Synaptic transmission Flashcards
What is a synapse?
The junction between a neurone and another neurone or a neurone and an effector cell. The tiny gap between the two cells is called the synaptic cleft. The presynaptic neurone has a swelling called the presynaptic knob and contains neurotransmitters.
Describe the effect of an action potential on a synapse.
When an action potential reaches a synapse, it causes neurotransmitters to be released into the synaptic cleft and they bind to specific receptors on the postsynaptic membrane. This may trigger an action potential. The signals are unidirectional. Neurotransmitters that have not binded are either broken down by enzymes or are taken back into the presynaptic membrane.
Describe the action of a cholinergic synapse.
An action potential arrives at the synaptic knob of the presynaptic neurone and stimulates the voltage gated calcium ion channels to open. They diffuse into the synaptic knob. This causes the vesicles to fuse with the presynaptic membrane and release the neurotransmitter acetylcholine into the synaptic cleft by exocytosis. ACh diffuses across the synaptic cleft and bind to specific cholinergic receptors on the postsynaptic membrane which causes sodium ion channels to open in the postsynaptic membrane. The influx of sodium ions causes depolarisation and an action potential is generated if the threshold is reached. ACh is broken down by acetylcholinesterase and products are reabsorbed by the presynaptic neurone.
What is spatial summation?
Where two or more presynaptic neurones release their neurotransmitters at the same time onto the same postsynaptic neurone. The small amount of neurotransmitter released from each of these neurones can be enough all together to reach the threshold and trigger an action potential.
What is temporal summation?
Where two or more nerve impulses arrive in quick succession at the same presynaptic neurone which means that an action potential is more likely because more neurotransmitter is released into the synaptic cleft.
