Synaptic Transmission Flashcards
What is the synapse?
The synapse is specialised for the release & reception of a chemical Neurotransmitter (NT)
is 30-50 nm wide and prevents direct AP from one neuron to another
Transmission is unidirectional
Post synaptic potentials
Excitatory postsynaptic potential (EPSP) = depolarisation that brings the postsynaptic membrane closer to the threshold for AP generation
Inhibitory postsynaptic potential (IPSP) = hyperpolarisation that drives the postsynaptic membrane away from the threshold for firing
Excitatory Synapses
Binding of the NT increases the postsynaptic neuron’s ability to produce an AP
Binding of the NT causes opening of non-specific cation channels, allowing simultaneous diffusion of Na + and K +, causing net depolarisation, an EPSP (Excitory Post Synaptic Potentional)
It brings the membrane potential towards threshold
An example is glutamate
Inhibitory Synapses
Binding of the NT decreases the postsynaptic neurone’s ability to produce an AP
It causes opening of either a K+ or Cl- channel - in either case, the result is hyperpolarisation, an IPSP
The IPSP drives the membrane potential further away from threshold
An example is gamma (γ) - aminobutyric acid (GABA) and glycine
Neurotransmitters
Vary from synapse to synapse
Usually same NT released at particular synapses but sometimes co-transmission is possible
Quickly removed from synaptic cleft
Common NT examples are amines (dopamine etc), amino acids (GABA etc), Neuropeptides (endorphins etc.)
Neuromodulation
Neuromodulator is a chemical messenger released by a neuron that doesn’t cause ESPs or ISPs
Typically act through G-protein coupled receptors/intracellular messengers
Might act pre-synaptically or postsynaptically
Synaptic and extrasynaptic distribution
Examples might be serotonin or dopamine
Presynaptic Inhibition
GABA release at axoaxonal synapse inhibits opening Ca2+ channels in synaptic knob
Reducing the amount of NT released when an AP arrives
Presynaptic Facilitation
Activity at axoaxonal synapse increases amount of neurotransmitter released when AP arrives
Enhances and prolongs the effect of the NT
Synaptic Drug Interactions
Altering the synthesis, axonal transport, storage, or release of a NT
Modifying NT interaction with the postsynaptic receptor
Influencing NT reuptake or destruction
Replacing a deficient NT with a substitute transmitter
Drugs that alter synaptic transmission
Botulinum Toxin - Inhibits ACh release in neuromuscular junctions (NMJs) and other synapses
Tetanus Toxin - Prevents release of inhibitory neurotransmitter GABA affecting skeletal muscles (by the reduction of presynaptic inhibition)
Cocaine - Blocks reuptake of neurotransmitter dopamine at presynaptic terminals
Mesolimbic dopamine system
Dopamine pathway in the brain
Dopamine is responsible for controlling the brain’s pleasure and reward centres - it is out feel so there is good NT
Stimulated by actions that we find pleasurable so then we are encouraged to repeat them
Pathway stimulated by addictive drugs
