Module 3: Synaptic transmission Flashcards
what is temporal summation?
when 2 EPSPs from the same presynaptic neuron occur close in time to depolarise the membrane to threshold
what is spatial summation?
2 EPSP from different presynaptic neurons occur close in time to depolarise the membrane threshold
what’s the difference between temporal and spatial summation?
temporal: EPSP from same presynaptic neuron
Spatial: EPSP from 2 different presynaptic neurons
where does a synapse occur?
At the end of the axon - presynaptic neuron/axon terminal - and post synaptic neuron (attached to other neuron area)
where can synapses form on a neuron?
cell body: axosomatic
dendrite:axodendritic
hillock:axoaxonal synapse
which neuron to neuron synapse is most common?
axon-dendrite (axodendritic)
what is the name for the chemicals in the vesicles of the presynaptic neuron/axon terminal?
neurotransmitters
are neurotransmitter chemical or electrical?
chemical
what is the name of the gap between the presynaptic terminal and postsynaptic terminal?
the synaptic cleft
how do the receptor proteins work in the postsynaptic terminal?
the neurotransmitters chemically bond to the protein receptors, opening them
how do the electrical signals from the axon terminal convert into a chemical signal?
the voltage from the action potential triggers the +Ca2 voltage gated protein to open, flooding the presynaptic terminal and causing the vesciles to exocytosis to the membrane wall.
what happens when the neurotransmitters are in the synapse cleft?
the neurotransmitters bond to the ligand or g couple protein gates and cause them to open, allowing Na+,K+ and Cl- to flow bidirectionally across the postsynaptic membrane generating a local or graded potential
why is it useful to have many electrical transmitters happening?
allows to modification of the signal
what is a ligand gated ion channel?
a channel that is activated by chemicals (neurotransmitters) which allow ions to flow through and cause a direct change in the EPSP or IPSP
what does the ligand gate do?
creates a small and direct change in the voltage to create a local or graded potential
how is synaptic transmission terminated?
- breakdown by enzymes in the cleft
- diffusion away from the cleft and break down elsewhere
- reuptake into the presynaptic axon terminal or dealth with by the astrocytes
are synapses excitatory or inhibitory
both
what does it mean to have an excitatory postsynaptic potential (EPSP)?
it allows more positive ions into the cell, like Na+ and some positive out (K+) causing the cell the depolarise and becomes closer to triggering an action potential
what does it mean to have an inhibitory postsynaptic potential (IPSP)?
it allows more negative ions into the cell, like Cl- and some positive out (K+) causing the cell the hyperpolarise and becomes further away to triggering an action potential
why don’t local/graded potentials create action potentials on their own?
- they don’t have a strong enough voltage to cause one
- there’s not enough voltage gated Na+ channels in the areas to create a postivie feedback loop.
how do local/graded potentials create an action potential?
- temporal summation: same neuron firing twice
- spatial summation: 2 neurons firing twice
what does summation mean?
to stack
what are the 9 characteristics of graded potentials?
- local event in: dendrite, cell body or hillock
- peter out
- have different sizes of voltage
- no positive feedback loop due to lack of Na+ channels
- repolarisation occurs due to peetering out of stimulus
- can summate (stack)
- underlied by a chemical/ligand channel
- can be excitatory or inhibiory
- chemical stimulus/trigger
what are the 9 characteristics of an action potential?
- triggered by an accumulation of graded potentials in the hillock only
- can travel long distances due to voltage gated channels in the axon
- always the same size ( all or nothing) +30mV and doesn’t decay
- has a voltage stimulus.trigger
- has a positive feedback loop
- repolarisation is voltage dependent and mediated by K+ channels
- can’t summate due to refactory periods
- only excitatory
- underlied by voltage gated ion channels
what are the 3 dependents of the effect or synaptic transmission?
- type of cell it terminates on e.g. neuron, heart, skeletal muscle
- type of neurotransmitter the neuron releases e.g. excitatory or inhibitory (created during foetal development)
- types of neurotranmittor receptors on the postsynaptic membrane e.g. ligand gate
what is a synaptic transmission?
when a neuron axon attached to any cell
what is a neurotransmittor?
when a neuron axon attaches to another neuron
what are the 2 main types of neurotransmitters present in the synapses in neurons?
- ligand gated ion channels: fast and direct because neurotransmitters bind to channel and allow neurons to directly flow through
- G protein coupled receptor: slow and indirect because the activation doesn’t directly affect the neurons, but affects the neuron flow by changing width of opening in channel
excitatory neurotransmitters examples
glutamate and acetylcholine
inhibitory neurotransmitters examples
GABA and glycine
g protein receptor example
dopamine
do neurotransmittors have specicific channels they can bind to?
no, most of them can bind to both types of channels
what decides the effect of the neurotransmitter?
the receptors expressed by the postsynaptic cell
