Synaptic Transmittion Flashcards
How information is conducted within different things
Information is encoded and conducted within nerve cells ELECTRICALLY
Information is transferred between cells CHEMICALLY
Synaptic transmission process
- AP is generated and conducted to reach nerve terminal, voltage inside is +ve
- When AP arrives at never terminal, calcium is released into the nerve terminal through voltage gated calcium channels
- voltage gated channels will change shape and open to allow calcium to flow down electrochemical gradient - inside
- cell maintains Ca2+ conc inside low - can be used as signalling molecule in order for important processes to occur
- calcium triggers synaptic vesicles which are made from membrane to be transported up to the memebreane where they fuse together, synaptic vesicles this discharging contents into synaptic cleft - exocytosis - occurs many times - chemical signalling
- after Neuro transmitter diffuses into cleft and binds the receptors in post synaptic neuron to the chemically gated socium channels
- Na enters causing depolarisation - if threshold reached - action potential will be produced down synaptic neuron
- the depolarisation that arises would be an EPSP
- if EPSP Siri sing at same time on post synaptic cell, generated a depolarisation that’s big enough to bring to threshold (10mV) - the initial segment will then produce an AP
Local potentials
small, variable, non-propergated changes in voltage, localised to site of generation can be excitory or inhibitory, and can add if they arise close together in space + time
Action potentials
Reversal in membrane polarity , arising by crossing threshold.
Depolarisation doe to Na entery, repolarisation due to K exit
Conducted along axon by spread of local current indicate the axon resulting in the opening V-gates channels ahead of the wave of depolarisation, causing regenerating of the event.
Don’t vary in size - all or nothing.
How speed of conduction of AP can be enhanced
Myelin prevents short range local currents across the membrane, so current spreads further along the inside of the axon to depolarise membrane to threshold at next node of ranveir
Information is encoded and conducted within nerve cells _____
Information is transferred between cells ______
Electrically
Chemically
Synaptic transmission
- AP generated and conducted to reach nerve terminal - voltage inside is + ve
- when AP arrives at terminal, calcium is released into nerve terminal through voltage gates calcium channels
- voltage gates calcium channels will change shape and open to allow calcium flow down electrochemical gradient - inside
- cell maintains Ca2+ conc inside low - can be used as signalling molecule in order for important processed to occur
- calcium triggers synaptic vesicles which are made of membrane to be transported up to the membrane, then they fuse together, synaptic vesicles thus discharging contents into synaptic cleft - exocytosis - occurs many times - chemically signalling
- after neurotransmitter diffuses into cleft and binds the receptors in the post synaptic neuron to the chemically gated sodium channels
- Na enters causing depolaration - if threshold is reached - action potential will be produced down post - synaptic neuron.
- the depolarisation that arises would be an excitory post synaptic potential (EPSP)
- if EPSPs arise at same time on post synaptic cell, generates a depolarisation that’s big enough to bring the threshold - initial segment will then produce an AP
- calcium is reduced into ER or binding to proteins as well as pumping back out of terminal - calcium levels drop quickly - nerve terminal then stops exocytosis
- the affinity of the receptor for the neurotransmitter declines - neurotransmitter now unbinds - channel closes and terminated the ability of the neurotransmitter to allow the sodium to flow in
How inhibitory woks
- neurotransmitter is different
- GABA binds to an ion channel which doesn’t open sodium channels
- opens chloride channels
- prevents cell from reaching threshold
- initiating an inhibitory post synaptic potentials
How the thing doesn’t bind and rebind
- in the synapse an enzyme (AchE) acetlycholesterase - breaks down Ach into acetate and chlorine
- acetate diffuses away out of synaptic cleft
- nerve terminal that released Acetlycholine has transporter protein that picks the choline back up and recycles it to repacking intro vesicles to use again
Events occurring at the cholinergic synapse
- AP triggers the opening of voltage - gated calcium channels
- Calcium ions diffuse into the axon terminal, and triggers synaptic vesicles to release ACh by exocytosis
- Ach diffuses across synaptic cleft, binds to ACh-gated sodium ion channels and produces a graded depolarisation.
- Depolarisation ends as ACh is broken down into acetate and choline by AChE
- The axon terminal reabsorbs choline form the synaptic cleft and uses it to synthesis new molecules of ACh
Electrical synapses - gap junction
pre and post synapses cell membranes sit very close together and the two cells are joined by channels called gap junctions (transmsmebrane protein) - provide direct cytoplasmic connection between pre and post synaptic cell
How an electrical synapse works
- depolarisation form pre-synaptic cell passes directly to post synaptic cell without using chemical transmitter
- relatively rare, provide no opportunity for signal modulation - same side in pre and post synaptic cell
- eg light in eye to brain
Nerve vs muscle size of synapses and how many synapses are there on post synaptic cell
NERVE: synapses are tiny, each synapse may be one of thousands on the post synaptic cell.
NEREVE - SKELETAL: synapses are huge, each muscle fibre receives input from only one neuron at one site
Nerve - nerve vs nerve - skeletal likely hood of bringing to threshold
NERVE-NERVE: AP in individual neuron will rarely bring partner to threshold
NERVE-SKELETAL: AP in neuron will very likely bring muscle fibre to threshold
Nerve - nerve vs nerve - skeletal - excitory or inhibitory - what transmitters can be used
NERVE-NERVE: inputs may be excitory or inhibitory (ESPS + ISPS) many neurotransmitters may be used
NERVE-SKELETAL: only excitory inputs (no inhibition or IPSPs) only Ach used
