Synapses Flashcards
What is the presynaptic neurone?
The neurone along which the impulse has arrived
What is the postsynaptic neurone?
The neurone that receives the neurotransmitters
What is the synaptic cleft?
The gap which separates the pre and postsynaptic neurones
What is the synaptic knob?
The swollen end of the the presynaptic neurone
Why does the synaptic knob have many mitochondria and endoplasmic retitculum?
To enable it to manufacture neurotransmitters
What are synaptic vesicles?
Vesicles containing neurotransmitters, that fuse with the presynaptic membrane and release their contents into the synaptic cleft
What are neurotransmitter. receptors?
Receptors that the neurotransmitters bind to in the postsynaptic membrane
What are the two types of neurotransmitters?
Excitatory and inhibitory
What are excitatory neurotransmitters?
Neurotransmitters that result in the depolarisation of the postsynaptic membrane. This causes an action potential to be triggered
What is an example of an excitatory neurotransmitter?
Acetylcholine
What are inhibitory neurotrasmitters?
Neurotransmitters that result in the hyperpolarisation of the postsynaptic membrane. This prevents an action potential from being triggered
When the action potential reaches the end of the presynaptic neurone, what happens?
The depolarisation of the presynaptic membrane causes calcium ion channels to open, and calcium ions to diffuse into the presynaptic knob
What happens once calcium ions diffuse into the presynaptic knob?
It causes synaptic vesicles containing neurotransmitters to fuse to the presynaptic membrane, causing neurotransmitters to be released into the synaptic cleft
What happens once the neurotransmitters have been released into the cleft?
They bind with specific receptors on the postsynaptic neurone
What happens once the neurotransmitters bind to the receptors on the postsynaptic neurone?
This causes sodium ion channels to open, so sodium ions diffuse into the postsynaptic neurone; this depolarisation triggers an action potential
In what synapses is acetylcholine used?
Across cholinergic synapses
What happens to acetylcholine once the action potential has been triggered in the postsynaptic neurone?
It is hydrolysed into choline and ethanoic acid
What enzyme is used in the hydrolysation of acetylcholine?
Acetylcholinesterase
Why is the hydrolysation of acetylcholine important?
It allows it to be recycled and prevents it from continuously generating a new action potential
How is acetylcholine recycled?
Once it has been hydrolysed, the ethanoic acid and choline diffuse back into the presynaptic neurone, where ATP recombines it into acetylcholine
Why are synapses important?
- Ensure impulses are unidirectional
- Allow an impulse from one presynaptic neurone to be transmitted to multiple postsynaptic neurones (and visa versa)
How do synapses ensure impulses are unidirectional?
Neurotransmitter receptors are only present on the postsynaptic neurone
What is summation?
Where the amount of neurotransmitter from one impulse is not enough to result in an action potential, so the amount of neurotransmitter needs to build up sufficiently
What is spatial summation?
This occurs when a number of presynaptic neurones connect to one postsynaptic neurone; each releases neurotransmitters which together is enough for an action potential
What is temporal summation?
This occurs when a single presynaptic neurone releases neurotransmitters several times over a short period; this builds up in the synapse until the quantity is sufficient enough for an action potential
