Chapter 10.7: Transmission across synapses
A cholinergic synapse is one in which the neurotransmitter is a chemical called acetylcholine. This is
made up of two parts; acetyl (ethanoic acid) and choline. Cholinergic synapses are common in
vertebrates, where they occur in the central nervous system and at neuromuscular junctions
(junctions between muscles and neurones)
Application – effects of drugs on synapses
There are many different neurotransmitters responsible for the exchange of information across a
synapse. There are also many different types of receptor on the postsynaptic neurone. Some of
these neurotransmitters and receptors are excitatory, i.e. they create a new action potential in the
postsynaptic neurone. Others are inhibitory, i.e. they make it less likely that a new action potential
will be created in the postsynaptic neurone. Overall, the action of a neurotransmitter depends on
the receptor to which it binds.
Given that our perception of the world is through information received by receptors and transferred
to the brain by neurones and connect via synapses, it is not surprising that the effects of many
medicinal and recreational drugs are due to their actions on synapses. Drugs act on synapses in two
main ways:
They stimulate the nervous system by creating more action potentials in postsynaptic
neurones. A drug may do this by mimicking a neurotransmitter, stimulating the release of
more neurotransmitter or inhibiting the enzyme that breaks down the neurotransmitter. The
outcome is to enhance the body’s responses to impulses passed along the postsynaptic
neurone. For example, if the neurone transmits impulses from sound receptors, that person
will perceive the sound as louder.
They inhibit the nervous system by creating fewer action potentials in postsynaptic
neurones. A drug can do this by inhibiting the release of neurotransmitter or blocking the
receptors on sodium/potassium ion channels on the postsynaptic neurone. This causes the
body’s responses to be reduced. In this case, a person will hear a sound as being quieter.
The effects of a drug on neurotransmitter depend on the type of transmitter. For example, a drug
that inhibits an excitatory neurotransmitter will have one effect, but a drug that inhibits an inhibitory
neurotransmitter will enhance a particular effect. Examples:
- Endorphins are neurotransmitters used by certain sensory nerve pathways, especially pain
pathways. Endorphins block the sensation of pain by binding to pain receptor sites. Drugs
such as morphine, codeine and heroin bind to the specific receptors used by endorphins.
- Serotonin is a neurotransmitter involved in the regulation of sleep and certain emotions.
Reduced activity of the neurones that release serotonins is thought to be one cause of
clinical depression. Prozac is an antidepressant drug that affects serotonin within synaptic
clefts.
- GABA is a neurotransmitter than inhibits the formation of action potentials when it binds to
post synaptic neurones. Valium is a drug that enhances the binding of GABA to its receptors.
A cholinergic synapse is one in which the neurotransmitter is a chemical called acetylcholine. This is
made up of two parts; acetyl (ethanoic acid) and choline. Cholinergic synapses are common in
vertebrates, where they occur in the central nervous system and at neuromuscular junctions
(junctions between muscles and neurones)
Application – effects of drugs on synapses
There are many different neurotransmitters responsible for the exchange of information across a
synapse. There are also many different types of receptor on the postsynaptic neurone. Some of
these neurotransmitters and receptors are excitatory, i.e. they create a new action potential in the
postsynaptic neurone. Others are inhibitory, i.e. they make it less likely that a new action potential
will be created in the postsynaptic neurone. Overall, the action of a neurotransmitter depends on
the receptor to which it binds.
Given that our perception of the world is through information received by receptors and transferred
to the brain by neurones and connect via synapses, it is not surprising that the effects of many
medicinal and recreational drugs are due to their actions on synapses. Drugs act on synapses in two
main ways:
They stimulate the nervous system by creating more action potentials in postsynaptic
neurones. A drug may do this by mimicking a neurotransmitter, stimulating the release of
more neurotransmitter or inhibiting the enzyme that breaks down the neurotransmitter. The
outcome is to enhance the body’s responses to impulses passed along the postsynaptic
neurone. For example, if the neurone transmits impulses from sound receptors, that person
will perceive the sound as louder.
They inhibit the nervous system by creating fewer action potentials in postsynaptic
neurones. A drug can do this by inhibiting the release of neurotransmitter or blocking the
receptors on sodium/potassium ion channels on the postsynaptic neurone. This causes the
body’s responses to be reduced. In this case, a person will hear a sound as being quieter.
The effects of a drug on neurotransmitter depend on the type of transmitter. For example, a drug
that inhibits an excitatory neurotransmitter will have one effect, but a drug that inhibits an inhibitory
neurotransmitter will enhance a particular effect. Examples:
- Endorphins are neurotransmitters used by certain sensory nerve pathways, especially pain
pathways. Endorphins block the sensation of pain by binding to pain receptor sites. Drugs
such as morphine, codeine and heroin bind to the specific receptors used by endorphins.
- Serotonin is a neurotransmitter involved in the regulation of sleep and certain emotions.
Reduced activity of the neurones that release serotonins is thought to be one cause of
clinical depression. Prozac is an antidepressant drug that affects serotonin within synaptic
clefts.
- GABA is a neurotransmitter than inhibits the formation of action potentials when it binds to
post synaptic neurones. Valium is a drug that enhances the binding of GABA to its receptors.
