Synaptic Transmission Flashcards
Transmission across synapses, Features of Synapses, Summation, Inhibition, Synapses vs Neuromuscular Junctions
Name the process that occurs at the presynaptic membrane that causes Ca2+ voltage gated channels to open.
Depolarisation.
Name the neurotransmitter present in a cholinergic synapse.
Acetylcholine
Name the ion that enters into the presynaptic neurone.
Name the transport process it does this by.
Ca2+, enters by facilitated diffusion.
What fuses with the presynaptic membrane in order to release Ach?
Vesicles
Name the process that releases Ach into the synaptic cleft.
Exocytosis
After Ach has diffused across the synaptic cleft, what is it detected by on the post synaptic cell?
Receptors
Detection of Ach on receptors causes which ion channels to open?
Na+
How does opening of Na+ channels in the post synaptic cell lead to depolarisation?
Link this to the threshold.
Na+ diffuses in, making the inside of the axon less negative. If enough Na+ diffuses in and the threshold is reached, an action potential is generated.
What enzyme hydrolyses Ach?
Name the products.
Acetylcholinesterase.
Acetic acid (ethanoic) and choline
How is Ach ‘recycled’?
Products from hydrolysis are reabsorbed by the cell so Ach can be reformed.
Why is Ach recycled?
To prevent the neurone from becoming overstimulated.
State 2 ways that synaptic transmission is kept unidirectional.
Neurotransmitter only released from the pre-synaptic neurone
Receptors only present on post synaptic membrane.
What is summation?
The sum of excitatory and inhibitory effects of neurotransmitters.
How does summation increase the likelihood of a neurone firing?
It adds the impulses that converge on a single post synaptic neurone, leading to a rapid build up of neurotransmitter.
More neurotransmitter means threshold is more likely to be reached and an action potential is more likely generated.
Why might action potentials in low frequency prevent the next neurone from firing?
They release insufficient neurotransmitter to exceed the threshold.
Roughly how many presynaptic neurones does spatial summation involve?
What do these neurones all share?
Several - they all share the same synaptic cleft.
How does spatial summation allow an action potential to be triggered?
Link this to threshold.
The presynaptic cells collectively release sufficient neurotransmitter to reach threshold and trigger an action potential.
How many pre synaptic cells does temporal summation involve?
One
How does temporal summation work?
One pre synaptic neurone releases neurotransmitter many times over a short time period. Sufficient neurotransmitter causes threshold to be reached and an action potential triggered.
Inhibitory synapses cause which type of polarisation in post synaptic membranes?
Which channel proteins open?
Which ions move in/out by which transport process?
Hyperpolarisation.
Cl- channels open so it diffuses into the post synaptic membrane.
K+ channels open and it diffuses out.
At inhibitory synapses, why is more Na+ required for depolarisation?
Hyperpolarisation means more Na+ is required to raise the potential difference of the inside of the axon. This reduces the likelihood of threshold being met and an action potential being formed at the post synaptic membrane.
Where are receptors found at neuromuscular junctions compared to synapses?
Neuromuscular - Receptors found on muscle fibre.
Synapse - Receptors found on post synaptic membrane.
Muscle fibres form clefts. What is stored in these clefts?
Muscle fibres form clefts to store enzymes such as acetylcholinesterase, that break down neurotransmitter.
Give one similarity between cholinergic synapses and neuromuscular junctions.
Unidirectional.
Cholinergic synapses are between 2 …
Neurones
Neuromuscular junctions are between…
Motor neurones and muscles
Are neurotransmitters at cholinergic synapses excitatory or inhibitory?
Both excitatory and inhibitory.
Are neuromuscular junctions excitatory or inhibitory?
Always excitatory.
Where does the action potential move from in pre synaptic cells at cholinergic synapses?
Action potential moves from pre to post synaptic cell.
Where does the action potential move from in neuromuscular junctions?
It propagates along the sarcolemma down T tubules.
Briefly explain how a drug may stimulate the nervous system to fire more action potentials.
How do they lead to more Na+ entering?
Drugs are a similar shape to the neurotransmitter which stimulate the release of more neurotransmitter.
They inhibit the enzyme that breaks down neurotransmitter so Na+ continues to enter.
Briefly explain how a drug may inhibit the nervous system to reduce action potentials.
How do they inhibit release of neurotransmitter?
They inhibit release of neurotransmitter by, for example, preventing the opening of Ca2+ channels. They also block receptors by mimicking the shape of neurotransmitter.
