KA4-b) Neurotransmitters at synapses Flashcards
What is the synaptic cleft?
The narrow space between an axon ending of one neurone and the dendrite of the next neurone is called the synaptic cleft.
What is the presynaptic neurone?
The nerve cell before the synaptic cleft is called the presynaptic neurone.
What is the postsynaptic neurone?
The nerve cell after the synaptic cleft is called the postsynaptic neurone.
What are neurotransmitters?
Chemicals that relay impulses across the synaptic cleft ( acetycholine, noradrenaline)
Describe how chemical transmission at the synapse occurs.
Neurotransmitters are stored in vesicles in the axon endings of the presynaptic neurone. They are released into the cleft on arrival of an impulse.
They diffuse across the cleft and bind to receptors on the membrane of the postsynaptic neurone.
Where do vesicles occur?
Vesicles containing neurotransmitters occur on one side of the synapse only. This means nerve impulses travel in one direction only.
What do mitochondrion provide to release neurotransmitter?
Mitochondrion provide ATP to release neurotransmitters.
Why are neurotransmitters removed after the impulse has been transmitted?
Neurotransmitters are removed after the impulse has been transmitted to prevent continuous stimulation of postsynaptic neurones.
How are neurotransmitters removed from the synaptic cleft?
Through re uptake or enzyme degradation.
How are neurotransmitters removed from the cleft by re-uptake?
Neurotransmitters undergo re uptake by being being reabsorbed directly into the presynaptic membrane and stored in a vehicle ready for use.
How are neurotransmitters removed from the cleft by enzyme degradation?
Neurotransmitters are broken down by an enzyme into non active products which are then reabsorbed by the presynaptic neurone and resynthesised into active neurotransmitters.
State what determines if a signal is inhibitory or excitatory?
Neurotransmitters bind with receptors. The type of receptor determines whether the signal is excitatory (increases) or inhibitory (decreases)
State what happens to signals from weak stimuli.
Weak stimuli signals are either filtered out or transmitted (summation). Synapse can filter out weak stimuli arising from insufficient secretion of neurotransmitters. There needs to be a minimum number of neurotransmitters that attach to receptors for an impulse to be transmitted. This is known as threshold. For a weak stimuli to be transmitted a series of weak stimuli releasing enough neurotransmitters to trigger an impulse is needed. This is known as summation.
