Synapses Flashcards
How wide are synaptic clefts?
20-50 nanometres
What are the 2 types of synapse?
Electrical synapses
Chemical synapses
How do electrical synapses work?
Use gap junctions to allow direct ion flow between neurons
What is the directionality of electrical synapses?
Bidirectional
Where are electrical synapses found?
Synchronized networks
How do chemical synapses work?
Use neurotransmitters to transmit signals across a synaptic cleft
What is the directionality of chemical synapses?
Unidirectional
Where are peptide neurotransmitters synthesized?
Neuron cell body
Where are amine and small-molecule neurotransmitters synthesized?
Pre-synaptic terminal
Neurotransmitters packaged into vesicles in the pre-synaptic neuron are stored near which areas?
Active zones
Describe the process of how neurotransmitters are released into the synaptic cleft via exocytosis.
An AP travels down the axon to the pre-synaptic terminal, where is depolarizes the membrane, opening voltage-gated Ca2+ channels. Ca2+ influx triggers the fusion of synaptic vesicles with the pre-synaptic membrane. The vesicles release neurotransmitters into the synaptic cleft via exocytosis
What are the 3 ways a neurotransmitter can be inactivated?
Reuptake
Degradation by enzymes
Diffusion away from synapse
What are the 3 chemical classes of neurotransmitters?
Amino acids
Amines
Peptides
What are the 3 amino acid neurotransmitters?
Gamma-aminobutyric acid (GABA)
Glutamate
Glycine
What are the 6 amine neurotransmitters?
Acetylcholine
Epinephrine
Norepinephrine
Histamine
Dopamine
Serotonin
What is the major excitatory neurotransmitter?
Glutamate
What is the major inhibitory neurotransmitter?
GABA
Since peptide neurotransmitters are synthesized in the cell body, by what mechanism do they reach the pre-synaptic terminal?
Vesicles travel along the axon via fast axonal transport mediated by the microtubule system
Neurotransmitters are packaged into vesicles in the pre-synaptic terminals via what?
Vesicular transporters (proton-coupled antiporters)
What are the 2 types of v-snares?
Synaptotagmin
Synaptobrevin
What are the 2 types of t-snares?
SNAP-25
Syntaxin
Which specific SNARE does calcium bind to to trigger vesicle fusion with the pre-synaptic membrane?
Synaptotagmin
What are the 2 types of neurotransmitter receptor?
Ionotropic (ligand-gated ion channels)
Metabotropic (G-protein coupled receptors)
What are the 2 potential membrane changes at the ionotropic receptors – describe polarization changes, type of cell influx, and type of neurotransmitter involved.
Depolarization (EPSP) – cation influx e.g. Na+ - excitatory neurotransmitters e.g. Glutamate
Hyperpolarization (IPSP) – anion influx e.g. Cl- - inhibitory neurotransmitters e.g. GABA
Define synaptic integration.
The process by which a neuron combines multiple synaptic inputs (both excitatory and inhibitory) to determine whether it will generate an action potential
What are the 3 key mechanisms of synaptic integration?
Spatial summation
Temporal summation
Shunting inhibition
Describe what is meant by spatial summation in relation to synaptic integration.
Multiple synapses are activated simultaneously
Describe what is meant by temporal summation in relation to synaptic integration.
A single synapse is activated repeatedly in quick succession
Describe what is meant by shunting inhibition in relation to synaptic integration.
When an IPSP is located near the soma or axon hillock, reducing the magnitude of EPSPs and reducing the likelihood that EPSPs would initiate an action potential
Synaptic plasticity / long-term synaptic changes are fundamental to which neural process?
Learning and memory formation in the hippocampus
What are the 2 forms of long-term synaptic change?
Long-term potentiation (LTP) and long-term depression (LTD)
Which 2 receptors and enzyme are involved in long-term synaptic changes?
AMPA and NMDA glutamate receptors
Calmodulin kinase
