
Neurotransmitters can be either excitatory or
inhibitory.

Excitatory neurotransmitters – promote an
action potential to occur in the post synaptic
neuron

Inhibitory neurotransmitters – make it more
difficult for an action potential to occur in the
post synaptic neuron

Generates an action potential in the post
synaptic neuron

A neurotransmitter is released from the presynaptic neuron and causes the post-synaptic
neuron to open its Na+ channels.

If the post synaptic neuron was originally at a
resting potential of -70mV, when Na+ enters
the neuron, the membrane potential
increases to become close to zero (it’s
depolarized!)

If threshold levels are reached, this is the
generation of an action potential in the post
synaptic neuron and thus the transmission of
a nerve impulse from one neuron to another

This is when a post synaptic neuron is
inhibited from producing an action potential
(and thus continuing a nerve impulse)

HOW?

Inhibitory neurotransmitters make the post
synaptic neuron more negative

Post synaptic neurons open it’s Cl- channels,
allowing Cl- to enter the neuron

This hyperpolarizes the membrane (makes it
more negative)
 Ie: a membrane potential lower than -70mV

(Another method could be the opening of K+
channels to cause K+ to move out of the neuron
which would also make the neuron more
negative)

This makes is more difficult to generate an
action potential on the post-synaptic
membrane because the resting potential is
now further away from the threshold value.

The means that a nerve impulse will (likely)
not be transmitted from neuron to neuron

Decision making is the summation of EPSP
and IPSP signals

More than 1 pre-synaptic neuron can form a
synapse with the same post-synaptic neuron
If the sum of the signals is excitatory, the
axon fires
If the sum of the signal is inhibitory, the axon
does not fire.



If there are
more EPSPs
than IPSPs,
then an action
potential will
be generated.

The neurotransmitters we’ve discussed so far
have all been fast-acting, crossing the
synaptic cleft and binding to receptors less
than a millisecond after an action potential
arrived at the pre-synaptic membrane.

Some neurotransmitters are slow-acting or
neuromodulators and take hundreds of
milliseconds to act on the post-synaptic
membrane.

Instead of acting on a single post-synaptic
neuron, they diffuse into the surrounding
fluid and act on groups of neurons.

Ex: noradrenalin/norepinephrine, dopamine,
and serotonin are slow acting
neurotransmitters.

Slow acting neurotransmitters do not affect
ion movement across the post synaptic
membranes directly but instead cause the
release of secondary messengers inside post
synaptic neuron which regulate fast synaptic
transmission.

In this way they can modulate fast acting
neurons for relatively long periods of time.

Involve changes in neurons caused by
neuromodulators.

Neuromodulators release secondary
messengers inside the post-synaptic neurons
and can promote synaptic transmission by
 increasing the number of receptors in post-
synaptic membrane
 chemical modification to increase the rate of ion
movements when a neurotransmitters binds

The secondary messengers can persist for
days and cause what is known as long-term
potentiation (LTP), allowing new synapses to
form in the hippocampus and other areas of
the brain.

This is central from memory and learning.

Remember, neurotransmitters are chemicals
that allow neurons to communicate with each
other.

There are over a hundred different brain
neurotransmitters

The two main excitatory neurotransmitters are
acetylcholine and noradrenalin.

The two classes of neurotransmitters are
cholinergic and adrenergic
CHOLINERGIC
ADRENERGIC
Ex of
Neurotransmitter
Acetylcholine
- Released by all motor
neurons
- Activated skeletal muscle
Noradrenalin
- Hormone and a
neurotransmitter
- Most important role is
effect on heart
- Also increase blood flow to
skeletal muscles and
glucose release
System
Parasympathetic
- Ie involved in relaxation
Sympathetic
- Ie involved in “fight or
flight” reactions
Effect on Mood
Calming effect on mood
Increase alertness, energy,
and euphoria

Neurotransmitter produced by the brain

It causes you to feel good

Any activity that increases the effect of
dopamine is potentially addictive because the
individual will want to continue the “good
feelings” it creates.

Many drugs interfere with dopamine and extend the
time this substance is found at the synapse, which
make us feel good.

In drug addiction, dopamine receptors are constantly
stimulated.

Over stimulation, decreases the number of dopamine
receptors (desensitization)

As a result, when the drug has worn off, users
experience less joy (because less receptors) out of
every day events – thus, reinforcing drug use

Also, drug intake needs to be increase to achieve the
same “high”

Can affect the brain and personality by either
increases or decreasing post-synaptic
transmission

Psychoactive drugs affect the level of
neurotransmitters
In this way they can increase or decrease post
synaptic transmission

Enhance the release of a neurotransmitters
1)


2)
Ex: Ecstasy
Increases euphoria,
diminishes anxiety
Stop the release of a neurotransmitter
Mimic the effect of a neurotransmitter
3)


Ex: LSD, morphine and heroin
Mimic endorphins which are natural pain killers
Block the removal of a neurotransmitter
from the synapse (and prolong the effect of
the neurotransmitter)
4)

Ex: Cocaine
Block the receptors of the neurotransmitter
(preventing depolarization or
hyperpolarization)
5)

PCP/Angel Dust

Encourage synaptic transmission

For many drugs, after frequent use, the number
of receptors on the post-synaptic membrane are
reduced which leads to a decrease in the affect
of the drugs.
Increasing doses are needed to obtain the same
affect.


Examples:
 Nicotine, Cocaine, Amphetamines



These are drugs that promote activity of the
nervous system (by mimicking the sympathetic
nervous system)
Make the user more alert, energetic, and selfconfident.
Many excitatory drugs are stimulants

Some mild simulants are present in food and
drinks such caffeine in coffee, tea, soft drinks

May be prescribed to treat depression and
narcolepsy


Found in cigarettes
Is both a stimulant and a relaxant

As a stimulant, it causes an increase in
adrenaline which increases heart rate, blood
pressure and blood sugar levels.

As a result it may appear to increase
concentration

Effect can also reduce appetite

As a relaxant it mimic acetylcholine

Acts on cholinergic synapses of the body and
brain to release dopamine – which causes
pleasure and makes it addictive

A stimulant made from extracts of the Coca
plant

Stimulates the CNS and causes feelings of
euphoria, talkativeness, increased mental
alertness.

Temporary decrease in need for food and sleep.

Large amounts will cause erratic and violent
behaviour

Blocks the re-uptake of dopamine, so dopamine
accumulates in the synapse

Thus addictive feelings of happiness are created
(Cocaine is highly addictive)

It also makes the user feel less tired or hungry
and enhances endurance

The “high” that cocaine provides is usually
followed by a “crash” when the effect of the
drug wears off resulting in depression,
irritability, and paranoia

Remember, the brain will reduce the number
of dopamine receptors when overloaded with
cocaine

Thus, when drug has worn off, users
experience less joy from everyday life further
reinforcing increase cocaine use.


Drug Free World (8 min)
http://www.drugfreeworld.org/real-lifestories/cocaine.html


ASAP Science
https://www.youtube.com/watch?v=vxI7PTVRfhQ


For chenchen
https://www.youtube.com/watch?v=PoGXr6hUTD4

Stimulate the CNS

cause the release of noradrenaline and
dopamine and inhibit their uptake

This leads to increased concentration and
performance


10 years of drug abuse
http://www.youtube.com/watch?v=Opi_Eac
MJcg

Mimics dopamine.
Binds to dopamine receptors (on post
synaptic membrane)
Used for treatment in the early stages of
Parkinson’s disease to reduce the effects of
insufficient dopamine secretion.
Also used as an anti-depressant


Parkinson’s
http://www.pennmedicine.org/encyclopedia/em_DisplayAnimation.aspx?gcid=000095&ptid=17




Reduce synaptic transmission
Many are sedatives

Examples

 Benzodiazepines
 Alcohol
 Tetrahydrocannabinol (THC)

Tranquilizers which slow down the CNS

Ex: Valium (Diazepam), which can be used to
treat anxiety, insomnia, and muscle spasms

They hyperpolarize the post-synaptic
membranes so that impulses are not sent
(increase release of neurotransmitter GABA
which causes Cl- to enter neuron)



Depresses the CNS
It reduces social inhibitions and makes the
person feel cheerful and relaxed.

It causes a receptor of GABA to remain open
longer, further hyperpolarizing the
postsynaptic membrane

This explains the sedative effect of alcohol

(Also helps to increase the release of
dopamine – but not well understood how)

Found in the Cannabis plant (marijuana)
Causes relaxation and can act as a pain killer by
binding to the endorphin receptors causing
hyperpolarization
 Often create feelings of lightheadedness and
increased appetite.


Other receptors it binds to (cannabinoid receptors)
will negative affect mental and physical activities:




Learning
Coordination
Problem solving
Short term memory

Affects hippocampus of the brain, which is important
for short-term memory.

Affects cerebellum (involved in coordination) which
causes motor impairment

The impairment of memory and decision making
abilities cause students using THC to statistically gain
lower grades than those not using it.

Scientific research is not unified either way on THC
being addictive or not


Marijuana and the brain
http://www.youtube.com/watch?v=oeF6rFN9
org

Act by interfering with neural transmission
between areas of sensory perception and the
CNS, causing the temporary loss of sensation
in all or parts of the body

Local anaesthetics (such as those used by the
dentist or when getting stiches) cause
numbness in an area of the body

A patient who has been given a general
anaesthetic will normally have no awareness
of the medical procedures they have
undergone as they are unconscious and lack
total sensation.

Inhibit sensory organs as will as signals to
motor neurons

Drug Addiction is the repeated and
compulsive use of psychoactive drugs

Can be affected by genetic predisposition,
social environment, and dopamine secretion

Controversial

Studies have shown that if there is one
addictive person in a family, there is a greater
chance of there being another

Believed there is an “addiction gene” that
may be turned on in an individual due to
environmental context

One example is the DRD2 gene, which codes
for the dopamine receptor protein.

There are multiple alleles of this gene and
recent studies have shown that people with
the A1 allele for the gene consumed less
alcohol than those homozygous for the A2
allele for the gene.

There is an increased chance of addiction for
people:
 living in an environment where there is substance
abuse
 Who suffer from a childhood trauma and/or
neglect

Psychoactive drugs may become a way for
dealing with this

May addictive drugs (including opiates,
cocaine, nicotine, alcohol) affect dopamine
secretion, causing prolonged periods of high
dopamine levels in the brain.