E4 Neurotransmitters and synapses Ms. TRS

E.4.1 State that some presynaptic neurons excite postsynaptic transmission and others inhibit postsynaptic transmission. 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.

At the synapse… There are two main types of actions, excitatory and inhibitory. Excitatory actions depolarize the postsynaptic membrane. Inhibitory actions hyperpolarize the postsynaptic membrane, making it more difficult to reach the threshold for the action potential.

Excitatory Neurotransmitters NT stimulates an AP in the Post-Synaptic neuron Acetylcholine is an example of a generally excitatory neurotransmitter. It is active in muscle contraction. Glutamate is another important excitatory NT; it is the most abundant NT in the CNS. Excitatory NTs increase permeability of the postsynaptic membrane to positive ions. This allows Na+ ions to diffuse into the postsynaptic neuron, leading to depolarization and generation of Action Potential

Inhibitory Neurotransmitters NT prevents an AP in the Post-Synaptic neuron GABA (-aminobutyric acid) is the most common inhibitory neurotransmitter. Inhibitory NTs cause hyperpolarization of post synaptic neuron (makes neuron more negative), thereby inhibiting action potentials. When inhibitory NTs bind to receptors, either K+ ions move out of the cell, or Cl- ions move in.

Decision making in the CNS At any given time, a neuron may receive both inhibitory and excitatory signals. If summation of these signals is inhibitory, then it will not fire an action potential. If it is excitatory and reaches the required threshold, then an action potential will fire.

Summation

Psychoactive drugs E.4.3 Explain how psychoactive drugs affect the brain and personality by either increasing or decreasing postsynaptic transmission. E.4.4 List three examples of excitatory and three examples of inhibitory psychoactive drugs.

Inhibitory Drugs Excitatory Drugs Increase synaptic transmission Psychoactive drugs affect the brain and personality by either increasing or decreasing post synaptic transmission Excitatory Drugs Increase synaptic transmission Includes many (but not all) stimulant drugs Nicotine, cocaine, amphetamine Inhibitory Drugs Decrease synaptic transmission Includes many (but not all) depressant drugs Benzodiazepines (Valium), alcohol, THC

Psychoactive drugs

Effects of THC and Cocaine E.4.5 Explain the effects of THC and cocaine in terms of their actions at synapses in the brain. E.4.6 Discuss the causes of addiction, including genetic predisposition, social factors and dopamine secretion.

Effects of Cocaine Normal conditions: Dopamine acts as an excitatory NT. Re absorbed into the pre-synaptic neuron after stimulation With Cocaine: Cocaine blocks receptors on reuptake pump, dopamine is not reabsorbed, so remains in the synaptic cleft. This increases post-synaptic transmission Changes on mood: Dopamine is a pleasure NT- enhances feeling of pleasure, feelings last longer as Dopamine is not taken back to the pre-synaptic neuron Effect on behaviour: Feelings of Euphoria Increased energy and alertness Addictive Associated with depression(dopamine production by body is reduced).

Effects of THC Normal: GABA HAS AN INHIBITORY EFFECT ON THE RELEASE OF DOPAMINE. With THC: THC inhibits GABA Release by binding to Cannaboid receptors, so GABA cannot inhibit dopamine. Therefore more dopamine is released. Effect on mood: Higher levels of Dopamine stimulate reward centres – increase feelings of pleasure Effect on behaviour: Intoxication(drunk feeling) - hunger - memory impairment

Causes of Addiction What is it?? Is a nuerological disorder with genetic, social and environmental characteristics Addiction often involves actions of dopamine neurons This is part of why so many psychoactive drugs have the common factor of acting on the dopaminergic system

Social factors Peer pressure and age: Strong peer pressure especially during adolescence increases chance of using drugs. Availability: Easy access to drugs increases chances of addiction. Legality and religion: In countries where use of drugs is prohibited by the law and culture, use of drugs and addiction is rare. Family and community: Relaxed attitudes to drugs can encourage addiction Mental health: depression, abuse and low self esteem can lead to drug use and addiction.