lecture 29 - Synaptic transmission Flashcards
glutamate transporter
removes glutamate to presynaptic terminals and astrocytes. Other transporters take it to be stored in synaptic vesicles
what are the 2 classes of neurotransmitters?
- small molecule neurotransmitters (‘classical’)
- neuropeptides (‘neuromodulators’)
substance P and endorphins
neuropeptides
synapse found in retina
electrical synapse
what does the increase of permeability to Cl-, due to IPSPs, cause ?
decreased cell membrane resistance. They make the current induced by EPSPs less efficient in bringing postsynaptic membrane to threshold.
metabotropic
indirectly gated glutamate receptors
how are most amino acids inactivated?
re-uptake
factors affecting synaptic action:
(a) type of neurotransmitter/neuroregulator
(b) type of neurotansmitter receptor expressed in post-synaptic membrane/ multiple receptor subtypes
(c) number of neurotransmitter receptors in the postsynaptic membrane - synaptic plasticity
Direct gating of ion channels (characteristics and features)
- transmitter binds directly to the ion channel complex and the pore opens
- very fast onset
- short-lived
neuromuscular junction =
chemical synaptic transmission between the axon terminals of motoneurons and the end-plates of muscle fibres
features of classical, small molecule neurotransmitters
fast action, acting directly
how small are the postsynaptic potentials?
around 0.1mV
AMPA, Kainate
directly gated glutamate receptors
too much glutamate release (or insufficient re-uptake) will lead to…
excitotoxicity: too much glutamate leads to excessive depolarisation of neurons. The long-term opening of NMDA receptors leads to excessive Ca2+ entering = damage to neurons
EPSPs and IPSPs work together TRUE/FALSE?
FALSE they work independently
axodentritic synapse
where the axon of one neuron communicates with the dentrite of another via chemical synapses
indirect gating of ion channels (characteristics and features)
- transmitter binds to G-protein coupled receptor or metabotropic receptors
- activates biochemical pathway, eventually opening pore
- slower onset
- longer-lasting
where would you find Pyramidal cells and what do they look like?
cerebral cortex of the brain. Pyramid shape
NPY
a neuropeptide
2 forms of synapses
- chemical synapse
2. electrical synapse
IPSPs + EPSPs
cancel out
spatial summation
synapse activation occurs at the same time at many different synapses and the EPSPs add together
small molecule neurotransmitters include:
- Amino acids (glutamate, GABA, glycine)
- Acetylcholine (ACh)
- Amines (serotonin, dopamine, noradrenaline)
- others include ATP and Nitric oxide
inhibitory synapses cause a ________ of the post-synaptic membrane. The neurotransmitters involved are mainly ______ and ________ . Their ionic mechanism is the opening of the ion channels for __ and __ .
inhibitory synapses cause a hyperpolarisation of the post-synaptic membrane. The neurotransmitters involved are mainly GABA and glycine . Their ionic mechanism is the opening of the ion channels for K+ and Cl- .
through which type of cell junction are electrical synapses transmitted?
gap junction
where would you find Purkinje cells?
in the cerebellum
what are the two main chemical synapses in the CNS?
- excitatory synapses (EPSPs)
2. inhibitory synapses (IPSPs)
excitatory synapses cause a ________ of the post-synaptic membrane. The neurotransmitters involved are mainly ________ _____ and ________ . Their ionic mechanism is the transient opening of the ion channels for __ and __ and sometimes __.
excitatory synapses cause a depolarisation of the post-synaptic membrane. The neurotransmitters involved are mainly glutamic acid(glutamate)_ and Acetylcholine(ACH)_ . Their ionic mechanism is the transient opening of the ion channels for K+ and Na+ and sometimes Ca2+.
features of neuropeptides
- Large molecules
- indirectly act on postsynatptic membrane
- slow and more dififfuse action
3 mechanisms of neurotransmitter inactivation
- diffusion - away from the synaptic cleft
- enzymatic degradation - e.g. ACH degraded by acetylcholinesterase
- Re-uptake - neurotransmitter transporters take them away
_______ ________ arrives at the _________ terminal. The voltage-gated ___ channels open and there is a rapid influx of ___. _______ containing neurotransmitter move to the _________ membrane and fuse. The neurotransmitter ______ across the ______ ____ and binds to the ___________ receptors. Synaptic channels open. Postsynaptic _______ _________ is created.
action potential arrives at the presynaptic terminal. The voltage-gated Ca2+ channels open and there is a rapid influx of Ca2+. Vesicles containing neurotransmitter move to the presynaptic membrane and fuse. The neurotransmitter diffuses across the synaptic cleft and binds to the postsynaptic receptors. Synaptic channels open. Postsynaptic action potential is created.
NMDA
a directly gated glutamate receptor
temporal summation
the higher the frequency of the synapse activation, from 1 synapse, the EPSPs can sum to reach threshold
end-plate potential due to ?
EPSP - therefore, increased permeability of (non-selective) ion channels to Na+ and K+ in the postsynaptic membrane
_______ synapse are used almost entirely in the brain
chemical
synaptic plasticity =
- process of weakening or strengthening synaptic transmission.
- Important in learning and memory.
- LTP (long-term potentiation) or LTD (long-term depression)
synaptic delay =
time between arrival of AP at presynaptic knob to AP regeneration in the postsynaptic knob. Aproximately = 0.5ms
3 key features of chemical synapses
- specificity - specific neurotransmitters have specific effects
- complexity - type, time, strength, etc.
- plasticity - changes in synaptic structure and function
is end-plate potential supra- or sub- threshold
ALWAYS suprathreshold and ALWAYS triggers an AP
each neuron receives only 1 synapse TRUE/ FALSE
FALSE. they receive around 10,000
