Module 5: Cholinergic Synapse Flashcards
A synapse is …
Impulses are transmitted across the synapse using chemicals called …
the junction between 2 neurones
neurotransmitters
Neurotransmitters can either be …
excitatory or inhibitory
What do excitatory neurotransmitters result in ?
Describe what effect this has on generation of an action potential
the depolarisation of the post synaptic neurone , if threshold is reached this triggers an action potential in the post synaptic neurone
What do inhibitory neurotransmitters result in?
Describe what effect this has on generation of an action potential
the hyperpolarisation of the post synaptic membrane which prevents an action potential being generated
Using the cholinergic synapse as an example , describe the first 2 steps of synaptic transmission.
1)an action potential reaches the axon terminal of the presynaptic neurone
2)the action potential triggers the opening of voltage gated calcium ion channels , therefore calcium ions diffuse into the presynaptic neurone
Name the specific voltage gated ion channel involved in cholinergic synapses
voltage gated calcium ion channels
Describe the next 2 steps of synaptic transmission at a cholinergic synapse
3)influx of calcium ions causes vesicles to move forwards and fuse with the presynaptic membrane , acetylcholine is then released from vesicles and leaves the neurone by exocytosis
4)acetylcholine binds to receptors on the receptor gated sodium ion channels causing them to open , so sodium ions diffuse into postsynaptic neurone down their EC gradient
Name the specific neurotransmitter that is involved in cholinergic synpases
acetylcholine
Describe the final 2 steps of synaptic transmission at a cholinergic synapse
5)influx of sodium ions causes generation of another action potential in the postsynaptic neurone
6)any remaining acetylcholine in the synaptic cleft is broken down by acetylcholinesterase into acetic acid and choline so that its more easily absorbed by the presynaptic neurone
Name the enzyme used to break down acetylcholine
What is formed by this reaction?
acetylcholinesterase
acetic acid and choline
Give 3 roles of synapses in the nervous system
1)they ensure impulses are unidirectional as receptors are only present on the postsynaptic membrane
2)they allow an impulse from one neurone to be transmitted to a number of neurones at multiple synapses
3)a number of neurones may feed into the same synapse with a single postsynaptic neurone
Sometimes the amount of neurotransmitter released from a single impulse is not enough to trigger an action potential , as threshold isn’t reached.
What can happen to allow threshold to be reached?
What is this process known as?
through several impulses . neurotransmitter can build up sufficiently to reach the threshold level
known as summation
What are the 2 types of summation , describe each
spatial-occurs when a number of presynaptic neurones connect to one postsynaptic neurone
-each releases neurotransmitters which builds up to a high enough level in the synapse to trigger an action potential
temporal-occurs when a single presynaptic neurone releases neurotransmitters as a result of an action potential several times over a short period
