Synapses Flashcards
(16 cards)
What is a synapse?
Junction where information is transferred from one neurone to another neurone or effector cell
What is the function of a synapse?
Allow transmission in only one direction: from presynaptic neurones to postsynaptic neurones or effector cells
What are the key roles of synapses in neuronal communication?
- transmit info through release of neurotransmitter chemicals
- single impulse from a presynaptic neurone can initiate impulses in multiple postsynaptic neurones or effector cells
- impulses from several presynaptic neurones can be combined into a single postsynaptic response
What are the main structures in a synapse?
- presynaptic neurone
- synaptic knob
- synaptic vesicle
- synaptic cleft
- postsynaptic neurone
- neurotransmitter receptor
How is the synaptic knob adapted for it’s function?
Contains the organelles needed for neurotransmitter production like mitochondria to release energy
What is an excitatory neurotransmitter?
Neurotransmitter causing depolarisation of post synaptic membrane triggering an action potential if the threshold is released
What is an example of an excitatory neurotransmitter?
Acetylcholine in the CNS and at neuromuscular junctions
What is an inhibitory neurotransmitter?
Neurotransmitter causing hyperpolarisation of the post synaptic membrane preventing an action potential
What is an example of an inhibitory neurotransmitter?
Acetylcholine at cardiac synapses
What is summation?
Process combining inputs to make the generation of an action potential in a postsynaptic neurone or effector cell more likely
What is spatial summation?
Multiple presynaptic neurones converge on a single postsynaptic neurone or effector cell
What is temporal summation?
Repeated firing by a presynaptic neurone leads to continuous neurotransmitter release
What are the key stages in synaptic transmission?
1) action potential arrives at presynaptic knob
2) causes VG Ca2+ channels to open and Ca2+ flows into presynaptic knob
3) causes synaptic vesicles containing neurotransmitters to move towards and fuse with presynaptic membrane
4) vesicles release neurotransmitters into synaptic cleft through exocytosis and neurotransmitters rapidly diffuse across synaptic cleft
5) on reaching other side neurotransmitters bind to receptor proteins on the postsynaptic membrane causing receptors to change shape
6) opens NA+ ion channels in postsynaptic membrane leading to the depolarisation of postsynaptic membrane
7) If depolarisation reaches threshold level an action potential is triggered in postsynaptic neurone
What is a cholinergic synapse?
Synapses using acetylcholine (ACh) as neurotransmitter
What happens after ACh binds to receptors and triggers a response?
1) ACh is broken down by enzyme acetylcholinesterase into choline and ethanoic acid (acetate)
2) breakdown products are then reabsorbed into the presynaptic knob via active transport
3) can then be recycled to synthesise more ACh
4) Ach is transported into synaptic vesicles ready for another action potential
Why is it important to remove neurotransmitters like ACh from synapses?
Prevent stimulus being maintained and allow another stimulus to affect the synapse preventing continuous stimulation and allows for neurotransmitter recycling
