1. OPTION E E4 NEUROTRANSMITTERS AND SYNAPSES

2. E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
Pre-synaptic neurons can either excite or inhibit post-synaptic transmissions. (AP = “all-or-nothing”)
This depends on which neurotransmitter (NT) is used and which receptors they bind to.

3. Excitatory: NT stimulates an AP in the post-synaptic neuron
E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
Excitatory: NT stimulates an AP in the post-synaptic neuron
NT binding to the receptors opens sodium gates, causing sodium to flow in, depolarizing the neuron.
Na+ in, neuron more positive, depolarization occurs.
NT: e.g. glutamate, acetylcholine (Ach), norepinephrine (NE),
dopamine

4. Inhibitory: NT prevents an AP in the post-synaptic neuron
E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
Inhibitory: NT prevents an AP in the post-synaptic neuron
NT binding to the receptors opens potassium gates, causing chloride to flow in, hyperpolarizing the neuron.
Cl- in, neuron more negative, more difficult to depolarize, impulse inhibited.
NT: e.g. GABA, dopamine

5. GABA = -Aminobutyric acid
E.4.1 STATE THAT SOME PRESYNAPTIC NEURONS EXCITE POST SYNAPTIC TRANSMISSION WHILE OTHERS INHIBIT POST-SYNAPTIC TRANSMISSION.
GABA = -Aminobutyric acid
GABA is a NT that opens chloride (Cl-) ion channels on the post-synaptic membrane. Cl- rushes in, hyperpolarizing the post-synaptic neuron and reducing APs.
GABA is important in regulating nervous processes – a “calming” or depressive effect (reducing activity).
It prevents neurons from overfiring,
and can be used as a drug to help
people with anxiety or stress-related
disorders.
Alcohol mimics the effect of GABA,
further increasing hyperpolarization
and therefore greatly reducing
nerve activity.

6. E.4.2 Explain how decision-making in the CNS can result from the interaction between the activities of excitatory and inhibitory presynaptic neurons at synapses.
Important points to remember:
- axons of many neurons feed into the dendrite of the post-
synaptic neuron
- each axon contributes to the membrane potential of the post-
- effects of the each input
can be either excitatory
or inhibitory
- effect is summative and
is added up at the axon
hillock.

7. multiple firing from one input
E.4.2 Explain how decision-making in the CNS can result from the interaction between the activities of excitatory and inhibitory presynaptic neurons at synapses.
If the summative effect of the inputs reaches threshold, an AP is propagated.
Spatial Summation:
multiple inputs
Temporal Summation:
multiple firing from one input

8. Excitatory drugs Inhibitory drugs
E.4.3 Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission.
Excitatory drugs
Inhibitory drugs
Block re-uptake pumps for NTs
- NT remains in synapse
e.g. cocaine’s effect on
dopamine
Mimic inhibitory NTs
↑ hyperpolarization of
post-synaptic neuron
fewer APs
e.g. alcohol mimics GABA
effects, reducing APs
Mimic excitatory NTs
- ↑ depolarization, more APs
e.g. nicotine
Blocks excitatory NTs
prevents APs
e.g. opiates (heroin)
block pain pathway by
competitive inhibition
Block inhibitory NTs
- prevent inhibition of APs
e.g. caffeine competitively
inhibit adenosine

9. Nicotine: stimulate alertness and memory, nausea and vomiting
E.4.4 List three examples of excitatory and three examples of inhibitory psychoactive drugs.
Excitatory
Nicotine: stimulate alertness and memory, nausea and vomiting
Cocaine/crack: increases heart rate, respiration, alertness
Amphetamines/ecstasy: causes anxiety and psychosis.

10. Benzodiazepines: muscle relaxant, reduces anxiety.
E.4.4 List three examples of excitatory and three examples of inhibitory psychoactive drugs.
Inhibitory
Benzodiazepines: muscle relaxant, reduces anxiety.
Cannabis: slows and prevents movement, impairs reasoning skills.
Alcohol: reduces heart rate, breathing rate, and blood pressure.

11. Excitatory drugs = Cocaine
E.4.5 Explain the effects of THC and cocaine in terms of their action at synapses in the brain.
Excitatory drugs = Cocaine
Normal:
Dopamine acts as an excitatory NT
Dopamine is re-uptaken at the pre-synaptic neuron pumps
With Cocaine:
Blocks receptors on reuptake pump
Dopamine not re-uptaken; remains in synaptic cleft
More dopamine is released
Increased post-synaptic transmission
Effect on mood/behavior
Enhanced feelings of pleasure (dopamine is a “pleasure” NT)
Increased energy and alertness
Highly addictive
Associated with depression (body reduces its own dopamine)

12. Inhibitory drugs = THC (cannibis)
E.4.5 Explain the effects of THC and cocaine in terms of their action at synapses in the brain.
Inhibitory drugs = THC (cannibis)
Normal:
Two pathways to consider
1) pathway released dopamine, increasing feelings of pleasrue
2) GABA has an inhibitory effect on release of dopamine
With THC:
Inhibits GABA release by binding to cannaboid receptors
GABA cannot inhibit dopamine
More dopamine is released
Increased post-synaptic transmission
Effect on mood/behavior
Enhanced feelings of pleasure (dopamine is a “pleasure” NT)
Intoxication (drunk feeling), hunger, memory impairment

13. E4.6 Discuss the causes of addiction, including genetic predisposition, social factors, and dopamine secretion.
Addiction
- a chronic neurological disorder with genetic, psychosocial and environmental characteristics.
- is characterized by changes in the brain resulting in a
compulsive desire to use a drug.
- “Reward centers” in the brain play a key role in
reinforcing behavior that may lead to addiction.

14. E4.6 Discuss the causes of addiction, including genetic predisposition, social factors, and dopamine secretion.
Reward Pathway
- makes one feel good when he/she engages in behaviors
that are necessary for survival (e.g. eating, drinking)
Dopamine is the NT most prevalent
in the reward pathway.
- generate a feeling of pleasure
- high levels of dopamine cause a
feeling of euphoria
- user may seek to repeat by using
the drug again (addictive)
- withdrawal of the drug leads to
anxiety, depression and craving

15. E4.6 Discuss the causes of addiction, including genetic predisposition, social factors, and dopamine secretion.
Some people are genetically more pre-disposed to becoming addicted than others.
May be the result of genetically determined deficiency of dopamine receptors.
The children of addicts are more likely to become addicts themselves.

16. E4.6 Discuss the causes of addiction, including genetic predisposition, social factors, and dopamine secretion.
Psychosocial factors are a heavy influence in addiction:
peer pressure
availability
legality or religion
family
cultural tradition
timing (adolescents more susceptible)
poverty/ social deprivation
traumatic life experience
mental health problem