synaptic transmission 2 Flashcards
What can neuro transmitters be
Neurotransmitters Can be Excitatory, Inhibitory or Both
What are excitatory neurotransmitters
Excitatory neurotransmitters depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached. E.g. acetylcholine is an excitatory neurotransmitter at cholinergic synapses in the CNS — it binds to ch olin ergic receptors to cause an action potential in the postsynaptic membrane — and at neuromuscular junctions
What are inhibitory neurotransmitters
Inhibitory neurotransmitters hyperpolarize the postsynaptic membrane (make the potential difference more negative), preventing it from firing an action potential. E.g. ace t ylch olin e is an inhibitory neurotransmitter at cholinergic synapses in the heart. When it binds to receptors here, it can cause potassium ion channels to open on the postsynaptic membrane, hyperpolarising it
What does summation at synapses do
Summation at Synapses Finely Tunes the Nervous Response
What happens if a stimulus is weak
If a stimulus is weak, only a small amount of neurotransmitter will be released from a neurone into the synaptic cleft. This might not be enough to excit e the p ostsynaptic membrane to the threshold level and stimulate an action p otential
What is summation
l. Summation is where the effect of neurotransmitter released from many neurones (or one neurone that’s stimulated a lot in a short perio d of time) is added together.
What are the two types of summation
Spatial summation, temporal summation
What happens in spatial summation
1) Sometimes many neurones co n nect to one neurone
2) The small amount of neurotransmitter ^released from each of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an action potential.
3) If some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential.
What happens in temporal summation
Temporal summation is wh ere two or more nerve impulses arrive in quick 4 successio n from the same presynap tic neurone. This makes an action potential more likely because more neurotransmitter is released into the synaptic cleft.
What are neuromuscular junctions
Neuromuscular Junctions are Synapses Between Neurones and Muscles
What do neuromuscular junctions use
neuromuscular junctions use the neurotransmitter ace t ylch olin e (ACh), which binds to cholinergic receptors calle d nico tinic ch olinergic receptors.
Neuromuscular junctions work in almost the same way as the cholinergic synapse, but what are the differences
The postsynaptic membrane has lots of folds that form clefts. These clefts store the enz yme that breaks down ACh (acet ylcholinesterase — AChE). • The postsynaptic membrane has more receptors than other synapses.
ACh is always excit atory at a neuromuscular ju nction. So when a motor neurone fires an action potential, it n orm ally triggers a response in a muscle c e ll. This isn’t always the case for a synapse between two neurones
What are agonists
Some drugs are the same shape as neurotransmitters so they mimic their action at receptors (these drugs are calle d agonists). This means more receptors are activated. E.g. nico tine mimics ace t ylch olin e so binds to nico tinic cholinergic receptors in the brain
What are antagonists
Some drugs block recept ors so they ca n’t be activated by neurotransmitters (these drugs are calle d antagonists). This means fewer rece ptors (if any) can ^ be activa ted. E.g. curare blocks the effects of ac e tylch olin e by blocking nic o tinic ch olin erg ic receptors at neuromuscular junctio ns, so muscle c e lls X] can’t be stimulated. This results in the muscle being paralysed.
What happens when some drugs inhibit the enzyme that breaks down neurotransmitters
This means there are more neurotransmitters in the synap tic cleft to bind to recep tors and they’re there for longer. e nzym e E.g. nerve gases stop ac e tylch olin e from being broken d own in the inhib itor synaptic cle ft. This can lead to loss of muscle control.
