Synaptic Transmission Flashcards
(20 cards)
Describe the differences between graded and action potentials
Location: dendrites & cell body not axon hillock. Amplitude, smaller but can summate to result in an AP. Usually longer in duration 5ms to minutes. Decremental not all or none conduction. Depolarising or hyperpolarising signal unlike depolarising APs. No refractory period, shorter distance of transmission - usually cell body to hillock.
Describe the structure of a synapse
you know this I ain’t typing it
Describe the sequence of events in synaptic transmission
again I ain’t typing all that
How long does it take for neurotransmitter to be secreted following AP arrival?
0.5ms
Difference between fast vs slow synaptic transmission?
Fast transmission, e.g. at the NMJ, is fast and short-lived, usually involving the neurotransmitter binding to ligand-gated ion channels on the post-synaptic membrane. Slow synaptic transmission involves neurotransmitter activating a G-protein-linked receptor, and the change in cells in slower but longer-lasting (e.g. norepinephrine effect on adrenoreceptors in the peripheral blood vessels)
What is an excitatory post-synaptic potential?
An epsp occurs when neurotransmitter binds to and opens non-selective cation channels on the post synaptic membrane, causing a brief depolarisation of the cell that shifts the membrane potential closer to the threshold for AP generation, rendering the postsynaptic cell more excitable.
What is the duration of an epsp?
Peaks in 1-5ms and decays to nothing over the ensuing 20-50ms
What determines the value of depolarisation due to an epsp?
The number of cation channels opened - as more opening means increased permeability of the post-synaptic membrane relative to K+ permeability, bringing the membrane potential closer to zero and the threshold. In neurons, epsps rarely exceed a few mV, but NMJ endplate potentials are usually about 40mV in amplitude
How does fast inhibitory synaptic transmission work?
neurotransmitters such as GABA and glycine activate chloride channels on the post-synaptic membrane, causing brief hyperpolarisation - called an ipsp.
How does Cl- channel opening cause an ipsp?
The resting membrane potential of the post-synaptic membrane is about -70mV, while equilibrium for K+ ions is about -80mV, and is similar for Cl- ions. When Cl- channels open, membrane because more permeable to Cl- relative to K+, shifting the membrane potential to a more negative value.
What is summation?
E/ipsps are not all-or-none but graded with the intensity of activation, so can be superimposed on each other sequentially or from multiple synapses at once - temporal or spatial summation.
What are the three sites for synapses?
Axodendritic. Axosomatic. Axoaxonic, allowing the presynaptic neuron blockage AP propoagation to the axon terminal of the post-synaptic axon, presynaptic inhibition
What are the major classes of neurotransmitters and examples of each?
Esters – Acetylcholine (ACh)
Monoamines – Norepinephrine, dopamine, serotonin
Amino Acids – Glutamate, GABA
Purines – Adenosine, ATP
Peptides – Enkephalins, Substance P, VIP
Inorganic Gases – Nitric oxide (NO)
How does slow synaptic transmission work?
Nerve fibres have a number of varicosities along their length that secrete neurotransmitter into the extracellular fluid around a number of target cells rather than into a small, specific cleft. Seen in the autonomic nervous system e.g. adrenergic autonomic nerve fibres on smooth muscle.
What is dual transmission?
Some nerve terminals contain two different neurotransmitters and both may be released following an AP - cotransmission. E.g. parasympathetic nerves at salivary glands release VIP and Ach, former stimulates increased local blood flow and latter salivation from acinar cells.
Where does neurotransmitter go following transmission?
It’s either hydrolysed by an enzyme (only for Ach), taken up into secreting or neighbouring cells, or diffuses away followed by either of the other two means.
What is carried to the axon and distal dendrite by fast anterograde transport?
All newly synthesised organelles, including vesicles and precursor molecules for peptide neurotransmission
What is carried to the axon and distal dendrite by slow anterograde transport?
soluble cytoplasmic and cytoskeletal proteins
What is the importance of retrograde axonal transport?
enables the neuron to recycle material used for synaptic transmission and allows transport of growth factors from the terminal to the cell body - allow 2 way communication between target tissue and neuron possibly important in development
How is retrograde axonal transport exploited?
Some viruses, like polio or rabies, use it to gain entry to the CNS. Tetanus toxin does the same.
