Conduction and Synapses Flashcards
What is the morphology of neuron?
Soma - cell body, dendrite - receive and process signal, axon - AP conduction, hillock - signals are summated to see if AP will occur, synapse
Have many receptors/channels that are activated by a NT ligand…
dendrites
Densely packed with channels activated by changes in membrane voltage…
axons
Action potential shape is due to…
properties of Na+ and K+ voltage channels
Sodium channel open states
no delay, stays open for msec
Opens with 1 msec delay, stays open as long as membrane is depolarized, this efflux leads to repolarization
voltage K+
How does refractory period form after AP?
previous action potential (depolarized) area is returned to resting potential via K+ efflux. This creates an orthodromic propagation
What affects conduction of propagation?
axon diameter (larger the faster), myelination thickness, and temperature (speed increase w temp)
What is purpose of Nodes of Ranvier?
Allow for saltatory conduction which is where in those gaps the AP is regenerated, without this the whole membrane would need to be depolarized (continuous conduction) which is slow
What are components of electrical synapse?
gap junctions which are made of connexons and allow ions, metabolites to pass through. This is important for things like cardiac muscle. This changes post synaptic potential immediately but is small
What are components of post and pre synaptic terminals?
Pre-synaptic is axon terminal release of NTs triggered by Ca2+ channels. Post-synaptic can be dendrites, or NT receptors
This opens when action potential reaches the presynaptic terminal and there’s depolarization of presynaptic terminal membrane…
Ca2+ channels causing calcium influx and can stay open during depolarization. This leads to synaptic vesicle fusion
How does Ca2+ trigger synaptic vesicle fusion?
Ca2+ binds to synaptotagmin on vesicle which initiates engagement of SNARE complex to fuse to active zone, then exocytosis. (SNARE proteins: synaptobrevin, Snap-25, Syntaxin)
Ionotropic vs metabotropic postsynaptic receptors
iontropic is ligand gated ion channel, quick, but short and metabotropic is GPCR, slower, but longer lasting
step wise, passive change in membrane potential that varies and is proportional to input stimulus; can be inhibitory or excitatory
graded potential
What are examples of graded potentials?
PSPs, End Plate potentials -generated in motor endplate (muscle) in response to motor signal and is greater than EPSP, and receptor potential
Why do graded potentials degrade quicker than AP?
because signals degrade and the summation of signals is important; need convergence of input
How does ACh affect NMJ?
ACh release binds to ionotropic nicotinic receptors which then open for Na+ influx; agonist is nicotine
Why are EPPs larger?
multiple axons releasing NTs, motor endplate has larger surface area, and more channels open this leads to APs in adjacent cells, not the EP
How does alpha latrotoxin affect NMJ?
increases Ca causing uncontrolled exocytosis of ACh, prolonged depolarization then depletion, death from respiratory paralysis
Organophosphates
bind to AChE so no breakdown of ACh leads to seizures, drooling, respiratory failure, constriction
Myasthenia gravis
antibodies against NMJ AChrs, fewer motor units activated, and ACh is degraded before is can bind to the few receptors; treat with anti AChE (pyrdostigmine)
