6.2.2: Synaptic transmission Flashcards
Synaptic transmission
1) Action potential arrives at synaptic knob. Depolarisation of presynaptic membrane.
2) Calcium channels open and calcium ions enter
3) Synaptic vesicles fuse with presynaptic membrane and release acetylcholine
4) Acetylcholine diffuses down concentration gradient across the cleft
5) Acetylcholine attaches to complementary receptors on the postsynaptic membrane
6) Sodium channels open and sodium ions diffuse in leading to depolarisation
What is summation?
The rapid build up of neurotransmitters in the synapse to generate an action potential by spatial or temporal summation. This is needed because some action potentials don’t have sufficient concentrations of neurotransmitters being released for an action potential.
What is spatial summation?
Different neurones converge at one synapse. Action potential arrives from several neurone at the synapse so enough neurotransmitters can reach threshold and cause an action potential
What is temporal summation?
Only one neurone and impulses arrive repeatedly over a short period of time to add up to rough to exceed threshold.
What is inhibitory synapse?
Chloride ions move into the post synaptic neurone and potassium ions move out. Resting potential becomes hyper polarised and post synaptic neurone is less likely to reach threshold
What is an excitatory synapse?
Resting potential becomes less negative so less sodium ions needed for threshold
What is the neuromuscular junction?
Synapse between the motor neurone and a muscle
Similarities between neuromuscular junction and cholinergic synapse (2)
1) Action potential arrives at presynaptic knob
2) Both use acetylcholine which bind to acetylcholine receptors
Differenced between neuromuscular junction and cholinergic synapse (4)
1) Only excitatory
2) Depolarises cell of muscle fibre rather than post synaptic neurone
3) Has membrane that folds that forms clefts so has a larger surface area
4) Motor neurone firing action potential triggers a response in muscles
