lecture 9 presynaptic Flashcards
Presynaptic
the neuron that
releases the neurotransmitter or
sends a signal, usually caused by
a presynaptic action potential.
Postsynaptic
the neuron that receives a signal from the presynaptic neuron. Known
as the “downstream” neuron
Electrical synapses
where gap junctions connect the
cytoplasm between two cells and allow the direct
passage of electrical current (ions). They allow for the
fast and often bidirectional transfer of electrical
information between cells
what is the specialized
membrane protein (channel) that connect two cells at
gap junctions
connexon
why are electrical synapses useful
Electrical synapses are especially useful for synchronizing populations of neurons or when the response needs to be very reliable and quick (optic nerve)
chemical synapses
connections between two cells where information can be transferred from one cell to
the next without being physically connected. At chemical synapses, an action potential in the
presynaptic cell triggers the release of neurotransmitter molecules which bind to receptors on
the postsynaptic cell membrane and lead to a response in the postsynaptic cell.
excitatory
where the release of neurotransmitter increases the likelihood
that the postsynaptic neuron fires an action potential
inhibitory
where the release of neurotransmitter decreases the likelihood that the postsynaptic neuron fires an action potential)- they may be strong or weak as well as fast or slow
______ is a chemical synapse between a motor neuron axon and
a muscle fiber. Typically it is a large, powerful, fast synapse with multiple vesicles released per
presynaptic action potential
Neuromuscular Junction (NMJ)
area on the presynaptic
neuron where vesicles fuse with the cell
membrane to release neurotransmitter
Active zone
Postsynaptic density
structures on the
post-synaptic neuron that contains
neurotransmitter receptors and associated
cyto-skeletal elements
Synaptic cleft
space between the pre- and
postsynaptic neurons at a chemical synapse.
Approximately 20-30 nm
Vesicle
membrane bound organelle that
contains neurotransmitter molecules in the
presynaptic terminal. Approximately 40 nm
in diameter.
molecule that is
packaged in vesicles in the presynaptic
neuron and released to bind to receptors.
Vesicles typically contain hundreds of
molecules of neurotransmitter
Neurotransmitter
calcium channels clustered near the active zone of a
presynaptic terminal that are voltage gated
and open when the presynaptic terminal is
depolarized by an action potential
Voltage-gated Calcium channel
Quantal hypothesis
neurotransmitter is released in discrete “packets” or “quanta”
Vesicle hypothesis
neurotransmitter is packaged into and released from membrane
bound vesicles
Calcium hypothesis
voltage-dependent calcium entry couples presynaptic action
potential to neurotransmitter release
SNARE hypothesis
interactions between SNARE proteins on the vesicle and
presynaptic membrane, modulated by calcium, lead to vesicle fusion
End plate potential (EPP)
change in membrane potential of a muscle fiber (the area
near the synapse is also called the end plate) as a result of a presynaptic action
potential which evokes the release of vesicles at the neuromuscular junction. Also
known as an evoked response.
Miniature end plate potential (mini or mEPP)
change in membrane potential of a
muscle fiber after a vesicle in the presynaptic terminal spontaneously fuses with the
presynaptic cell membrane
the average number of quanta (vesicles) that are released after a
single presynaptic action potential
Quantal Content
the average size of the postsynaptic membrane depolarization (in mV)
after a single quantal event (i.e. fusion of one vesicle with the presynaptic terminal cell
membrane)
Quantal Size
The size of an EPSP is approximately equal to…
quantal content (how many vesicles released) multiplied by the quantal size (size of
response to 1 vesicle). EPSP ≈ QC * QSEPSP ≈ QC * QS
general term for an excitatory synaptic
potential. An EPPs are a subset of EPSPs that occur at the NMJ. The size (amplitude) of
an EPSP can be large as it is at the NMJ where the quantal content may be over 100
(more than 100 vesicles released from the presynaptic terminal) or small as is frequently
found at synapses in the central nervous system
Excitatory Post Synaptic Potential (EPSP)
SNARE complex
a group of proteins that cause vesicle fusion and release of
neurotransmitter in response to an elevation in Ca2+ levels in the presynaptic terminal. Consists
of proteins on both the presynaptic cell membrane at the active zone. When vesicles fuse, the
membrane surrounding the vesicle fuses with the cell membrane. During this fusion a pore
forms in the vesicle membrane and the neurotransmitter is emptied into the synaptic cleft
where it can diffuse the short distance to the postsynaptic receptors
t snares
Syntaxin and SNAP-25
v snares
Synaptobrevin and Synaptotagmin
______ is a critical calcium sensor, it binds calcium and triggers vesicle fusion.
Synaptotagmin
Compare chemical and electrical synapses including any advantages or disadvantages.
List the steps and key machinery involved in synaptic release.
Link the synaptic terms: vesicles, quanta, calcium’s role at the synapse, and the SNARE
complex
Diagram and label a typical chemical synapse
Explain the relationships between quantal size, quantal content, vesicles, and evoked
neurotransmitter release (i.e. EPP) size
advantages of chemical synapses
1) unidirectional
2) can excite or inhibit depending on neurotransmitter
3) amplification is possible from a small amount of neurotransmitter
4) modulation: synapse can increase or decrease in potency
first nt discovered
acetylcholine
what nerve slows heart rate when stimulated
vagus nerve
examples of snareopathies
botulism (paralytic disease found in food), or for botox
tetanus (uncontrollable muscle spasms, bacteria through wound)
