Synapses Flashcards
The synapse
Junction that allows 2 neurones to communicate with each other using neurotransmitters
Pre synaptic neurone
The one receiving the action potential that will send it to the next one
Post synaptic neurone
The neurone that receives neurotransmitter from pre synaptic neurone to stimulate the generation of a new action potential
Where in the neurones are impulses transmitted over the synapse?
From the synaptic knob of pre synaptic neurone (at axon terminal end) to the dendrites of the cell body on the post synaptic neurone
Types of synapses
Excitatory
Inhibitory
Excitatory synapse
Stimulates the development of new action potentials at post synaptic neurone
Neurotransmitters
Allows for communication of neurones over the synapse by diffusion of the neurotransmitter from one neurone to the next
What neurotransmitter is on the specification ?
Acetyl choline
Cholinergenic synapse
Type of synapse that communicates to next neurone using acetyl choline
What happens when action potentials arrive at the synaptic knob of presynaptic neurone?
Depolarises the pre synaptic membrane
What happens when the synaptic knob is depolarised?
Voltage gated Ca2+ channel proteins are triggered to open so
Ca2+ ions diffuse into synaptic knob down electrochemical gradient using channel proteins
What happens when Ca2+ ions enter the synaptic knob?
Causes synaptic vesicles in synaptic knob to fuse with the presynaptic neurone membrane
Fusion of synaptic vesicles with synaptic knob
The synaptic vesicles containing acetyl choline will release acetyl choline into synaptic cleft
Once acetyl choline is in the synaptic cleft…
It will diffuse to the post synaptic membrane and bind to receptors on the membrane
When acetylcholine binds to receptors on post synaptic membrane in an excitatory synapse
Na+ channel proteins are triggered to open (on post synaptic membrane) so Na+ ions are triggered to diffuse into the post synaptic neurone
In an excitatory synapse, what happens when Na+ diffuses into post synaptic neurone?
Causes depolarisation of neurone membrane
If threshold is reached, this generates new action potentials to be sent along post synaptic neurone
Inhibitory synapse
Stops the generation of new action potentials at the post synaptic membrane
What happens in an inhibitory synapse when acetyl choline binds to receptors on post synaptic neurone?
Triggers opening of K+ channel proteins so K+ diffuses out of the post synaptic neurone by facilitated diffusion
Causes hyper polarisation of post synaptic neurone
So less likely to reach threshold and won’t generate an action potential
Summation
Determining whether threshold will be reached thus an action potential generated in post synaptic neurone
2 types of summation
Temporal
Spatial
Temporal summation
A higher frequency of impulses is sent along presynaptic neurone so more neurotransmitter is released so more likely for post synaptic membrane to reach threshold and generate a new impulse
Spatial summation
If a post synaptic neurone membrane is connected at the synapse to 2 or more pre synaptic neurones so will receive neurotransmitter from more than 1 neurone
More likely to trigger enough depolarisation and reach threshold to generate new impulse
Neurone to myofibril synapse
Same mechanism but the post synaptic neurone is the myofibril, it’s membrane is the sarcolemma and an impulse is sent along the muscle fibre not neurone
When returning to the rest state, what happens at the pre synaptic neurone?
Can2+ ions are actively transported OUT of the synaptic knob to stop synaptic vesicles fusing with the membrane thus stops release of acetyl choline
Excess acetyl choline in the synaptic cleft is…
Hydrolysed by the enzyme acetyl cholinesterase into ACETATE + CHOLINE
What enzyme hydrolyses acetyl choline?
Acetyl cholinesterase
What is acetyl choline hydrolysed into?
Acetate + choline
Choline from hydrolysis of acetyl choline will…
Diffuse back into pre synaptic knob by facilitated diffusion
Then reforms acetyl choline by reacting with acetate
How is acetyl choline repackaged into synaptic vesicles
By active transport
Why do synaptic knobs have a lot of mitochondria?
For a lot of aerobic respiration to produce a lot of ATP:
Active transport of acetyl choline into synaptic knob
For Na+K+protein pump for resting potential
Why can an impulse only be transmitted from presynaptic to post synaptic?
Acetyl choline can only be released from pre synaptic neurone
Receptors to acetyl choline only present on post synaptic neurone
