lecture 9 presynaptic

Question 1

Presynaptic

Answer 1

the neuron that
releases the neurotransmitter or
sends a signal, usually caused by
a presynaptic action potential.

Question 2

Postsynaptic

Answer 2

the neuron that receives a signal from the presynaptic neuron. Known
as the “downstream” neuron

Question 3

Electrical synapses

Answer 3

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

Question 4

what is the specialized
membrane protein (channel) that connect two cells at
gap junctions

Answer 4

connexon

Question 5

why are electrical synapses useful

Answer 5

Electrical synapses are especially useful for synchronizing populations of neurons or when the response needs to be very reliable and quick (optic nerve)

Question 6

chemical synapses

Answer 6

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.

Question 7

excitatory

Answer 7

where the release of neurotransmitter increases the likelihood
that the postsynaptic neuron fires an action potential

Question 8

inhibitory

Answer 8

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

Question 9

______ 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

Answer 9

Neuromuscular Junction (NMJ)

Question 10

area on the presynaptic
neuron where vesicles fuse with the cell
membrane to release neurotransmitter

Answer 10

Active zone

Question 11

Postsynaptic density

Answer 11

structures on the
post-synaptic neuron that contains
neurotransmitter receptors and associated
cyto-skeletal elements

Question 12

Synaptic cleft

Answer 12

space between the pre- and
postsynaptic neurons at a chemical synapse.
Approximately 20-30 nm

Question 13

Vesicle

Answer 13

membrane bound organelle that
contains neurotransmitter molecules in the
presynaptic terminal. Approximately 40 nm
in diameter.

Question 14

molecule that is
packaged in vesicles in the presynaptic
neuron and released to bind to receptors.
Vesicles typically contain hundreds of
molecules of neurotransmitter

Answer 14

Neurotransmitter

Question 15

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

Answer 15

Voltage-gated Calcium channel

Question 16

Quantal hypothesis

Answer 16

neurotransmitter is released in discrete “packets” or “quanta”

Question 17

Vesicle hypothesis

Answer 17

neurotransmitter is packaged into and released from membrane
bound vesicles

Question 18

Calcium hypothesis

Answer 18

voltage-dependent calcium entry couples presynaptic action
potential to neurotransmitter release

Question 19

SNARE hypothesis

Answer 19

interactions between SNARE proteins on the vesicle and
presynaptic membrane, modulated by calcium, lead to vesicle fusion

Question 20

End plate potential (EPP)

Answer 20

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.

Question 21

Miniature end plate potential (mini or mEPP)

Answer 21

change in membrane potential of a
muscle fiber after a vesicle in the presynaptic terminal spontaneously fuses with the
presynaptic cell membrane

Question 22

the average number of quanta (vesicles) that are released after a
single presynaptic action potential

Answer 22

Quantal Content

Question 23

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)

Answer 23

Quantal Size

Question 24

The size of an EPSP is approximately equal to…

Answer 24

quantal content (how many vesicles released) multiplied by the quantal size (size of
response to 1 vesicle). EPSP ≈ QC * QSEPSP ≈ QC * QS

Question 24

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

Answer 24

Excitatory Post Synaptic Potential (EPSP)

Question 25

SNARE complex

Answer 25

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

Question 26

t snares

Answer 26

Syntaxin and SNAP-25

Question 27

v snares

Answer 27

Synaptobrevin and Synaptotagmin

Question 28

______ is a critical calcium sensor, it binds calcium and triggers vesicle fusion.

Answer 28

Synaptotagmin

Question 29

Compare chemical and electrical synapses including any advantages or disadvantages.

Question 30

List the steps and key machinery involved in synaptic release.

Question 31

Link the synaptic terms: vesicles, quanta, calcium’s role at the synapse, and the SNARE
complex

Question 32

Diagram and label a typical chemical synapse

Question 33

Explain the relationships between quantal size, quantal content, vesicles, and evoked
neurotransmitter release (i.e. EPP) size

Question 34

advantages of chemical synapses

Answer 34

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

Question 35

first nt discovered

Answer 35

acetylcholine

Question 36

what nerve slows heart rate when stimulated

Answer 36

vagus nerve

Question 37

examples of snareopathies

Answer 37

botulism (paralytic disease found in food), or for botox
tetanus (uncontrollable muscle spasms, bacteria through wound)