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 PostSynaptic 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 Clions 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.
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
T. Re absorbed into the pre-synaptic neuron after
timulation
With Cocaine: Cocaine blocks receptors on
euptake pump, dopamine is not reabsorbed, so
emains in the synaptic cleft.
his increases post-synaptic transmission
hanges on mood: Dopamine is a pleasure NTnhances feeling of pleasure, feelings last longer as
opamine is not taken back to the pre-synaptic
euron
ffect on behaviour:
eelings of Euphoria
ncreased energy and alertness
ddictive
ssociated with depression(dopamine production by
ody 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.