OPTION E E4 NEUROTRANSMITTERS AND SYNAPSES

1. OPTION EE4 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. http://www.youtube.com/watch?v=LT3VKAr4roo http://learn.genetics.utah.edu/content/addiction/reward/neurontalk.html

3. 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. 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. 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- synaptic neuron - effects of the each input can be either excitatory or inhibitory - effect is summative and is added up at the axon hillock.

7. 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 http://hsc.uwe.ac.uk/synapses_neuro/summation.htm

8. 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 http://outreach.mcb.harvard.edu/animations/synapse.swf

9. 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. http://www.talktofrank.com/drugs-on-the-brain http://www.jellinek.nl/brain/index.html

10. 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. http://www.jellinek.nl/brain/index.html

11. E.4.5 Explain the effects of THC and cocaine in terms of their action at synapses in the brain. 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) Excitatory drugs = Cocaine http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_cocaine.html#drogues

12. E.4.5 Explain the effects of THC and cocaine in terms of their action at synapses in the brain. 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 Inhibitory drugs = THC (cannibis) http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_cannabis.html#drogues

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