Synapses Flashcards
2 types of synapses?
Electrical and chemical
Affect of arrival of action potential at pre synaptic bulb 3
Depolarises presynaptic membrane
Voltage gated Ca2+ channels open
RAPID influx of Ca2+ into bulb down conc grad
Affect of presence of Ca2+ on presynaptic bulb
Cause vesicles to move towards and fuse with membrane of presynaptic bulb
Neurotransmitter released into cleft via exocytosis
Diffuses across cleft
What do neurotransmitters do once they reach the dendrite of the post synaptic neurone
Bind to complementary receptors
Ligand gated Na+ chanels open
Rapid influx of Na+ into dendrite, down conc grad
Depolarisation- initiates A.P
Specific neurotransmitter
Acetylcholine
What would happen if the neurotransmitter remained in the synaptic cleft
Would keep binding to receptors
Ligand gated chanels would stay open
Dendrite would remain depolarised
Cant fire another A.P
Enzyme which removes acetylcholine from cleft
acetylcholinesterase
Products of hydrolysis of acetylcholine and what happens to them
Choline and Ethanoic acid
Diffuse back across cleft
ATP used to reform and package neurotransmitter into vesicles
Function off synapses 4
Transmit impulse between neurones
Ensure one direction of transmission
Allow acclimatisation
Allow summation
How do synapses ensure one direction of transmission
Vesicles containing neurotransmitters are only in presynaptic bulb
Receptor molecules are only at post synaptic membranes
Acclimatisation
After repeated stimulation synapse might run out of neurotransmitter, becomes fatigued
Allows filtering of low level stimuli (unimportant) e.g bad smell
2 types of summation
Spatial and temporal
Temporal summation
Post synaptic neurone is only stimulated if there is frequent A.Ps in presynaptic mem
Spatial summation
Several presynaptic neurones must receive impulse for impulse to be initiated in post synaptic neurone
2 types of gated channels at chemical synapses
Voltage gated Ca2+
Ligand gated Na+
ligand gated channel?
Opens when ligand binds to complementary site
At which synapses is acetylcholine released
Neuromuscular synapses
Cholinergic synapses
Dependency?
When as a result of changes to CNS person cannot cope without a cirtain drug
Tolerance
When a drug is continually taken synapse may adapt
More of the drug is required to produce original, desired affect
Excitory drugs
Stimulate nervous system by creating more A.Ps
Inhibitory drugs
Inhibit nervous system by reducing number of A.Ps
What do psychoactive drugs have an affect on 4
CNS, brain function: mood, perception, consciousness, behaviour
Affect of organophosphorus insecticides
Inhibit enzyme acetylcholinesterase
Acetylcholine remains in cleft, prolonged affect
Repeated depolarisation of post synaptic neurone + firing of A.Ps
If acetylcholinesterase is inhibited at neuromuscular synapses? 4
Muscle repeatedly contracts
Depletes ATP
Paralysis
Death
