nerves:synapses Flashcards
chemical synapses occur between neurons and:
neurons
muscle cells
gland cells
what are the 8 stages of transmission of a synapse?
- AP depolarises presynaptic ending
- influx Ca2+ into presynaptic ending
- vesicles migrate towards plasma membrane
- release transmitter into cleft=exocytosis
- tx diffuses into cleft
- tx binds to receptors on post-synaptic cell
- changes in post-synaptic cell
- inactivation of tx
what is an excitatory synapse?
increased activity due to the cell being depolarised
brings MP nearer firing threshold
what is an inhibitory synapse?
decreased activity due to the cell being hyperpolarised
takes MP further from firing threshold
what is summation?
EPSPs add together, as postsynaptic potentials v small, single has little effect on MP of post-synaptic cell
EPSP + IPSP cancels
what is the consequence of summation?
post-synaptic cell will fire if it receives sufficient excitation to drive MP beyond threshold
-receives many excitatory inputs w/i short time
what is convergence?
each neuron receives many inputs from other cells
what is divergence?
each neuron then synapses with many other cells
what is a neuromuscular junction?
synapse between motor nerve and muscle fibre
area contact greater the nerve-nerve
tx=acetylcholine
enzyme=acetyl cholinesterase
what are the events at NMJ?
1,AP depolarises motor nerve ending
- Influx of Ca 2+ into nerve ending
- Vesicles migrate towards plasma membrane
- Release of ACh into cleft (exocytosis)
- ACh diffuses in cleft
- ACh binds to receptors on post-synaptic cell
- Action potential in muscle cell contraction
- Transmitter (ACh) broken down by acetyl cholinesterase
- Choline & acetate taken up by neuron
how can drugs affect the synapse?
synthesis/storage of tx release of tx action of tx on receptor 2nd msgr system inactivation of tx
what is the effect of botox?
paralyse facial muscles to remove wrinkles
prevents the release of tx from motor nerves
