L8 Synaptic Transmission Flashcards
Synaptic transmission
Interaction between neuron and another neuron, muscle, or gland
Motorneurons
Nerves that innervate muscle fibers
Synapses
Junction between presynaptic neuron and a postsynaptic neuron
What are two types of synaptic transmission? And what is their flow direction?
Electrical (gap junctions)
Chemical
Unidirectional
Always from presynaptic neuron to postsynaptic neuron
Electrical synapse / gap junctions
Ions flow directly through gap junctions channels
direct current flows faster
Mainly seen in the heart
Chemical synapse
Presynaptic neuron releases neurotransmitters
Ions winter synaptic cleft and then flow through postsynaptic channels
Presynaptic neuron
Neuron that conducts action potential toward the synapse
Postsynaptic neuron
Neuron whose action potential are propagated away from the synapse
Synaptic knob
Contains synaptic vesicles
Synaptic vesicles
Stores neurotransmitter (carries signal across membrane)
Synaptic cleft
Space between pre and post synaptic neurons
Synaptic delay
Time needed for conversion of the electrical signal from the presynaptic neuron (action potential) to an electrical signal in the postsynaptic neuron (EPSP or ISPS) by chemical means
0.5-1msec
What’s Excitation -secretion coupling in chemical synapses?
Process of converting chemical signal back to electrical signal
What’s are the steps in excitation-secretion coupling?
- An action potential depolarizes the axon terminal
- Depolarization opens voltage-gated Ca2+ channels and Ca2+ enters the cell
- Calcium entry triggers exocytosis of synaptic vesicle contains
- Neurotransmitter differs across the synaptic cleft and binds with receptors on the postsynaptic Cell
- Neurotransmitter binding initiates a response in the postsynaptic cell
Post synaptic sensory affects response how?
More receptors, more response
Less receptors, less response
What are two types of receptors?
For fastest neurotransmission ligand-gated ion channels AKA Ionotrophic
Slow transmission - G protein-coupled receptors AKA metabotropic
What’s the result at the post synaptic membrane ?
Graded synaptic potential
Excitatory or inhibitory
What ends the signal?
Diffusion -slow
Enzymatic degradation -in synaptic cleft
Reuptake - recycled or destroyed in synaptic knob
Cholinergic synapse
Employs ACh as its neurotransmitter
Action potential travels down axon opens voltage gate Ca2+ channels in synaptic knob
Triggers exocytosis of synaptic vesicles and the release of ACh which crosses the synapse
Reserve synaptic vesicles move up to the active sites and release their ACh
ACh diffuses across the synaptic cleft to bind to ACh receptors
ACh receptors trigger opening of ligand gated Na+ channels producing local potential (postsynaptic potential)
When reaches -55mV, triggers action potential to begin
Cholinergic synaptic vesicle fusion and exocytosis
Vesicle that contains ACh has 2 proteins attached- synaptotagmin and synaptonrevin
2 proteins on plasma membrane- SNAP25 and syntaxin
Proteins automatically dock when they get close enough= SNAREs complex
Won’t release ACh until Ca2+ binds to synaptotagmin
Removal of acetylcholine
Enzyme breaks down ACh to choline and acetic acid
Choline is recycled back into presynaptic knob
Acetic acid diffuses away
Excitatory adrenergic synapse
Neurotransmitter = norepinephrine (NE)
Receptor is not an ion gate but a transmembrane protein associate with a G protein
Unstimulated NE receptor is bound to a G protein
Binding of NE to the site cause G protein to be released
The G protein binds to adenylate cyclase which activates the enzyme and concerts ATP to cAMP
cAMP produces an internal chemical that binds to a ligand-gated sodium channel depolarizing the cell
Causes EPSP
Inhibitory GABA-ergic synapse
Neurotransmitter = GABA (gamma aminobutyric acid)
Binds to ion gates and causes a change in membrane potential
However the gate in this case is a Cl- channel and makes the RMP even more negative which then inhibits neuron firing (IPSP)
