Synapses Flashcards
What does the presynaptic knob contain
- large number of mitochondria = respiration produces ATP which is needed for stymies of neurotransmitters and active transport
- endoplasmic reticulum = synthesis of neurotransmitters
What happens in the presynaptic knob when an action potential arrives
- action potential arrives
- causes ca2+ channels to open enter via facilitated diffusion
- synaptic vesicles move and fuse with presynaptic membrane
- releases neurotransmitter into synaptic cleft
How do neurotransmitter cross synaptic cleft
Simple diffusion
What happens at postsynaptic neuron when action potential arrives
- neurotransmitter binds to specific receptor on Na+ channels causing them to open in postsynaptic membrane
- Na+ diffuses in to the post synaptic neurone causing depolarisation and creating action potential
Why is synaptic transmission unidirectional
- only presynaptic neurone contains vesicles containing neurotransmitter
- only postsynaptic membrane has receptor channel proteins
What is summation
Low frequency of action potential may mean insufficient neurotransmitter to trigger action potential
2 types of summation
Temporal and spatial
Define temporal summation
One presynaptic neurone releases neurotransmitter servers times in quick succession
Define spatial summation
Multiple presynaptic neurones release neurotransmitter
Describe sequence of events in led in transmission across cholinergic synapses ( 5 marks )
- depolarisation of presynaptic membrane
- ca2+ channels open and ca2+ ions enter
- causes synaptic vesicles to move and fuse with presynaptic nob and release neurotransmitter
- neurotransmitter diffuse across synaptic cleft
- attached to receptors on postsynaptic membrane
- sodium ions enter lading to depolarisation
How does neurotransmitter stimulate nerve impulse in postsynaptic neurone (3 marks)
- Neurotransmitter diffuses across synapse
- attaches to receptors on postsynaptic membrane
- stimulates entry of sodium ions and depolarisation
A neurotransmitter released in some inhibitor synapses in the brain , causes negatively charge chloride ions to enter postsynaptic membrane.
How does this inhibit postsynaptic neurone (3 marks)
- makes post synaptic neurone more negative
- more sodium ions are needed to reach threshold
- for depolarisation to occur
How might drugs increase synaptic transmission
- Inhibit AChE
- mimic shape of neurotransmitters
How might drugs decrease synaptic transmission
- inhibit release of neurotransmitter
- decrease permeability of postsynaptic membrane to ions
- hyperpolairse postsynaptic membrane
What are cholinergic synapses
Use acetylcholine a primary neurotransmitter excitatory or inhibitory
