranes
– Inhibit production of new NTs
Let’s do this animation
http://www.jellinek.eu/brain/index.html?KeepThis=true&TB_iframe=true&height=
588&width=672
E.4.4 List three examples of
excitatory and three examples of
inhibitory psychoactive drugs
E.4.5 Explain the effects of THC
& cocaine in terms of their action
at the synapses in the brain.
THC & Cocaine affect mood, synapse
and behaviour
E.4.6 Discuss the causes of
addiction, including genetic
predisposition, social factors and
dopamine secretion.
Causes of Addiction
Addiction
• A chronic neurological disorder with genetic,
psychosocial and environmental characteristics
– Characterized by changes in the brain resulting in a
compulsive desire to use a drug
– Body often develops a tolerance and needs more
and more of the drug to produce the same result
Reward Centers
• Plays a key role in reinforcing behavour that
may lead to addiction
• Dopamine is the neurotransmitter most
prevalent in the reward pathways
– Drugs that stimulate the reward pathways
generate a feeling of pleasure
– High levels of dopamine cause a feeling of
euphoria & drugs that affect reward pathways are
particularly addictive (THC and cocaine)
Genetic Predisposition
Genetic Predisposition
• Study of twins
– Identical twins = 100 %
– Fraternal twins = 50 %
Male twins – if one twin suffers an addiction, the
rate of addiction in the second twin is 50% greater
with identical twins than fraternal
Genetic Predisposition
• Children of addicts are more likely to become
addicts themselves.
• The effect of genetics could be to produce a
different allele of a receptor gene, or to carry
modified versions of other genes linked to
drug metabolism and reward pathways.
Remember:
Susceptibility does not
mean inevitability!
Social Factors
Peer Pressure
Timing
Availability
Social Factors
Legality/Religion
Community
Family
Social Factors
Mental Health Issues
Mental Health
Depression
Abuse
Low selfesteem
Dopamine Secretion
• Dopamine activates the “reward pathway”
• Receptors constantly stimulated in drug
addiction
• Over-stimulation decreases the number of
receptors and the remaining receptors
become less sensitive to dopamine
• More and more of the drug is needed to have
the normal sense of well-being
Dopamine secretion
• Scientists studying knockout mice
– Genetically manipulated mice addicted to cocaine
• Found glutamate may be as or more
important than dopamine
– May oversee the learning and memories which
lead to cocaine-seeking
Check out this synaptic cleft!!!