OPTION E E4 NEUROTRANSMITTERS AND SYNAPSES

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

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

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

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.

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.

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

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

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

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

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) http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_cocaine.html#drogues

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 http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_cannabis.html#drogues

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.

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

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.

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