Action at synapses
- Created by: 08rmorris
- Created on: 04-04-15 10:58
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- Synapses
- The junction between two neurones
- an action potential cannot cross this gap between the neurones (synaptic cleft)
- Instead is carried by chemicals called neurotransmitters
- Made by the cell sending the impulse (pre-synaptic neurone)
- Stored in synaptic vesicles at the end of the axon
- The cell that is receiving the impulse (post-synaptic neurone) has chemical -gated ion channels in its membrane, called nueroreceptors
- Stored in synaptic vesicles at the end of the axon
- Made by the cell sending the impulse (pre-synaptic neurone)
- Instead is carried by chemicals called neurotransmitters
- an action potential cannot cross this gap between the neurones (synaptic cleft)
- 1. At the end of the pre-synaptic neurone there are voltage-gated calcium channels
- When an action potential reaches the synapse these channels open
- Causing calcium ions to diffuse into the cell down their concentration gradient
- When an action potential reaches the synapse these channels open
- 2. these calcium ions cause the synaptic vesicles to fuse with the membrane
- Releasing their contents by exocytosis
- 3. The neurotransmitters diffuse across the synaptic cleft
- 4. The neurotransmitter binds to the neuroreceptors in the post-synaptic membrane
- Causing the ion channels to open
- 5. This causes a depolarisation of the post-synaptic cell membrane
- called the post-synaptic potential (PSP)
- which may initiate an action potential
- called the post-synaptic potential (PSP)
- 6. The neurotransmitter must be removed from the synaptic cleft to stop the synapse being permanently on
- This can be achieved by breaking down the neurotransmitter by a specific enzyme in the synaptic cleft
- he breakdown products are absorbed by the pre-synaptic neurone by endocytosis
- used to re-synthesise more neurotransmitter; using energy from the mitochondria
- he breakdown products are absorbed by the pre-synaptic neurone by endocytosis
- Alternatively the neurotransmitter may be absorbed intact b the pre-syanptic neurone
- This can be achieved by breaking down the neurotransmitter by a specific enzyme in the synaptic cleft
- The junction between two neurones
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