Synaptic transmission Flashcards
What is a synapse?
The junction between a neurone and another neurone or between a neurone and an effector
What is a synaptic cleft?
The tiny gap between the cells at a synapse
What is a presynaptic neurone?
The neurone before the synapse
What is a post synaptic neurone?
The neurone after the synapse
What is a synaptic knob?
A swelling on the pre-synaptic neurone
Where are synaptic vesicles found and what do they contain?
In the synaptic knob
Neurotransmitter
What is the effect of an action potential on a synapse?
When an action potential reaches the end of a neurone, it causes neurotransmitters to be released into the synaptic cleft.
They diffuse across to the post synaptic membrane and bind to specific receptors.
When neurotransmitters bind to receptors, they might trigger an action potential and cause muscle contraction or cause a hormone to be secreted
How are impulses unidirectional?
The receptors are only on the post synaptic membrane
Why are neurotransmitters removed from the cleft and how?
To prevent the reaction from keep happening
Taken back into the presynaptic neurone and broken down by enzymes and products taken into the neurones
What are cholinergic synapses?
Synapses which use acetylcholine
What happens when an action potential arrives at the synaptic knob of the presynaptic neurone?
The action potential stimulates voltage-gated calcium ion channels in the presynaptic neurone to open, causing calcium ions to diffuse into the synaptic knob and are pumped out by active transport after
What does the influx of calcium ions into the synaptic knob cause?
The synaptic vesicles to fuse with the presynaptic membrane and the vesicles release the neurotransmitter acetylcholine into the synaptic cleft by exocytosis
What happens when ACh diffuses across the synaptic cleft?
It binds to specific cholinergic receptors on the post synaptic membrane, causing sodium ion channels in the post synaptic neurone to open.
What does the influx of sodium ons into the post synaptic membrane cause?
Depolarisation
What does the depolarisation of the post synaptic membrane cause?
An action potential is triggered if the generator potential reaches the threshold level.
ACh is removed from the synaptic cleft
What enzyme breaks down acetylcholine?
Acetylcholinesterase
What are the two types of neurotransmitter?
Excitatory
Inhibitory
What do excitatory neurotransmitters do?
Depolarise the post synaptic membrane, increasing the chance of an action potential being fired if threshold is reached
What do inhibitory neurotransmitters do?
Hyperpolarise the postsynaptic membrane, preventing an action potential from being fired
What is an inhibitory synapse?
A synapse where inhibitory neurotransmitters are released from the presynaptic membrane
What is summation?
The effect of neurotransmitters released from many neurones or one thats stimulated a lot in a short period of time, is added together
What are the two types of summation?
Spatial
Temporal
Why does summation happen?
If there is only a weak stimulus, it may not cause enough neurotransmitter to be released to excite the postsynaptic membrane to the threshold level and stimulate an action potential
What is spatial summation?
Two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone
What is temporal summation?
Two or more nerve impulses arrive in quick succession from the same presynaptic neurone
What is a neuromuscular junction?
Specialised cholinergic synapse between a motor neurone and a muscle cell
What neurotransmitter does a neuromuscular junction use?
Acetylcholine
What differences are there between a neuromuscular junction and a normal cholinergic synapse?
At a neuromuscular junction;
- The post synaptic membrane has lots of folds that form clefts, clefts store AChE
- The postsynaptic membrane has more receptors than other synapses
- ACh is always excitatory so when a motor neurone fires an action potential, it normally triggers a response in a muscle cell
What effects can the use of drugs have on synapses?
- some are the same shape as neurotransmitters so they mimic their action at receptors causing more to be activated
- Some block receptors so they cant be activated by neurotransmitters
- Some inhibit the enzyme that breaks down neurotransmitters
- Some stimulate the release of neurotransmitter from the presynaptic neurone so more receptors are activated
- Some inhibit the release of neurotransmitters from the presynaptic neurone so fewer receptors are activated §
What are antagonist drugs?
Drugs that block receptors so they cant be activated by neurotransmitters
What are agonist drugs?
Drugs that are the same shape as neurotransmitters so they mimic their action at receptors
