module 5 - 13.5 synapses Flashcards
what is the synaptic cleft?
a gap that separates the axon of one neurone from the dendrite of the next neurone
what is involved in the structure of a synapse?
- synaptic cleft
- presynaptic neurone
- postsynaptic neurone
- synaptic knob
- synaptic vesicles
- neurotransmitter receptors
- voltage gated calcium ion channel proteins
what is the presynaptic neurone?
action potential (impulse) arrives at the synapse along its neurone
what is the postsynaptic neurone?
neurone that receives the neurotransmitter
what is the synaptic knob?
swollen end of the presynaptic neurone, with many mitochondria and extensive ER to synthesise neurotransmitters
what are the synaptic vesicles?
contain neurotransmitter that fuses with presynaptic membrane and diffuses into synaptic cleft
what are neurotransmitters that are sodium ion channel proteins?
specific protein molecules in postsynaptic plasma membrane where the transmitter will bind too
what does polarised mean?
more positive charge on outside than inside
what does depolarised mean?
more negative charge on outside than inside 1 (Na+ goes into cell)
what does repolarisation mean?
more positive goes out, more negative on inside (K+ goes out of cell)
what is an excitatory neurotransmitter/what does it do?
- cross synaptic cleft
- cause localised depolarisation of postsynaptic membrane, if this reaches threshold potential then action potential is initiated
- common in CNS and neurotransmitter junctions
- e.g. acetylcholine
what is an inhibitory neurotransmitter/what does it do?
- cross synaptic cleft
- cause hyperpolarisation of the postsynaptic membrane
- prevent action potentials being initiated
- e.g. GABA
what is an electrical synapse?
- the place where there is a direct physical connection between pre and postsynaptic neurone
- connection takes the form of a channel (gap junction) that allows current int eh form of ions to flow directly from one cell to another
- allows very fast cell signalling
what is an example of an electrical synapse?
transmission of the depolarising current from cell to cell, across chambers of the heart, so cells contract in unison
what is meant by ‘unidirectional impulses’ as a role of a synapse?
- neurotransmitter receptors are only present in postsynaptic membrane
- allows impulse from one neurone to transmit to a number of neurone
what is meant by ‘divergence’ as a role of a synapse?
impulses from a single neurone are passed to more than one neurone
what is meant by ‘convergence’ as a role of a synapse?
impulses from morethan one neurone are passed to a single postsynaptic neurone, so stimuli from different receptors produce a single result
what is meant by ‘filter out’ as a role of a synapse?
filter out background and low level stimuli, ensuring that only stimulation that is strong enough will be passed on
what is summation?
- each stimulus from presynaptic neurone causes same amount of neurotransmitter release into synaptic cleft
- sometimes neurotransmitter from a single impulse isn’t enough to initiate action potential in postsynaptic neurone
- if the amount of neurotransmitter buildup in synaptic cleft, an action potential is initiated
what are the 2 types of summation?
- temporal summation
- spatial summation
what are 2 types of drugs?
- recreational drugs
- medicinal drugs
what are the 2 types of modes of action of drugs on synapses?
- STIMULATE the NS by creating more action potentials in postsynaptic neurone
- INHIBIT the NS by reducing amount of action potentials in postsynaptic neurone
what is GABA?
- an inhibitory neurotransmitter
- causes hypoerpolarisation of postsynaptic membrane
explain GABA receptors and ethanol?
- GABA receptor is a chloride ion channel protein and pore opens when GABA binds to its binding site
- influx of chloride ions into postsynaptic neurone prevents action potentials from being initiated
- ethanol also binds to the GABA receptors and the pore remains open longer, so more Cl- goes into postsynaptic neurone
- this increases inhibitory effects on GABA synapses and cause ethanol induced effects on humans
