Exam 1 Week 2: ppt 8 Pre-Synaptic Events

Question 1

What are synapses?

Answer 1

•Synapses are the connections between adjacent neurons

• Synapses are specialized structures that communicates information between neurons.
• They are Sites where information transmission can remain unaltered, modified, or stopped altogether.
• Synapses are also the sites of action of therapeutic and recreational drugs

Question 2

Two kinds of synaptic junctions

Answer 2

Chemical junctions (most common)

Electrical (ephaptic or gap) junctions (uncommon - I think they are in the heart mostly)

Synapses are the connections between adjacent neurons. Most are chemical junctions (top) but electrical (ephaptic or gap) junctions (bottom) do exist. Because they are the vast majority of synapses and because they are the sites where drugs act we will Concentrate on chemical synapses in this course.

Question 3

How many synaptic connections does an avarage neuron have?

how many inputs does it have?

Answer 3

•An average neuron has >1,000 synaptic connections with some >10,000 inputs

Question 4

Convergence

Answer 4

inputs from multiple sources into a single neuron

Question 5

Divergence

Answer 5

Divergence –outputs to multiple destinations from a single neuron

Question 6

Synonyms for synaptic terminal

Answer 6

synaptic ending

bouton

Question 7

How many synaptic endings are on a CNS neuron?

What percentge are on dendrites?

What percentage ore on soma?

Answer 7

–Up to 10,000- 20,000 synaptic endings on a CNS neuron
80-90% endings on dendrites and 10-20% on soma

Question 8

Steps of chemical synaptic transmission (5)

Answer 8

1. •Transmitter Synthesis
2. •Transmitter Packaging
3. •Transmitter Release
4. •Transmitter–receptor interaction (PSPs)
5. •Inactivation of Transmitter

Question 9

Structure/Function of presynaptic membrane

Answer 9

The Presynaptic membrane has thousands of transmitter vesicles with 2-10,000 transmitter molecules in each vesicle. For most transmitters there is Cytoplasmic synthesis of transmitter and uptake into vesicle.

Question 10

How many transmitter molecules are there per vessicle?

Answer 10

2-10,000

Question 11

For most transmitteres, where are they synthesized and packgaed into vessicles?

Answer 11

For most transmitters there is Cytoplasmic synthesis of transmitter and uptake into vesicle.

Question 12

What transmitters can be synthesized and packaged in the terminal cytoplasm?

Which must be synthesized in the nucleus and transporetd to the synaptic terminal?

Answer 12

Only small transmitters can be synthesized in the cytoplasim

Proteins and polypeptied transmitters must be synthesized in the nucleus and transported to the synaptic terminal

Question 13

Function: The presynaptic membrane

Answer 13

• Transmitter specific transport proteins in membranes
• Vesicle & terminal membranes identical
• Uptake/reuptake of transmitter into terminal & vesicles

Along the Presynaptic membrane and the membrane of the synaptic vesicles are Transmitter specific transport proteins in membranes. This is true because Vesicle & terminal membranes are identical. These Transmitter specific transport proteins allow for Uptake/reuptake of transmitter into the terminal & vesicles.

Question 14

How much transmitter is within the presynaptic nembrane?

Answer 14

Enough transmitter for > 10,000 pre-synaptic action potentials without replenishment

There is Enough transmitter within Presynaptic vesicles for > 10,000 pre-synaptic action potentials without replenishment. However with active synthetic enzymes within the presynaptic membrane and with reuptake of transmitters replenishment can be easily accomplished. So there is no reason for a lack of transmitters under normal circumstances.

Question 15

how big is the synaptic gap?

Answer 15

20-30 micrometers across gap

Question 16

Transmitter Release

Answer 16

•Transmitter Release

• –Activation of pre-synaptic terminal – APs enter bouton
• –Voltage-gated Ca++ channels open
• –100 fold increase in intracellular [Ca++]
• –Trigger transmitter release into gap
  
  • Ca++ bind to synaptotagmins, proteins found on synaptic vesicles
  • Triggers SNARE proteins to fuse vesicles with the presynaptic membrane creating a fusion pore

Transmitter Release is triggered by activation of pre-synaptic terminal when cction potentials enter the bouton from the axon. The action potentials entering the bouton trigger the opening of Voltage-gated Ca++ channels. This produces a 100 fold increase in intracellular [Ca++] which triggers the release of transmitter into the synaptic gap. This release is produced by Ca++ binding to synaptotagmins, proteins found on synaptic vesicles. This Triggers SNARE proteins to fuse vesicles with the presynaptic membrane creating a fusion pore.

Question 17

What else is released into the synaptic cleft in addition to neurotransmitters?

Answer 17

Trophic SUbstances

• Non-transmitter substances released at synapses
• Both non-vesicular & vesicular release
• Maintain association between pre & post-synaptic neurons
• Can regulate post-synaptic excitability by:
  • –Attract receptors to synaptic area
  • –Increasing the affinity of post-synaptic receptors for the transmitter

In addition to neurotransmitters, Trophic substances, Non-transmitter substances, are released at synapse. The release of trophic substances can be Both non-vesicular & vesicular release. Trophic substances are important for Maintaining the association between pre & post-synaptic neurons. For instance trophic substances release by the presynaptic membrane can stimulate the post-synaptic cell to move transmitter receptors to the synaptic contact site and concentrate them there to enhance the post-synaptic response the presynaptic release of transmitter. Trophic substance can also act to Increase the affinity of post-synaptic receptors for the transmitter

Question 18

Recycling of vesicles

Answer 18

–Recycling of vesicles

Vesicle merges with the pre-synaptic membrane & releases transmitter under influence of intracellular Ca++ (1)

• Empty vesicle may pinch right off (2) (“kiss & run”)
• More commonly, vesicle merges with membrane and pushed out the synaptic release zone by other vesicles merging with the membrane (3)
  
  • Eventually vesicle will pinch off the membrane (3) to be refilled with transmitter
  • Is then recycled into the active release pool of vesicles (4)

Synaptic vesicles are recycled. Vesicle merges with the pre-synaptic membrane & releases transmitter under influence of intracellular Ca++ (1 in this illustration). The Empty vesicle may pinch right off (2 in this picture) and be recycled to be immediately be refilled and reused. This is called the “kiss & run” effect. This occurs generally only when there is a very high activity at a synaptic contact. More commonly, vesicle merges with membrane and pushed out the synaptic release zone by other vesicles merging with the membrane (3 in this illustration). Eventually vesicle will pinch off the membrane (3 in this illustration) to be refilled with transmitter, It is then recycled into the active release pool of vesicles (4 in this illustration)

Question 19

Three main classes of neurotransmitters:

Answer 19

1. Amino acids – small, synthesized, and packaged in synaptic vesicles
2. Amines – small, synthesized, and packaged in synaptic vesicles
3. Peptides – large, synthesized and packaged in dense-core vesicles

Question 20

The principle amino acid transmitters: (4)

Answer 20

1. Glycine – inhibitory
2. Glutamate – excitatory
3. Aspartate – excitatory
4. Gamma – amino butyric acid (GABA)-inhibitory

Question 21

The principal amine transmitters:

Answer 21

1. •Acetylcholine (ACh)
2. •Catecholamines
   
   • –Dopamine (DA)
   • –Norepinephrine (NE)
   • –Epinephrine
3. •Indole amines
   
   • –Serotonin (5-HT)
   • –Histamine

Question 22

Three catecholamines

Answer 22

1. –Dopamine (DA)
2. –Norepinephrine (NE)
3. –Epinephrine

Question 23

Two Indole amines

Answer 23

1. –Serotonin (5-HT)
2. –Histamine

Question 24

Three examples of polypeptide & protein neurotransmitters:

Answer 24

There are a wide range of polypeptide and protein neurotransmitters

Some of these include:

1. Dynorphin
2. Enkephalin
3. Substance P

Question 25

is the action of nurotransmitters excitatory or inhibitory?

Answer 25

The action of a neurotransmitter may be excitatory or inhibitory

What effect it has is determined by both the specific neurotransmitter and the type of postsynaptic receptor for that neurotransmitter

Question 26

What determines if the action of a neurotransmitter is excitatory or inhibitory?

Answer 26

It is determined by both the specific neurotransmitter and the type of postsynaptic receptor for that neurotransmitter