Lecture 3: Synaptic Transmission Flashcards
Types of synapse, synaptic structure, vesicular release, receptors and neurotransmitters
What is a synapse?
Junction where information is passed from one neuron to another (or to muscle)
The term ‘synapse’ originates from the work of Michael Foster.
Who were key figures in the discovery of synapses?
Michael Foster and Charles Sherrington
Charles Sherrington received the Nobel Prize in Physiology or Medicine in 1932.
What are the two main types of synapses?
- Electrical
- Chemical
What are the key features of an electrical synapse?
*no delay
*can be two way
*little plasticity
What is the typical width of a synaptic cleft in a chemical synapse?
~ 20-40 nm wide
What is the typical width of a synaptic cleft in a electrical synapse?
20 nm
What are the types of chemical neurotransmitters and give one example of each?
- Amino acids e.g. GABA
- Amines e.g. dopamine
- Neuroactive Peptides e.g. orexin
- Others e.g. acetylcholine
What is the role of calcium ions (Ca2+) in neurotransmitter release?
Ca2+ entry leads to fusion of docked vesicles and release of neurotransmitter (exocytosis)
Ca2+ binds to synaptotagmin, acting as the Ca2+ sensor.
What are the basic steps of neurotransmitter release?
- Docking/priming
- Ca2+ entry
- Vesicle fusion (exocytosis)
- Recycling of vesicles (endocytosis)
What is the function of SNAP and SNARE proteins?
Anchor vesicles to the presynaptic membrane
What is the difference between ionotropic and metabotropic receptors?
- Ionotropic: Fast signalling, permeable to Na+/K+
- Metabotropic: Slower signalling, involves second messenger cascade
What neurotransmitter does choline acetyltransferase (CHAT) synthesize?
Acetylcholine
What is the function of acetylcholinesterase (AChE)?
Metabolizes acetylcholine in the extracellular space
List the criteria for identifying a substance as a neurotransmitter.
- Synthesized in the neuron
- Show activity-dependent release from terminals
- Duplicate effects of stimulation when applied exogenously
- Actions blocked by competitive antagonists
- Removed from the synaptic cleft by specific mechanisms
What is the significance of Otto Loewi’s work?
Demonstrated that a chemical messenger (‘Vagusstoff’) slows heart rate, providing evidence for acetylcholine as a neurotransmitter
Fill in the blank: Chemical synapses are ________ from presynaptic neuron to modulate postsynaptic neuron.
chemical released
True or False: Electrical synapses have a delay in transmission.
False
What happens during the recycling of vesicles?
Endocytosis occurs after neurotransmitter release
What are dendritic spines?
Major constituent of the postsynaptic density and marker of synapses
What neurotransmitters are released from vesicles containing 1000-2000 molecules per vesicle?
Acetylcholine
What is required for chemical synaptic transmission?
- Nerve terminal
- Neurotransmitter synthesis
- Packaging into vesicles
- Transmitter release
- Binding to receptors
- Removal of transmitter
What are the key features of a chemical synapse?
*delay (at least 0.5 ms)
*one way
*plastic
What is a key physical difference between electrical and chemical synapses?
In an electrical synapse, the two membranes are very close together where as there tends to be a bigger gap between the post and pre synaptic membrane in a chemical synapse.
In summary, what occurs at a chemical synapse?
Chemical released from presynaptic neuron to modulate postsynaptic neuron or muscle
What is the role of connexons?
to form permeable ion channels. 6 connexons form hemi channels that come together to form gap junctions
What are connexins called in invertebrates?
innexins
What is the average width of a vesicle in a synapse?
40-50 nm
*Axodendritic- axon terminal to dendrite, excitatory
*Axosomatic- axon terminal to soma, inhibitory
*Axoaxonic- axon terminal to another axon, modulatory
Where are peptide neurotransmitters synthesised?
in the soma
