Exam 1: Slide 4

Question 1

Otto Loewi

Answer 1

In 1926, this German physiologist proved that electrical signals can cause neurotransmitter release

Question 2

What did Otto Loewi’s experiment entail?

Answer 2

1) two frog hearts were bathed in fluid
2) The first heart was electrically stimulated, which caused slowing of the heart
3) The fluid surrounding the stimulated heart was then transferred to the fluid surrounding the second heart
4) Just being bathed in the fluid of the first heart caused the second heart to slow as well
5) Because the second heart responded by slowing down, even though it was not electrically stimulated, Loewi concluded that a chemical must have been released from the first heart
6) The chemical was later identified as the neurotransmitter acetylcholine

Question 3

Three Primary Neurotransmitter Criteria

Answer 3

1. The substance must be present within the presynaptic neuron
2. The substance must be released in response to presynaptic depolarization and the release must be calcium dependent
3. Specific receptors for the substance must be present on the postsynaptic cell

Question 4

How does neurotransmitter release occur?

Answer 4

Work in the 1970s demonstrated that neurotransmitter release occurs as a result of vesicles fusing with the presynaptic membrane and releasing their neurotransmitter contents

Question 5

The critical step in vesicular fusion is

Answer 5

the influx of calcium via the voltage gated calcium channels

Question 6

Evidence for Calcium

Answer 6

• Artificially injecting calcium into the presynaptic terminal causes neurotransmitter release
• Preventing internal calcium increase during an action potential prevents neurotransmitter release

Question 7

The basic process of vesicular fusion is as follows: (1)

Answer 7

1. The protein synapsin is present on vesicles and binds to the cytoskeleton of the neuron

Question 8

The basic process of vesicular fusion is as follows: (2)

Answer 8

2. When calcium enters the cells following an action potential, proteins called Ca2+/calmodulin-dependent protein kinase type II (CaMKII) bind this calcium and cause synapsin to release from the vesicle

Question 9

The basic process of vesicular fusion is as follows: (3)

Answer 9

3. Once synapsin releases, the vesicle can move to the presynaptic membrane at the synapse

Question 10

The basic process of vesicular fusion is as follows: (4)

Answer 10

4. The two types of protein classes involved in vesicular fusion are SNAREs and SNAPs. Both work to prime the vesicle for fusion. They ensure the vesicle is in the proper position to fuse i.e. “docked”

Question 11

The basic process of vesicular fusion is as follows: (5)

Answer 11

5. Synaptotagmin is located on the vesicle and senses calcium influx as well. It causes the docked vesicle to fuse with the membrane

Question 12

There are two broad categories of neurotransmitter (NT):

Answer 12

• small molecule and peptides

- Neurons can release one type or both types of neurotransmitters

Question 13

Which frequency releases which type of NT

Answer 13

in neurons that release both, low - frequency activity causes release of small molecule NTs and high - frequency causes release of peptides

Question 14

Where are the different types of NT made?

Answer 14

The NTs are made differently as well: small molecule in the axon terminals and peptides in the cell body

Question 15

Small molecule neurotransmitter synthesis and transport:

Answer 15

• Synthesis occurs locally within axon terminals
• The enzymes needed to synthesize the neurotransmitters are sent from the cell body to the axon terminals by slow axonal transport
• The neurotransmitter is then loaded into vesicles at the terminal—the vesicles are visually clear (i.e. small clear-core vesicles)

Question 16

Peptide synthesis and transport:

Answer 16

• Synthesis occurs in the cell body
• The peptide is put in to vesicles and sent from the cell body to the axon terminals by fast axonal transport
• The vesicles get to the axon terminal and then are released once the signal is sent