CSB332H1 Lecture Notes - Lecture 8: End-Plate Potential, Nicotinic Acetylcholine Receptor, Postsynaptic Potential
14 May 2018
School
Department
Course
Professor
Excitatory Postsynaptic Potential
Lecture 8(b): Role of Ca2+
Nitrophen:
• AP is not required to initiate the release of neurotransmitters from the presynaptic neuron
o Neurotransmitters can be released if there is enough Ca2+ in the presynaptic neuron
• Nitrophen is a substance that functions to bind and cage to Ca2+
o Prevents Ca2+ activity when not exposed to light
o Applying UV light to Nitrophen will cause the ‘cage’ to break, and Ca2+ can function
Biophysical
Experiment:
• Depolarizing presynaptic neuron allows the opening of VG-Ca2+ channels;
influx of Ca2+
o Postsynaptic neuron was capable of generating an AP
ð Injecting Nitrophen to the presynaptic cell will bind to the Ca2+
(temporarily inhibiting Ca2+ function)
o Shining UV light to the presynaptic cell; Ca2+ is released and is
capable of triggering neurotransmitter release
ð Biophysical experiment – release a large amount of Ca2+ in presynaptic
neuron which generates the same size EPSP without generating an AP in
the presynaptic neuron
o Therefore, this experiment proves (without a doubt) that
neurotransmitter release is dependent on Ca2+ in the
presynaptic neuron and not an AP
Neuromuscular Junction (NMJ):
• NMJ is the synapse between an axon terminal of a motoneuron with the motor end plate
(how voluntary muscle contraction works)
o NMJ is better to use than a giant squid axon due to being a mammalian system
§ Endplate/NMJ is highly-excitable region of muscle fibers
Synaptic Potentials:
• End Plate Potential (EPP) is measureable:
o EPP is the postsynaptic potential change in muscle that is
produced by ACh which is released from the presynaptic terminals
• Muscle cells also have a threshold value they must meet to generate an AP
o ACh is released, they will bind to ligand-gated channels (ACh; nicotinic receptors)
on the NMJ causing them to open and allow for the:
§ Influx of Na+ and Ca2+
§ Efflux of K+
ð Nicotinic receptors are ligand-gated
ACh channels; cation channels
o Responsible for achieving
threshold value in NMJ to
generate AP
Document Summary
Biophysical experiment: depolarizing presynaptic neuron allows the opening of vg-ca2+ channels; influx of ca2, postsynaptic neuron was capable of generating an ap. Injecting nitrophen to the presynaptic cell will bind to the ca2+ (temporarily inhibiting ca2+ function: shining uv light to the presynaptic cell; ca2+ is released and is capable of triggering neurotransmitter release. Endplate/nmj is highly-excitable region of muscle fibers. Ach channels; cation channels: responsible for achieving threshold value in nmj to generate ap. Amplitude (size) of mepp varies in discrete steps; suggesting that neurotransmitters are being released through discrete quantities (discrete quanta) Neurotransmitter release: amplitude of mepp is always a multiple of the smallest common denominator" (i. e. 1 quanta, some postsynaptic cells receive more than one quanta giving rise to a larger meep. Release of ach is done by a current; release specific quantities that are measureable: 1 quanta (~7000 ach) = smallest size meep.
