Understanding Neurotransmitters and Synapses in Brain Function

1. A.5 NEUROPHARMACOLOGY

2. Neurotransmitters & Synapses • Review 6.5 transmission of a nerve impulse (Pre and Post synaptic clefts) • Neurotransmitters transfer information across the synapse • Are either excitatory or inhibitory

3. Excitatory neurotransmitters • Depolarize the postsynaptic cell sending the action potential forward • Encourages transmission by making the electrochemical gradient more positive • Increases permeability of postsynaptic membrane making it easier for Na+ to move in

4. Inhibitory Neurotransmitters • Hyperpolarize the postsynaptic cell inhibiting the action potential from being sent • Discourages transmission • Makes the electrochemical gradient more negative • Positive ions move out • Harder to excite

5. Summation • The sum of the potentials, positive and negative, determine if an action potential occurs. • More than one presynaptic neuron can form a synapse with the same postsynaptic neuron

7. Slow and Fast Neurotransmitters • Neurotransmitters are classified in two ways • Fast-acting: opening gated ion channels • Initiate cellular responses (milliseconds) • Slow-acting: using second messengers or proteins and not directly opening gated ion channels • Take a few hundred milliseconds up to a few minutes • Modulate fast acting neurotransmitters • Involved in learning and the formation of memory • Do not just affect one neuron but diffuse to affect an area of neurons

8. Memory and Learning • Memory and learning involve changes in neurons caused by slow-acting neurotransmitters • Cause the release of secondary messengers to promote synaptic transmission • Increasing the number or receptors in the post synaptic membrane • Chemical modification of these receptors to increase rate of ion movement • Secondary messengers can remain for days and cause LTP (long-term potentiation) • Deals with synaptic plasticity • Linked to hippocampus and other areas on the brain

9. Psychoactive Drugs the Brain • Can increase or decrease transmission of neurotransmitters (usually dopamine, serotonin, GABA or acetylcholine) • Can affect: • Mood • Thinking processes • Personality & behavior • Influence levels of consciousness

10. Psychoactive drugs act on synapses • Inhibit neurotransmitter from being released • Mimicking the neurotransmitter • Drug binds to receptors and prevents neurotransmitter from binding (inhibiting) • Drug binds to receptors and activates the channel in the same way as the neurotransmitter (stimulating) • Drug can interfere with the enzymatic breakdown of the neurotransmitter (repeated action potentials sent) • Drug can interfere with the process of reuptake (repeated action potentials sent)

11. Excitatory Psychoactive drugs • Stimulate action potentials to be sent (excite) • Usually associated • Dopamine: activates reward pathway (euphoria, well being and overall happiness) • Acetylcholine: regulates muscles & glands • Examples • Nicotine • Cocaine • amphetamines

12. Inhibitory psychoactive drugs • Inhibit action potentials from being sent (calm) • Usually associated with • GABA: stops neural transmission • Serotonin: many roles like balancing mood and regulating sleep • Examples • Benzodiazepines • Alcohol • Tetrahydrocannabinol (THC)

13. Effects of THC and Cocaine

14. Effects of Cocaine and THC

15. Endorphins • Morphine like proteins (oligopeptides) that act on the CNS, affecting emotions and decreasing the perception of pain

16. Anaesthetics • Cause the reversible loss of sensation and awareness • Interfere with neural transmission by blocking sensory perception in the CNS • Local • general

17. Addiction

18. Causes of Addiction