What are Synapses and How do they work? Flashcards
What is a synapse?
Connection between 2 neurons
What do synapses allow?
Neurons to communicate with eachother (cell communication)
What are the 2 types of synapses?
-Electrical
-Chemical
Electrical Synapses
Only a few and are found in the brain
Chemical Synapses
Different synapses use different chemicals (neurotransmitters)
What chemical does the sympathetic nervous system use?
noreadrenaline
What chemical does the parasympathetic nervous system use?
Acetyl Choline (ACh)
What are synapses that use ACh called?
Cholinergic synapses
What is attached to the presynaptic neuron?
Presynaptic bulb/knob
What is in the presynaptic bulb/knob?
-Lots of mitochondira and SER
-Vesicles containing ACh
-Voltage gated Ca2+ channels
What is in the postsynaptic neuron?
-Nicotine ACh receptors with Na+ channels within
-Acetylcholinesterate (AChE)
What is the gap called between the presynaptic membrane and postsynaptic membrane?
Synaptic Cleft (~20nm)
What is the first step in how a synapse works?
An action potential at presynaptic bulb/knob (+40 mV) causing the voltage gated Ca2+ channels to open
What is the second step in how a synapse works?
Ca2+ diffuses (facilitated) into presynaptic bulb/knob causing vesicles containing ACh to move towards and fuse with presynaptic membrane and release Ach into cleft via exocytosis
What is the third step in how a synapse works?
-ACh diffuses across cleft and binds to nicotenic ACh
-If 2 bind causes the Na+ channel within the receptor to open
What is the fourth step in how a synapse works?
Na+ enter postsynaptic neurone so if enough enters so reaches threshold potential of -55mV causing voltage gated Na+ channels to open causing depolarisation
What is different for different neurotransmitters?
ACh replaced
What happens after synapse is produced?
AChE breaks down ACh
Why is it important ACh is broken down?
So don’t keep getting action potential in postsynaptic neuron
Equation for breakdown of ACh
ACh –> Acetic Acid + Choline
What happens to Acetic Acid and Choline?
Diffuse back to presynaptic bulb and are converted back to ACh and are repackaged back into vesicles
What does the diffusion of Acetic Acid and Choline require?
Lots of ATP (from lots of mitochondria)
Why is lots of ATP required for not just the diffusion?
ATP is also used to pump Ca2+ out of presynaptic bulb afterwards
