Neurotransmission Flashcards
What is neurotransmission`/
Communication of information between neurons in the brain
What is the function of neurons?
To communicate information.
Give an example of the function of neuron communication
Maintaining homeostasis
What is a synapse?
A specialised junction where transmission of information takes place between a nerve fibre and another nerve, or a muscle of gland.
Loewi’s demonstration of chemical neurotransmission
Where the vagus nerve of an isolated frog’s heart was stimulated, the heart rate decreased (upper panel). If the perfusion fluid from the stimulated heart was transferred to a second heart, its rate decreased as well (lower panel).
Neurotransmission substance requirements
- The substance must be present within the presynaptic neuron.
- The substance must be released in response to presynaptic depolarization, and the release must be Ca2+-dependent.
- Specific receptors for the substance must be present on the postsynaptic cell.
What does demonstrating the identity of a neurotransmitter at a synapse require?
Showing
- It’s presence
- It’s release
- The postsynaptic presence of specific receptors
What is action potential?
The electrical signals in neurons that convey information from the brain to organs
Central nervous system synapses process
- Action potential reaches axon terminal of presynaptic neuron
- Ca2+ enters synaptic knob (presynaptic axon terminal)
- Neurotransmitter is released by exocytosis into the synaptic cleft
- Neurotransmitter bind to receptors that are an integral part of chemically gated channels on subsynaptic membrane of posysynaptic neuron
- Binding of neurotransmitter to receptor opens that specific channel
What are the three types of neuronal communication?
- Chemical transmission*
- Electrical transmission*
- Ephaptic transmission
Whats involved in ephaptic transmission?
Where two axons are so close together that the current produced by one has a major effect on the adjacent axon
What does wiring transmission require?
Requires close contact with specialised sites within neurons
What does volume transmission require (not)?
Does not require specific connections between cells. It is a slower and less specific form of neurotransmission.
How do neurotransmitters move by in volume trasnmission?
- Diffusion through the blood stream
- Cerebral Spinal Fluid (CSF)
What is the release of neurotransmitter involved in volume transmission?
Extrasynaptic release of chemical messenger (neurotransmitter)
What is chemcial transmission?
Communication between neurons that involves the rapid release of a chemical messenger that diffuses across to the receiving cell and causes a change in the postsynaptic cell’s properties.”
Where does chemical transmission occur at?
Synapse
How is information transmitted in a chemical synapse?
Form of chemical message
Give the basic details of chemical transmission
- Synthesis and storage of neurotransmitter
- Conduction of action potential down the axon of a neuron
- Opening of voltage-gated Ca2+ channels
- Release of transmitter into the synaptic cleft
- Activation of postsynaptic receptors
- Breakdown/ reuptake of neurotransmitters
Give the ‘biochemical’ details of chemical transmission
- Transmitter is synthesized and then stored in vesicles.
- An action potential invades presynaptic terminal.
- Depolarization of presynaptic terminal causes opening of voltage-gated Ca2+ channels.
- Influx of Ca2+ through channels
- Ca2+ causes vesicles to fuse with presynaptic membrane.
- Transmitter is released into synaptic cleft via exocytosis
- Transmitter binds to receptor molecules to postsynaptic membrane
- Opening of closing of postsynaptic channels
- Postsynaptic current causes excitatory or inhibitatory postsynaptic potential that changes the excitability of the postsynaptic cell.
- Retrieval of vesicular membrane from plasma membrane
What are neurotransmitters?
Chemicals that are released at a synapse by the presynaptic neuron and consequently affect the postsynaptic cell in a specific manner
What are the three main categories of neurotransmitters?
- Amino acids
- Peptides
- Monoamines
What is acetylcholine involved in?
Voluntary movement of the muscles
What is glutamate involved in?
Major excitatory neurotransmitter, roles in memory and learning
What is dopamine involved in?
Motivation, pleasure associated with addiction and love
What is serotonin involved in?
Emotions, wakefulness and temperature regulation
What is GABA involved in?
The major inhibitory neurotransmitter
What do neurotransmitters bind to and what does this cause?
Bind to specific postsynaptic receptors, causing either excitation or inhibition of postsynaptic neuronal activity.
What are neurotransmitters stored in?
In synaptic vesicles
What is the purpose of neurotransmitters being stored in synaptic vesicles?
- Protect from enzyme degradation
- Ready for release
What are the types of vesicles?
- Small clear-core vesicles (50 nm diameter)
- Large, dense core vesicles (100 nm)
What are small clear-core vesicles triggered by?
Triggered by single action potentials (low MW neurotransmitters)
What are large dense-core vesicles released by?
Burst firing or repetitive stimulation (bioamines and neuropeptides)
Name the small molecule transmitters.
- Acetylcholine
- Amino acids
- Purines
- Biogenic amines
Name the peptide transmitters.
- Substance P
- Opioids
- Somatostatin
- Vasopressin
Give the details of small-molecule transmission
- Synthesis of enzymes in cell body
- Slow axonal transport of enzymes
- Synthesis and packaging of neurotransmitter
- Release and diffusion of neurotransmitter
- Transport of precursors into terminal
Give the details of peptide transmission
- Synthesis of neurotransmitter precursors and enzymes
- Transport of enzymes and pre-peptide precursors down microtubule tracks
- Enzymes modify pre-peptides to produce peptide neurotransmitter
- Neurotransmitter diffuses away and is degraded by proteolytic enzymes
What do action potentials do to synaptic terminals?
Action potentials depolarise synaptic terminals
What happens when action potentials depolarise synaptic terminals?
Voltage-sensitive Ca+ channels are opened
What is involved in docking in presynaptic vesicles?
Movement of vesicle from reserve pool to tight association with plasma membrane