6.2.2 Synaptic transmission Flashcards
What are synapses?
Gaps between neurons.
What is the first stage of synaptic transmission?
An action potential arrives at a synaptic knob. Depolarisation of synaptic knob leads to the opening of Ca2+ channels and Ca2+ diffuses into synaptic knob.
What happens after Ca2+ diffuses into synaptic knob?
Vesicles containing neurotransmitter move towards and fuse with the pre-synaptic membrane. Neurotransmitter is released into the synaptic cleft.
What happens after neurotransmitter is released into the synaptic cleft?
Neurotransmitter diffuses down concentration gradient, across synaptic cleft, to post-synaptic membrane. Neurotransmitter binds by complementary shape to receptors on the surface of the post-synaptic membrane.
What happens after the neurotransmitter binds to the receptors on the post-synaptic membrane?
Na+ ion channels on the post-synaptic membrane open and Na+ diffuse in. If enough neurotransmitter and Na+ ions diffuse in, above threshold, the post-synaptic neuron becomes depolarised.
What happens after the post-synaptic neuron becomes depolarised?
Neurotransmitter is degraded and released from the receptor. The Na+ channel closes and the post-synaptic neuron can re-establish resting potential. The neurotransmitter is transported back into the pre-synaptic neuron, where it is recycled.
What is the neurotransmitter in a cholinergic synapse?
Acetylcholine.
What enzyme breaks down acetylcholine?
Acetylcholinesterase.
What does acetylcholinesterase do?
Breaks down acetylcholine into choline and acetate, which are then recycled back into the presynaptic knob.
What is summation?
The rapid build up of neurotransmitters in the synapse to help generate an action potential.
What are the 2 methods of summation?
Spatial and temporal.
Why is summation needed?
Some action potentials do not result in sufficient concentrations of neurotransmitter being released to generate a new action potential.
What is spatial summation?
Many neurons release neurotransmitters into the synapse in order to obtain an action potential.
What is temporal summation?
One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value.
What does the inhibitory synapse do?
Causes chloride ions to move into the post-synaptic neuron and potassium ions to move out. Combined effect causes the membrane potential to increase to -80mv (hyperpolarization), meaning a new action potential is highly unlikely.
What is the neuromuscular junction?
A synapse that occurs between a motor neuron and a muscle and is very similar to a synaptic junction.
Describe the sequence of events involved in transmission across a cholinergic synapse.
- Depolarisation of presynaptic membrane. 2. Calcium channels open and calcium ions enter synaptic knob. 3. Ca2+ ions cause synaptic vesicles to move to/fuse with presynaptic membrane and release acetylcholine/neurotransmitter. 4. Acetylcholine/neurotransmitter diffuses across. 5. Acetylcholine attaches to receptors on the postsynaptic membrane. 6. Sodium ions enter leading to depolarisation.
Why is it important that a neurotransmitter such as serotonin is transported back out of synapses?
If not removed, it keeps binding to receptors and keeps causing depolarisation.
