Synaptic Transmission Flashcards
Dendrites
receive information from synapses or stimulus and “passively” propagate
postsynaptic potentials
Axon hillock
site of action potential activation in
response to integration (summing) of passive postsynaptic potentials that
depolarize the cell above a threshold
Axon
conducts signals in the form of action potentials
Synapse
transmits signals to down stream partners that allows rapid cell-to-cell communication
Synaptic modulation
allows for both robust function as
well as higher levels of complexity including learning and memory
Electrical Synapse
Current flows from the presynaptic neuron into postsynaptic neuron via the electrical connection of the gap junction; current passing through one neuron during depolarization will be passed onto the adjacent neuron
- FAST (responsible for reflexes where transmission must be <ms)
Gap junction
a hemi-channel made of 6 connexins that can close in response to modulatory
factors like:
- low pH
- elevated Ca2+
- voltage- gated
- chemical neurotransmitters
allow for simple electrical connection between pre and post-synaptic neurons
Escape Reflexes
FAST synaptic transmission <1ms
Graded response
dependent on number of gap junctions and size/morphology of neurons
Limitations of electrical synapses
- transmission signal dependent on morphology/size of communicating
cells - no amplification of signal possible
- limited modulation of signal strength
- can not flip the sign of the response so post-synaptic neurons follows presynaptic neuron (cannot have an inhibitory response in postsynaptic neuron upon excitatory stimulus in presynaptic neuron)
Chemical synapse
Signal transmitted across synaptic cleft (~20-40 nm) by diffusion of a neurotransmitter
Benefits of chemical synapses
- SLOWER than electrical synapse (a few ms) but still FAST
- HIGHLY directed (to a single receptor cell i.e one postsynaptic neuron)
- AMPLIFICATION of signal possible (one vesicle contains 1000s of NT and can open 1000s of postsynaptic channels) which can be modulated
- can be excitatory OR inhibitory (depending on what receptors are present and what channels are open/closed)
Active zone
site on the presynaptic neuron where NT-containing vesicles are released
SNARE Complex
organization of proteins that when extracellular calcium enters the cell, causes fusion of NT-containing vesicles and release of NTs
What occurs after an action potential?
voltage-gated calcium channels open and NT release can be done; calcium MUST be around in order to release NT
What causes voltage-gated calcium channels to open?
Depolarization of the presynaptic neuron
Process of NT release
SNARE proteins form SNARE complex–> pull vesicle close to membrane and pull membranes of pre and postsynaptic neurons together -> calcium influx changes conformation of SNARE complex –> fusion and exocytosis of vesicle and NT release
Botulinum Toxins
proteases that
inhibit neurotransmitter release by
cleaving the SNARE protein; muscle unable to contract for lack of neurotransmitter, and relaxes; result is temporary muscle rigidity