3.6.2.2 synaptic transmission Flashcards
what are synapses and the synaptic cleft
synapses are junctions between neurones.
the synaptic cleft is a gap at the synapse which prevent an electrical impulse passing directly from one neurone to the other.
why is synaptic transmission the slowest part of a nerve impulse being transmitted
it takes time for neurotransmitters to diffuse across the synaptic cleft and bind to receptor sites
why are synapses unidirectional
receptors are only found on the post synaptic membrane
neurotransmitters are only produced and sent from the pre synaptic neurotransmitter
what is spatial summation
more than one pre synaptic neurone converges to one post synaptic neurone
how does spatial summation result in an action potential
there is a greater number of neurotransmitters that diffuse across the synapse to the post synaptic membrane. so more neurotransmitters bind to receptor sites and cause an influx of Na+ leading to depolarisation
what is temporal summation
increase in frequency of action potentials that arrive at the pre synaptic membrane
how does temporal summation result in an action potential
increase in frequency of action potential, more neurotransmitters bind to receptor sites, influx of Na+ causing depolarisation
what are inhibitory synapses and how do they work
they reduce the likelihood of an action potential by release neurotransmitters that cause the post synaptic membrane to become even more negatively charged (hyperpolarised)
how do inhibitory synapses reduce chance of an action potential
they hyperpolarise the post synaptic membrane.
the stimulus must be stronger in order to release enough neurotransmitters to depolarise the post synaptic membrane.
step 1 of synaptic transmission
- action potential arrives at the pre synaptic membrane.
- this depolarises the pre synaptic membrane and stimulates voltage gated Ca2+ channels to open
- Ca2+ enter the presynaptic knob
step 2 of synaptic transmission
- Ca2+ cause synaptic vesicles containing acetylcholine to fuse with the pre synaptic membrane.
- this releases acetylcholine into the synaptic cleft
step 3 of synaptic transmission
- acetylcholine diffuses across the synaptic cleft and binds to receptor sites on Na+ channels.
the Na+ channels open and Na+ enter the post synaptic knob via facilitated diffusion. - this depolarises the post synaptic membrane
step 4 of synaptic transmission
- if enough Na+ enter the post synaptic membrane so it becomes depolarised and reaches the threshold value and action potential will be triggered.
step 5 of synaptic transmission
- acetylcholinesterase hydrolyses acetylcholine into acetyl and choline which diffuse across the synaptic cleft back into te pre synaptic membrane
step 6 of synaptic transmission
- ATP reelased during respiration is used to recombine acetyl and choline and is stored for future use
why is acetylcholine hydrolysed
so there arent continuous action potentials triggered
what is the neuromuscular junction
the synapse between a motor neurone and a muscle
compare the neuromuscular junction with a cholinergic synapse
both are unidirectional.
the NMJ is only excitatory, a cholinergic synapse can be excitatory or inhibitory.
the NMJ is an end point for action potentials, a cholinergic synapse generates action potentials at the next neurone.
how is an action potential triggered at the neuromuscular junction
Na+ ions diffuse into the muscle fibre and if the threshold is reached depolarization occurs and an action potential is triggered and spreads down t-tubules. this causes the sarcoplasmic reticulum to release Ca2+ into the sarcoplasm starting muscle contraction.
